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Preliminary Technical Data
FEATURES
16-Bit Resolution and Monotonicity Current Output Ranges: 4-20mA, 0-20mA or 0-24mA 0.1% typ Total Unadjusted Error (TUE) 5ppm/C Output Drift Voltage Output Ranges: 0-5V, 0-10V, 5V, 10V, 10% over-range 0.05% Total Unadjusted Error (TUE) 3ppm/C Output Drift Flexible Serial Digital Interface On-Chip Output Fault Detection On-Chip Reference (10 ppm/C Max) Asynchronous CLEAR Function Power Supply Range AVDD : 10.8V to 40 V AVSS : -26.4V to -3V/0V Output Loop Compliance to AVDD - 2.5 V Temperature Range: -40C to +85C TSSOP and LFCSP Packages
Single Channel, 16-Bit, Serial Input, Current Source & Voltage Output DAC AD5422
GENERAL DESCRIPTION
The AD5422 is a low-cost, precision, fully integrated 16-bit converter offering a programmable current source and programmable voltage output designed to meet the requirements of industrial process control applications. The output current range is programmable to 4mA to 20 mA, 0mA to 20mA or an overrange function of 0mA to 24mA. Voltage output is provided from a separate pin that can be configured to provide 0V to 5V, 0V to 10V, 5V or 10V output ranges, an over-range of 10% is available on all ranges. Analog outputs are short and open circuit protected and can drive capacitive loads of 1uF and inductive loads of 1H. The device is specified to operate with a power supply range from 10.8 V to 40 V. Output loop compliance is 0 V to AVDD - 2.5 V. The flexible serial interface is SPI and MICROWIRE compatible and can be operated in 3-wire mode to minimize the digital isolation required in isolated applications. The device also includes a power-on-reset function ensuring that the device powers up in a known state and an asynchronous CLEAR pin which sets the outputs to zero-scale / mid-scale voltage output or the low end of the selected current range. The total output error is typically 0.1% in current mode and 0.05% in voltage mode. Table 1. Related Devices
Part Number AD5412 Description Single Channel, 12-Bit, Serial Input Current Source and Voltage Output DAC Single Channel, 16-Bit, Serial Input Current Source DAC Single Channel, 12-Bit, Serial Input Current Source DAC
APPLICATIONS
Process Control Actuator Control PLC
AD5420 AD5410
Rev. PrE
Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other rights of third parties that may result from its use. Specifications subject to change without notice. No license is granted by implication or otherwise under any patent or patent rights of Analog Devices. Trademarks and registered trademarks are the property of their respective owners.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A. Tel: 781.329.4700 www.analog.com Fax: 781.461.3113 (c)2007 Analog Devices, Inc. All rights reserved.
AD5422 TABLE OF CONTENTS
Features .............................................................................................. 1 Applications....................................................................................... 1 General Description ......................................................................... 1 Revision History ............................................................................... 2 Functional Block Diagram .............................................................. 3 Specifications..................................................................................... 4 AC Performance Characteristics ................................................ 7 Timing Characteristics ................................................................ 8 Absolute Maximum Ratings.......................................................... 10 ESD Caution................................................................................ 10 Pin Configuration and Function Descriptions........................... 11 Typical Performance Characteristics Voltage output............... 13 Typical Performance Characteristics current output ............... 17 Typical Performance Characteristics general ............................ 20 Terminology .................................................................................... 22 Theory of Operation ...................................................................... 24 Architecture................................................................................. 24 Serial Interface ............................................................................ 24 Default configuration................................................................. 28 Transfer Function ....................................................................... 28 Data Register ............................................................................... 29 Control Register.......................................................................... 29
Preliminary Technical Data
RESET register ............................................................................ 29 Status register .............................................................................. 30 Features ............................................................................................ 31 fault alert...................................................................................... 31 voltage output short circuit protection.................................... 31 Asynchronous Clear (CLEAR) ................................................. 31 Internal Reference ...................................................................... 31 External current setting resistor............................................... 31 Voltage ouTput over-range........................................................ 31 Digital Power Supply.................................................................. 31 External boost function............................................................. 31 digital Slew rate control ............................................................. 32 IOUT Filtering Capacitors ............................................................ 32 Applications Information .............................................................. 33 driving inductive loads .............................................................. 33 Transient voltage protection ..................................................... 33 Layout Guidelines....................................................................... 33 Galvanically Isolated Interface ................................................. 33 Microprocessor Interfacing....................................................... 33 Thermal and supply considerations......................................... 34 Outline Dimensions ....................................................................... 35 Ordering Guide .......................................................................... 35
REVISION HISTORY
PrE - Preliminary Version, November 22, 2007
Rev. PrE | Page 2 of 37
Preliminary Technical Data FUNCTIONAL BLOCK DIAGRAM
DVCC SELECT DVCC CAP1 CAP2 AVSS AVDD
AD5422
CLEA R SELECT CLEA R LATCH SCLK SDIN SDO
AD5422
R2 R3 BOOST INPUT SHIFT REGISTER AND CONTROL LOGIC
16
/
16-BIT DAC
IOUT FAULT RSET R1
POWER ON RESET
VREF RANGE SCALING
+VSENSE VOUT -VSENSE
DGND*
REFOUT
REFIN
AGND
CCOMP2 CCOMP1
*LFCSP Package
Figure 1.
Rev. PrE | Page 3 of 37
AD5422 SPECIFICATIONS
Preliminary Technical Data
AVDD = 10.8V to 40V, AVSS = -26.4V to -3V/0V, AVDD + |AVSS| < 52.8V, AGND = DGND = 0 V, REFIN= +5 V external; DVCC = 2.7 V to 5.5 V, VOUT : RL = 2 k, CL = 200 pF, IOUT : RL = 300, HL = 50mH; all specifications TMIN to TMAX, 10 V / 0 to 24 mA range unless otherwise noted. Table 2.
Parameter VOLTAGE OUTPUT Output Voltage Ranges Value1 0 to 5 0 to 10 -5 to +5 -10 to +10 Unit V V V V Output unloaded 16 0.1 3 0.012 1 5 3 1 3 0.05 8 0.05 3 16 0.1 0.012 1 +10 3 10 0.05 3 0.05 3 0.8 0.5 3 12 15 12 Bits % FSR max ppm typ % FSR max LSB max mV max ppm FSR/C max mV max ppm FSR/C max % FSR max ppm FSR/C max % FSR max ppm FSR/C max AVSS = 0 V Bits % FSR max % FSR max LSB max mV max ppm FSR/C max mV max % FSR max ppm FSR/C max % FSR max ppm FSR/C max V max V typ ppm FSR/C max ppm FSR/500 hr typ ppm FSR/1000 hr typ mA typ
Rev. PrE | Page 4 of 37
Test Conditions/Comments
ACCURACY Bipolar Output Resolution Total Unadjusted Error (TUE) TUE TC2 Relative Accuracy (INL) Differential Nonlinearity (DNL) Bipolar Zero Error Bipolar Zero TC2 Zero-Scale Error Zero-Scale TC2 Gain Error Gain TC2 Full-Scale Error Full-Scale TC2 Unipolar Output Resolution Total Unadjusted Error (TUE) Relative Accuracy (INL) Differential Nonlinearity (DNL) Zero Scale Error Zero Scale TC2 Offset Error Gain Error Gain TC2 Full-Scale Error Full-Scale TC2 OUTPUT CHARACTERISTICS2 Headroom Output Voltage TC Output Voltage Drift vs. Time Short-Circuit Current
Over temperature, supplies, and time, typically 0.05% FSR
Guaranteed monotonic @ 25C, error at other temperatures obtained using bipolar zero TC @ 25C, error at other temperatures obtained using zero scale TC @ 25C, error at other temperatures obtained using gain TC @ 25C, error at other temperatures obtained using gain TC
Over temperature, supplies, and time, typically 0.05% FSR Guaranteed monotonic (at 16 bit-resolution) @ 25C, error at other temperatures obtained using gain TC
@ 25C, error at other temperatures obtained using gain TC @ 25C, error at other temperatures obtained using gain TC
Vout = 3/4 of Full-Scale
Preliminary Technical Data
Parameter Load Capacitive Load Stability RL = RL = 2 k RL = DC Output Impedance Power-On Time DC PSRR CURRENT OUTPUT Output Current Ranges Value1 2 20 TBD 1 0.3 10 TBD Unit k min nF max nF max F max typ s typ V/V Test Conditions/Comments For specified performance
AD5422
External compensation capacitor of 4nF connected.
0 to 24 0 to 20 4 to 20 16 0.3 5 0.012 1 0.05 5 0.02 8 0.05 8 AVDD - 2.5 TBD TBD TBD 1 10 50
mA mA mA Bits % FSR max ppm/C typ % FSR max LSB max % FSR max v/C typ % FSR max ppm FSR/C max % FSR max ppm FSR/C V max ppm FSR/500 hr typ ppm FSR/1000 hr typ max H max A/V max M typ
ACCURACY Resolution Total Unadjusted Error (TUE) TUE TC2 Relative Accuracy (INL) Differential Nonlinearity (DNL) Offset Error Offset Error Drift Gain Error Gain TC2 Full-Scale Error Full-Scale TC2 OUTPUT CHARACTERISTICS2 Current Loop Compliance Voltage Output Current Drift vs. Time Resistive Load Inductive Load DC PSRR Output Impedance REFERENCE INPUT/OUTPUT Reference Input2 Reference Input Voltage DC Input Impedance Reference Range Reference Output Output Voltage Reference TC Output Noise (0.1 Hz to 10 Hz)2 Noise Spectral Density2 Output Voltage Drift vs. Time2 Capacitive Load Load Current Short Circuit Current Line Regulation2 Load Regulation2 Thermal Hysteresis2
Over temperature, supplies, and time, typically 0.1% FSR
Guaranteed monotonic
@ 25C, error at other temperatures obtained using gain TC @ 25C, error at other temperatures obtained using gain TC
5 30 4 to 5 4.998 to 5.002 10 18 120 40 50 TBD 5 7 10 TBD TBD
V nom k min V min to V max V min to V max ppm/C max V p-p typ nV/Hz typ ppm/500 hr typ ppm/1000 hr typ nF max mA typ mA typ ppm/V typ ppm/mA ppm
Rev. PrE | Page 5 of 37
1% for specified performance Typically 40 k
@ 25C
@ 10 kHz
AD5422
Parameter DIGITAL INPUTS2 VIH, Input High Voltage VIL, Input Low Voltage Input Current Pin Capacitance DIGITAL OUTPUTS 2 SDO VOL, Output Low Voltage VOH, Output High Voltage High Impedance Leakage Current High Impedance Output Capacitance FAULT VOL, Output Low Voltage VOL, Output Low Voltage VOH, Output High Voltage POWER REQUIREMENTS AVDD AVSS DVCC Input Voltage Output Voltage Output Load Current Short Circuit Current AIDD AISS DICC Power Dissipation Value1 2 0.8 1 10 Unit V min V max A max pF typ
Preliminary Technical Data
Test Conditions/Comments DVCC = 2.7 V to 5.5 V, JEDEC compliant
Per pin Per pin
0.4 DVCC - 0.5 1
V max V min A max
sinking 200 A sourcing 200 A
5 0.4 0.6 3.6 10.8 to 40 -26.4 to 0 2.7 to 5.5 4.5 5 20 TBD TBD 1 TBD TBD TBD
pF typ V max V typ V min V min to V max V min to V max V min to V max V typ mA typ mA typ mA mA mA max mW typ mW typ mW typ Internal supply disabled DVCC can be overdriven up to 5.5V 10k pull-up resistor to DVCC @ 2.5 mA 10k pull-up resistor to DVCC
Output unloaded Output unloaded VIH = DVCC, VIL = GND, TBD mA typ AVDD = 40V, AVSS = 0 V, VOUT unloaded AVDD = 40V, AVSS = -15 V, VOUT unloaded AVDD = 15V, AVSS = -15 V, VOUT unloaded
1 2
Temperature range: -40C to +85C; typical at +25C. Guaranteed by characterization. Not production tested.
Rev. PrE | Page 6 of 37
Preliminary Technical Data
AC PERFORMANCE CHARACTERISTICS
AVDD = 10.8V to 40V, AVSS = -26.4V to -3V/0V, AVDD + |AVSS| < 52.8V, AGND = DGND = 0 V, REFIN= +5 V external; DVCC = 2.7 V to 5.5 V, VOUT : RL = 2 k, CL = 200 pF, IOUT : RL = 300, HL = 50mH; all specifications TMIN to TMAX, 10 V / 0 to 24 mA range unless otherwise noted. Table 3.
Parameter1 DYNAMIC PERFORMANCE VOLTAGE OUTPUT Output Voltage Settling Time Unit Test Conditions/Comments
AD5422
Output Current Settling Time Slew Rate Power-On Glitch Energy Digital-to-Analog Glitch Energy Glitch Impulse Peak Amplitude Digital Feedthrough Output Noise (0.1 Hz to 10 Hz Bandwidth) Output Noise (100 kHz Bandwidth) 1/f Corner Frequency Output Noise Spectral Density AC PSRR CURRENT OUTPUT Output Current Settling Time
8 10 5 10 1 10 10 20 1 0.1 80 1 100 TBD
s typ s max s max s max V/s typ nV-sec typ nV-sec typ mV typ nV-sec typ LSB p-p typ V rms max kHz typ nV/Hz typ dB
Full-scale step (10 V) to 0.03% FSR 512 LSB step settling To 0.1% FSR
Measured at 10 kHz 200mV 50/60Hz Sinewave superimposed on power supply voltage. To 0.1% FSR , L = 1H To 0.1% FSR , L < 1mH
TBD TBD
s typ s typ
1
Guaranteed by characterization, not production tested.
Rev. PrE | Page 7 of 37
AD5422
TIMING CHARACTERISTICS
Preliminary Technical Data
AVDD = 10.8V to 40V, AVSS = -26.4V to -3V/0V, AVDD + |AVSS| < 52.8V, AGND = DGND = 0 V, REFIN= +5 V external; DVCC = 2.7 V to 5.5 V, VOUT : RL = 2 k, CL = 200 pF, IOUT : RL = 300, HL = 50mH; all specifications TMIN to TMAX, 10 V / 0 to 24 mA range unless otherwise noted. Table 4.
Parameter1, 2, 3 Write Mode t1 t2 t3 t4 t5 t5 t6 t7 t8 t9 t10 Readback Mode t11 t12 t13 t14 t15 t16 t17 t18 t19 t20 Daisychain Mode t21 t22 t23 t24 t25 t26 t27 t28 t29 Limit at TMIN, TMAX 33 13 13 13 40 5 5 5 40 20 5 82 33 33 13 40 5 5 40 40 33 82 33 33 13 40 5 5 40 40 Unit ns min ns min ns min ns min ns min s min ns min ns min ns min ns min s max ns min ns min ns min ns min ns min ns min ns min ns min ns max ns max ns min ns min ns min ns min ns min ns min ns min ns min ns max Description SCLK cycle time SCLK low time SCLK high time LATCH delay time LATCH high time LATCH high time (After a write to the CONTROL register) Data setup time Data hold time LATCH low time CLEAR pulsewidth CLEAR activation time SCLK cycle time SCLK low time SCLK high time LATCH delay time LATCH high time Data setup time Data hold time LATCH low time Serial output delay time (CL SDO4 = 15pF) LATCH rising edge to SDO tri-state SCLK cycle time SCLK low time SCLK high time LATCH delay time LATCH high time Data setup time Data hold time LATCH low time Serial output delay time (CL SDO4 = 15pF)
1 2
Guaranteed by characterization. Not production tested. All input signals are specified with tR = tF = 5 ns (10% to 90% of DVCC) and timed from a voltage level of 1.2 V. 3 See Figure 2, Figure 3, and Figure 4. 4 CL SDO = Capacitive load on SDO output. Rev. PrE | Page 8 of 37
Preliminary Technical Data
t1
SCLK 1 2 24
AD5422
t2
t3
t4
t5
LATCH
t6
SDIN DB23
t7
t8
DB0
CLEAR
t9
t10
OUTPUT
Figure 2. Write Mode Timing Diagram
t11
SCLK 1 2 24 1 2 8 9 22 23 24
t12
t13
t14
t15
LATCH
t16
SDIN DB23
t17
t18
DB0 DB23 NOP CONDITION DB0
INPUT WORD SPECIFIES REGISTER TO BE READ SDO UNDEFINED DATA X X X
t 19
X DB15 SELECTED REGISTER DATA CLOCKED OUT DB0
t 20
FIRST 8 BITS ARE DON'T CARE BITS
Figure 3. Readback Mode Timing Diagram
t21
SCLK 1 2 24 25 26 48
t22
t23
t24
t25
LATCH
t26
SDIN DB23 INPUT WORD FOR DAC N SDO DB23 UNDEFINED DB0 DB23
t27
t28
DB0
t 29
DB0 DB23
INPUT WORD FOR DAC N-1 DB0 INPUT WORD FOR DAC N
Figure 4. Daisychain Mode Timing Diagram
Rev. PrE | Page 9 of 37
AD5422 ABSOLUTE MAXIMUM RATINGS
TA = 25C unless otherwise noted. Transient currents of up to 100 mA do not cause SCR latch-up. Table 5.
Parameter AVDD to AGND, DGND AVSS to AGND, DGND AVDD to AVSS DVCC to AGND, DGND Digital Inputs to AGND, DGND Digital Outputs to AGND, DGND REFIN/REFOUT to AGND, DGND VOUT to AGND, DGND IOUT to AGND, DGND AGND to DGND Operating Temperature Range Industrial Storage Temperature Range Junction Temperature (TJ max) 24-Lead TSSOP Package JA Thermal Impedance 40-Lead LFCSP Package JA Thermal Impedance Power Dissipation Lead Temperature Soldering Rating -0.3V to 48V +0.3 V to -48 V -0.3V to 60V -0.3 V to +7 V -0.3 V to DVCC + 0.3 V or 7 V (whichever is less) -0.3 V to DVCC + 0.3 V or 7V (whichever is less) -0.3 V to +7 V AVSS to AVDD -0.3V to AVDD -0.3V to +0.3V -40C to +851C -65C to +150C 125C
1
Preliminary Technical Data
Stresses above those listed under Absolute Maximum Ratings may cause permanent damage to the device. This is a stress rating only; functional operation of the device at these or any other conditions above those indicated in the operational section of this specification is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability.
ESD CAUTION
42C/W 28C/W (TJ max - TA)/ JA JEDEC Industry Standard J-STD-020
Power dissipated on chip must be de-rated to keep junction temperature below 125C. Assumption is max power dissipation condition is sourcing 24mA into Ground from AVDD with a 3mA on-chip current.
Rev. PrE | Page 10 of 37
Preliminary Technical Data PIN CONFIGURATION AND FUNCTION DESCRIPTIONS
+VSENSE DVCC -VSENSE AVDD AVSS NC NC NC NC
AD5422
AVSS
1
24 AVDD 23 -VSENSE
DVCC 2 FAULT GND
3 4
40
39
38
37
36
35
34
33
32
VOUT
31 30 29 28 27
AD5422
22 +VSENSE 21 VOUT
NC 1 FAULT 2 GND 3 CLEAR SELECT 4 CLEAR 5 LATCH 6 SCLK 7 SDIN 8 SDO 9 NC 10
11 12 13 14 15 16 17 18 19 20
NC CAP2 CAP1 BOOST IOUT CCOMP2 CCOMP1 DVCC SELECT NC NC
CLEAR SELECT 5 CLEAR
6
20 BOOST TOP VIEW (Not to Scale) 19 I OUT 18 CCOMP2 17 CCOMP1 16 DVCC SELECT 15 REFIN 14 REFOUT 13 RSET
AD5422
TOP VIEW (Not to Scale)
26 25 24 23 22 21
LATCH 7 SCLK SDIN
8 9
SDO 10 AGND 11 GND 12
RSET
REFOUT
REFIN
AVSS
AGND
DGND
GND
NC
NC
Figure 5. TSSOP Pin Configuration
Figure 6. LFCSP Pin Configuration
Table 6. Pin Function Descriptions
TSSOP Pin No. 1 2 3 LFCSP Pin No. 14,37 39 2 Mnemonic AVSS DVCC FAULT Description Negative Analog Supply Pin. Voltage ranges from -3 V to -24 V. This pin can be connected to 0V if output voltage range is unipolar. Digital Supply Pin. Voltage ranges from 2.7 V to 5.5 V. Fault alert, This pin is asserted low when an open circuit is detected in current mode or an over temperature is detected. Open drain output, must be connected to a pull-up resistor. These pins must be connected to 0V. No Connection.
4,12
5 6
3,15 1,10,11,19, 20,21,22,30, 31,35,38,40 4 5
GND NC
CLEAR SELECT CLEAR
Selects the voltage output clear value, either zero-scale or mid-scale code. See Table 20 Active High Input. Asserting this pin will set the current output to the bottom of the selected range or will set the voltage output to the user selected value (zero-scale or mid-scale). Positive edge sensitive latch, a rising edge will parallel load the input shift register data into the DAC register, also updating the output. Serial Clock Input. Data is clocked into the shift register on the rising edge of SCLK. This operates at clock speeds up to 30 MHz. Serial Data Input. Data must be valid on the rising edge of SCLK. Serial Data Output. Used to clock data from the serial register in daisy-chain or readback mode. Data is clocked out on the falling edge of SCLK . See Figure 3 and Figure 4. Ground reference pin for analog circuitry. Ground reference pin for digital circuitry. (AGND and DGND are internally connected in TSSOP package). An external, precision, low drift 15k current setting resistor can be connected to this pin to improve the IOUT temperature drift performance. Refer to Features section. Internal Reference Voltage Output. REFOUT = 5 V 2 mV. External Reference Voltage Input. Reference input range is 4 V to 5 V. REFIN = 5 V for specified performance. This pin when connected to GND disables the internal supply and an external supply must be connected to the DVCC pin. Leave this pin unconnected to enable the internal supply. Refer to features section. Optional compensation capacitor connection for the voltage output buffer. Connecting a 4nF capacitor between these pins will allow the voltage output to drive up to 1F.
Rev. PrE | Page 11 of 37
7 8 9 10 11 N/A 13 14 15 16
6 7 8 9 12 13 16 17 18 23
LATCH SCLK SDIN SDO AGND DGND RSET REFOUT REFIN DVCC SELECT CCOMP1 CCOMP2
17 18
24 25
NC
AD5422
TSSOP Pin No. 19 20 N/A N/A 21 22 23 24 Paddle LFCSP Pin No. 26 27 28 29 32 33 34 36 Paddle Mnemonic IOUT BOOST CAP1 CAP2 VOUT +VSENSE -VSENSE AVDD AVSS
Preliminary Technical Data
Description Current output pin. Optional external transistor connection. Connecting an external transistor will reduce the power dissipated in the AD5422. Refer to the features section. Connection for optional output filtering capacitor. Refer to Features section. Connection for optional output filtering capacitor. Refer to Features section. Buffered Analog Output Voltage. The output amplifier is capable of directly driving a 2 k, 2000 pF load. Sense connection for the positive voltage output load connection. Sense connection for the negative voltage output load connection. Positive Analog Supply Pin. Voltage ranges from 10.8V to 60V. Negative Analog Supply Pin. Voltage ranges from -3 V to -24 V. This pin can be connected to 0V if output voltage range is unipolar.
Rev. PrE | Page 12 of 37
Preliminary Technical Data TYPICAL PERFORMANCE CHARACTERISTICS
VOLTAGE OUTPUT
AD5422
Figure 7. Integral Non Linearity Error vs DAC Code (Four Traces)
Figure 10. Integral Non Linearity vs. Temperature (Four Traces)
Figure 8. Differential Non Linearity Error vs. DAC Code (Four Traces)
Figure 11. Differential Non Linearity vs. Temperature (Four Traces)
Figure 9. Total Unadjusted Error vs. DAC Code (Four Traces)
Figure 12. Integral Non Linearity vs. Supply Voltage (Four Traces)
Rev. PrE | Page 13 of 37
AD5422
Preliminary Technical Data
Figure 13.Differential Non Linearity Error vs. Supply Voltage (Four Traces)
Figure 16. Total Unadjusted Error vs.Reference Voltage (Four Traces)
Figure 14. Integral Non Linearity Error vs. Reference Voltage (Four traces)
Figure 17. Total Unadjusted Error vs. Supply Voltage (Four Traces)
Figure 15. Differential Non Linearity Error vs. Reference Voltage (Four Traces)
Figure 18. Offset Error vs.Temperature
Rev. PrE | Page 14 of 37
Preliminary Technical Data
AD5422
Figure 19. Bipolar Zero Error vs. Temperature
Figure 22. Source and Sink Capability of Output Amplifier Zero-Scale Loaded
Figure 20. Gain Error vs. Temperature Figure 23.Full-Scale Positive Step
Figure 21. Source and Sink Capability of Output Amplifier Full-Scale Code Loaded
Figure 24. Full-Scale Negative Step
Rev. PrE | Page 15 of 37
AD5422
Preliminary Technical Data
Figure 25. Digital-to-Analog Glitch Energy
Figure 28. VOUT vs. Time on Power-up
Figure 26. Peak-to-Peak Noise (0.1Hz to 10Hz Bandwidth)
Figure 29. VOUT vs, Time on Output Enabled
Figure 27. Peak-to-Peak Noise (100kHz Bandwidth)
Rev. PrE | Page 16 of 37
Preliminary Technical Data TYPICAL PERFORMANCE CHARACTERISTICS
CURRENT OUTPUT
AD5422
Figure 30. Integral Non Linearity vs. Code
Figure 33. Integral Non Linearity vs. Temperature
Figure 31.Differential Non Linearity vs. Code
Figure 34. Differential Non Linearity vs. Temperature
Figure 32. Total Unadjusted Error vs. Code
Figure 35. Integral Non Linearity vs. Supply
Rev. PrE | Page 17 of 37
AD5422
Preliminary Technical Data
Figure 36. Differential Non Linearity vs. Supply Voltage
Figure 39. Total Unadjusted Error vs. Reference Voltage
Figure 37. Integral Non Linearity vs. Reference Voltage
Figure 40. Total Unadjusted Error vs. Supply Voltage
Figure 38. Differential Non Linearity vs. Reference Voltage
Figure 41. Offset Error vs. Temperature
Rev. PrE | Page 18 of 37
Preliminary Technical Data
AD5422
Figure 42. Gain Error vs. Temperature
Figure 44. IOUT vs. Time on Power-up
Figure 43. Voltage Compliance vs. Temperature
Figure 45. IOUT vs. Time on Output Enabled
Rev. PrE | Page 19 of 37
AD5422 TYPICAL PERFORMANCE CHARACTERISTICS
GENERAL
Preliminary Technical Data
Figure 46. DICC vs.Logic Input Voltage
Figure 49. DVCC Output Voltage vs. DICC Load Current
Figure 47. AIDD/AISS vs AVDD/AVSS
Figure 50. Refout Turn-on Transient
Figure 48. AIDD vs AVDD
Figure 51. Refout Output Noise (0.1Hz to 10Hz Bandwidth)
Rev. PrE | Page 20 of 37
Preliminary Technical Data
AD5422
Figure 52. Refout Output Noise (100kHz Bandwidth)
Figure 55. Refout Histogram of Thermal Hysteresis
Figure 53. Refout Line Transient
Figure 56. Refout Voltage vs. Load Current
Figure 54. Refout Load Transient
Rev. PrE | Page 21 of 37
AD5422 TERMINOLOGY
Relative Accuracy or Integral Nonlinearity (INL) For the DAC, relative accuracy, or integral nonlinearity (INL), is a measure of the maximum deviation, in LSBs, from a straight line passing through the endpoints of the DAC transfer function. A typical INL vs. code plot can be seen in Figure 7. Differential Nonlinearity (DNL) Differential nonlinearity (DNL) is the difference between the measured change and the ideal 1 LSB change between any two adjacent codes. A specified differential nonlinearity of 1 LSB maximum ensures monotonicity. This DAC is guaranteed monotonic by design. A typical DNL vs. code plot can be seen in Figure 10. Monotonicity A DAC is monotonic if the output either increases or remains constant for increasing digital input code. The AD5724R/ AD5734R/AD5754R are monotonic over their full operating temperature range. Bipolar Zero Error Bipolar zero error is the deviation of the analog output from the ideal half-scale output of 0 V when the DAC register is loaded with 0x8000 (straight binary coding) or 0x0000 (twos complement coding). A plot of bipolar zero error vs. temperature can be seen in Table TBD. Bipolar Zero TC Bipolar zero TC is a measure of the change in the bipolar zero error with a change in temperature. It is expressed in ppm FSR/C. Full-Scale Error Full-Scale error is a measure of the output error when full-scale code is loaded to the DAC register. Ideally, the output should be full-scale - 1 LSB. Full-scale error is expressed in percent of full-scale range (% FSR). Negative Full-Scale Error/Zero-Scale Error Negative full-scale error is the error in the DAC output voltage when 0x0000 (straight binary coding) or 0x8000 (twos complement coding) is loaded to the DAC register. Ideally, the output voltage should be negative full-scale - 1 LSB. A plot of zero-scale error vs. temperature can be seen in Table TBD Zero-Scale TC This is a measure of the change in zero-scale error with a change in temperature. Zero-scale error TC is expressed in ppm FSR/C. Output Voltage Settling Time Output voltage settling time is the amount of time it takes for the output to settle to a specified level for a full-scale input change. A plot of settling time can be seen in Table TBD
Preliminary Technical Data
Slew Rate The slew rate of a device is a limitation in the rate of change of the output voltage. The output slewing speed of a voltageoutput D/A converter is usually limited by the slew rate of the amplifier used at its output. Slew rate is measured from 10% to 90% of the output signal and is given in V/s. Gain Error This is a measure of the span error of the DAC. It is the deviation in slope of the DAC transfer characteristic from ideal expressed in % FSR. A plot of gain error vs. temperature can be seen in Table TBD Gain TC This is a measure of the change in gain error with changes in temperature. Gain Error TC is expressed in ppm FSR/C. Total Unadjusted Error Total unadjusted error (TUE) is a measure of the output error taking all the various errors into account, namely INL error, offset error, gain error, and output drift over supplies, temperature, and time. TUE is expressed in % FSR. Current Loop Voltage Compliance The maximum voltage at the IOUT pin for which the output currnet will be equal to the programmed value. Power-On Glitch Energy Power-on glitch energy is the impulse injected into the analog output when the AD5422 is powered-on. It is specified as the area of the glitch in nV-sec. See Table TBD Digital-to-Analog Glitch Impulse Digital-to-analog glitch impulse is the impulse injected into the analog output when the input code in the DAC register changes state, but the output voltage remains constant. It is normally specified as the area of the glitch in nV-sec and is measured when the digital input code is changed by 1 LSB at the major carry transition (0x7FFF to 0x8000). See Table TBD Glitch Impulse Peak Amplitude Glitch impulse peak amplitude is the peak amplitude of the impulse injected into the analog output when the input code in the DAC register changes state. It is specified as the amplitude of the glitch in mV and is measured when the digital input code is changed by 1 LSB at the major carry transition (0x7FFF to 0x8000). See Table TBD. Digital Feedthrough Digital feedthrough is a measure of the impulse injected into the analog output of the DAC from the digital inputs of the DAC, but is measured when the DAC output is not updated. It is specified in nV-sec and measured with a full-scale code change on the data bus. Power Supply Rejection Ratio (PSRR) PSRR indicates how the output of the DAC is affected by changes in the power supply voltage. Reference TC
Rev. PrE | Page 22 of 37
Preliminary Technical Data
Reference TC is a measure of the change in the reference output voltage with a change in temperature. It is expressed in ppm/C. Line Regulation Line regulation is the change in reference output voltage due to a specified change in supply voltage. It is expressed in ppm/V. Load Regulation Load regulation is the change in reference output voltage due to a specified change in load current. It is expressed in ppm/mA. Thermal Hysteresis Thermal hysteresis is the change of reference output voltage after the device is cycled through temperatures from +25C to
AD5422
-40C to +85C and back to +25C. This is a typical value from a sample of parts put through such a cycle. See Table TBDfor a histogram of thermal hysteresis.
VO _ HYS = VO (25 C) - VO _ TC
VO _ HYS ( ppm) = where:
VO(25C) = VO at 25C VO_TC = VO at 25C after temperature cycle
VO (25 C) - VO _ TC VO (25 C)
x 10 6
Rev. PrE | Page 23 of 37
AD5422 THEORY OF OPERATION
The AD5422 is a precision digital to current loop and voltage output converter designed to meet the requirements of industrial process control applications. It provides a high precision, fully integrated, low cost single-chip solution for generating current loop and unipolar/bipolar voltage outputs. The current ranges available are; 0 to 20mA, 0 to 24mA and 4 to 20mA, the voltage ranges available are; 0 to 5V, 5V, 0 to 10V and 10V, the current and voltage outputs are available on separate pins and only one is active at any one time. The desired output configuration is user selectable via the CONTROL register.
Preliminary Technical Data
+VSENSE VOUT -VSENSE
3V
R1 RL
16-BIT DAC
RANGE SCALING
REFIN
Figure 59. Voltage Output
ARCHITECTURE
The DAC core architecture of the AD5422 consists of two matched DAC sections. A simplified circuit diagram is shown in Figure 57. The 4 MSBs of the 16-bit data word are decoded to drive 15 switches, E1 to E15. Each of these switches connects 1 of 15 matched resistors to either ground or the reference buffer output. The remaining 12 bits of the data-word drive switches S0 to S11 of a 12-bit voltage mode R-2R ladder network.
R 2R 2R S0 VREF 2R S1 2R S11 R 2R E1 2R E2 2R E15 VOUT
Voltage Output Amplifier
The voltage output amplifier is capable of generating both unipolar and bipolar output voltages. It is capable of driving a load of 2 k in parallel with 1 F to AGND. The source and sink capabilities of the output amplifier can be seen in Figure TBD. The slew rate is 1 V/s with a full-scale settling time of 10 s, (10V step). Figure 59 shows the voltage output drving a load, RL on top of a common mode voltage of up to 3V. In output module applications where a cable could possibly become disconnected from +VSENSE resulting in the amplifier loop being broken and most probably resulting in large destructive voltages on VOUT, a resistor, R1, of value 2k to 5k should be included as shown to ensure the amplifier loop is kept closed.
12-BIT R-2R LADDER
FOUR MSBs DECODED INTO 15 EQUAL SEGMENTS
Driving Large Capacitive Loads
The voltage output amplifier is capable of driving capacitive loads of up to 1uF with the addition of a non-polarised 4nF compensation capacitor between the CCOMP1 and CCOMP2 pins. Without the compensation capacitor, up to 20nF capacitive loads can be driven.
Figure 57. DAC Ladder Structure
The voltage output from the DAC core is either converted to a current (see diagram, Figure 58) which is then mirrored to the supply rail so that the application simply sees a current source output with respect to ground or it is buffered and scaled to output a software selectable unipolar or bipolar voltage range (See diagram, Figure 59). The current and voltage are output on separate pins and cannot be output simultaneously.
AVDD R2 T2 A2 16-BIT DAC T1 A1 IOUT
Reference Buffers
The AD5422 can operate with either an external or internal reference. The reference input has an input range of 4 V to 5 V, 5 V for specified performance. This input voltage is then buffered before it is applied to the DAC.
SERIAL INTERFACE
R3
The AD5422 is controlled over a versatile 3-wire serial interface that operates at clock rates up to 30 MHz. It is compatible with SPI(R), QSPITM, MICROWIRETM, and DSP standards.
Input Shift Register
The input shift register is 24 bits wide. Data is loaded into the device MSB first as a 24-bit word under the control of a serial clock input, SCLK. Data is clocked in on the rising edge of SCLK. The input register consists of 8 control bits and 16 data bits as shown in Table 7. The 24 bit word is unconditionally latched on the rising edge of LATCH. Data will continue to be clocked in irrespective of the state of LATCH, on the rising edge of LATCH the data that is present in the input register will be latched, in other words the last 24 bits to be clocked in before
Rev. PrE | Page 24 of 37
R1
Figure 58. Voltage to Current conversion circuitry
Preliminary Technical Data
the rising edge of LATCH will be the data that is latched. The timing diagram for this operation is shown in Figure 2.
AD5422
Rev. PrE | Page 25 of 37
AD5422
Table 7. Input Shift Register Format
MSB D23 D22 D21 D20 D19 D18 ADDRESS WORD D17 D16 D15 D14 D13 D12 D11 D10
Preliminary Technical Data
D9 D8 D7 DATA WORD
D6
D5
D4
D3
D2
D1
LSB D0
Table 8. Control Word Functions
Address Word 00000000 00000001 00000010 01010101 01010110 Function No Operation (NOP) DATA Register Readback register value as per Read Address (See Table 10) CONTROL Register RESET Register
CONTROLLER DATA OUT SERIAL CLOCK CONTROL OUT
AD5422*
SDIN SCLK LATCH
DATA IN
SDO
SDIN
AD5422*
SCLK LATCH
Standalone Operation
The serial interface works with both a continuous and noncontinuous serial clock. A continuous SCLK source can only be used if LATCH is taken high after the correct number of data bits have been clocked in. In gated clock mode, a burst clock containing the exact number of clock cycles must be used, and LATCH must be taken high after the final clock to latch the data. The first rising edge of SCLK that clocks in the MSB of the dataword marks the beginning ot the write cycle. Exactly 24 rising clock edges must be applied to SCLK before LATCH is brought high. If LATCH is brought high before the 24th rising SCLK edge, the data written will be invalid. If more than 24 rising SCLK edges are applied before LATCH is brought high, the input data will also be invalid.
SDO
SDIN
AD5422*
SCLK LATCH
SDO
*ADDITIONAL PINS OMITTED FOR CLARITY
Figure 60. Daisy Chaining the AD5422
Rev. PrE | Page 26 of 37
Preliminary Technical Data
Daisy-Chain Operation
For systems that contain several devices, the SDO pin can be used to daisy chain several devices together as shown in Figure 60. This daisy-chain mode can be useful in system diagnostics and in reducing the number of serial interface lines. Daisychain mode is enabled by setting the DCEN bit of the CONTROL register. The first rising edge of SCLK that clocks in the MSB of the dataword marks the beginning of the write cycle. SCLK is continuously applied to the input shift register. If more than 24 clock pulses are applied, the data ripples out of the shift register and appears on the SDO line. This data is clocked out on the falling edge of SCLK and is valid on the next rising edge. By connecting the SDO of the first device to the SDIN input of the next device in the chain, a multidevice interface is constructed. Each device in the system requires 24 clock pulses. Therefore, the total number of clock cycles must equal 24 x N, where N is the total number of AD5422 devices in the chain. When the serial transfer to all devices is complete, LATCH is taken high. This latches the input data in each device in the daisy chain. The serial clock can be a continuous or a gated clock. A continuous SCLK source can only be used if LATCH is taken high after the correct number of clock cycles. In gated clock
AD5422
mode, a burst clock containing the exact number of clock cycles must be used, and LATCH must be taken high after the final clock to latch the data. See Figure 4 for a timing diagram.
Readback Operation
Readback mode is invoked by setting the control word and read address as shown in Table 9 and Table 10 when writing to the input register. The next write to the AD5422 should be a NOP command which will clock out the data from the previously addressed register as shown in Figure 3. By default the SDO pin is disabled, after having addressed the AD5422 for a read operation, a rising edge on LATCH will enable the SDO pin in anticipation of data being clocked out, after the data has been clocked out on SDO, a rising edge on LATCH will disable (tri-state) the SDO pin once again. To read back the data register for example, the following sequence should be implemented: 1. Write 0x020001 to the AD5422 input register. This configures the part for read mode with the data register selected. Follow this with a second write, a NOP condition, 0x000000 During this write, the data from the register is clocked out on the SDO line.
2.
Table 9. Input Shift Register Contents for a read operation
MSB D23 0 D22 0 D21 0 D20 0 D19 0 D18 0 D17 1 D16 0 D15 X D14 X D13 X D12 X D11 X D10 X D9 X D8 X D7 X D6 X D5 X D4 X D3 X D2 X LSB D1 D0 Read Address
Table 10. Read Address Decoding
Read Address 00 01 10 Function Read Status Register Read Data Register Read Control Register
Rev. PrE | Page 27 of 37
AD5422
DEFAULT CONFIGURATION
On initial power-up of the AD5422 the power-on-reset circuit ensures that all registers are loaded with zero-code, as such the default output is the current output with the 4mA to 20mA range selected, the current output until a value is programmed is 0mA. The voltage output pin will be in three-state. An alternative current range or a voltage output range may be selected via the CONTROL register.
Preliminary Technical Data
VREFIN is the reference voltage applied at the REFIN pin. Gain is an internal gain whose value depends on the output range selected by the user as shown in Table 11. Table 11.
Output Range +5 V +10 V 5 V 10 V Gain Value 1 2 2 4
TRANSFER FUNCTION
Voltage Output
For a unipolar voltage output range, the output voltage expression is given by
D VOUT = VREFIN x Gain N 2
Current Output
For the 0 to 20mA, 0 to 24mA and 4 to 20mA current output ranges the output current expressions are respectively given by
20mA I OUT = N x D 2
24mA I OUT = N x D 2 16mA I OUT = N x D + 4mA 2
where:
D is the decimal equivalent of the code loaded to the DAC. N is the bit resolution of the DAC.
For a bipolar voltage output range, the output voltage expression is given by
D VOUT = VREFIN x Gain N 2
- Gain x VREFIN 2
where:
D is the decimal equivalent of the code loaded to the DAC. N is the bit resolution of the DAC.
Rev. PrE | Page 28 of 37
Preliminary Technical Data
DATA REGISTER
AD5422
The DATA register is addressed by setting the control word of the input shift register to 0x01. The data to be written to the DATA register is entered in positions D15 to D0 as shown in Table 12,
Table 12. Programming the Data Register
MSB D15 D14 D13 D12 D11 D10 D9 D8 D7 DATA WORD D6 D5 D4 D3 D2 D1 LSB D0
CONTROL REGISTER
The CONTROL register is addressed by setting the control word of the input shift register to 0x55. The data to be written to the CONTROL register is entered in positions D15 to D0 as shown in Table 13. The CONTROL register functions are shown in Table 14.
Table 13. Programming the CONTROL Register
MSB D15 CLRSEL D14 OVRRNG D13 REXT D12 OUTEN D11 D10 D9 SR CLOCK D8 D7 D6 D5 SR STEP D4 SREN D3 DCEN D2 R2 D1 R1 LSB D0 R0
Table 14. Control Register Functions
Option CLRSEL OVRRNG Description See Table 20 for a description of the CLRSEL operation Setting this bit increases the voltage output range by 10%. Further details in Features section Setting this bit selects the external current setting resistor, Further details in Features section Output enable. This bit must be set to enable the outputs, The range bits select which output will be functional. See Features Section. Digital Slew Rate Control See Features Section. Digital Slew Rate Control Digital Slew Rate Control enable Daisychain enable Output range select. See Table 15
Table 15. Output Range Options
R2 0 0 0 0 1 1 1 R1 0 0 1 1 0 1 1 R0 0 1 0 1 1 0 1 Output Range Selected 0 to +5V Voltage Range 0 to 10V Voltage Range 5V Voltage Range 10V Voltage Range 4 to 20 mA Current Range 0 to 20 mA Current Range 0 to 24 mA Current Range
REXT
OUTEN
SR CLOCK SR STEP SREN DCEN R2,R1,R0
RESET REGISTER
The RESET register is addressed by setting the control word of the input shift register to 0x56. The data to be written to the RESET register is entered in positions D15 to D0 as shown in Table 16. The RESET register options are shown in Table 16 and Table 17.
Table 16. Programming the RESET Register
MSB D15 D14 D13 D12 D11 D10 D9 D8 D7 D6 D5 D4 D3 D2 D1 LSB D0 RESET
Table 17. RESET register Functions
Option RESET Description Setting this bit performs a reset operation, restoring the AD5422 to its initial power on state
Rev. PrE | Page 29 of 37
AD5422
STATUS REGISTER
Preliminary Technical Data
The STATUS register is a read only register. The STATUS register functionality is shown in Table 18 and Table 19.
Table 18. Decoding the STATUS Register
MSB D15 D14 D13 D12 D11 D10 D9 D8 D7 D6 D5 D4 D3 D2 IOUT FAULT D1 SLEW ACTIVE LSB D0 OVER TEMP
Table 19. STATUS Register Functions
Option IOUT FAULT SLEW ACTIVE OVER TEMP Description This bit will be set if a fault is detected on the IOUT pin. This bit will be set while the output value is slewing (slew rate control enabled) This bit will be set if the AD5422 core temperature exceeds approx. 150C.
Rev. PrE | Page 30 of 37
Preliminary Technical Data FEATURES
FAULT ALERT
The AD5422 is equipped with a FAULT pin, this is an opendrain output allowing several AD5422 devices to be connected together to one pull-up resistor for global fault detection. The FAULT pin is forced active by any one of the following fault scenarios; 1) The Voltage at IOUT attempts to rise above the compliance range, due to an open-loop circuit or insufficient power supply voltage. The IOUT current is controlled by a PMOS transistor and internal amplifier as shown in Figure 58. The internal circuitry that develops the fault output avoids using a comparator with "window limits" since this would require an actual output error before the FAULT output becomes active. Instead, the signal is generated when the internal amplifier in the output stage has less than approxiamately one volt of remaining drive capability (when the gate of the output PMOS transistor nearly reaches ground). Thus the FAULT output activates slightly before the compliance limit is reached. Since the comparison is made within the feedback loop of the output amplifier, the output accuracy is maintained by its open-loop gain and an output error does not occur before the FAULT output becomes active. If the core temperature of the AD5422 exceeds approx. 150C.
Table 20. CLEAR SELECT Options
CLR SELECT 0 1
AD5422
Output CLR Value Unipolar Output Range Bipolar Output Range 0V 0V Mid-Scale Negative Full-Scale
INTERNAL REFERENCE
The AD5422 contains an integrated +5V voltage reference with initial accuracy of 2mV max and a temperature drift coefficient of 10 ppm max. The reference voltage is buffered and externally available for use elsewhere within the system. See Figure 56 for a load regulation graph of the Integrated reference.
EXTERNAL CURRENT SETTING RESISTOR
Referring to Figure 58, R1 is an internal sense resistor as part of the voltage to current conversion circuitry. The stability of the output current over temperature is dependent on the stability of the value of R1. As a method of improving the stability of the output current over temperature an external precision 15k low drift resistor can be connected to the RSET pin of the AD5422 to be used instead of the internal resistor R1. The external resistor is selected via the CONTROL register. See Table 13.
VOLTAGE OUTPUT OVER-RANGE
An over-range facility is provided on the voltage output. When enabled via the CONTROL register, the selected output range will be over-ranged by 10%.
2)
The OPEN CCT and OVER TEMP bits of the STATUS register are used in conjunction with the FAULT pin to inform the user which one of the fault conditions caused the FAULT pin to be asserted. See Table 18 and Table 19.
DIGITAL POWER SUPPLY
By default the DVCC pin accepts a power supply of 2.7V to 5.5V, alternatively, via the DVCC SELECT pin an internal 4.5V power supply may be output on the DVCC pin for use as a digital power supply for other devices in the system or as a termination for pull-up resistors. This facility offers the advantage of not having to bring a digital supply across an isolation barrier. The internal power supply is enabled by leaving the DVCC SELECT pin unconnected. To disable the internal supply DVCC SELECT should be tied to 0V.
VOLTAGE OUTPUT SHORT CIRCUIT PROTECTION
Under normal operation the voltage output will sink/source 5mA and maintain specified operation. The maximum current that the voltage output will deliver is 10mA, this is the short circuit current.
ASYNCHRONOUS CLEAR (CLEAR)
CLEAR is an active high clear that allows the voltage output to be cleared to either zero-scale code or mid-scale code, userselectable via the CLEAR SELECT pin or the CLRSEL bit of the CONTROL register as described in Table 20. (The Clear select feature is a logical OR function of the CLEAR SELECT pin and the CLRSEL bit). The Current output will clear to the bottom of its programmed range. It is necessary to maintain CLEAR high for a minimum amount of time (see Figure 2) to complete the operation. When the CLEAR signal is returned low, the output remains at the cleared value until a new value is programmed.
EXTERNAL BOOST FUNCTION
The addition of an external boost transistor as shown in Figure 61 will reduce the power dissipated in the AD5422 by reducing the current flowing in the on-chip output transistor (dividing it by the current gain of the external circuit). A discrete NPN transistor with a breakdown voltage, BVCEO, greater than 60V can be used. The external boost capability has been developed for those users who may wish to use the AD5422 at the extremes of the supply voltage, load current and temperature range. The boost transistor can also be used to reduce the amount of temperature induced drift in the part. This will minimise the temperature induced drift of the on-chip voltage reference, which improves drift and linearity.
Rev. PrE | Page 31 of 37
AD5422
BOOST MJD31C OR PBSS8110Z
Preliminary Technical Data
Table 22. Slew Rate Step Size Options
SR STEP 000 001 010 011 100 101 110 111 Step Size (LSBs) 1 2 4 8 16 32 64 128
AD5422
IOUT
1k 0.022 F
RLOAD
Figure 61. External Boost Configuration
DIGITAL SLEW RATE CONTROL
The Slew Rate Control feature of the AD5422 allows the user to control the rate at which the output value changes. This feature is available on both the current and voltage outputs. With the slew rate control feature disabled the output value will change at a rate limited by the output drive circuitry and the attached load. If the user wishes to reduce the slew rate this can be achieved by enabling the slew rate control feature.With the feature enabled via the SREN bit of the CONTROL register, (See Table 13) the output, instead of slewing directly between two values, will step digitally at a rate defined by two parameters accessible via the CONTROL register as shown in Table 13. The parameters are SR CLOCK and SR STEP. SR CLOCK defines the rate at which the digital slew will be updated, e.g. if the selected update rate is 1MHz the output will update every 1s, SR STEP defines by how much the output value will change at each update. Together both parameters define the rate of change of the output value.Table 21 and Table 22 outline the range of values for both the SR CLOCK and SR STEP parameters.
Table 21. Slew Rate Update Clock Options
SR CLOCK 0000 0001 0010 0011 0100 0101 0110 0111 1000 1001 1010 1011 1100 1101 1110 1111 Update Clock Frequency (Hz) 1000000 500000 333333 250000 200000 100000 50000 33333 25000 20000 12500 10000 8333 6666 5000 3921
The following equation describes the slew rate as a function of the step size, the update clock frequency and the LSB size.
SlewRate =
Where:
StepSize x UpdateClockFrequency x LSBSize 1x 10 6
Slew Rate is expressed in A/s For IOUT or V/s for VOUT LSBSize = Fullscale Range / 65536
When the slew rate control feature is enabled, all output changes will change at the programmed slew rate, i.e. if the CLEAR pin is asserted the output will slew to the clear value at the programmed slew rate. The output can be halted at its current value with a write to the CONTROL register. To avoid halting the output slew, the SLEW ACTIVE bit can be used to check that the slew has completed before writing to the AD5422 registers. See Table 18.
IOUT FILTERING CAPACITORS
Two capacitors may be placed between the pins CAP1, CAP2 and AVDD as shown in Figure 62. The capacitors form a filter on the current output circuitry reducing the bandwidth and the rate of change of the output current.
AVDD C1 AVDD CAP1 C2
AD5422
CAP2 IOUT
AGND
Figure 62. IOUT Filtering Capacitors
Rev. PrE | Page 32 of 37
Preliminary Technical Data APPLICATIONS INFORMATION
DRIVING INDUCTIVE LOADS
When driving inductive or poorly defined loads connect a 0.01F capacitor between IOUT and GND. This will ensure stability with loads beyond 50mH. There is no maximum capacitance limit. The capacitive component of the load may cause slower settling, though this may be masked by the settling time of the AD5422.
AD5422
avoid radiating noise to other parts of the board and should never be run near the reference inputs. A ground line routed between the SDIN and SCLK lines helps reduce crosstalk between them (not required on a multilayer board that has a separate ground plane, but separating the lines helps). It is essential to minimize noise on the REFIN line because it couples through to the DAC output. Avoid crossover of digital and analog signals. Traces on opposite sides of the board should run at right angles to each other. This reduces the effects of feed through the board. A microstrip technique is by far the best, but not always possible with a double-sided board. In this technique, the component side of the board is dedicated to ground plane, while signal traces are placed on the solder side.
TRANSIENT VOLTAGE PROTECTION
The AD5422 contains ESD protection diodes which prevent damage from normal handling. The industrial control environment can, however, subject I/O circuits to much higher transients. In order to protect the AD5422 from excessively high voltage transients , external power diodes and a surge current limiting resistor may be required, as shown in Figure 63. The constraint on the resistor value is that during normal operation the output level at IOUT must remain within its voltage compliance limit of AVDD - 2.5V and the two protection diodes and resistor must have appropriate power ratings.
AVDD
GALVANICALLY ISOLATED INTERFACE
In many process control applications, it is necessary to provide an isolation barrier between the controller and the unit being controlled to protect and isolate the controlling circuitry from any hazardous common-mode voltages that might occur. The iCoupler(R) family of products from Analog Devices provides voltage isolation in excess of 2.5 kV. The serial loading structure of the AD5422 make it ideal for isolated interfaces because the number of interface lines is kept to a minimum. Figure 64 shows a 4-channel isolated interface to the AD5422 using an ADuM1400. For further information, visit http://www.analog.com/icouplers.
AVDD
AD5422
IOUT
RP RLOAD
AGND
Figure 63. Output Transient Voltage Protection
LAYOUT GUIDELINES
In any circuit where accuracy is important, careful consideration of the power supply and ground return layout helps to ensure the rated performance. The printed circuit board on which the AD5422 is mounted should be designed so that the analog and digital sections are separated and confined to certain areas of the board. If the AD5422 is in a system where multiple devices require an AGND-to-DGND connection, the connection should be made at one point only. The star ground point should be established as close as possible to the device. The AD5422 should have ample supply bypassing of 10 F in parallel with 0.1 F on each supply located as close to the package as possible, ideally right up against the device. The 10 F capacitors are the tantalum bead type. The 0.1 F capacitor should have low effective series resistance (ESR) and low effective series inductance (ESI) such as the common ceramic types, which provide a low impedance path to ground at high frequencies to handle transient currents due to internal logic switching. The power supply lines of the AD5422 should use as large a trace as possible to provide low impedance paths and reduce the effects of glitches on the power supply line. Fast switching signals such as clocks should be shielded with digital ground to
Controller Serial Clock Out Serial Data Out SYNC Out Control out
ADuM1400 * VIA VIB VIC VID ENCODE ENCODE ENCODE ENCODE DECODE DECODE DECODE DECODE VOA VOB VOC VOD To SCLK To SDIN To LATCH To CLEAR
*ADDITIONAL PINS OMITTED FOR CLARITY
Figure 64. Isolated Interface
MICROPROCESSOR INTERFACING
Microprocessor interfacing to the AD5422 is via a serial bus that uses protocol compatible with microcontrollers and DSP processors. The communications channel is a 3-wire (minimum) interface consisting of a clock signal, a data signal, and a latch signal. The AD5422 require a 24-bit data-word with data valid on the rising edge of SCLK. For all interfaces, the DAC output update is initiated on the rising edge of LATCH. The contents of the registers can be read using the readback function.
Rev. PrE | Page 33 of 37
AD5422
THERMAL AND SUPPLY CONSIDERATIONS
The AD5422 is designed to operate at a maximum junction temperature of 125C. It is important that the device is not operated under conditions that will cause the junction temperature to exceed this value . Excessive junction temperature can occur if the AD5422 is operated from the maximum AVDD and driving the maximum current (24mA) directly to ground. In this case the ambient temperature should be controlled or AVDD should be reduced. The conditions will depend on the device package.
2.5
TSSOP LFCSP
Preliminary Technical Data
At maximum ambient temperature of 85C the 24-lead TSSOP package can dissipate 950mW and the 40-lead LFCSP package can dissipate 1.42W. To ensure the junction temperature does not exceed 125C while driving the maximum current of 24mA directly into ground (also adding an on-chip current of 3mA), AVDD should be reduced from the maximum rating to ensure the package is not required to dissipate more power than stated above. See Table 23, Figure 65 and Figure 66.
45 43 41 39 TSSOP LFCSP
2 Power Dissipation (W)
1.5
Supply Voltage (V)
37 35 33 31
1
0.5
29 27
0 40 45 50 55 60 65 70 Ambient Temperature (C) 75 80 85
25 25 35 45 55
Ambient Temperature (C)
65
75
85
Figure 65. Maximum Power Dissipation Vs Ambient Temperature
Figure 66. Maximum Supply Voltage Vs Ambient Temperature
Table 23. Thermal and Supply considerations for each package
TSSOP Maximum allowed power dissipation when operating at an ambient temperature of 85C Maximum allowed ambient temperature when operating from a supply of 60V and driving 24mA directly to ground. Maximum allowed supply voltage when operating at an ambient temperature of 85C and driving 24mA directly to ground. LFCSP
TJ max - TA JA
=
125 - 85 42
= 950 mW
TJ max - TA JA
=
125 - 85 28
= 1.42W
TJ max - PD x JA = 125 - 40 x 0.027 x 42 = 79C
TJ max - TA AI DD x JA 125 - 85 0.027 x 42
(
)
TJ max- PD x JA = 125 - 40 x 0.027 x 28 > 85C
TJ max - TA AI DD x JA 125 - 85 0.027 x 28
(
)
=
= 35V
=
= 53V
Rev. PrE | Page 34 of 37
Preliminary Technical Data OUTLINE DIMENSIONS
7.90 7.80 7.70 5.02 5.00 4.95
AD5422
24
13
4.50 4.40 4.30 6.40 BSC
1 12
EXPOSED PAD (Pins Up)
3.25 3.20 3.15
TOP VIEW 1.20 MAX 1.05 1.00 0.80 0.65 BSC 0.30 0.19
BOTTOM VIEW
8 0 0.20 0.09 0.75 0.60 0.45
COMPLIANT TO JEDEC STANDARDS MO-153-ADT
Figure 67. 24-Lead Thin Shrink Small Outline Package, Exposed Pad [TSSOP_EP] (RE-24) Dimensions shown in millimeters
6.00 BSC SQ 0.60 MAX
31 30 40 1
0.60 MAX PIN 1 INDICATOR
PIN 1 INDICATOR
TOP VIEW
5.75 BCS SQ
0.50 BSC 0.50 0.40 0.30
EXPOSED PAD
(BOT TOM VIEW)
4.25 4.10 SQ 3.95
10 11
21 20
0.25 MIN 4.50 REF
12 MAX
0.80 MAX 0.65 TYP 0.05 MAX 0.02 NOM
1.00 0.85 0.80
COMPLIANT TO JEDEC STANDARDS MO-220-VJJD-2
Figure 68. 40-Lead Lead Frame Chip Scale Package (CP-40) Dimensions shown in millimeters
ORDERING GUIDE
Model AD5422BREZ AD5422BCPZ Temperature Range -40C to 85C -40C to 85C Package Description 24 Lead TSSOP_EP 40 Lead LFCSP Package Option RE-24 CP-40
Rev. PrE | Page 35 of 37
101306-A
SEATING PLANE
0.30 0.23 0.18
0.20 REF
COPLANARITY 0.08
050806-A
SEATING PLANE 0.10 COPLANARITY
0.15 0.05
AD5422 NOTES
Preliminary Technical Data
Rev. PrE | Page 36 of 37
Preliminary Technical Data NOTES
AD5422
(c)2007 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners. PR06996-0-11/07(PrE)
Rev. PrE | Page 37 of 37

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