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LTM8022 1A, 36V DC/DC Module FEATURES
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DESCRIPTION
The LTM(R)8022 is a complete 1A, DC/DC step-down power supply. Included in the package are the switching controller, power switches, inductor, and all support components. Operating over an input voltage range of 3.6V to 36V, the LTM8022 supports an output voltage range of 0.8V to 10V, and a switching frequency range of 200kHz to 2.4MHz, each set by a single resistor. Only the bulk input and output filter capacitors are needed to finish the design. The low profile package (2.82mm) enables utilization of unused space on the bottom of PC boards for high density point of load regulation. The LTM8022 is packaged in a thermally enhanced, compact (11.25mm x 9mm) and low profile (2.82mm) overmolded Land Grid Array (LGA) package suitable for automated assembly by standard surface mount equipment. The LTM8022 is RoHS compliant.
, LT, LTC and LTM are registered trademarks of Linear Technology Corporation. Module is a trademark of Linear Technology Corporation. All other trademarks are the property of their respective owners.
Complete Step-Down Switch Mode Power Supply Wide Input Voltage Range: 3.6V to 36V 0.8V to 10V Output Voltage 1A Output Current Adjustable Switching Frequency: 200kHz to 2.4MHz Current Mode Control (e4) RoHS Compliant Package with Gold Pad Finish Programmable Soft-Start Tiny, Low Profile (11.25mm x 9mm x 2.82mm) Surface Mount LGA Package
APPLICATIONS
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Automotive Battery Regulation Power for Portable Products Distributed Supply Regulation Industrial Supplies Wall Transformer Regulation
TYPICAL APPLICATION
7VIN to 36VIN , 5V/1A ModuleTM Regulator
VIN* 7V TO 36V 2.2F VOUT 5V 1A 4.7F 80 SHARE BIAS PG RT GND SYNC ADJ 29.4k 93.1k 40
8022 TA01a
Efficiency and Power Loss
100 90 VIN = 12V 0.8 0.7 0.6 POWER LOSS (W) EFFICIENCY POWER LOSS 0.5 0.4 0.3 50 0.2 0.1 0.1 0.01 LOAD CURRENT (A) 1
8022 TA01b
VIN
VOUT
LTM8022 AUX RUN/SS
EFFICIENCY (%)
70 60
30 0.001
0
*RUNNING VOLTAGE RANGE. PLEASE REFER TO APPLICATIONS INFORMATION FOR START-UP DETAILS
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LTM8022 ABSOLUTE MAXIMUM RATINGS
(Note 1)
PIN CONFIGURATION
(See Table 3, Pin Assignment)
GND (BANK 3) 7 6 5 4 3 VOUT (BANK 2) 2 1 A B C D E F G H SYNC PG RUN/SS BIAS AUX SHARE RT ADJ
VIN, RUN/SS Voltage .................................................40V ADJ, RT, SHARE, Voltage .............................................5V VOUT , AUX .................................................................10V SYNC, PG ..................................................................30V BIAS ..........................................................................16V VIN + BIAS .................................................................56V Internal Operating Temperature.............. -40C to 125C Solder Temperature............................................... 250C Storage Temperature.............................. -55C to 125C
VIN (BANK 1)
LGA Package 50-Lead (11.25mm 9mm
2.82mm)
TJMAX = 125C, JA = 24C/W JA DERIVED FROM 6.6cm x 5cm 4-LAYER PCB, WEIGHT = 0.93g
ORDER INFORMATION
LEAD FREE FINISH LTM8022EV#PBF LTM8022IV#PBF LTM8022MPV#PBF PART MARKING* LTM8022V LTM8022V LTM8022MPV PACKAGE DESCRIPTION 50-Pin (11.25mm x 9mm x 2.82mm) LGA 50-Pin (11.25mm x 9mm x 2.82mm) LGA 50-Pin (11.25mm x 9mm x 2.82mm) LGA TEMPERATURE RANGE (Note 2) -40C to 85C -40C to 85C -55C to 125C
Consult LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container. Consult LTC Marketing for information on non-standard lead based finish parts. For more information on lead free part marking, go to: http://www.linear.com/leadfree/ This product is only offered in trays. For more information go to: http://linear.com/packaging/
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LTM8022 ELECTRICAL CHARACTERISTICS
SYMBOL VIN VOUT RADJ(MIN) IOUT(MAX) IQVIN PARAMETER Input DC Voltage Output DC Voltage Minimum Allowable RADJ Continuous Output DC Current VIN Quiescent Current 0V < IOUT < 1A, RADJ Open 0V < IOUT < 1A, RADJ = 43.2k (Note 3) 4V < VIN < 36V, COUT = 51F (Note 4) VRUN/SS = 0.2V, RT = 174k VBIAS = 3V, Not Switching, RT = 174k (E, I) VBIAS = 3V, Not Switching, RT = 174k (MP) VBIAS = 0V, Not Switching, RT = 174k VRUN/SS = 0.2V, RT = 174k VBIAS = 3V, Not Switching, RT = 174k (E, I) VBIAS = 3V, Not Switching, RT = 174k (MP) VBIAS = 0V, Not Switching, RT = 174k 3.6V < VIN < 36V, IOUT = 1A, VOUT = 3.3V VIN = 24V, 0V < IOUT < 1A, VOUT = 3.3V, COUT = 51F VIN = 24V, IOUT = 1A, VOUT = 3.3V, COUT = 51F RT = 113k, COUT = 51F VIN = 36V, VOUT = 0V COUT = 51F ADJ = 1V, COUT = 51F VRUN/SS = 2.5V COUT = 51F COUT = 51F VFB Rising VPG = 30V VPG = 0.4V fSYNC = 550kHz, COUT = 51F fSYNC = 550kHz, COUT = 51F VSYNC = 0V 0.1 200 0.5 0.7 730 0.1 800 1 2.5 0.2
l l l
The l denotes the specifications which apply over the full operating temp, , erature range, otherwise specifications are at TA = 25C. VIN = 10V, VRUN/SS = 10V, VBIAS = 3V, RT = 60.4k, CIN = 2.2F COUT = 4.7F unless otherwise specified. (Note 2)
CONDITIONS
l
MIN 3.6
TYP 0.8 10
MAX 36
UNITS V V V k
42.2 0 0.1 25 25 85 0.03 50 50 1 0.1 0.4 10 325 3 765 790 1.9 2 5 10 805 2.4 1 0.5 60 350 120 0.5 120 200 5
A A A A A A A A A % % mV kHz A mV V A A V V mV A A V V A
IQBIAS
BIAS Quiescent Current
l l
VOUT/VOUT VOUT/VOUT VOUT(AC_RMS) fSW ISC(OUT) VADJ VBIAS(MIN) IADJ IRUN/SS VIH(RUN/SS) VIL(RUN/SS) VPG(TH) IPGO IPG(SINK) VSYNC(IL) VSYNC(IH) ISYNC(BIAS)
Line Regulation Load Regulation Output Ripple (RMS) Switching Frequency Output Short-Circuit Current Voltage at ADJ Pin Minimum BIAS Voltage for Proper Operation Current Out of ADJ Pin RUN/SS Pin Current RUN/SS Input High Voltage RUN/SS Input Low Voltage PG Threshold PG Leakage PG Sink Current SYNC Low Threshold SYNC High Threshold SYNC Pin Bias Current
Note 1: Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. Exposure to any Absolute Maximum Rating condition for extended periods may affect device reliability and lifetime. Note 2: The LTM8022E is guaranteed to meet performance specifications from 0C to 85C ambient. Specifications over the full -40C to 85C ambient operating temperature range are assured by design, characterization and correlation with statistical process controls. The LTM8022I is guaranteed to meet specifications over the full -40C to 85C
ambient operating temperature range. The LTM8022MP is guaranteed to meet specifications over the full -55C to 125C temperature range. Note that the maximum internal temperature is determined by specific operating conditions in conjunction with board layout, the rated package thermal resistance and other environmental factors. Note 3: Guaranteed by design. Note 4: COUT = 51F is composed of a 4.7F ceramic capacitor and a 47F electrolytic.
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LTM8022 TYPICAL PERFORMANCE CHARACTERISTICS
Efficiency vs Load (8VOUT)
95 12VIN 90 24VIN EFFICIENCY (%) 85 EFFICIENCY (%) 36VIN 80 85 24VIN 36VIN EFFICIENCY (%) 90 12VIN
(TA = 25C, unless otherwise noted) Efficiency vs Load (3.3VOUT)
90 85 80 75 70 65 60 36VIN 5VIN 12VIN 24VIN
Efficiency vs Load (5VOUT)
80
75
75
70
70
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 OUTPUT CURRENT (A)
8022 G01
65
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 OUTPUT CURRENT (A)
8022 G02
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 OUTPUT CURRENT (A)
8022 G03
Minimum Required Input Voltage vs Output Voltage, IOUT = 1A
12 11 10 INPUT VOLTAGE (V) 9 8 7 6 5 4 3 2 0 2 4 6 8 OUTPUT VOLTAGE (V) 10
8022 G04
Output Start-up Waveform VIN = 36V, 5VOUT, IOUT = 1A
VOUT 2V/DIV IIN 0.2A/DIV RUN/SS 5V/DIV 50s/DIV
8022 G05
Output Start-up Waveform VIN = 36V, 3.3VOUT, IOUT = 1A
VOUT 2V/DIV IIN 0.2A/DIV RUN/SS 5V/DIV 50s/DIV
8022 G06
Input Current vs Output Current (8VOUT)
800 700 INPUT CURRENT (mA) INPUT CURRENT (mA) 600 500 12VIN 400 300 200 36VIN 100 0 0 200 400 800 600 OUTPUT CURRENT (mA) 1000
8022 G07
Input Current vs Output Current (5VOUT)
500 450 400 350 300 250 200 150 100 50 0 0 200 600 800 400 OUTPUT CURRENT (mA) 1000
8022 G08
Input Current vs Output Current (3.3VOUT)
900 800 700 INPUT CURRENT (mA) 600 500 400 300 200 100 36VIN 0 0 800 200 600 400 OUTPUT CURRENT (mA) 1000
8022 G09
24VIN
12VIN 24VIN 36VIN
5VIN
12VIN
24VIN
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LTM8022 TYPICAL PERFORMANCE CHARACTERISTICS
Output Current vs Input Voltage (Output Short)
3200 3000 OUTPUT CURRENT (mA) BIAS CURRENT (mA) 2800 2600 2400 2200 2000 1800 1600 0 10 20 INPUT VOLTAGE (V)
8022 G10
(TA = 25C, unless otherwise noted) Minimum Required Input Voltage vs Output Load (8VOUT)
1200 1000 LOAD CURRENT (mA) 800 600 400 200 0 1000
8022 G11
BIAS Quiescent Current vs Load Current
16 14 12 10 8 5VOUT 6 4 2 0 3.3VOUT 8VOUT
25C 85C 0 10 20 30 INPUT VOLTAGE (V) 40
8022 G13
30
40
0
200
400 800 600 LOAD CURRENT (mA)
Minimum Required Input Voltage vs Output Load (5VOUT)
1200 1000 LOAD CURRENT (mA) 800 600 400 200 0 0 10 20 30 INPUT VOLTAGE (V) 25C 85C 40
8022 G14
Minimum Required Input Voltage vs Output Load (3.3VOUT)
1200 1000 LOAD CURRENT (mA) 800 600 400 200 0 0 10 20 30 INPUT VOLTAGE (V) 25C 85C 40
8022 G15
Temperature Rise vs Load (3.3VOUT)
25 35 30 TEMPERATURE RISE (C) TEMPERATURE RISE (C)
Temperature Rise vs Load (5VOUT)
40 35 TEMPERATURE RISE (C) 30 25
Temperature Rise vs Load (8VOUT)
20
25 20 36VIN 15 12VIN 10 5 0 0 200 400 24VIN
15 36VIN 10 12VIN 24VIN 5
36VIN 20 15 10 5 0 12VIN
24VIN
0
0
200
400
600 800 LOAD (mA)
1000
1200
800 600 LOAD (mA)
1000
1200
0
200
400
800 600 LOAD (mA)
1000
1200
8022 G16
8022 G17
8022 G18
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LTM8022 PIN FUNCTIONS
VIN (Bank 1): The VIN pin supplies current to the LTM8022's internal regulator and to the internal power switch. This pin must be locally bypassed with an external, low ESR capacitor of at least 2.2F . VOUT (Bank 2): Power Output Pins. Apply the output filter capacitor and the output load between these pins and GND pins. AUX (Pin F5): Low current voltage source for BIAS. In many designs, the BIAS pin is simply connected to VOUT . The AUX pin is internally connected to VOUT and is placed adjacent to the BIAS pin to ease printed circuit board routing. Although this pin is internally connected to VOUT , do NOT connect this pin to the load. If this pin is not tied to BIAS, leave it floating. The Application Information section gives specific information about the BIAS and AUX connections BIAS (Pin G5): The BIAS pin connects to the internal power bus. Connect to a power source greater than 2.4V. If the output is greater than 2.4V, connect this pin there. If the output voltage is less, connect this to a voltage source between 2.4V and 30V. Also, make sure that BIAS + VIN is less than 56V. RUN/SS (Pin H5): Tie RUN/SS pin to ground to shut down the LTM8022. Tie to 2.5V or more for normal operation. If the shutdown feature is not used, tie this pin to the VIN pin. RUN/SS also provides a soft-start function; see the Applications Information section. GND (Bank 3): Tie these GND pins to a local ground plane below the LTM8022 and the circuit components. Return the feedback divider (RADJ) to this pin. RT (Pin G7): The RT pin is used to program the switching frequency of the LTM8022 by connecting a resistor from this pin to ground. The Applications Information section of the data sheet includes a table to determine the resistance value based on the desired switching frequency. Minimize capacitance at this pin. SHARE (Pin F7): Tie this to the SHARE pin of another LTM8022 when paralleling the outputs. Otherwise, leave this pin floating. SYNC (Pin G6): External Clock Synchronization Input. Ground this pin for low ripple Burst Mode(R) operation at low output loads, or connect to a stable voltage source above 0.7V to disable Burst Mode operation. Do not leave this pin floating. Tie to a clock source for synchronization. Clock edges should have rise and fall times faster than 1s. See Synchronization in the Applications Information section. PG (Pin H6): Open Collector Output of an Internal Comparator. PG remains low until the ADJ pin is within 10% of the final regulation voltage. PG output is valid when VIN is above 3.6V and RUN/SS is high. If this function is not used, leave this pin floating. ADJ (Pin H7): The LTM8022 regulates its ADJ pin to 0.79V. Connect the adjust resistor from this pin to ground. The value of RADJ is given by the equation, RADJ = 394.21/(VOUT - 0.79), where RADJ is in k.
Burst Mode is a registered trademark of Linear Technology Corporation.
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LTM8022 BLOCK DIAGRAM
VIN 0.1F 4.7H 4.7pF 499k 10F VOUT AUX
BIAS
SHARE CURRENT MODE CONTROLLER PG SYNC
RUN/SS
GND
RT
ADJ
8022 BD
OPERATION
The LTM8022 is a standalone non-isolated step-down switching DC/DC power supply. It can deliver up to 1A of DC output current with only bulk external input and output capacitors. This module provides a precisely regulated output voltage programmable via one external resistor from 0.8VDC to 10VDC. The input voltage range is 3.6V to 36V. Given that the LTM8022 is a step-down converter, make sure that the input voltage is high enough to support the desired output voltage and load current. A simplified Block Diagram is shown above. The LTM8022 contains a current mode controller, power switching element, power inductor, power Schottky diode and a modest amount of input and output capacitance. The LTM8022 is a fixed frequency PWM regulator. The switching frequency is set by simply connecting the appropriate value resistor from the RT pin to GND. An internal regulator provides power to the control circuitry. The bias regulator normally draws power from the VIN pin, but if the BIAS pin is connected to an external voltage higher than 2.4V, bias power will be drawn from the external source (typically the regulated output voltage). This improves efficiency. The RUN/SS pin is used to place the LTM8022 in shutdown, disconnecting the output and reducing the input current to less than 1A. To further optimize efficiency, the LTM8022 automatically switches to Burst Mode operation in light load situations. Between bursts, all circuitry associated with controlling the output switch is shut down reducing the input supply current to 50A in a typical application. The oscillator reduces the LTM8022's operating frequency when the voltage at the ADJ pin is low. This frequency foldback helps to control the output current during start-up and overload. The LTM8022 contains a power good comparator which trips when the ADJ pin is at 92% of its regulated value. The PG output is an open-collector transistor that is off when the output is in regulation, allowing an external resistor to pull the PG pin high. Power good is valid when the LTM8022 is enabled and VIN is above 3.6V.
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LTM8022 APPLICATIONS INFORMATION
Table 1. Recommended Component Values and Configuration
VIN* VOUT CIN COUT RADJ BIAS fOPTIMAL(kHz) 3.6V to 36V 0.82V 2.2F 247F 1206 13M 2.4V, <16V 250 3.6V to 36V 1V 2.2F 200F 1206 1.87M 2.4V, <16V 300 3.6V to 36V 1.2V 2.2F 100F 1206 953k 2.4V, <16V 325 3.6V to 36V 1.5V 2.2F 100F 1206 549k 2.4V, <16V 375 3.6V to 36V 1.8V 2.2F 68F 1206 383k 2.4V, <16V 450 3.8V to 36V 2V 2.2F 47F 1206 324k 2.4V, <16V 475 3.8V to 36V 2.2V 2.2F 47F 0805 274k 2.4V, <16V 525 3.8V to 36V 2.5V 2.2F 47F 0805 226k 2.4V, <16V 575 4.75V to 36V 3.3V 2.2F 22F 0805 154k AUX 750 6.8V to 36V 5V 2.2F 4.7F 1206 93.1k AUX 1000 11.5V to 36V 8V 2.2F 4.7F 0805 53.6k AUX 1200 3.6V to 15V 0.82V 2.2F 200F 1206 13M VIN 500 3.6V to 15V 1V 2.2F 147F 1206 1.87M VIN 615 3.6V to 15V 1.2V 2.2F 100F 1206 953k VIN 650 3.6V to 15V 1.5V 2.2F 100F 1206 549k VIN 700 3.6V to 15V 1.8V 2.2F 68F 1206 383k VIN 800 3.6V to 15V 2V 2.2F 47F 1206 324k VIN 800 3.6V to 15V 2.2V 2.2F 47F 0805 274k VIN 850 3.6V to 15V 2.5V 2.2F 47F 0805 226k VIN 950 4.75V to 15V 3.3V 2.2F 22F 0805 154k AUX 950 6.8V to 15V 5V 2.2F 4.7F 1206 93.1k AUX 1150 11.5V to 15V 8V 2.2F 4.7F 0805 53.6k AUX 1200 9V to 24V 0.82V 2.2F 247F 1206 13M 2.4V, <16V 375 9V to 24V 1V 2.2F 200F 1206 1.87M 2.4V, <16V 400 9V to 24V 1.2V 2.2F 100F 1206 953k 2.4V, <16V 450 9V to 24V 1.5V 2.2F 100F 1206 549k 2.4V, <16V 575 9V to 24V 1.8V 2.2F 68F 1206 383k 2.4V, <16V 650 9V to 24V 2V 2.2F 47F 0805 324k 2.4V, <16V 700 9V to 24V 2.2V 2.2F 22F 0805 274k 2.4V, <16V 775 9V to 24V 2.5V 2.2F 22F 0805 226k 2.4V, <16V 850 9V to 24V 3.3V 2.2F 22F 0805 154k AUX 950 9V to 24V 5V 2.2F 4.7F 1206 93.1k AUX 1150 11.5V to 24V 8V 2.2F 4.7F 0805 53.6k AUX 1200 18V to 24V 10V 2.2F 2.2F 0805 42.2k AUX 1250 18V to 36V 0.82V 2.2F 247F 1206 13M 2.4V, <16V 250 18V to 36V 1V 2.2F 200F 1206 1.87M 2.4V, <16V 300 18V to 36V 1.2V 2.2F 100F 1206 953k 2.4V, <16V 325 18V to 36V 1.5V 2.2F 100F 1206 549k 2.4V, <16V 375 18V to 36V 1.8V 2.2F 68F 1206 383k 2.4V, <16V 450 18V to 36V 2V 2.2F 47F 0805 324k 2.4V, <16V 475 18V to 36V 2.2V 2.2F 22F 0805 274k 2.4V, <16V 525 18V to 36V 2.5V 2.2F 22F 0805 226k 2.4V, <16V 575 18V to 36V 3.3V 2.2F 22F 0805 154k AUX 750 18V to 36V 5V 2.2F 4.7F 1206 93.1k AUX 1000 18V to 36V 8V 2.2F 4.7F 0805 53.6k AUX 1200 18V to 36V 10V 2.2F 2.2F 0805 42.2k AUX 1250 4.75V to 32V -3.3V 2.2F 22F 0805 154k AUX 700 7V to 31V -5V 2.2F 10F 0805 93.1k AUX 1000 13V to 28V -8V 2.2F 10F 0805 53.6k AUX 1100 *Running voltage range. Please refer to Applications Information for start-up details. RT(OPTIMAL) 150k 124k 113k 93.1k 79k 73.2k 64.9k 59.0k 42.2k 29.4k 23.7k 69.8k 54.9k 49.9k 44.2k 39.2k 39.2k 36.5k 31.6k 31.6k 25.5k 23.7k 93.1k 88.7k 79.0k 59.0k 49.9k 44.2k 41.2k 36.5k 31.6k 25.5k 23.7k 22.6k 150k 124k 113k 93.1k 79k 73.2k 64.9k 59.0k 42.2k 29.4k 23.7k 22.6k 44.2k 29.4k 26.7k fMAX (kHz) 250 300 325 375 450 475 525 575 750 1050 1600 615 650 750 890 1050 1100 1200 1350 1725 2400 1900 375 400 500 575 650 700 775 850 1100 1550 2000 1450 250 300 325 375 450 475 525 575 750 1050 1600 1450 775 1075 1350 RT(MIN) 150k 124k 113k 93.1k 79k 73.2k 64.9k 59.0k 42.2k 28.0k 15.8k 54.9k 49.9k 42.2k 34.8k 28.0k 26.7k 23.7k 20.5k 14.3k 7.87k 12.1k 93.1k 88.7k 69.8k 59.0k 49.9k 44.2k 41.2k 36.5k 26.7k 16.5k 11.3k 18.2k 150k 124k 113k 93.1k 79k 73.2k 64.9k 59.0k 42.2k 28.0k 15.8k 18.2k 41.2k 27.4k 20.5k
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LTM8022 APPLICATIONS INFORMATION
For most applications, the design process is straight forward, summarized as follows: 1. In Table 1, find the row that has the desired input voltage range and output voltage. 2. Apply the recommended CIN, COUT, RADJ and RT values. 3. Connect BIAS as indicated. While these component combinations have been tested for proper operation, it is incumbent upon the user to verify proper operation over the intended system's line, load and environmental conditions. If the desired output voltage is not listed in Table 1, set the output by applying an RADJ resistor whose value is given by the equation RADJ = 394.21/(VOUT - 0.79), where RADJ is in k and VOUT is in volts. Verify the LTM8022's operation over the system's intended line, load and environmental conditions. Capacitor Selection Considerations The CIN and COUT capacitor values in Table 1 are the minimum recommended values for the associated operating conditions. Applying capacitor values below those indicated in Table 1 is not recommended, and may result in undesirable operation. Using larger values is generally acceptable, and can yield improved dynamic response, if it is necessary. Again, it is incumbent upon the user to verify proper operation over the intended system's line, load and environmental conditions. Ceramic capacitors are small, robust and have very low ESR. However, not all ceramic capacitors are suitable. X5R and X7R types are stable over temperature and applied voltage and give dependable service. Other types, including Y5V and Z5U, have very large temperature and voltage coefficients of capacitance. In an application circuit they may have only a small fraction of their nominal capacitance, resulting in much higher output voltage ripple than expected. Ceramic capacitors are also piezoelectric. In Burst Mode operation, the LTM8022's switching frequency depends on the load current, and can excite a ceramic capacitor at audio frequencies, generating audible noise. Since the LTM8022 operates at a lower current limit during Burst Mode operation, the noise is typically very quiet to a casual ear. If this audible noise is unacceptable, use a high performance electrolytic capacitor at the output. The input capacitor can be a parallel combination of a 2.2F ceramic capacitor and a low cost electrolytic capacitor. A final precaution regarding ceramic capacitors concerns the maximum input voltage rating of the LTM8022. A ceramic input capacitor combined with trace or cable inductance forms a high Q (under damped) tank circuit. If the LTM8022 circuit is plugged into a live supply, the input voltage can ring to twice its nominal value, possibly exceeding the device's rating. This situation is easily avoided; see the Hot-Plugging Safely section. Frequency Selection The LTM8022 uses a constant-frequency PWM architecture that can be programmed to switch from 200kHz to 2.4MHz by using a resistor tied from the RT pin to ground. Table 2 provides a list of RT resistor values and their resultant frequencies.
Table 2. Switching Frequency vs RT Value
SWITCHING FREQUENCY (MHz) 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 RT VALUE (k) 187 121 88.7 68.1 56.2 46.4 40.2 34 29.4 23.7 19.1 16.2 13.3 11.5 9.76 8.66
Operating Frequency Tradeoffs It is recommended that the user apply the optimal RT value given in Table 1 for the input and output operating condition. System level or other considerations, however, may necessitate another operating frequency. While the LTM8022 is flexible enough to accommodate a wide range
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LTM8022 APPLICATIONS INFORMATION
of operating frequencies, a haphazardly chosen one may result in undesirable operation under certain operating or fault conditions. A frequency that is too high can reduce efficiency, generate excessive heat or even damage the LTM8022 if the output is overloaded or short-circuited. A frequency that is too low can result in a final design that has too much output ripple or too large of an output cap. The maximum frequency and corresponding RT value at which the LTM8022 should be allowed to switch is given in Table 1 in the RT(MIN) and fMAX columns, while the recommended frequency and RT value over the given input range is given in the RT(OPTIMAL) and fOPTIMAL columns. There are additional conditions that must be satisfied if the synchronization function is used. Please refer to the Synchronization section for details. Burst Mode Operation To enhance efficiency at light loads, the LTM8022 automatically switches to Burst Mode operation which keeps the output capacitor charged to the proper voltage while minimizing the input quiescent current. During Burst Mode operation, the LTM8022 delivers single cycle bursts of current to the output capacitor followed by sleep periods where the output power is delivered to the load by the output capacitor. In addition, VIN and BIAS quiescent currents are reduced to typically 20A and 50A, respectively, during the sleep time. As the load current decreases towards a no load condition, the percentage of time that the LTM8022 operates in sleep mode increases and the average input current is greatly reduced, resulting in higher efficiency. Burst Mode operation is enabled by tying SYNC to GND. To disable Burst Mode operation, tie SYNC to a stable voltage source above 0.7V. Do not leave this pin floating. BIAS Pin Considerations The BIAS pin is used to provide drive power for the internal power switching stage and operate internal circuitry. For proper operation, it must be powered by at least 2.4V. If the output voltage is programmed to be 2.4V or higher, simply tie BIAS to AUX, which is internally tied to VOUT . If VOUT is less than 2.4V, BIAS can be tied to VIN or some other voltage source. In all cases, ensure that the maximum voltage at the BIAS pin is less than 16V and the sum of VIN+ BIAS is less than 56V. If BIAS power is applied from a remote or noisy voltage source, it may be necessary to apply a decoupling capacitor locally to the LTM8022. Minimum Input Voltage The LTM8022 is a step-down converter, so a minimum amount of headroom is required to keep the output in regulation. For most applications at full load, the input needs to be at least 1.5V above the desired output. In addition, the input voltage required to turn on depends upon how the RUN/SS pin is tied. As shown in Figure 1, it takes more input voltage to turn on if RUN/SS is tied to VIN than if the turn-on is controlled by raising RUN/SS when VIN is in the required operating range. This is shown in Figure 1.
6.0 5.5 INPUT VOLTAGE (V) 5.0 TO START 4.5 RUN/SS ENABLED 4.0 3.5 3.0 TO RUN VOUT = 3.3V TA = 25C f = 650kHz
0
200
400 600 800 LOAD CURRENT (mA)
1000
8022 F01a
7.5
7.0 INPUT VOLTAGE (V)
VOUT = 5V TA = 25C f = 650kHz
6.5 TO START 6.0 RUN/SS ENABLE
5.5 TO RUN 5.0 0 200 600 400 800 LOAD CURRENT (mA) 1000
8022 F01b
Figure 1. The LTM8022 Needs More Voltage to Start Than to Run
8022fb
10
LTM8022 APPLICATIONS INFORMATION
Load Sharing Two or more LTM8022's may be paralleled to produce higher currents. To do this, tie the VIN, VOuT and SHARE pins of all the paralleled LTM8022's together. Synchronize the LTM8022s to avoid beat frequencies if required. To ensure that paralleled modules start up together, the RUN/SS pins may be tied together, as well. If the RUN/SS pins are not tied together, make sure that the same valued soft-start capacitors are used for each module. An example of two LTM8022 modules configured for load sharing is given in the Typical Applications section. Soft-Start The RUN/SS pin can be used to soft-start the LTM8022, reducing the maximum input current during start-up. The RUN/SS pin is driven through an external RC filter to create a voltage ramp at this pin. Figure 2 shows the start-up and shutdown waveforms with the soft-start circuit. By choosing an appropriate RC time constant, the peak start-up current can be reduced to the current that is required to regulate the output, with no overshoot. Choose the value of the resistor so that it can supply at least 20A when the RUN/SS pin reaches 2.5V. Synchronization The internal oscillator of the LTM8022 can be synchronized by applying an external 250kHz to 2MHz clock signal to the SYNC pin. The resistor tied from the RT pin to ground should be chosen such that the LTM8022 would free run 20% lower than the intended synchronization frequency (see Frequency Selection section). When the LTM8022 is synchronized to an external clock source, Burst Mode operation is disabled. The part will skip power switching cycles as necessary to maintain regulation. Ensure that the SYNC pin is not left floating. Tie it to GND if not used. Shorted Input Protection Care needs to be taken in systems where the output will be held high when the input to the LTM8022 is absent. This may occur in battery charging applications, or in battery backup systems where a battery or some other supply is diode ORed with the LTM8022's output. If the VIN pin is allowed to float, and the RUN/SS pin is held high (either by a logic signal or because it is tied to VIN), then the LTM8022's internal circuitry will pull its quiescent current through its internal power switch. This is fine if your system can tolerate a few milliamps in this state. If you ground the RUN/SS pin, the SW pin current will drop to essentially zero. However, if the VIN pin is grounded while the output is held high, then parasitic diodes inside the LTM8022 can pull large currents from the output through the VIN pin. Figure 3 shows a circuit that will run only when the input voltage is present and that protects against a shorted or reversed input.
VIN
VIN LTM8022
VOUT AUX
VOUT
RUN 15k RUN/SS GND 0.22F
IL 0.5A/DIV RUN/SS VRUN/SS 2V/DIV
BIAS PG
RT GND SYNC ADJ
VOUT 2V/DIV 2ms/DIV
8022 F02
8022 F03
Figure 2. To Soft-Start the LTM8022, Add a Resistor and Capacitor to the RUN/SS Pin
Figure 3. The Input Diode Prevents a Shorted Input from Discharging a Back-Up Battery Tied to the Output. It Also Protects the Circuit From a Reversed Input. The LTM8022 Runs Only When the Input is Present
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11
LTM8022 APPLICATIONS INFORMATION
PCB Layout Most of the headaches associated with PCB layout have been alleviated or even eliminated by the high level of integration of the LTM8022. The LTM8022 is nevertheless a switching power supply, and care must be taken to minimize EMI and ensure proper operation. Even with the high level of integration, you may fail to achieve specified operation with a haphazard or poor layout. See Figure 4 for a suggested layout. Ensure that the grounding and heatsinking are acceptable. A few rules to keep in mind are: 1. Place the RADJ and RT resistors as close to their respective pins as possible. 2. Place the CIN capacitor as close as possible to the VIN and GND connection of the LTM8022. 3. Place the COUT capacitor as close as possible to the VOUT and GND connection of the LTM8022. 4. Place the CIN and COUT capacitors such that their ground current flow directly adjacent or underneath the LTM8022. 5. Connect all of the GND connections to as large a copper pour or plane area as possible on the top layer. Avoid breaking the ground connection between the external components and the LTM8022. 6. Use vias to connect the GND copper area to the boards internal ground plane. Liberally distribute these GND vias to provide both a good ground connection and thermal path to the internal planes of the printed circuit board.
GND PLANE
RT SHARE
RADJ
SYNC PG RUN/SS AUX BIAS LTM8022
COUT VOUT PLANE
CIN VIN PLANE
8022 F04
Figure 4. Layout Showing Suggested External Components, GND Plane and Thermal Vias
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12
LTM8022 APPLICATIONS INFORMATION
Hot-Plugging Safely The small size, robustness and low impedance of ceramic capacitors make them an attractive option for the input bypass capacitor of LTM8022. However, these capacitors can cause problems if the LTM8022 is plugged into a live supply (see Linear Technology Application Note 88 for a complete discussion). The low loss ceramic capacitor combined with stray inductance, in series with the power source, forms an underdamped tank circuit. In this case, the voltage at the VIN pin of the LTM8022 can ring to twice the nominal input voltage, possibly exceeding the LTM8022's rating and damaging the part. If the input supply is poorly controlled or the user will be plugging the LTM8022 into an energized supply, the input network should be designed to prevent this overshoot. Figure 5 shows the waveforms that result when an LTM8022 circuit is connected to a 24V supply through six feet of 24-gauge twisted pair. The first plot is the response with a 2.2F ceramic capacitor at the input. The input voltage rings as high as 35V and the input current peaks at 20A. One method of damping the tank circuit is to add another capacitor with a series resistor to the circuit. In Figure 5b an aluminum electrolytic capacitor has been added. This capacitor's high equivalent series resistance damps the circuit and eliminates the voltage overshoot. The extra capacitor improves low frequency ripple filtering and can slightly improve the efficiency of the circuit, though it is likely to be the largest component in the circuit. An alternative solution is shown in Figure 5c. A 0.7 resistor is added in series with the input to eliminate the voltage overshoot (it also reduces the peak input current). A 0.1F capacitor improves high frequency filtering. This solution is smaller and less expensive than the electrolytic capacitor. For high input voltages its impact on efficiency is minor, reducing efficiency less than one half percent for a 5V output at full load operating from 24V. Thermal Considerations The LTM8022 output current may need to be derated if it is required to operate in a high ambient temperature or deliver a large amount of power. The amount of current derating is dependent upon the input voltage, output power and ambient temperature. The derating curves in the Typical Performance Characteristics section can be used as a guide. These curves were generated by an LTM8022 mounted to a 33cm2 4-layer FR4 printed circuit board. Boards of other sizes and layer count can exhibit different thermal behavior, so it is incumbent upon the user to verify proper operation over the intended system's line, load and environmental operating conditions. The die temperature of the LTM8022 must be lower than the maximum rating of 125C, so care should be taken in the layout of the circuit to ensure good heat sinking of the LTM8022. To estimate the junction temperature, approximate the power dissipation within the LTM8022 by applying the typical efficiency stated in this datasheet to the desired output power, or, if you have an actual module, by taking a power measurement. Then calculate the temperature rise of the LTM8022 junction above the surface of the printed circuit board by multiplying the module's power dissipation by the thermal resistance. The actual thermal resistance of the LTM8022 to the printed circuit board depends upon the layout of the circuit board, but the thermal resistance given on page 2, which is based upon a 33cm2 4-layer FR4 PC board, can be used a guide. Finally, be aware that at high ambient temperatures the internal Schottky diode will have significant leakage current (see Typical Performance Characteristics) increasing the quiescent current of the LTM8022.
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13
LTM8022 APPLICATIONS INFORMATION
CLOSING SWITCH SIMULATES HOT PLUG IIN DANGER VIN LTM8022 VIN 20V/DIV RINGING VIN MAY EXCEED ABSOLUTE MAXIMUM RATING
+
4.7F
LOW IMPEDANCE ENERGIZED 24V SUPPLY
STRAY INDUCTANCE DUE TO 6 FEET (2 METERS) OF TWISTED PAIR
IIN 10A/DIV 20s/DIV
(5a)
LTM8022
+
22F 35V AI.EI.
+
4.7F
VIN 20V/DIV
IIN 10A/DIV
(5b)
20s/DIV
0.7 LTM8022
VIN 20V/DIV
+
0.1F 4.7F IIN 10A/DIV
20s/DIV
8022 F05
(5c)
Figure 5. A Well Chosen Input Network Prevents Input Voltage Overshoot and Ensures Reliable Operation When the LTM8022 is Connected to a Live Supply
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14
LTM8022 TYPICAL APPLICATIONS
0.82V Step-Down Converter
VIN* 3.6V TO 15V VOUT 0.82V 1A VIN 2.2F BIAS RUN/SS SHARE RT 69.8k GND SYNC ADJ 13M
8022 TA02
VOUT LTM8022 AUX PG 200F
*RUNNING VOLTAGE RANGE. PLEASE REFER TO APPLICATIONS INFORMATION FOR START-UP DETAILS
1.8V Step-Down Converter
VIN* 3.6V TO 15V 2.2F BIAS RUN/SS SHARE RT 39.2k GND SYNC ADJ 383k VOUT 1.8V 1A
VIN LTM8022
VOUT 68F AUX PG
8022 TA03
*RUNNING VOLTAGE RANGE. PLEASE REFER TO APPLICATIONS INFORMATION FOR START-UP DETAILS
8022fb
15
LTM8022 TYPICAL APPLICATIONS
2.5V Step-Down Converter
VOUT 2.5V 1A VIN* 3.8V TO 36V
VIN 2.2F LTM8022 RUN/SS SHARE 3.3V BIAS RT 59k
VOUT 47F AUX PG
GND SYNC ADJ 226k
8022 TA04
*RUNNING VOLTAGE RANGE. PLEASE REFER TO APPLICATIONS INFORMATION FOR START-UP DETAILS
-5V at 1A Positive-to-Negative Converter
-5V at 1A Positive-to-Negative Converter Load Current vs Input Voltage
1200
VIN* 7V TO 31V
IN LTM8022 RUN/SS SHARE 2.2F
OUT 1000 AUX LOAD CURRENT (mA) BIAS PG 10F 800 600 400 200 VOUT -5V 0 0 10 20 30 INPUT VOLTAGE (V) 40
8022 TA05b
OPTIONAL SCHOTTKY CLAMP
RT 29.4k
GND SYNC ADJ 93.1k
8022 TA05
*RUNNING VOLTAGE RANGE. PLEASE REFER TO APPLICATIONS INFORMATION FOR START-UP DETAILS
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16
LTM8022 TYPICAL APPLICATIONS
Two LTM8022's in Parallel, 3.3V at 1.8A
VIN* 5.5V TO 36V
IN LTM8022 RUN/SS SHARE 2.2F RT
OUT AUX BIAS PG GND SYNC ADJ
VOUT 3.3V 1.8A
43.2k
78.7k
OPTIONAL SYNC IN LTM8022 RUN/SS SHARE 2.2F RT 43.2k
8022 TA06
OUT AUX BIAS PG GND SYNC ADJ 10F
*RUNNING VOLTAGE RANGE. PLEASE REFER TO APPLICATIONS INFORMATION FOR START-UP DETAILS NOTE: SYNCRONIZE THE TWO MODULES TO AVOID BEAT FREQUENCIES IF REQUIRED. OTHERWISE, TIE EACH SYNC TO GND
8022fb
17
aaa Z
LTM8022
4 aaa Z
bbb Z
PAD 1 CORNER
Z
4.445
3.175
1.905
0.635
0.000
0.635
1.905
3.175
4.445
0.9525
SUGGESTED PCB LAYOUT TOP VIEW
0.635
0.3175
18
X Y
11.25 BSC 2.72 - 2.92 7 6 0.605 - 0.665 9.00 BSC 0.27 - 0.37 2.45 - 2.55 MOLD CAP SUBSTRATE 7.62 BSC 5 4 3 2 1.27 BSC 1 PADS SEE NOTES H G F DETAIL A PACKAGE SIDE VIEW
3
PACKAGE DESCRIPTION
8.89 BSC 0.605 - 0.665
DETAIL A
PACKAGE TOP VIEW
E
D
C PACKAGE BOTTOM VIEW
B
A
C(0.30) PAD 1
NOTES: 1. DIMENSIONING AND TOLERANCING PER ASME Y14.5M-1994 2. ALL DIMENSIONS ARE IN MILLIMETERS 3 LAND DESIGNATION PER JESD MO-222, SPP-010 AND SPP-020 DETAILS OF PAD #1 IDENTIFIER ARE OPTIONAL, BUT MUST BE LOCATED WITHIN THE ZONE INDICATED. THE PAD #1 IDENTIFIER MAY BE EITHER A MOLD OR A MARKED FEATURE 4
3.810
(Reference LTC DWG # 05-08-1804 Rev B)
2.540
LGA Package 50-Lead (11.25mm x 9.00mm x 2.82mm)
1.270
5. PRIMARY DATUM -Z- IS SEATING PLANE 6. THE TOTAL NUMBER OF PADS: 50
LTMXXXXXX Module
0.000
0.3175
0.3175
1.270
SYMBOL TOLERANCE 0.15 aaa 0.10 bbb
TRAY PIN 1 BEVEL PACKAGE IN TRAY LOADING ORIENTATION
LGA 50 0507 REV B
2.540
3.810
8022fb
LTM8022 PACKAGE DESCRIPTION
Table 3. LTM8022 Pinout (Sorted by Pin Number)
PIN A1 A2 A3 A4 A5 A6 A7 B1 B2 B3 B4 B5 B6 B7 C1 C2 C3 C4 C5 C6 C7 D1 D2 D3 D4 SIGNAL DESCRIPTION VOUT VOUT VOUT VOUT GND GND GND VOUT VOUT VOUT VOUT GND GND GND VOUT VOUT VOUT VOUT GND GND GND GND GND GND GND PIN D5 D6 D7 E1 E2 E3 E4 E5 E6 E7 F5 F6 F7 G1 G2 G3 G5 G6 G7 H1 H2 H3 H5 H6 H7 SIGNAL DESCRIPTION GND GND GND GND GND GND GND GND GND GND AUX GND SHARE VIN VIN VIN BIAS SYNC RT VIN VIN VIN RUN/SS PG ADJ
8022fb
Information f rnished by Linear Technology Corporation is believed to be acc rate and reliable. However, no responsibility is ass med for its se. Linear Technology Corporation makes no representation that the interconnection of its circ its as described herein will not infringe on existing patent rights.
19
LTM8022 TYPICAL APPLICATION
3.3V Step Down Converter
VOUT 3.3V 1A
VIN* 4.75V TO 36V
IN LTM8022 RUN/SS SHARE 2.2F
OUT AUX BIAS PG 22F
RT 42.2k
GND SYNC ADJ 154k
8022 TA07
*RUNNING VOLTAGE RANGE. PLEASE REFER TO APPLICATIONS INFORMATION FOR START-UP DETAILS
RELATED PARTS
PART NUMBER LTM4600/LTM4602 LTM4601/LTM4603 LTM4604/LTM4608 LTM4605/LTM4607 LTM8020 LTM8023 DESCRIPTION 10A and 6A DC/DC Module 12A and 6A DC/DC Module 4A, 8A Low Voltage DC/DC Module Buck-Boost DC/DC Module 200mA, 36V DC/DC Module 2A, 36V DC/DC Module COMMENTS Pin Compatible, 4.5V VIN 28V Pin Compatible; Remote Sensing; PLL, Tracking and Margining, 4.5V VIN 28V 2.375V VIN 5.5V, 9mm x 15mm x 2.3mm (LTM4604), 9mm x 15mm x 2.5mm (LTM4608) Up to 160W, External Inductor; High Efficiency (Up to 98%), 15mm x 15mm x 2.8mm LGA 4V VIN 36V, 1.25V VOUT 5V, 6.25mm x 6.25mm x 2.32mm LGA 3.6V VIN 36V, 0.8V VOUT 10V, 11.25mm x 9mm x 2.82mm LGA, Pin Compatible with LTM8022
8022fb
20 Linear Technology Corporation
(408) 432-1900
LT 1008 REV B * PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
FAX: (408) 434-0507 www.linear.com
(c) LINEAR TECHNOLOGY CORPORATION 2008

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