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19-2447; Rev 0; 4/02
KIT ATION EVALU ABLE AVAIL
Power Drivers for Peltier TEC Modules
General Description Features
o Direct Current Control Prevents TEC Current Surges o On-Chip Power MOSFETs o High-Efficiency Switch-Mode Design o Ripple Cancellation for Low Noise o No Dead-Zone or Hunting at Low-Output Current o Adjustable TEC Voltage Limit o Separately Adjustable Heating and Cooling Current Limits o ITEC Output Monitors TEC Current o 1% Accurate Voltage Reference o 500kHz/1MHz Switching Frequency o 3A Output Current (MAX1968) o 6A Output Current (MAX1969) o Thermally Enhanced TSSOP-EP Package
MAX1968/MAX1969
The MAX1968/MAX1969 are highly integrated and costeffective, high-efficiency, switch-mode drivers for Peltier thermoelectric cooler (TEC) modules. Both devices utilize direct current control to eliminate current surges in the TEC. On-chip FETs minimize external components while providing high efficiency. A 500kHz/1MHz switching frequency and a unique ripple cancellation scheme reduce component size and noise. The MAX1968 operates from a single supply and provides bipolar 3A output by biasing the TEC between the outputs of two synchronous buck regulators. Bipolar operation allows for temperature control without "dead zones" or other nonlinearities at low load currents. This arrangement ensures that the control system does not hunt when the set point is very close to the natural operating point, requiring a small amount of heating or cooling. An analog control signal precisely sets the TEC current. The MAX1969 provides unipolar output up to 6A. Reliability is optimized with settable limits for both TEC voltage and current, with independently set limits for heating and cooling current. An analog output also monitors TEC current. The MAX1968/MAX1969 are available in a low-profile 28-pin TSSOP-EP package and is specified over the -40C to +85C temperature range. The thermallyenhanced TSSOP-EP package with exposed metal pad minimizes operating junction temperature. An evaluation kit is available to speed designs.
Ordering Information
PART MAX1968EUI MAX1969EUI TEMP RANGE -40C to +85C -40C to +85C PIN-PACKAGE 28 TSSOP-EP* 28 TSSOP-EP*
*EP = exposed paddle
Applications
Fiber Optic Laser Modules WDM, DWDM Laser Diode Temperature Control Fiber Optic Network Equipment EDFA Optical Amplifiers Telecom Fiber Interfaces ATE Biotech Lab Equipment
CTLI COMP MAX1968 LX2 GND LX1 OS2 OS2 CS VDD PVDD1 PVDD2 PGND1 PGND2 3V TO TEC CURRENT- 5.5V CONTROL SIGNAL
Typical Operating Circuit
TEC
Pin Configuration and Functional Diagram appear at end of datasheet. ________________________________________________________________ Maxim Integrated Products 1
For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at 1-888-629-4642, or visit Maxim's website at www.maxim-ic.com.
Power Drivers for Peltier TEC Modules MAX1968/MAX1969
ABSOLUTE MAXIMUM RATINGS
VDD to GND ..............................................................-0.3V to +6V SHDN, MAXV, MAXIP, MAXIN, CTLI, FREQ to GND .......................................................-0.3V to +6V COMP, OS1, OS2, CS, REF, ITEC to GND ...........................................-0.3V to (VDD + 0.3V) PVDD1, PVDD2 to GND ...............................-0.3V to (VDD + 0.3V) PVDD1, PVDD2 to VDD ..................................................-0.3V to +0.3V PGND1, PGND2 to GND .......................................-0.3V to +0.3V COMP, REF, ITEC Short to GND ...................................Indefinite Peak LX Current (MAX1968) (Note 1).................................4.5A Peak LX Current (MAX1969) (Note 1)....................................+9A Continuous Power Dissipation (TA = +70C) 28-Pin TSSOP-EP (derate 23.8mW/C above +70C).....1.9W Operating Temperature Range ...........................-40C to +85C Maximum Junction Temperature .....................................+150C Storage Temperature Range .............................-65C to +150C Lead Temperature (soldering 10s) ..................................+300C
Note 1: LX has internal clamp diodes to PGND and PVDD_. Applications that forward bias these diodes should take care not to exceed the IC's package power dissipation limits.
Stresses beyond those listed under "Absolute Maximum Ratings" may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability.
ELECTRICAL CHARACTERISTICS
(VDD = PVDD1 = PVDD2 = SHDN = 5V, PGND1 = PGND2 = FREQ = GND, CTLI = MAXV = MAXIP = MAXIN = REF, CREF = 1F, CCOMP = 0.1F, LLX_ = 3.3H, CCS = COS2 = 1F, ITEC < 3ARMS (MAX1968), ITEC < 6ARMS (MAX1969), TA = 0C to +85C, unless otherwise noted. Typical values are at TA = +25C.)
PARAMETER Input Supply Range SYMBOL VDD VDD = 5V, ITEC = 0 to 3A, VOUT = VOS1 - VOS2 (MAX1968) VDD = 5V, ITEC = 0 to 6A, VOUT = VOS1 (MAX1969) VDD = 3V, ITEC = 0 to 3A, VOUT = VOS1 - VOS2 (MAX1968) VDD = 3V, ITEC = 0 to 6A, VOUT = VOS1 (MAX1969) Maximum TEC Current Reference Voltage Reference Load Regulation ITEC(MAX) VREF VREF MAX1968 MAX1969 VDD = 3V to 5.5V, IREF = 150A VDD = 3V to 5.5V, IREF = +10A to -1mA VOS1 < VCS VOS1 > VCS Switch-Fault Reset Voltage NFET On-Resistance PFET On-Resistance NFET Leakage RDS(ON-N) RDS(ON-P) ILEAK(N) VDD = 5V, I = 0.5A VDD = 3V, I = 0.5A VDD = 5V, I = 0.5A VDD = 3V, I = 0.5A VLX = VDD = 5V, TA = +25C VLX = VDD = 5V, TA = +85C VMAXI_ = VREF VMAXI_ = VREF/3 VMAXI_ = VREF VMAXI_ = VREF/3 140 40 140 40 50 1.485 1.500 1.2 150 50 150 50 150 0.04 0.06 0.06 0.09 0.02 1 -2.3 CONDITIONS MIN 3.0 -4.3 TYP MAX 5.5 +4.3 4.3 V +2.3 2.3 3 6 1.515 5 160 60 160 60 250 0.07 0.08 0.10 0.12 10 mV A mV A V mV UNITS V
Output Voltage Range
VOUT
Current-Sense Threshold Accuracy
2
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Power Drivers for Peltier TEC Modules
ELECTRICAL CHARACTERISTICS (continued)
(VDD = PVDD1 = PVDD2 = SHDN = 5V, PGND1 = PGND2 = FREQ = GND, CTLI = MAXV = MAXIP = MAXIN = REF, CREF = 1F, CCOMP = 0.01F, LLX_ = 3.3H, CCS = COS2 = 1F, ITEC < 3ARMS (MAX1968), ITEC < 6ARMS (MAX1969), TA = 0C to +85C, unless otherwise noted. Typical values are at TA = +25C.)
PARAMETER PFET Leakage No Load Supply Current Shutdown Supply Current Thermal Shutdown UVLO Threshold Switching Frequency Internal Oscillator OS1, OS2, CS Input Current SHDN, FREQ Input Current SHDN, FREQ Input Low Voltage SHDN, FREQ Input High Voltage SYMBOL ILEAK(P) IDD (NO LOAD) IDD-SD CONDITIONS VLX = 0, TA = +25C VLX = 0, TA = +85C VDD = 5V VDD = 3.3V VDD = 5V (Note 2) MIN TYP 0.02 1 32 20 2 +165 2.4 2.25 400 -100 -5 2.6 2.5 550 2.8 2.75 650 +100 +5 VDD x 0.25 VDD x 0.75 -2 -2 -0.1 9.5 0.5 50 VOS1 to VCS = +100mV or -100mV VITEC VOS1 to VCS = +100mV or -100mV, IITEC = 10A -10 -0.1 10 1.0 100 +2 +2 +0.1 10.5 2.0 175 +10 +0.1 100 30 3 MAX 10 A UNITS
MAX1968/MAX1969
mA mA C V kHz A A V V % % A V/V M A/V % %
TSHUTDOWN Hysteresis = 15C VUVLO fSW-INT IOS1, IOS2, ICS ISHDN, IFREQ VIL VIH VDD rising VDD falling FREQ = GND 0 or VDD 0 or VDD VDD = 3V to 5.5V VDD = 3V to 5.5V VMAXV = VREF x 0.67, VOS1 to VOS2 = 4V, VDD = 5V VMAXV = VREF x 0.33, VOS1 to VOS2 = 2V, VDD = 3V IMAXV-BIAS, IMAXI_-BIAS ACTLI RCTLI gm VMAXV = VMAXI_ = 0.1V or 1.5V VCTLI = 0.5V to 2.5V (Note 3) 1M terminated at REF
MAXV Threshold Accuracy
MAXV, MAXIP, MAXIN Input Bias Current CTLI Gain Accuracy CTLI Input Resistance Error-Amp Transconductance ITEC Accuracy ITEC Load Regulation
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Power Drivers for Peltier TEC Modules MAX1968/MAX1969
ELECTRICAL CHARACTERISTICS
(VDD = PVDD1 = PVDD2 = SHDN = 5V, PGND1 = PGND2 = FREQ = GND, CTLI = MAXV = MAXIP = MAXIN = REF, CREF = 1F, CCOMP = 0.1F, LLX_ = 3.3H, CCS = COS2 = 1F, ITEC < 3ARMS (MAX1968), ITEC < 6ARMS (MAX1969), TA = -40C to +85C, unless otherwise noted.) (Note 4)
PARAMETER Input Supply Range SYMBOL VDD VDD = 5V, ITEC = 0 to 3A, VOUT = VOS1 - VOS2 (MAX1968) VDD = 5V, ITEC = 0 to 6A, VOUT = VOS1 (MAX1969) VDD = 3V, ITEC = 0 to 3A, VOUT = VOS1 - VOS2 (MAX1968) VDD = 3V, ITEC = 0 to 6A, VOUT = VOS1 (MAX1969) Maximum TEC Current Reference Voltage Reference Load Regulation ITEC(MAX) VREF VREF MAX1968 MAX1969 VDD = 3V to 5.5V, IREF = 150A VDD = 3V to 5.5V, IREF = +10A to -1mA VOS1 < VCS VOS1 > VCS Switch-Fault Reset Voltage NFET On-Resistance PFET On-Resistance NFET Leakage PFET Leakage No Load Supply Current Shutdown Supply Current UVLO Threshold Switching-Frequency Internal Oscillator RDS(ON-N) RDS(ON-P) ILEAK(N) ILEAK(P) IDD(NO
LOAD)
CONDITIONS
MIN 3.0 -4.3
TYP
MAX 5.5 +4.3 4.3
UNITS V
Output Voltage Range
VOUT
V -2.3 +2.3 2.3 3 6 1.475 1.515 5 135 35 135 35 50 165 65 165 65 250 0.07 0.08 0.07 0.12 10 10 10 10 100 30 3 2.4 2.25 400 2.8 2.75 650 mV A A mA mA V kHz mV A V mV
VMAXI_ = VREF VMAXI_ = VREF / 3 VMAXI_ = VREF VMAXI_ = VREF / 3
Current-Sense Threshold Accuracy
VDD = 5V, I = 0.5A VDD = 3V, I = 0.5A VDD = 5V, I = 0.5A VDD = 3V, I = 0.5A VLX = VDD = 5V, TA = +25C VLX = VDD = 5V, TA = -40C VLX = 0, TA = +25C VLX = 0, TA = -40C VDD = 5V VDD = 3.3V SHDN = GND, VDD = 5V (Note 2) VDD rising VDD falling FREQ = GND
IDD-SD VUVLO fSW-INT
4
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Power Drivers for Peltier TEC Modules
ELECTRICAL CHARACTERISTICS (continued)
(VDD = PVDD1 = PVDD2 = SHDN = 5V, PGND1 = PGND2 = FREQ = GND, CTLI = MAXV = MAXIP = MAXIN = REF, CREF = 1F, CCOMP = 0.01F, LLX_ = 3.3H, CCS = COS2 = 1F, ITEC < 3ARMS (MAX1968), ITEC < 6ARMS (MAX1969), TA = -40C to +85C, unless otherwise noted.) (Note 4)
PARAMETER OS1, OS2, CS Input Current SHDN, FREQ Input Current SHDN, FREQ Input Low Voltage SHDN, FREQ Input High Voltage SYMBOL IOS1, IOS2, ICS ISHDN, IFREQ VIL VIH 0 or VDD 0 or VDD VDD = 3V to 5.5V VDD = 3V to 5.5V VMAXV = VREF x 0.67, VOS1 to VOS2 = 4V, VDD = 5V VMAXV = VREF x 0.33, VOS1 to VOS2 = 2V, VDD = 3V IMAXV-BIAS, IMAXI_-BIAS ACTLI RCTLI gm VOS1 to VCS = +100mV or -100mV VMAXV = VMAXI_ = 0.1V or 1.5V VCTLI = 0.5V to 2.5V (Note 3) 1M terminated at REF -0.1 9.5 0.5 50 -10 +0.1 10.5 2.0 175 +10 A V/V M A/V % VDD x 0.75 CONDITIONS MIN -100 -5 TYP MAX +100 +5 VDD x 0.25 V UNITS A A
MAX1968/MAX1969
MAXV Threshold Accuracy
-2
+2
%
MAXV, MAXIP, MAXIN Input Bias Current CTLI Gain Accuracy CTLI Input Resistance Error-Amp Transconductance ITEC Accuracy
Note 2: Includes power FET leakage. Note 3: CTLI Gain is defined as:
ACTLI =
(VCTLI - VREF ) VOS1 - VCS
Note 4: Specifications to -40C are guaranteed by design, not production tested.
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Power Drivers for Peltier TEC Modules MAX1968/MAX1969
Typical Operating Characteristics
(VDD = 5V, VCTLI = 1V, VFREQ = GND, RLOAD = 1, circuit of Figure 1, TA = +25C, unless otherwise noted.)
EFFICIENCY vs. TEC CURRENT VDD = 5V
MAX1968 toc01
EFFICIENCY vs. TEC CURRENT VDD = 3.3V
80 70 EFFICIENCY (%) 60 50 40 30 20 RLOAD = 0.85 VOS1 100mV/div AC-COUPLED FREQ = 500kHz
MAX1968 toc02
OUTPUT VOLTAGE RIPPLE
MAX1968 toc03
90 80 70 EFFICIENCY (%) 60 50 40 30 20 10 0 0 1 2 3 TEC CURRENT (A) RLOAD = 1 FREQ = 500kHz
90
VOS2 100mV/div AC-COUPLED
10 0 0 1
2
3
400ns/div
TEC CURRENT (A)
VDD RIPPLE
TEC CURRENT RIPPLE
MAX1968 toc04 MAX1968 toc05
TEC CURRENT vs. CTLI VOLTAGE
MAX1968 toc06
VCTLI 1V/div 0V VDD 100mV/div AC-COUPLED ITEC 2mA/div
ITEC 1A/div
0A
DC CURRENT = 1A 200ns/div 400ns/div 20ms/div
ZERO-CROSSING TEC CURRENT vs. CTLI VOLTAGE
MAX1968 toc07
VITEC vs. TEC CURRENT
MAX1968 toc08
ITEC vs. TEMPERATURE
1.012 1.010 TEC CURRENT (A) 1.008 1.006 1.004 1.002 1.000 0.998 0.996 FREQ = 500kHz VCTLI = 1.9V RTEC = 1 -40 -20 0 20 40 60 80
MAX1968 toc09
3.0 2.5 1.5V 2.0 VITEC (V)
1.014
VCTLI 100mV/div
ITEC 500mA/div
1.5 1.0 0.5 0
0A
0.994 -3 -1 1 3 TEC CURRENT (A) TEMPERATURE (C)
1ms/div
6
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Power Drivers for Peltier TEC Modules MAX1968/MAX1969
Typical Operating Characteristics (continued)
(VDD = 5V, VCTLI = 1V, VFREQ = GND, RLOAD = 1, circuit of Figure 1, TA = +25C, unless otherwise noted.)
SWITCHING FREQUENCY vs. TEMPERATURE
MAX1968 toc10
SWITCHING FREQUENCY CHANGE vs. VDD
MAX1968 toc11
REFERENCE VOLTAGE CHANGE vs. VDD
REFERENCE VOLTAGE CHANGE (mV) 0.5 0 -0.5 -1.0 -1.5 -2.0 -2.5 -3.0 -3.5
MAX1968 toc12
650 630 SWITCHING FREQUENCY (kHz) 610 590 570 550 530 510 490 470 450 -40 -20 0 20 40 60 80 TEMPERATURE (C) FREQ = 500kHz VCTLI = 1.5V RTEC = 1
35 SWITCHING FREQUENCY CHANGE (kHz) FREQ = 500kHz 30 25 20 15 10 5 0 3.0 3.5 4.0 4.5 5.0
1.0
5.5
3.0
3.5
4.0
4.5
5.0
5.5
VDD (V)
VDD (V)
REFERENCE VOLTAGE CHANGE vs. TEMPERATURE
MAX1968 toc13
REFERENCE LOAD REGULATION VDD = 3.3V
MAX1968 toc14
REFERENCE LOAD REGULATION VDD = 5V
REFERENCE VOLTAGE CHANGE (mV) 0.4 0.2 0 -0.2 -0.4 -0.6 -0.8 -1.0 -1.2 SINK SOURCE
MAX1968 toc15
2 REFERENCE VOLTAGE CHANGE (mV) 1 0 -1 -2 -3 -4 -5 -40 -20 0 20 40 60 80 TEMPERATURE (C)
0.6 REFERENCE VOLTAGE CHANGE (mV) 0.4 0.2 0 -0.2 -0.4 -0.6 -0.8 -1.0 -1.2 -1.4 -0.4 -0.2 0 0.2 0.4 0.6 0.8 SINK SOURCE
0.6
1.0
-0.4
-0.2
0
0.2
0.4
0.6
0.8
1.0
LOAD CURRENT (mA)
LOAD CURRENT (mA)
STARTUP AND SHUTDOWN WAVEFORMS
MAX1968 toc16
CTLI STEP RESPONSE
MAX1968 toc17
VDD STEP RESPONSE
MAX1968 toc18
VSHDN 5V/div IDD 200mA/div 0V VCTLI 1V/div 0A ITEC 500mA/div 0A VCTLI = 2V 2ms/div 1ms/div 0A ITEC 2A/div 1.5V
VDD 2V/div
0V ITEC 20mA/div 1A
10ms/div
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Power Drivers for Peltier TEC Modules MAX1968/MAX1969
Typical Operating Characteristics (continued)
(VDD = 5V, VCTLI = 1V, VFREQ = GND, RLOAD = 1, circuit of Figure 1, TA = +25C, unless otherwise noted.) THERMAL STABILITY, HEATING
MAX1968 toc19
THERMAL STABILITY, COOLING
MAX1968 toc20
TEMPERATURE 0.001C/div
TEMPERATURE 0.001C/div
TTEC = +25C TA = +5C 4s/div
TTEC = +25C TA = +45C 4s/div
THERMAL STABILITY, ROOM TEMPERATURE
MAX1968 toc21
TEMPERATURE 0.001C/div
TTEC = +25C TA = +25C 4s/div
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Power Drivers for Peltier TEC Modules
Pin Description
PIN 1 2 3 4 5, 7 6, 8, 10 9, 11 12 13 14 15 16 17 18, 20 19, 21, 23 22, 24 25 26 27 28 NAME VDD GND CTLI REF PGND2 LX2 PVDD2 FREQ ITEC OS2 OS1 CS SHDN PVDD1 LX1 PGND1 COMP MAXIN MAXIP MAXV Analog Supply Voltage Input Analog Ground. Connect to underside metal slug. TEC Current Control Input. Sets differential current into the TEC. Center point is 1.50V (no TEC current). The current is given by: ITEC = (VOS1 - VCS) / RSENSE = (VCTLI - 1.50) / (10 x RSENSE). When (VCTLI - VREF) > 0, VOS2 > VOS1 > VCS. 1.50V Reference Output. Bypass REF to GND with a 1F ceramic capacitor. Power Ground 2. Internal synchronous rectifier ground connections. Connect all PGND pins together at power ground plane. Inductor Connection. Connect all LX2 pins together. For MAX1969, connect LX1 and LX2 pins together. Power 2 Inputs. Must be same voltage as VDD. Connect all PVDD2 inputs together at the VDD power plane. Switching Frequency Select. High = 1MHz, Low = 500kHz. TEC Current Monitor Output. The ITEC output voltage is a function of the voltage across the TEC currentsense resistor. VITEC = 1.50V + (VOS1 - VCS) x 8. Output Sense 2. OS2 senses one side of the differential TEC voltage. OS2 is a sense point, not a power output. For MAX1969, connect OS2 to GND. Output Sense 1. OS1 senses one side of the differential TEC voltage. OS1 is a sense point, not a power output. Current-Sense Input. The current through the TEC is monitored between CS and OS1. The maximum TEC current is given by 150mV / RSENSE and is bipolar. Shutdown Control Input. Active-low shutdown control. Power 1 Inputs. Must be same voltage as VDD. Connect all PVDD1 inputs together at the VDD power plane. Inductor Connection. Connect all LX1 pins together. For MAX1969, connect all LX1 and LX2 pins together. Power Ground 1. Internal synchronous rectifier ground connections. Connect all PGND pins together at power ground plane. Current Control-Loop Compensation. For most designs connect a 0.01F capacitor from COMP to GND. Maximum Negative TEC Current. Connect MAXIN to REF to set default negative current limit -150mV / RSENSE. For MAX1969, connect MAXIN to GND. Maximum Positive TEC Current. Connect MAXIP to REF to set default positive current limit +150mV / RSENSE. Maximum Bipolar TEC Voltage. Connect an external resistive-divider from REF to GND to set the maximum voltage. The maximum TEC voltage is 4 x VMAXV. FUNCTION
MAX1968/MAX1969
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Power Drivers for Peltier TEC Modules MAX1968/MAX1969
Functional Diagram
ON OFF SHDN REF REF FREQ VDD PVDD1
3V TO 5.5V
MAXV
MAX VTEC = VMAXV 4 LX1
MAXIP
MAX ITEC = (VMAXIP / VREF) (0.15V / RSENSE) PGND1
MAXIN
MAX ITEC = -(VMAXIN / VREF) (0.15V / RSENSE)
PWM CONTROL AND GATE CONTROL
CS RSENSE OS1
CS OS2 ITEC OS1 PVDD2 VDD REF LX2
CTLI COMP
PGND2
GND
MAX1968
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Power Drivers for Peltier TEC Modules
Detailed Description
The MAX1968/MAX1969 TEC drivers consist of two switching buck regulators that operate together to directly control TEC current. This configuration creates a differential voltage across the TEC, allowing bidirectional TEC current for controlled cooling and heating. Controlled cooling and heating allow accurate TEC temperature control within the tight tolerances of laser driver specifications. The voltage at CTLI directly sets the TEC current. An external thermal-control loop is typically used to drive CTLI. Figures 1 and 2 show examples of thermal control-loop circuits.
Design Procedure
Inductor Selection
Small surface-mount inductors are ideal for use with the MAX1968/MAX1969. 3.3H inductors are suitable for most applications. Select the output inductors so that the LC resonant frequency of the inductance and the output capacitance is less than 1/5 the selected switching frequency. For example, 3.3H and 1F have a resonance at 87.6kHz, which is adequate for 500kHz operation f= where: f = resonant frequency of output filter. 1 2 LC
MAX1968/MAX1969
Ripple Cancellation
Switching regulators like those used in the MAX1968/MAX1969 inherently create ripple voltage on the output. The regulators in the MAX1968 switch in phase and provide complementary in-phase duty cycles so ripple waveforms at the TEC are greatly reduced. This feature suppresses ripple currents and electrical noise at the TEC to prevent interference with the laser diode.
Capacitor Selection
Filter Capacitors Decouple each power-supply input (V DD , PV DD 1, PVDD2) with a 1F ceramic capacitor close to the supply pins. In some applications with long distances between the source supply and the MAX1968/MAX1969, additional bypassing may be needed to stabilize the input supply. In such cases, a low-ESR electrolytic capacitor of 100F or more at VDD is usually sufficient. Compensation Capacitor A compensation capacitor is needed to ensure current control-loop stability. Select the capacitor so that the unity-gain bandwidth of the current control loop is less than or equal to 1/12th the resonant frequency of the output filter: R TEC g CCOMP m x f 2 x RSENSE where: f = loop frequency, less than or equal to the output filter resonant frequency gm = loop transconductance, typically 100A/V CCOMP = value of the compensation capacitor RTEC = TEC series resistance RSENSE = sense resistor
Switching Frequency
FREQ sets the switching frequency of the internal oscillator. With FREQ = GND, the oscillator frequency is set to 500kHz. The oscillator frequency is 1MHz when FREQ = VDD.
Voltage and Current-Limit Settings
Both the MAX1968 and MAX1969 provide control of the maximum differential TEC voltage. Applying a voltage to MAXV limits the maximum voltage across the TEC. The MAX1968 provides control of the maximum positive and negative TEC current. The voltage at MAXIP and MAXIN sets the maximum positive and negative current through the TEC. These current limits can be independently controlled. The MAX1969 only controls TEC current in one direction. The maximum TEC current is controlled by MAXIP. Connect MAXIN to GND when using the MAX1969.
Current Monitor Output
ITEC provides a voltage output proportional to the TEC current (ITEC). See the Functional Diagram for more detail: VITEC = 1.5V + 8 x (VOS1 - VCS)
Reference Output
The MAX1968/MAX1969 include an on-chip voltage reference. The 1.50V reference is accurate to 1% over temperature. Bypass REF with 1F to GND. REF may be used to bias an external thermistor for temperature sensing as shown in Figures 1 and 2.
Setting Voltage and Current Limits
Certain TEC parameters must be considered to guarantee a robust design. These include maximum positive current, maximum negative current, and the maximum voltage allowed across the TEC. These limits should be used to set the MAXIP, MAXIN, and MAXV voltages.
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Power Drivers for Peltier TEC Modules MAX1968/MAX1969
Setting Max Positive and Negative TEC Current
MAXIP and MAXIN set the maximum positive and negative TEC currents, respectively. The default current limit is 150mV / RSENSE when MAXIP and MAXIN are connected to REF. To set maximum limits other than the defaults, connect a resistor-divider from REF to GND to set VMAXI_. Use resistors in the 10k to 100k range. VMAXI_ is related to ITEC by the following equations: VMAXIP = 10(ITECP(MAX) x RSENSE) VMAXIN = 10(ITECN(MAX) x RSENSE) where ITECP(MAX) is the maximum positive TEC current and ITECN(MAX) is the negative maximum TEC current. Positive TEC current occurs when CS is less than OS1: ITEC x RSENSE = CS - OS1 when ITEC < 0. ITEC x RSENSE = OS1 - CS when ITEC > 0. The MAX1969 controls the TEC current in one direction (unipolar). Set the maximum unipolar TEC current by applying a voltage to MAXIP. Connect MAXIN to GND. The equation for setting MAXIP is the same for the MAX1968 and MAX1969. Take care not to exceed the positive or negative current limit on the TEC. Refer to the manufacturer's data sheet for these limits.
Control Inputs/Outputs
Output Current Control The voltage at CTLI directly sets the TEC current. CTLI is typically driven from the output of a temperature control loop. For the purposes of the following equations, it is assumed that positive TEC current is heating.The transfer function relating current through the TEC (ITEC) and VCTLI is given by: ITEC = (VCTLI - VREF)/(10 x RSENSE) where VREF is 1.50V and: ITEC = (VOS1 - VCS)/RSENSE CTLI is centered around REF (1.50V). ITEC is zero when CTLI = 1.50V. When VCTLI > 1.50V the MAX1968 is heating. Current flow is from OS2 to OS1. The voltages on the pins relate as follows: VOS2 > VOS1 > VCS The opposite applies when cooling. When VCTLI < 1.50V current flows from OS1 to OS2: VOS2 < VOS1 < VCS Shutdown Control The MAX1968/MAX1969 can be placed in a power-saving shutdown mode by driving SHDN low. When the MAX1968/MAX1969 are shut down, the TEC is off (OS1 and OS2 decay to GND) and supply current is reduced to 2mA (typ). ITEC Output ITEC is a status output that provides a voltage proportional to the actual TEC current. ITEC = REF when TEC current is zero. The transfer function for the ITEC output is: VITEC = 1.50 + 8 x (VOS1 - VCS) Use ITEC to monitor the cooling or heating current through the TEC. The maximum capacitance that ITEC can drive is 100pF.
Setting MAX TEC Voltage
Apply a voltage to the MAXV pin to control the maximum differential TEC voltage. MAXV can vary from 0 to REF. The voltage across the TEC is four times VMAXV and can be positive or negative: |VOS1 - VOS2| = 4 x VMAXV Set VMAXV with a resistor-divider between REF and GND using resistors from 10k to 100k. VMAXV can vary from 0 to REF.
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Power Drivers for Peltier TEC Modules MAX1968/MAX1969
3.3H VDD 1F FREQ 50m 10k LX1 CS 1F TO REF
3V TO 5.5V
MAX1968
PVDD1 1F PGND1 PVDD2 1F PGND2 OS2 3.3H REF 50k 1F 100k MAXIP MAXIN 100k ITEC ON MAXV 100k 240k 10F 0.022F VDD 1F VDD 10k 0.1F 0.1F 510k U3A U2 TO REF
MAX4475 MAX4477
OS1 10F
RTHERM
LX2 1F COMP 0.01F
CTL1
GND
SHDN OFF
100k TEMPERATURE SET POINT* 10k
10k
U3B *SEE FIGURE 2 FOR TEMPERATURE SET POINT SET BY A DAC
MAX4477
Figure 1. Typical Application Circuit for MAX1968
______________________________________________________________________________________
13
Power Drivers for Peltier TEC Modules MAX1968/MAX1969
3V TO 5.5V 1F
VDD
LX1 CS
3.3H 1F
TO REF
FREQ 25m PVDD1 1F PGND1 10F PVDD2 1F PGND2 MAX1969 REF 100k 50k 1F LX2 OS2 RTHERM OS1
10k
MAXIP MAXIN 100k
COMP 0.01F
ITEC ON MAXV 100k 10F 0.022F VDD 1 F 0.1F 10k CTLI 240k GND SHDN OFF VDD
0.1F
U3A
U2
MAX4475
510k to REF VDD 100k DAC INPUTS DAC
MAX5144
MAX4477
10k
*SEE FIGURE 1 FOR TEMPERATURE SET POINT SET BY A POTENTIOMETER
TEMPERATURE SET POINT*
U3B
MAX4477
Figure 2. Typical Application Circuit for MAX1969
14
______________________________________________________________________________________
Power Drivers for Peltier TEC Modules
Applications Information
The MAX1968/MAX1969 typically drive a thermoelectric cooler inside a thermal control loop. TEC drive polarity and power are regulated based on temperature information read from a thermistor, or other temperature-measuring device to maintain a stable control temperature. Temperature stability of 0.01C can be achieved with carefully selected external components. There are numerous ways to implement the thermal loop. Figures 1 and 2 show a design that employs precision op amps, along with a DAC or potentiometer to set the control temperature. The loop may also be implemented digitally, using a precision A/D to read the thermistor or other temperature sensor, a microcontroller to implement the control algorithm, and a DAC (or filtered PWM signal) to send the appropriate signal to the MAX1968/MAX1969 CTLI input. Regardless of the form taken by the thermal control circuitry, all designs are similar in that they read temperature, compare it to a set-point signal, and then send an error-correcting signal to the MAX1968/MAX1969 that moves the temperature in the appropriate direction. TRANSISTOR COUNT: 2959 PROCESS: BiCMOS
Chip Information
MAX1968/MAX1969
Pin Configuration
TOP VIEW
VDD 1 GND 2 CTLI 3 REF 4 PGND2 5 LX2 6 PGND2 7 LX2 8 PVDD2 9 LX2 10 PVDD2 11 FREQ 12 ITEC 13 OS2 14 28 MAXV 27 MAXIP 26 MAXIN 25 COMP 24 PGND1
MAX1968 MAX1969
23 LX1 22 PGND1 21 LX1 20 PVDD1 19 LX1 18 PVDD1 17 SHDN 16 CS 15 OS1
TSSOP-EP
NOTE: GND IS CONNECTED TO THE UNDERSIDE METAL SLUG.
______________________________________________________________________________________
15
Power Drivers for Peltier TEC Modules MAX1968/MAX1969
Package Information
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information, go to www.maxim-ic.com/packages.)
TSSOP, 4.0,EXP PADS.EPS
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
16 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 (c) 2002 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.

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