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LTM8031 Ultralow Noise EMC 36V, 1A DC/DC Module Regulator FEATURES
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DESCRIPTION
The LTM(R)8031 is an electromagnetic compatible (EMC) 36V, 1A 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 LTM8031 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 LTM8031 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 LTM8031 is RoHS compliant.
L, LT, LTC, LTM, Module, Linear Technology and the Linear logo 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 1A Output Current 0.8V to 10V Output Voltage Switching Frequency from 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/1A DC/DC Module Regulator
VIN* 7VDC TO 36VDC VIN FIN LTM8031 RUN/SS OUT 10F AUX BIAS SHARE PGOOD VOUT 5V 1A EMISSIONS LEVEL (dBV/m)
LTM8031 EMI Performance
VIN = 36V
80 70 60 50 40 30 20 10 0
1F
RT SYNC GND ADJ 44.2k 47.5k
8031 TA01a
EN55022 CLASS B LIMIT
*RUNNING VOLTAGE RANGE. SEE APPLICATIONS FOR START-UP DETAILS
-10
0 100 200 300 400 500 600 700 800 900 1000 FREQUENCY (MHz)
8031 TA01b
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LTM8031 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 = 20.7C/W, JC(BOTTOM) = 8.4C/W, JC(TOP) = 25.6C/W, JBOARD = 13.8C/W VALUES DETERMINED PER JESD 51-9 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 LTM8031EV#PBF LTM8031IV#PBF TRAY LTM8031EV#PBF LTM8031IV#PBF PART MARKING* LTM8031V LTM8031V PACKAGE DESCRIPTION 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
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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LTM8031 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 1A, RADJ Open 0.2A < IOUT 1A, 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 1A, VOUT = 3.3V VIN = 24V, IOUT = 1A, VOUT = 3.3V RT = 113k
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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
1 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)
BIAS Quiescent Current
l
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)
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 = 1A, fSW = 550kHz, 5H LISN 0.7 200
0.1 800
1 0.5
0.1 83 63 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 LTM8031E 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. The LTM8031I is guaranteed to meet specifications over the full -40C 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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LTM8031 TYPICAL PERFORMANCE CHARACTERISTICS TA = 25C, unless otherwise noted.
3.3VOUT Efficiency
100 90 EFFICIENCY (%) EFFICIENCY (%) 80 70 60 50 40 0 200 400 600 800 OUTPUT CURRENT (mA) 1000
8031 G01
5VOUT Efficiency
100 90 EFFICIENCY (%) 12VIN 24VIN 36VIN 0 200 400 600 800 OUTPUT CURRENT (mA) 1000
8031 G02
8VOUT Efficiency
100 90 80 70 60 50 40 0 200 400 600 800 OUTPUT CURRENT (mA) 1000
8031 G03
80 70 60 50 40
5VIN 12VIN 24VIN 36VIN
12VIN 24VIN 36VIN
Input Current vs Output Current, 3.3VOUT
800 700 INPUT CURRENT (mA) 600 500 400 300 200 100 0 0 200 800 600 OUTPUT CURRENT (mA) 400 1000
8031 G04
Input Current vs Output Current, 5VOUT
500 450 400 INPUT CURRENT (mA) 350 300 250 200 150 100 50 0 0 200 600 800 400 OUTPUT CURRENT (mA) 1000
8031 G05
Input Current vs Output Current, 8VOUT
800 700 INPUT CURRENT (mA) 600 500 400 300 200 100 0 0 200 400 800 600 OUTPUT CURRENT (mA) 1000
8031 G06
5VIN 12VIN 24VIN 36VIN
12VIN 24VIN 36VIN
12VIN 24VIN 36VIN
Minimum VIN vs Output Current 2.5V VOUT
5.0 4.8 4.6 4.4 VIN (V) VIN (V) 4.2 4.0 3.8 RUNNING 3.6 3.4 0 200 800 600 OUTPUT CURRENT (mA) 400 1000
8031 G07
Minimum VIN vs Output Current 3.3V VOUT
6.1 7.6 7.1
Minimum VIN vs Output Current 5V VOUT
RUN/SS = VIN OR TOGGLED
5.6 RUN/SS = VIN VIN (V) 5.1 6.6 6.1 5.6 5.1 4.6 4.1 3.6 0 200 600 800 400 OUTPUT CURRENT (mA) 1000
8031 G08
RUN/SS = VIN
RUNNING OR RUN/SS TOGGLED
4.6 RUN/SS TOGGLED 4.1 RUNNING
3.6
0
200
400 800 600 OUTPUT CURRENT (mA)
1000
8031 G09
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LTM8031 TYPICAL PERFORMANCE CHARACTERISTICS TA = 25C, unless otherwise noted.
Minimum VIN vs Output Current 8V VOUT
12 11 10 9 VIN (V) 8 7 6 5 4 0 200 800 600 OUTPUT CURRENT (mA) 400 1000
8031 G10
Minimum Input Running Voltage vs Output Voltage, IOUT = 1A
16 35 30 BIAS CURRENT (mA) 25 20 15 10 5 0 10
8031 G11
Bias Current vs Output Current
8VOUT 5VOUT 3.3VOUT
RUN/SS = VIN
14 12
RUNNING OR RUN/SS TOGGLED VIN (V)
10 8 6 4 2 0 0 2 4 6 VOUT (V) 8
0
200
400 600 800 OUTPUT CURRENT (mA)
1000
8031 G12
Output Current vs Input Voltage (Output Shorted)
2.75 2.70 OUTPUT CURRENT (A) INPUT CURRENT (A) 2.65 2.60 2.55 2.50 2.45 2.40 2.35 0 4 8 12 16 20 24 28 32 36 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0
Input Current vs Input Voltage (Output Shorted)
30 25 TEMPERATURE RISE (C) 20 15 10 5 0
Temperature Rise vs Load Current, VOUT = 3.3V
36VIN 24VIN 12VIN 5VIN
0
10
20 VIN (V)
30
40
8031 G14
0
200
VIN (V)
8031 G13
400 600 800 OUTPUT CURRENT (mA)
1000
8031 G15
Temperature Rise vs Load Current, VOUT = 5V
30 25 TEMPERATURE RISE (C) 20 15 10 5 0 1 200 400 600 800 OUTPUT CURRENT (mA) 1000
8031 G16
Temperature Rise vs Load Current, VOUT = 8V
30 25 TEMPERATURE RISE (C) 20 15 10 5 0 1 200 400 600 800 OUTPUT CURRENT (mA) 1000
8031 G17
Temperature Rise vs Load Current, VOUT = 10V
30 25 TEMPERATURE RISE (C) 20 15 10 5 0 1 200 400 600 800 OUTPUT CURRENT (mA) 1000
8031 G18
36VIN 24VIN 12VIN
36VIN 24VIN 12VIN
36VIN 24VIN
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LTM8031 TYPICAL PERFORMANCE CHARACTERISTICS TA = 25C, unless otherwise noted.
Radiated Emissions
90 80 EMISSIONS LEVEL (dBV/m) 70 60 50 40 30 20 10 0 -10 0 100 200 300 400 500 600 700 800 900 1000 FREQUENCY (MHz)
8031 G19
Radiated Emissions
90 80 EMISSIONS LEVEL (dBV/m) 70 60 50 40 30 20 10 0 -10 0 100 200 300 400 500 600 700 800 900 1000 FREQUENCY (MHz)
8031 G20
VIN = 36V VOUT = 10V AT 1A
VIN = 36V VOUT = 2.5V AT 1A
EN55022 CLASS B LIMIT
EN55022 CLASS B LIMIT
PIN FUNCTIONS
VIN (Bank 3): The VIN pin supplies current to the LTM8031's internal regulator and to the internal power switch. This pin must be locally bypassed with an external, low ESR capacitor of at least 1F . 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 LTM8031 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 LTM8031. 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 LTM8031 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 LTM8031 when paralleling the outputs.
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LTM8031 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 Synchronization 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 LTM8031 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 AUX 22pF 249k 10F GND BIAS
GND
SHARE
CURRENT MODE CONTROLLER
RUN/SS
SYNC
RT
PGOOD
ADJ
8031 BD
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LTM8031 OPERATION
The LTM8031 is a standalone nonisolated 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 LTM8031 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 LTM8031 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 LTM8031 contains a current mode controller, power switching element, power inductor, power Schottky diode and a modest amount of input and output capacitance. The LTM8031 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 LTM8031 in shutdown, disconnecting the output and reducing the input current to less than 1A. To further optimize efficiency, the LTM8031 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 LTM8031'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 LTM8031 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 LTM8031 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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LTM8031 APPLICATIONS INFORMATION
Table 1. Recommended Component Values and Configuration (See Typical Performance Characteristics for Load Conditions)
VIN 3.6V to 36V 3.6V to 36V 3.6V to 36V 3.6V to 36V 3.6V to 36V 4.75V to 36V 6.8V to 36V 10.5V to 36V 13V to 36V 3.6V to 15V 3.6V to 15V 3.6V to 15V 3.6V to 15V 3.6V to 15V 4.75V to 15V 6.8V to 15V 10.5V to 15V 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 VOUT 0.82V 1.20V 1.80V 2.00V 2.50V 3.30V 5.00V 8.00V 10.00V 0.82V 1.20V 1.80V 2.00V 2.50V 3.30V 5.00V 8.00V 0.82V 1.20V 1.80V 2.00V 2.50V 3.30V 5.00V 8.00V 10.00V CIN 1F 0805 50V 1F 0805 50V 1F 0805 50V 1F 0805 50V 1F 0805 50V 1F 0805 50V 1F 0805 50V 1F 0805 50V 1F 0805 50V 1F 0805 50V 1F 0805 50V 1F 0805 50V 1F 0805 50V 1F 0805 50V 1F 0805 50V 1F 0805 50V 1F 0805 50V 1F 0805 50V 1F 0805 50V 1F 0805 50V 1F 0805 50V 1F 0805 50V 1F 0805 50V 1F 0805 50V 1F 0805 50V 1F 0805 50V COUT 2 x 100F 1206 6.3V 100F//47F 1206 6.3V 100F 1206 100F 1206 47F 0805 6.3V 22F 1206 6.3V 10F 1206 6.3V 4.7F 1206 10V 4.7F 0805 16V 2 x 100F 1206 6.3V 100F 1206 6.3V 100F 1206 100F 1206 47F 0805 6.3V 22F 1206 6.3V 10F 1206 6.3V 4.7F 1206 10V 2 x 100F 1206 6.3V 100F//47F 1206 6.3V 100F 1206 100F 1206 47F 0805 6.3V 22F 1206 6.3V 10F 1206 6.3V 4.7F 1206 10V 4.7F 0805 16V RADJ 5.11M 475k 191k 162k 115k 78.7k 46.4k 26.7k 21.0k 5.11M 475k 191k 162k 115k 78.7k 46.4k 26.7k 5.11M 475k 191k 162k 115k 78.7k 46.4k 26.7k 21.0k BIAS 2.8V, <25V 2.8V, <25V 2.8V, <25V 2.8V, <25V 2.8V, <25V AUX AUX AUX AUX VIN VIN VIN VIN VIN AUX AUX AUX 2.8V, <25V 2.8V, <25V 2.8V, <25V 2.8V, <25V 2.8V, <25V AUX AUX AUX AUX fOPTIMAL 250kHz 300kHz 420kHz 450kHz 550kHz 675kHz 975kHz 1200kHz 1250kHz 500kHz 600kHz 650kHz 650kHz 700kHz 950kHz 1150kHz 1200kHz 350kHz 450kHz 600kHz 650kHz 700kHz 950kHz 1150kHz 1200kHz 1250kHz RT(OPTIMAL) 150k 124k 84.5k 78.7k 61.9k 48.7k 29.4k 23.7k 22.6k 69.8k 56.2k 51.1k 51.1k 47.5k 32.4k 25.5k 23.7k 105k 78.7k 56.2k 51.1k 47.5k 32.4k 25.5k 23.7k 22.6k fMAX 250kHz 325kHz 450kHz 475kHz 575kHz 725kHz 1000kHz 1600kHz 2050kHz 600kHz 750kHz 1000kHz 1100kHz 1350kHz 1650kHz 2400kHz 2400kHz 375kHz 475kHz 650kHz 700kHz 850kHz 1050kHz 1550kHz 2400kHz 2400kHz RT(MIN) 150k 113k 78.7k 73.2k 59.0k 44.2k 28.0k 15.8k 10.5k 56.2k 42.2k 28.0k 26.7k 20.5k 15.0k 7.87k 7.87k 93.1k 73.2k 51.1k 47.5k 37.4k 28.0k 16.5k 7.87k 7.87k
Note: An input bulk capacitor is required.
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LTM8031 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 LTM8031's switching frequency depends on the load current, and can excite a ceramic capacitor at audio frequencies, generating audible noise. Since the LTM8031 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 1F ceramic capacitor and a low cost electrolytic capacitor. A final precaution regarding ceramic capacitors concerns the maximum input voltage rating of the LTM8031. A ceramic input capacitor combined with trace or cable inductance forms a high Q (under damped) tank circuit. If the LTM8031 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 LTM8031 is compliant with the radiated emissions requirements of EN55022 class B. Graphs of the LTM8031'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 LTM8031 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 LTM8031 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 56.2 47.5 39.2 34 28.0 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 LTM8031 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 unnecessarily large output capacitor. The maximum frequency (and attendant RT value) at which the LTM8031 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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LTM8031 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 LTM8031. Load Sharing Two or more LTM8031s may be paralleled to produce higher currents. This may, however, alter the EMI performance of the LTM8031s. To do this, tie the VIN, ADJ, VOUT and SHARE pins of all the paralleled LTM8031s together. To ensure that paralleled modules start up together, the RUN/SS pins may be tied together, as well. Synchronize the LTM8031s 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 LTM8031 modules configured for load sharing is given in the Typical Applications section. For 2A applications also see the LTM8032, 2A EMC DC/DC Module regulator Burst Mode Operation To enhance efficiency at light loads, the LTM8031 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 LTM8031 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 LTM8031 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 LTM8031 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 the Typical Performance Characteristics section, it takes only about 3.6VIN for the LTM8031 to run a 3.3V output at light load. If RUN/SS is pulled up to VIN, it takes 5.7VIN to start. If the LTM8031 is enabled via the RUN/SS pin, the minimum voltage to start at light loads is lower, about 4.4V. Similar curves for 2.5VOUT , 5VOUT and 8VOUT operation are also provided in the Typical Performance Characteristics section. Soft-Start The RUN/SS pin can be used to soft-start the LTM8031, 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 1 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.
RUN 15k RUN/SS 0.22F GND
IL 0.5A/DIV
VRUN/SS 2V/DIV
VOUT 2V/DIV
2ms/DIV
8031 F01
Figure 1. To Soft-Start the LTM8031, Add a Resistor and Capacitor to the RUN/SS Pin
Synchronization The internal oscillator of the LTM8031 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 LTM8031 oscillates 20% lower than the intended synchronization frequency (see the Frequency Selection section). The LTM8031 will not enter Burst Mode operation while synchronized to an external clock, but will instead skip pulses to maintain regulation.
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11
LTM8031 APPLICATIONS INFORMATION
Shorted Input Protection Care needs to be taken in systems where the output will be held high when the input to the LTM8031 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 LTM8031'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 LTM8031'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 LTM8031 can pull large currents from the output through the VIN pin, potentially damaging the device. Figure 2 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 LTM8031. The LTM8031 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 3 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 LTM8031. 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 LTM8031. 4. Place the CIN and COUT capacitors such that their ground currents flow directly adjacent or underneath the LTM8031. 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 LTM8031. 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.
VIN
VIN
VOUT
VOUT
RUN/SS AUX LTM8031 BIAS ADJ RT SYNC GND
8031 F02
Figure 2. 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 LTM8031 Runs Only When the Input is Present
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12
LTM8031 APPLICATIONS INFORMATION
RT GND
COUT AUX BIAS
SYNC RUN/SS FIN
VIN
OPTIONAL FIN CAPACITOR VOUT
CIN
GND
8031 F03
Figure 3. Layout Showing Suggested External Components, GND Plane and Thermal Vias
circuit is connected to a 24V supply through six feet of 24gauge twisted pair. The first plot (4a) 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, as shown in Figure 4b. 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 4c, 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. Placing the electrolytic capacitor at the FIN terminals can also improve the LTM8031's EMI filtering as well as guard against overshoots caused by the Q of the integrated filter. Thermal Considerations The LTM8031 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 temperature rise curves given in the Typical Performance Characteristics section can be used as a guide. These curves were generated by a LTM8031 mounted to a 35cm2 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 junction-to-air and junction-to-board thermal resistances given in the Pin Configuration diagram may also be used to estimate the LTM8031 internal temperature. These thermal coefficients are determined per JESD 51-9 (JEDEC standard, test boards for area array surface mount package thermal measurements) through analysis and physical
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RADJ
Hot-Plugging Safely The small size, robustness and low impedance of ceramic capacitors make them an attractive option for the input bypass capacitor of LTM8031. However, these capacitors can cause problems if the LTM8031 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 LTM8031 can ring to twice the nominal input voltage, possibly exceeding the LTM8031's rating and damaging the part. A similar phenomenon can occur inside the LTM8031 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 LTM8031 into an energized supply, the input network should be designed to prevent this overshoot. Figure 4 shows the waveforms that result when an LTM8031
PGOOD
13
LTM8031 APPLICATIONS INFORMATION
CLOSING SWITCH SIMULATES HOT PLUG IIN DANGER LTM8031 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
(4a)
0.7 LTM8031 VIN 4.7F IIN 10A/DIV VIN 20V/DIV
+
0.1F
(4b)
20s/DIV
FIN LTM8031 VIN
VIN 20V/DIV
+
22F 35V AI.EI.
+
4.7F IIN 10A/DIV
(4c)
20s/DIV
8031 F04
Figure 4. A Well Chosen Input Network Prevents Input Voltage Overshoot and Ensures Reliable Operation When the LTM8031 is Hot-Plugged to a Live Supply
correlation. Bear in mind that the actual thermal resistance of the LTM8031 to the printed circuit board depends upon the design of the circuit board. The die temperature of the LTM8031 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 LTM8031. The bulk of the heat flow out of the LTM8031 is through the bottom of the module and the LGA pads into the printed
circuit board. Consequently a poor printed circuit board design can cause excessive heating, resulting in impaired performance or reliability. Please refer to the PCB Layout section for printed circuit board design suggestions. Finally, be aware that at high ambient temperatures the internal Schottky diode will have significant leakage current increasing the quiescent current of the LTM8031.
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14
LTM8031 TYPICAL APPLICATIONS
0.82V Step-Down Converter
VIN* 3.6V TO 15V 1F VOUT 0.82V 200F 1A VIN FIN LTM8031 AUX OUT
RUN/SS BIAS
SHARE
PGOOD
RT SYNC GND ADJ 69.8k 5.11M
*RUNNING VOLTAGE RANGE. SEE APPLICATIONS FOR START-UP DETAILS
8031 TA02
1.8V Step-Down Converter
VIN* 9V TO 24V 1F VOUT 1.8V 100F 1A
VIN FIN LTM8031
OUT
RUN/SS BIAS
AUX
SHARE
PGOOD
RT SYNC GND ADJ 56.2k 191k
*RUNNING VOLTAGE RANGE. SEE APPLICATIONS FOR START-UP DETAILS
8031 TA03
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15
LTM8031 TYPICAL APPLICATIONS
2.5V Step-Down Converter
VIN* 3.6V TO 36V 1F VOUT 2.5V 1A
VIN FIN LTM8031
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
8031 TA04
3.3V Step-Down Converter
VIN* 4.75V TO 36V VOUT 3.3V 1A
VIN FIN LTM8031
OUT 22F AUX BIAS
RUN/SS 1F
SHARE
PGOOD
RT SYNC GND ADJ 48.7k 78.7k
*RUNNING VOLTAGE RANGE. SEE APPLICATIONS FOR START-UP DETAILS
8031 TA08
5V Step-Down Converter
VIN* 6.8V TO 36V VOUT 5V 1A
VIN FIN LTM8031
OUT 10F AUX BIAS
RUN/SS 1F
SHARE
PGOOD
RT SYNC GND ADJ 29.4k 46.4k
*RUNNING VOLTAGE RANGE. SEE APPLICATIONS FOR START-UP DETAILS
8031 TA05
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16
LTM8031 TYPICAL APPLICATIONS
8V Step-Down Converter
VIN* 10.5V TO 36V VOUT 8V 1A
VIN FIN LTM8031
OUT 4.7F AUX BIAS
RUN/SS 1F
SHARE
PGOOD
RT SYNC GND ADJ 23.7k 26.7k
*RUNNING VOLTAGE RANGE. SEE APPLICATIONS FOR START-UP DETAILS
8031 TA06
Two LTM8031s Operating in Parallel (Also See the LTM8032, 2A Pin Compatible)
VOUT 8V 1.9A
VIN* 11.5V TO 36V
VIN FIN LTM8031
OUT
RUN/SS 1F SHARE
AUX BIAS
PGOOD
RT SYNC GND ADJ 23.7k 13.7k
OPTIONAL SYNC TIE TO GND IF NOT USED VIN FIN LTM8031 AUX BIAS 1F SHARE PGOOD OUT 10F
RUN/SS
RT SYNC GND ADJ
8031 TA07
23.7k
*RUNNING VOLTAGE RANGE. SEE APPLICATIONS FOR START-UP DETAILS
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17
LTM8031 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
LTM8031 PACKAGE DESCRIPTION
Table 3. LTM8031 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
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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
LTM8031 PACKAGE PHOTOGRAPH
RELATED PARTS
PART NUMBER LTM4606 LTM4612 LTM8023 LTM8025 LTM8032 DESCRIPTION Ultralow Noise 6A DC/DC Module Regulator Ultralow Noise High VOUT DC/DC Module Regulator 36V, 2A DC/DC Module Regulator 36V, 3A DC/DC Module Regulator 36V, 2A EMC DC/DC Module Regulator COMMENTS 4.5V VIN 28V, 0.6V VOUT 5V, 15mm x 15mm x 2.8mm LGA 5A, 5V VIN 36V, 3.3V VOUT 15V, 15mm x 15mm x 2.8mm LGA 3.6V VIN 36V, 0.8V VOUT 10V, 9mm x 11.75mm x 2.8mm LGA 3.6V VIN 36V, 0.8V VOUT 24V, 9mm x 15mm x 4.32mm LGA EN55022 Class B, 9mm x 15mm x 2.8mm LGA. Pin Compatible with the LTM8031
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20 Linear Technology Corporation
(408) 432-1900
LT 1009 * PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
FAX: (408) 434-0507 www.linear.com
(c) LINEAR TECHNOLOGY CORPORATION 2009

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