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FEATURES
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LTM8032 Ultralow Noise EMC Compliant 36V, 2A DC/DC Module DESCRIPTION
The LTM(R)8032 is an electromagnetic compatible (EMC) 36V, 2A DC/DC Module(R) buck converter designed to meet the radiated emissions requirements of EN55022. Conducted emission requirements can be met by adding standard filter components. Included in the package are the switching controller, power switches, inductor, filters and all support components. Operating over an input voltage range of 3.6V to 36V, the LTM8032 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 LTM8032 is packaged in a thermally enhanced, compact (9mm x 15mm) and low profile (2.82mm) overmolded land grid array (LGA) package suitable for automated assembly by standard surface mount equipment. The LTM8032 is RoHS compliant.
, LT, LTC, LTM and Module are registered trademarks 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 2A Output Current 0.8V to 10V Output Voltage Selectable Switching Frequency: 200kHz to 2.4MHz EN55022 Class B Compliant Current Mode Control (e4) RoHS Compliant Package with Gold Pad Finish Programmable Soft-Start Low Profile (9mm x 15mm 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
Ultralow Noise 5V/2A DC/DC Module Regulator
VIN* 7VDC TO 36VDC VIN FIN RUN/SS 2.2F SHARE PGOOD AUX OUT 10F VOUT 5V 2A EMISSIONS LEVEL (dBV/m) 90 80 70 60 50 40 30 20 10 0 -10 0 100 200 300 400 500 600 700 800 900 1000 FREQUENCY (MHz) 8031 TA01b EN55022 CLASS B LIMIT
LTM8032 EMI Performance
LTM8032 BIAS
RT SYNC GND ADJ 44.2k fSW = 700kHz *RUNNING VOLTAGE RANGE. SEE APPLICATIONS FOR START-UP DETAILS 47.5k
8032 TA01a
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LTM8032 ABSOLUTE MAXIMUM RATINGS
(Note 1)
PIN CONFIGURATION
1 A BANK 1 B C D E BANK 2 F G H J K BANK 3 L VIN FIN RUN/SS SYNC LGA PACKAGE 71-LEAD (9mm 15mm 2.82mm) TJMAX = 125C, JA = 15.8C/W, JC = 5.5C/W JA DERIVED FROM 6.35cm x 5.6 PCB WITH 4 LAYERS WEIGHT = 1.2g BIAS AUX RT SHARE ADJ PGOOD 2 TOP VIEW 3 4 5 VOUT 6 GND 7
VIN, FIN, RUN/SS Voltage..........................................40V ADJ, RT, SHARE Voltage .............................................5V VOUT, AUX .................................................................10V Current from AUX ................................................100mA PGOOD, SYNC ..........................................................30V BIAS ..........................................................................25V VIN + BIAS .................................................................56V Maximum Junction Temperature (Note 2)............. 125C Solder Temperature (Note 3)................................. 245C
ORDER INFORMATION
LEAD FREE FINISH LTM8032EV#PBF LTM8032IV#PBF LTM8032MPV#PBF TRAY LTM8032EV#PBF LTM8032IV#PBF LTM8032MPV#PBF PART MARKING* LTM8032V LTM8032V LTM8032MPV PACKAGE DESCRIPTION 71-Lead (9mm x 15mm x 2.82mm) LGA 71-Lead (9mm x 15mm x 2.82mm) LGA 71-Lead (9mm x 15mm x 2.82mm) LGA TEMPERATURE RANGE -40C to 125C -40C to 125C -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. 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://www.linear.com/packaging/
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LTM8032 ELECTRICAL CHARACTERISTICS
SYMBOL VIN VOUT IOUT IQ(VIN) PARAMETER Input DC Voltage Output DC Voltage Continuous Output DC Current VIN Quiescent Current 0.2A < IOUT 2A, RADJ Open 0.2A < IOUT 2A, RADJ = 21.6k VIN = 24V VRUN/SS = 0.2V VBIAS = 3V, Not Switching VBIAS = 0V, Not Switching VRUN/SS = 0.2V VBIAS = 3V, Not Switching VBIAS = 0V, Not Switching 10V VIN 36V, IOUT = 1A, VOUT = 3.3V VIN = 24V, 0.2A IOUT 2A, VOUT = 3.3V VIN = 24V, IOUT = 2A, VOUT = 3.3V RT = 113k
l l
The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. VIN = 10V, VRUN/SS = 10V, VBIAS = 3V, unless otherwise specified.
CONDITIONS
l
MIN 3.6
TYP 0.8 10
MAX 36
UNITS V V V
2 0.6 25 88 0.03 60 1 0.1 0.3 6 325 765 790 1.9 4 5 2.5 0.2 730 10 815 2.8 60 120 120 5
A A A A A A A % % mV kHz mV V A A V V mV A A V V A dBV dBV dBV
IQ(BIAS) VOUT VOUT fSW VADJ VBIAS(MIN) IADJ IRUN/SS VIH(RUN/SS) VIL(RUN/SS) VPG(TH) IPGO IPGSINK VSYNCIL VSYNCIH ISYNC(BIAS) VIN(RIPPLE)
BIAS Quiescent Current
l
Line Regulation Load Regulation Switching Frequency 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 ADJ Voltage Threshold for PGOOD to Switch PGOOD Leakage PGOOD Sink Current SYNC Input Low Threshold SYNC Input High Threshold SYNC Pin Bias Current 550kHz Narrowband Conducted Emission 1MHz Narrowband Conducted Emission 3MHz Narrowband Conducted Emission
VOUT(AC_RMS) Output Ripple (RMS)
VRUN/SS = 0V, VADJ = 0V, VOUT = 1V VRUN/SS = 2.5V
VPG = 30V VPG = 0.4V fSYNC = 550kHz fSYNC = 550kHz VSYNC = 0V, VBIAS = 0V VIN = 24V, VOUT = 3.3V, IOUT = 2A, fSW = 550kHz, 5H LISN 0.7 200
0.1 800
1 0.5
0.1 89 69 51
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 LTM8032E is guaranteed to meet performance specifications from 0C to 125C internal. Specifications over the -40C to 125C internal temperature range are assured by design, characterization and correlation with statistical process controls. LTM8032I is guaranteed
to meet specifications over the full -40C to 125C internal operating temperature range. The LTM8032MP is guaranteed to meet specifications over the full -55C to 125C internal operating 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: See Linear Technology Application Note 100.
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LTM8032 TYPICAL PERFORMANCE CHARACTERISTICS TA = 25C, unless otherwise noted.
3.3VOUT Efficiency
100 90 80 EFFICIENCY (%) EFFICIENCY (%) 70 60 50 40 30 20 10 0 0.01 1 0.1 OUTPUT CURRENT (A) 5.5VIN 12VIN 24VIN 36VIN 10
8031 G01
5VOUT Efficiency
100 90 80 EFFICIENCY (%) 12VIN 24VIN 36VIN 1 0.1 OUTPUT CURRENT (A) 10
8031 G02
8VOUT Efficiency
100 90 80 70 60 50 40 30 20 10 0 0.01 1 0.1 OUTPUT CURRENT (A) 12VIN 24VIN 36VIN 10
8031 G03
70 60 50 40 30 20 10 0 0.01
Input Current vs Output Current, 3.3VOUT
1600 1400 INPUT CURRENT (mA) 1200 1000 800 600 400 200 0 0 1000 500 1500 OUTPUT CURRENT (mA) 2000
8032 G04
Input Current vs Output Current, 5VOUT
1200 1000 INPUT CURRENT (mA) 800 600 400 200 0 0 500 1000 1500 OUTPUT CURRENT (mA) 2000
8032 G05
Input Current vs Output Current, 8VOUT
1800 1600 INPUT CURRENT (mA) 1400 12VIN 24VIN 36VIN
5.5VIN 12VIN 24VIN 36VIN
12VIN 24VIN 36VIN
1200 1000 800 600 400 200 0 1 1000 500 1500 OUTPUT CURRENT (mA) 2000
8032 G06
Minimum Required Input Voltage vs Output Voltage, IOUT = 2A
14 12 INPUT VOLTAGE (V) INPUT VOLTAGE (V) 10 8 6 4 2 0 2 4 6 8 OUTPUT VOLTAGE (V) 10
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Minimum Required Input Voltage vs Load Current, VOUT = 2.5V
5.0 4.5 INPUT VOLTAGE (V) 4.0 3.5 3.0 2.5 2.0 0 TO RUN TO START 500 1000 1500 LOAD CURRENT (mA) 2000
8032 G08
Minimum Required Input Voltage vs Load Current, VOUT = 3.3V
6.0 5.5 5.0 4.5 4.0 3.5 3.0 0 500 1000 1500 LOAD CURRENT (mA) 2000
8032 G09
TO RUN TO START RUN/SS ENABLED
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LTM8032 TYPICAL PERFORMANCE CHARACTERISTICS TA = 25C, unless otherwise noted.
Minimum Required Input Voltage vs Load Current, VOUT = 5V
7.5 11.0 10.5 BIAS CURRENT (mA) INPUT VOLTAGE (V) 10.0 9.5 9.0 8.5 8.0 0 500 1000 1500 LOAD CURRENT (mA) 2000
8032 G11
Minimum Required Input Voltage vs Load Current, VOUT = 8V
30 25 20 15 10 5 0
Bias Current vs Output Current
3.3VOUT 5VOUT 8VOUT
7.0 INPUT VOLTAGE (V)
6.5
6.0
5.5
TO RUN TO START RUN/SS ENABLED 0 500 1500 1000 LOAD CURRENT (mA) 2000
8032 G10
TO RUN TO START RUN/SS ENABLED
5.0
0
500 1000 1500 OUTPUT CURRENT (mA)
2000
8032 G12
Output Current vs Input Voltage (Output Shorted)
3200 3000 OUTPUT CURRENT (mA) 2800 2600 2400 2200 2000 1800 1600 0 10 20 INPUT VOLTAGE (V)
8032 G13
Input Current vs Input Voltage (Output Shorted)
1200 1000 TEMPERATURE RISE (C) OUTPUT CURRENT (mA) 800 600 400 200 0 0 10 20 30 INPUT VOLTAGE (V) 40
8032 G14
Temperature Rise vs Load Current, VOUT = 2.5V
35 30 25 20 15 10 5 0 0 500 1000 1500 2000 LOAD CURRENT (mA)
8032 G15
5VIN 12VIN 24VIN 36VIN 2500
30
40
Temperature Rise vs Load Current, VOUT = 3.3V
40 35 TEMPERATURE RISE (C) 30 25 20 15 10 5 0 0 500 1000 5VIN 12VIN 24VIN 36VIN 2000 1500 LOAD CURRENT (mA) 2500
8032 G16
Temperature Rise vs Load Current, VOUT = 5V
40 35 TEMPERATURE RISE (C) 30 25 20 15 10 5 0 0 500 1000 12VIN 24VIN 36VIN 2000 1500 LOAD CURRENT (mA) 2500
8032 G17
Temperature Rise vs Load Current, VOUT = 8V
50 45 TEMPERATURE RISE (C) 40 35 30 25 20 15 10 5 0 0 500 12VIN 24VIN 36VIN 1500 2000 1000 LOAD CURRENT (mA) 2500
8032 G18
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LTM8032 TYPICAL PERFORMANCE CHARACTERISTICS TA = 25C, unless otherwise noted.
EMISSIONS LEVEL (dBV/m) 90 70 50 30 10 -10 0 100 200 300 400 500 600 700 800 900 1000 FREQUENCY (MHz) 8031 G20 VIN = 36V VOUT = 10V AT 2A EMISSIONS LEVEL (dBV/m)
Temperature Rise vs Load Current, VOUT = 10V
50 45 TEMPERATURE RISE (C) 40 35 30 25 20 15 10 5 0 0 500 24VIN 36VIN 1500 2000 1000 LOAD CURRENT (mA) 2500
8032 G19
Radiated Emissions
Radiated Emissions
90 70 50 30 10 -10 0 100 200 300 400 500 600 700 800 900 1000 FREQUENCY (MHz) 8031 G21 VIN = 13V VOUT = 10V AT 2A
PIN FUNCTIONS
VIN (Bank 3): The VIN pin supplies current to the LTM8032'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 . FIN (K3, L3): Filtered Input. This is the node after the input EMI filter. Use this only if there is a need to modify the behavior of the integrated EMI filter or if VIN rises or falls rapidly; otherwise, leave these pins unconnected. See the Applications Information section for more details. GND (Bank 2): Tie these GND pins to a local ground plane below the LTM8032 and the circuit components. Return the feedback divider (RADJ) to this net. VOUT (Bank 1): Power Output Pins. Apply the output filter capacitor and the output load between these pins and GND pins. AUX (Pin H5): 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. BIAS (Pin H4): The BIAS pin connects to the internal power bus. Connect to a power source greater than 2.8V. If the output is greater than 2.8V, connect this pin to AUX. If the output voltage is less, connect this to a voltage source between 2.8V and 25V. Also, make sure that BIAS + VIN is less than 56V. RUN/SS (Pin L5): Pull RUN/SS pin to less than 0.2V to shut down the LTM8032. 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. RT (Pin G7): The RT pin is used to program the switching frequency of the LTM8032 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 H7): Tie this to the SHARE pin of another LTM8032 when paralleling the outputs. Otherwise, do not connect.
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LTM8032 PIN FUNCTIONS
SYNC (Pin L6): This is the external clock synchronization input. Ground this pin for low ripple Burst Mode(R) operation at low output loads. Tie to a stable voltage source greater than 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 synchronizing section in Applications Information. PGOOD (Pin K7): The PGOOD pin is the open-collector output of an internal comparator. PGOOD remains low until the ADJ pin is within 10% of the final regulation voltage. The PGOOD 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 J7): The LTM8032 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: R ADJ = 196.71 VOUT - 0.79
where RADJ is in k.
Burst Mode is a registered trademark of Linear Technology Corporation.
BLOCK DIAGRAM
FIN EMI FILTER
VIN
4.7H
VOUT 249k 10F AUX GND BIAS
GND
SHARE
CURRENT MODE CONTROLLER
RUN/SS
SYNC
RT
PGOOD
ADJ
8032 BD
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LTM8032 OPERATION
The LTM8032 is a standalone nonisolated step-down switching DC/DC power supply. It can deliver up to 2A 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 LTM8032 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 given on the previous page. The LTM8032 is designed with an input EMI filter and other features to make its radiated emissions compliant with several EMC specifications including EN55022 class B. Compliance with conducted emissions requirements may be obtained by adding a standard input filter. The LTM8032 contains a current mode controller, power switching element, power inductor, power Schottky diode and a modest amount of input and output capacitance. The LTM8032 is a fixed frequency PWM regulator. The switching frequency is set by simply connecting the appropriate resistor value from the RT pin to GND. An internal regulator provides power to the control circuitry. The bias regulator can draw power from the VIN pin, but if the BIAS pin is connected to an external voltage higher than 2.8V, 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 LTM8032 in shutdown, disconnecting the output and reducing the input current to less than 1A. To further optimize efficiency, the LTM8032 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 LTM8032'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 LTM8032 contains a power good comparator which trips when the ADJ pin is at 90% of its regulated value. The PGOOD output is an open-collector transistor that is off when the output is in regulation, allowing an external resistor to pull the PGOOD pin high. Power good is valid when the LTM8032 is enabled and VIN is above 3.6V.
APPLICATIONS INFORMATION
For most applications, the design process is straight forward, summarized as follows: 1. Look at Table 1 and find the row that has the desired input range and output voltage. 2. Apply the recommended CIN, COUT, RADJ and RT values. 3. Connect BIAS as indicated. As the integrated input EMI filter may ring in response to an application of a step input voltage, a bulk capacitance, series resistance or some clamping mechanism may be required. See the Hot-Plugging Safely section for details. 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. 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
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LTM8032 APPLICATIONS INFORMATION
Table 1: Recommended Component Values and Configuration
VIN 3.6V to 36V 3.6V to 36V 3.6V to 36V 3.6V to 36V 3.6V to 36V 3.6V to 36V 4.0V to 36V 4.3V to 36V 5.5V to 36V 7V to 36V 10.5V to 36V 3.6V to 15V 3.6V to 15V 3.6V to 15V 3.6V to 15V 3.6V to 15V 3.6V to 15V 4.0V to 15V 4.3V to 15V 5.5V to 15V 7V to 15V 9V to 24V 9V to 24V 9V to 24V 9V to 24V 9V to 24V 9V to 24V 9V to 24V 9V to 24V 9V to 24V 9V to 24V 10.5V to 24V 13V to 24V 18V to 36V 18V to 36V 18V to 36V 18V to 36V 18V to 36V 18V to 36V 18V to 36V 18V to 36V 18V to 36V 18V to 36V 18V to 36V 18V to 36V VOUT 0.82V 1.00V 1.20V 1.50V 1.80V 2.00V 2.20V 2.50V 3.30V 5.00V 8.00V 0.82V 1.00V 1.20V 1.50V 1.80V 2.00V 2.20V 2.50V 3.30V 5.00V 0.82V 1.00V 1.20V 1.50V 1.80V 2.00V 2.20V 2.50V 3.30V 5.00V 8.00V 10.00V 0.82V 1.00V 1.20V 1.50V 1.80V 2.00V 2.20V 2.50V 3.30V 5.00V 8.00V 10.00V CIN 2.2F 2.2F 2.2F 2.2F 2.2F 2.2F 2.2F 2.2F 2.2F 2.2F 2.2F 2.2F 2.2F 2.2F 2.2F 2.2F 2.2F 2.2F 2.2F 2.2F 2.2F 2.2F 2.2F 2.2F 2.2F 2.2F 2.2F 2.2F 2.2F 2.2F 2.2F 2.2F 2.2F 2.2F 2.2F 2.2F 2.2F 2.2F 2.2F 2.2F 2.2F 2.2F 2.2F 2.2F 2.2F COUT 200F 1206 200F 1206 147F 1206 147F 1206 100F 1206 68F 1206 68F 1206 47F 1206 22F 1206 10F 1206 10F 1206 200F 1206 200F 1206 147F 1206 147F 1206 100F 1206 68F 1206 68F 1206 47F 1206 22F 1206 10F 1206 200F 1206 200F 1206 147F 1206 147F 1206 100F 1206 68F 1206 47F 1206 22F 1206 22F 1206 10F 1206 10F 1206 10F 1206 200F 1206 200F 1206 147F 1206 147F 1206 100F 1206 68F 1206 47F 1206 22F 1206 22F 1206 10F 1206 10F 1206 10F 1206 RADJ 5.62M 953k 487k 280k 196k 165k 140k 115k 78.7k 47.5k 27.4k 5.62M 953k 487k 280k 196k 165k 140k 115k 78.7k 47.5k 5.62M 953k 487k 280k 196k 165k 140k 115k 78.7k 47.5k 27.4k 21.5k 5.62M 953k 487k 280k 196k 165k 140k 115k 78.7k 47.5k 27.4k 21.5k BIAS 2.8V, <25V 2.8V, <25V 2.8V, <25V 2.8V, <25V 2.8V, <25V 2.8V, <25V 2.8V, <25V 2.8V, <25V AUX AUX AUX VIN VIN VIN VIN VIN VIN VIN VIN AUX AUX 2.8V, <25V 2.8V, <25V 2.8V, <25V 2.8V, <25V 2.8V, <25V 2.8V, <25V 2.8V, <25V 2.8V, <25V AUX AUX AUX AUX 2.8V, <25V 2.8V, <25V 2.8V, <25V 2.8V, <25V 2.8V, <25V 2.8V, <25V 2.8V, <25V 2.8V, <25V AUX AUX AUX AUX fOPTIMAL 250k 300k 350k 400k 450k 450k 500k 550k 600k 700k 800k 250k 300k 350k 400k 450k 450k 500k 550k 600k 700k 250k 300k 350k 400k 450k 450k 500k 550k 600k 700k 800k 900k 250k 300k 350k 400k 450k 450k 500k 550k 600k 700k 800k 900k RT(OPTIMAL) 150k 124k 105k 88.7k 78.7k 78.7k 69.8k 61.9k 54.9k 44.2k 39.2k 150k 124k 105k 88.7k 78.7k 78.7k 69.8k 61.9k 54.9k 44.2k 150k 124k 105k 88.7k 78.7k 78.7k 69.8k 61.9k 54.9k 44.2k 39.2k 34.0k 150k 124k 105k 88.7k 78.7k 78.7k 69.8k 61.9k 54.9k 44.2k 39.2k 34.0k fMAX 250k 300k 350k 400k 450k 450k 500k 600k 700k 1M 1.5M 600k 700k 800k 900k 1M 1.1M 1.25M 1.3M 1.7M 2M 400k 450k 500k 550k 650k 700k 750k 800k 1M 1.5M 1.5M 1.3M 250k 300k 350k 400k 450k 450k 500k 600k 700k 1M 1.5M 1.3M RT(MIN) 150k 124k 105k 88.7k 78.7k 78.7k 69.8k 54.9k 44.2k 29.4k 16.2k 54.9k 44.2k 39.2k 34.0k 29.4k 26.1k 22.1k 21.0k 14.0k 10.0k 88.7k 79.0k 69.8k 61.9k 49.9k 44.2k 42.2k 39.2k 29.4k 16.2k 16.2k 21.0k 150k 124k 105k 88.7k 78.7k 78.7k 69.8k 54.9k 44.2k 29.4k 16.2k 21.0k
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Note: An input bulk capacitor is required. 200F is 2 x 100F 147 is 100F||47F ,
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LTM8032 APPLICATIONS INFORMATION
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 LTM8032's switching frequency depends on the load current, and can excite a ceramic capacitor at audio frequencies, generating audible noise. Since the LTM8032 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 LTM8032. A ceramic input capacitor combined with trace or cable inductance forms a high Q (under damped) tank circuit. If the LTM8032 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. Electromagnetic Compliance The LTM8032 is compliant with the radiated emissions requirements of EN55022 class B. Graphs of the LTM8032's EMC performance are given in the Typical Performance Characteristics section. Further data, operating conditions and test setup are detailed in an EMI Test report available from Linear Technology. Frequency Selection The LTM8032 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. Operating Frequency Trade-Offs 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 LTM8032 is flexible enough to accommodate a wide range
Table 2. Switching Frequency vs RT Value
SWITCHING FREQUECNY (MHz) 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.2 1.4 1.5 1.8 2 2.2 2.4 RT VALUE (k) 187 124 88.7 69.8 54.9 44.2 39.2 34 29.4 23.7 19.1 16.2 13.3 11.5 9.76 8.66
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 LTM8032 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 attendant RT value) at which the LTM8032 should be allowed to switch is given in Table 1 in the fMAX column, while the recommended frequency (and RT value) for optimal efficiency over the given input condition is given in the fOPTIMAL column. There are additional conditions that must be satisfied if the synchronization function is used. Please refer to the Synchronization section for details. 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 2.8V. If the output voltage is programmed to be 2.8V or higher, simply tie BIAS to AUX. If VOUT is less than 2.8V, BIAS can be tied to VIN or some other voltage source. In all cases, ensure that the maximum voltage at the BIAS pin is both less than 25V and the sum of VIN and BIAS is less
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LTM8032 APPLICATIONS INFORMATION
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 LTM8032.
INPUT VOLTAGE (V) 6.0 5.5 5.0 4.5 4.0 3.5 3.0 0 500 1000 1500 LOAD CURRENT (mA) 2000
8032 F01a
VOUT = 3.3V
Load Sharing Two or more LTM8032s may be paralleled to produce higher currents. This may, however, alter the EMI performance of the LTM8032s. To do this, tie the VIN, ADJ, VOUT and SHARE pins of all the paralleled LTM8032s together. To ensure that paralleled modules start up together, the RUN/SS pins may be tied together, as well. Synchronize the LTM8032s to an external clock to eliminate beat frequencies, if required. 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 LTM8032 modules configured for load sharing is given in the Typical Applications section. Burst Mode Operation To enhance efficiency at light loads, the LTM8032 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 LTM8032 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 LTM8032 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 above 0.7V. Do not leave the SYNC pin floating. Minimum Input Voltage The LTM8032 is a step-down converter, so a minimum amount of headroom is required to keep the output in regulation. In addition, the input voltage required to turn on is higher than that required to run, and depends upon whether the RUN/SS is used. As shown in Figure 1, it takes only about 3.6VIN for the LTM8032 to run a 3.3V output at light load. If RUN/SS is pulled up to VIN, it takes
TO RUN TO START RUN/SS ENABLED
7.5
VOUT = 5V
7.0 INPUT VOLTAGE (V)
6.5
6.0
5.5
TO RUN TO START RUN/SS ENABLED 0 500 1500 1000 LOAD CURRENT (mA) 2000
8032 F01b
5.0
Figure 1. The LTM8032 Needs More Voltage to Start Than Run
5.5VIN to start. If the LTM8032 is enabled via the RUN/SS pin, the minimum voltage to start at light loads is lower, about 4.5V. A similar curve for 5VOUT operation is also provided in Figure 1. Soft-Start The RUN/SS pin can be used to soft-start the LTM8032, reducing the maximum input current during start-up. The RUN/SS pin is driven through an external RC network to create a voltage ramp at this pin. Figure 2 shows the startup 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.
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11
LTM8032 APPLICATIONS INFORMATION
VIN IL 1A/DIV VIN VOUT VOUT RUN/SS AUX LTM8032 BIAS ADJ RT SYNC GND
RUN 15k RUN/SS 0.22F GND
VRUN/SS 2V/DIV
VOUT 2V/DIV
8032 F03
2ms/DIV
8023 F02
Figure 2. To Soft-Start the LTM8032, 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 LTM8032 Runs Only When the Input is Present
Synchronization The internal oscillator of the LTM8032 can be synchronized by applying an external 250kHz to 2MHz clock to the SYNC pin. Do not leave this pin floating. The resistor tied from the RT pin to ground should be chosen such that the LTM8032 oscillates 20% lower than the intended synchronization frequency (see the Frequency Selection section). The LTM8032 will not enter Burst Mode operation while synchronized to an external clock, but will instead skip pulses to maintain regulation. Shorted Input Protection Care needs to be taken in systems where the output will be held high when the input to the LTM8032 is absent. This may occur in battery charging applications or in battery back-up systems where a battery or some other supply is diode ORed with the LTM8032'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 LTM8032'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 internal switch current will drop to essentially zero. However, if the VIN pin is grounded while the output is held high, then parasitic diodes inside the LTM8032 can pull large currents from the output through the VIN pin, potentially damaging the device. Figure 3 shows a circuit that will run only when the input voltage is present and that protects against a shorted or reversed input.
PCB Layout Most of the headaches associated with PCB layout have been alleviated or even eliminated by the high level of integration of the LTM8032. The LTM8032 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 heat sinking are acceptable. A few rules to keep in mind are: 1. Place the RADJ and RT resistors as close as possible to their respective pins. 2. Place the CIN capacitor as close as possible to the VIN and GND connection of the LTM8032. If a capacitor is connected to the FIN terminals, place it as close as possible to the FIN terminals, such that its ground connection is as close as possible to that of the CIN capacitor. 3. Place the COUT capacitor as close as possible to the VOUT and GND connection of the LTM8032. 4. Place the CIN and COUT capacitors such that their ground currents flow directly adjacent or underneath the LTM8032. 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 LTM8032.
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12
LTM8032 APPLICATIONS INFORMATION
RT GND
COUT AUX BIAS
SYNC RUN/SS FIN
VIN
OPTIONAL FIN CAPACITOR VOUT
CIN
GND
8032 F04
Figure 4. Layout Showing Suggested External Components, GND Plane and Thermal Vias
6. Use vias to connect the GND copper area to the board's 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. Hot-Plugging Safely The small size, robustness and low impedance of ceramic capacitors make them an attractive option for the input bypass capacitor of LTM8032. However, these capacitors can cause problems if the LTM8032 is plugged into a live or fast rising or falling 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 under-damped tank circuit, and the voltage at the VIN pin of the LTM8032 can ring to twice the nominal input voltage, possibly exceeding the LTM8032's rating and damaging the part. A similar phenomenon can occur inside the LTM8032 module, at the output of the integrated EMI filter, with the same potential of damaging the part.
If the input supply is poorly controlled or the user will be plugging the LTM8032 into an energized supply, the input network should be designed to prevent this overshoot. Figure 5 shows the waveforms that result when an LTM8032 circuit is connected to a 24V supply through six feet of 24-gauge twisted pair. The first plot (5a) 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. An alternative solution is shown in Figure 5b. 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. 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. By far the most popular method of controlling overshoot is shown in Figure 5c, where an aluminum electrolytic capacitor has been connected to FIN. 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. Figure 5c shows the capacitor added to the VIN terminals, but placing the electrolytic capacitor at the FIN terminals can improve the LTM8032's EMI filtering as well as guard against overshoots caused by the Q of the integrated filter. Thermal Considerations The LTM8032 output current may need to be derated if it is required to operate in a high ambient temperature or deliver a large amount of continuous power. The amount of current derating is dependent upon the input voltage, output power and ambient temperature. The derating curves given in the Typical Performance Characteristics section can be used as a guide. These curves were generated by a LTM8032 mounted to a 36cm2 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.
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RADJ
PGOOD
13
LTM8032 APPLICATIONS INFORMATION
CLOSING SWITCH SIMULATES HOT PLUG IIN DANGER LTM8032 VIN 4.7F VIN 20V/DIV RINGING VIN MAY EXCEED ABSOLUTE MAXIMUM RATING
+
LOW IMPEDANCE ENERGIZED 24V SUPPLY
STRAY INDUCTANCE DUE TO 6 FEET (2 METERS) OF TWISTED PAIR
IIN 10A/DIV 20s/DIV
(5a)
0.7 LTM8032 VIN 4.7F IIN 10A/DIV VIN 20V/DIV
+
0.1F
(5b)
20s/DIV
FIN LTM8032 VIN
VIN 20V/DIV
+
22F 35V AI.EI.
+
4.7F IIN 10A/DIV
(5c)
20s/DIV
8032 F05
Figure 5. A Well Chosen Input Network Prevents Input Voltage Overshoot and Ensures Reliable Operation When the LTM8032 is Hot-Plugged to a Live Supply
The die temperature of the LTM8032 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 LTM8032. To estimate the junction temperature, approximate the power dissipation within the LTM8032 by applying the typical efficiency stated in this data sheet to the desired output power, or, if you have an actual module, by taking a power measurement. Then calculate the temperature rise of the LTM8032 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 LTM8032 to the printed circuit board depends upon the layout of the circuit board, but the thermal resistance given in the Pin Configuration, as well as the internal temperature rise curves given in the Typical Performance Characteristics section, can be used a guide. Both the thermal resistance and internal temperature rise curves are based upon a 36cm2 4-layer FR4 PC board. Finally, be aware that at high ambient temperatures the internal Schottky diode will have significant leakage current, increasing the input quiescent current of the LTM8032.
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14
LTM8032 TYPICAL APPLICATIONS
0.82V Step-Down Converter
VIN* 3.6VDC TO 24VDC 2.2F VOUT 0.82V 200F 2A
VIN FIN LTM8032
OUT
RUN/SS BIAS
AUX
SHARE
PGOOD
RT SYNC GND ADJ 150k 5.62M
*RUNNING VOLTAGE RANGE. SEE APPLICATIONS FOR START-UP DETAILS
8032 TA02
1.8V Step-Down Converter
VIN* 3.6VDC TO 24VDC 2.2F VOUT 1.8V 100F 2A
VIN FIN LTM8032
OUT
RUN/SS BIAS
AUX
SHARE
PGOOD
RT SYNC GND ADJ 78.7k 196k
*RUNNING VOLTAGE RANGE. SEE APPLICATIONS FOR START-UP DETAILS
8032 TA03
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15
LTM8032 TYPICAL APPLICATIONS
2.5V Step-Down Converter
VIN* 4.3VDC TO 36VDC 2.2F VOUT 2.5V 2A
VIN FIN LTM8032
OUT 47F AUX
RUN/SS 3.3V BIAS
SHARE
PGOOD
RT SYNC GND ADJ 61.9k 115k
*RUNNING VOLTAGE RANGE. SEE APPLICATIONS FOR START-UP DETAILS
8032 TA04
3.3V Step-Down Converter
VIN* 5.5VDC TO 36VDC VOUT 3.3V 2A
VIN FIN RUN/SS 2.2F
OUT 22F AUX
LTM8032 BIAS
SHARE
PGOOD
RT SYNC GND ADJ 54.9k 78.7k
*RUNNING VOLTAGE RANGE. SEE APPLICATIONS FOR START-UP DETAILS
8032 TA08
5V Step-Down Converter
VIN* 7VDC TO 36VDC VOUT 5V 2A
VIN FIN RUN/SS 2.2F
OUT 10F AUX
LTM8032 BIAS
SHARE
PGOOD
RT SYNC GND ADJ 44.2k 47.5k
*RUNNING VOLTAGE RANGE. SEE APPLICATIONS FOR START-UP DETAILS
8032 TA05
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16
LTM8032 TYPICAL APPLICATIONS
8V Step-Down Converter
VIN* 10.5VDC TO 36VDC VOUT 8V 2A
VIN FIN RUN/SS 2.2F
OUT 10F AUX
LTM8032 BIAS
SHARE
PGOOD
RT SYNC GND ADJ 39.2k 27.4k
*RUNNING VOLTAGE RANGE. SEE APPLICATIONS FOR START-UP DETAILS
8032 TA06
Two LTM8032s Operating in Parallel
VIN* 5.5VDC TO 36VDC
VIN FIN RUN/SS 2.2F SHARE
OUT
VOUT 3.3V 3.5A
AUX
LTM8032 BIAS
PGOOD
RT SYNC GND ADJ 54.9k 40k
OPTIONAL SYNC TIE TO GND IF NOT USED VIN FIN RUN/SS 2.2F SHARE PGOOD AUX OUT 47F
LTM8032 BIAS
RT SYNC GND ADJ
8032 TA07
54.9k
*RUNNING VOLTAGE RANGE. SEE APPLICATIONS FOR START-UP DETAILS
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17
LTM8032 PACKAGE DESCRIPTION
LGA Package 71-Lead (15mm x 9mm x 2.82mm)
(Reference LTC DWG # 05-08-1823 Rev O)
2.670 - 2.970
aaa Z
7
6
5
4
3
2
1
PAD 1 O (0.635)
A
PAD 1 CORNER
4
B
C
D
E
15.00 BSC
12.700 BSC
F
G
H
MOLD CAP
SUBSTRATE
J
0.27 - 0.37 2.40 - 2.60
bbb Z
K
DETAIL A
1.270 BSC
L
Z
X
9.00 BSC
aaa Z
PADS SEE NOTES DETAIL A PACKAGE SIDE VIEW 0.635 0.025 SQ. 71x
eee S X Y
Y
1.27 BSC
3
7.620 BSC
DETAIL A
PACKAGE TOP VIEW
PACKAGE BOTTOM VIEW
3.810
2.540
1.270
0.000
1.270
2.540
3.810
6.350
DETAIL A
5.080 3.810 2.540 1.270 0.000 1.270 2.540 3.810 5.080 6.350
NOTES: 1. DIMENSIONING AND TOLERANCING PER ASME Y14.5M-1994 2. ALL DIMENSIONS ARE IN MILLIMETERS 3 4 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 MARKED FEATURE
TRAY PIN 1 BEVEL COMPONENT PIN 1
LTMXXXXXX Module
PACKAGE IN TRAY LOADING ORIENTATION
LGA 71 0108 REV O
5. PRIMARY DATUM -Z- IS SEATING PLANE 6. THE TOTAL NUMBER OF PADS: 71 SYMBOL TOLERANCE aaa 0.15 bbb 0.10 eee 0.05
SUGGESTED PCB LAYOUT TOP VIEW
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18
LTM8032 PACKAGE DESCRIPTION
Table 2. LTM8032 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 D5 D6 D7 E1 E2 E3 E4 E5 E6 E7 SIGNAL DESCRIPTION VOUT VOUT VOUT VOUT GND GND GND 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 GND GND GND PIN F1 F2 F3 F4 F5 F6 F7 G1 G2 G3 G4 G5 G6 G7 H1 H2 H3 H4 H5 H6 H7 J5 J6 J7 K1 K2 K3 K5 K6 K7 L1 L2 L3 L5 L6 L7 SIGNAL DESCRIPTION GND GND GND GND GND GND GND GND GND GND GND GND GND RT GND GND GND BIAS AUX GND SHARE GND GND ADJ VIN VIN FIN GND GND PGOOD VIN VIN FIN RUN/SS SYNC GND
8032fa
Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use. Linear Technology Corporation makes no representation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
19
LTM8032 PACKAGE PHOTOGRAPH
RELATED PARTS
PART NUMBER LTM4606 LTM4612 LTM8023 DESCRIPTION Ultralow Noise 6A DC/DC Module Ultralow Noise High VOUT DC/DC Module 36V, 2A DC/DC Module COMMENTS 4.5V VIN 28V, 0.6V VOUT 5V, 15mm x 15mm x 2.8mm Package 5A, 5V VIN 36V, 3.3V VOUT 15V, 15mm x 15mm x 2.8mm Package 3.6V VIN 36V, 0.8V VOUT 10V, 9mm x 11.75mm x 2.8mm Package
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20 Linear Technology Corporation
(408) 432-1900 FAX: (408) 434-0507
LT 0409 REV A * PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
www.linear.com
(c) LINEAR TECHNOLOGY CORPORATION 2009

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