LT3757 LINER [Linear Technology], LT3757 Datasheet
LT3757
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LT3757 Summary of contents
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... The fixed frequency, current-mode architecture results in stable operation over a wide range of supply and output voltages. The operating frequency of LT3757 can be set with an external resistor over a 100kHz to 1MHz range, and can be synchronized to an external clock using the SYNC pin. A low minimum operating supply voltage of 2.9V, and a low shutdown quiescent current of less than 1µA, make the LT3757 ideally suited for battery-operated systems. ...
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... LT3757MPMSE#TRPBF 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/ For more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/ (Note 1) Operating Temperature Range (Notes 2, 8) LT3757E . ............................................ –40°C to 125°C + 0.3V, 20V IN LT3757I . ............................................. –40°C to 125°C + 0.3V CC LT3757H ............................................ –40°C to 150°C LT3757MP ......................................... –55°C to 125°C Storage Temperature Range DFN . ................................................... – ...
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... FBX V = 1.6V FBX SS = 0V, Current Out of Pin Falling INTV CC UVLO Hysteresis V = 40V 15V IN 0 < I < 20mA INTVCC < V < 40V 6V 20mA IN INTVCC LT3757 MIN TYP MAX UNITS 2 0.1 1 µA 6 µA 1.6 2.2 mA 280 400 µA 100 110 120 mV l –65 µA 1.569 1.6 1.631 V l – ...
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... Gate V OH 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 LT3757E is guaranteed to meet performance specifications from the 0°C to 125°C junction temperature. Specifications over the –40°C to 125°C operating junction temperature range are assured by design, characterization and correlation with statistical process controls. The LT3757I is guaranteed over the full –40°C to 125°C operating junction temperature range. The LT3757H is guaranteed over the full –40°C to 150°C operating junction temperature range. High junction temperatures degrade operating lifetimes. Operating lifetime is derated at junction temperatures greater than 125° ...
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... TEMPERATURE (°C) SHDN/UVLO Current vs Voltage 150 SHDN/UVLO VOLTAGE (V) LT3757 T = 25°C, unless otherwise noted. A Normalized Switching Frequency vs FBX 120 100 1000 –0.8 0 0.4 0.8 900 –0.4 FBX VOLTAGE (V) 3757 G05 ...
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... LT3757 Typical perForMance characTerisTics INTV vs Temperature CC 7.4 7.3 7.2 7.1 7.0 –75 –50 – 100 125 TEMPERATURE (°C) 3757 G13 INTV Line Regulation CC 7.30 7.25 7.20 7.15 7. (V) IN 3757 G16 Gate Drive Rise and Fall Time vs INTV 3300pF L 25 RISE TIME 20 FALL TIME ...
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... IN V (Pin 10): Input Supply Pin. Must be locally bypassed IN with a 0.22µ larger, capacitor placed close to the pin. Exposed Pad (Pin 11): Ground. This pin also serves as the negative terminal of the current sense resistor. The Exposed Pad must be soldered directly to the local ground plane. LT3757 is CC can be connected CC can also CC 3757fb ...
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... A11 C1 – 1.72V + G6 A12 – + –0.88V + 1.6V A1 – FBX FBX – –0.8V FREQUENCY FOLDBACK Figure 1. LT3757 Block Diagram Working as a SEPIC Converter SHDN/UVLO A10 – 2µA 1.22V 2.5V INTERNAL REGULATOR AND UVLO I S2 17.5V + 10µA UVLO A9 – ...
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... The LT3757 has a switch current limit function. The current sense voltage is input to the current limit comparator A6. If the SENSE pin voltage is higher than the sense current limit threshold V (110mV, typical), A6 will reset SENSE(MAX) SR1 and turn off M1 immediately. The LT3757 is capable of generating either positive or negative output voltage with a single FBX pin. It can be configured as a boost, flyback or SEPIC converter to gen- erate positive output voltage inverting converter to generate negative output voltage. When configured as a SEPIC converter, as shown in Figure 1, the FBX pin is pulled up to the internal bias voltage of 1. volt- ...
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... CC JA for the MSE package. For an ambient board temperature 70°C and maximum junction temperature of 125°C, A the maximum I supply. be calculated as DRIVE MAX ( The LT3757 has an internal INTV function to protect the IC from excessive on-chip power dissipation. The I increases (see the INTV graph in the Typical Performance Characteristics section reaches the current limit, INTV DRIVE and may trigger the soft-start. Based on the preceding equation and the INTV Output Current vs V maximum MOSFET gate charge the LT3757 can drive at a given ...
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... RT pin to ground, as shown in Figure 1. The RT pin must have an external resistor to GND for proper operation of pin shorted to CC the LT3757. A table for selecting the value of R operating frequency is shown in Table 1. Table 1. Timing Resistor (R OSCILLATOR FREQUENCY (kHz) pin can be CC through a blocking meets the following LT3757 LT3757 D VCC R VCC V INTV OUT CC C VCC 4.7µF GND 3757 F03 Figure 3 ...
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... The resistors R1 and R2 are typically chosen so that the error caused by the current flowing into the FBX pin during normal operation is less than 1% (this translates to a maximum value about 158k). Soft-Start The LT3757 contains several features to limit peak switch currents and output voltage (V resistor T start-up or recovery from a fault condition. The primary purpose of these features is to prevent damage to external components or the load. High peak switch currents during start-up may occur in switching regulators. Since V the feedback loop is saturated and the regulator tries to charge the output capacitor as quickly as possible, resulting in large peak currents ...
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... Stability should then be checked across all operating conditions, including load current, input voltage and temperature. SENSE Pin Programming from exceeding the L For control and protection, the LT3757 measures the power MOSFET current by using a sense resistor (R between GND and the MOSFET source. Figure 4 shows a typical waveform of the sense voltage (V sense resistor important to use Kelvin traces between the SENSE pin and R close as possible to the GND terminal of the R proper operation. ...
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... GND C FLT Figure 5. The RC Filter on SENSE Pin APPLICATION CIRCUITS SENSE The LT3757 can be configured as different topologies. The first topology to be analyzed will be the boost converter, followed by the flyback, SEPIC and inverting converters. Boost Converter: Switch Duty Cycle and Frequency The LT3757 can be configured as a boost converter for the applications where the converter output voltage is higher than the input voltage. Remember that boost con- verters are not short-circuit protected. Under a shorted output condition, the inductor current is limited only by the input supply capability ...
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... FET • C • RSS The first term in the preceding equation represents the conduction losses in the device, and the second term, the switching loss. C which is usually specified in the MOSFET characteristics. For maximum efficiency, R minimized. From a known power dissipated in the power MOSFET, its junction temperature can be obtained using the following equation LT3757 to be the minimum of the L(PEAK PEAK ( ) ), the threshold voltage DS ), the gate to source DS(ON) and Q ), the maximum and the MOSFET’ ...
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... LT3757 applicaTions inForMaTion T must not exceed the MOSFET maximum junction J temperature rating recommended to measure the MOSFET temperature in steady state to ensure that absolute maximum ratings are not exceeded. Boost Converter: Output Diode Selection To maximize efficiency, a fast switching diode with low forward drop and low reverse leakage is desirable. The peak reverse voltage that the diode must withstand is equal to the regulator output voltage plus any additional ringing across its anode-to-cathode during the on-time. ...
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... SUGGESTED RCD SNUBBER – LT3757 GATE SENSE GND 3757 F06 Figure 7. A Simplified Flyback Converter LT3757 OUT S – – R SENSE 3757fb ...
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... LT3757 applicaTions inForMaTion Flyback Converter: Switch Duty Cycle and Turns Ratio The flyback converter conversion ratio in the continuous mode operation is OUT S = • − where the second to primary turns ratio Figure 8 shows the waveforms of the flyback converter in discontinuous mode operation. During each switching period T , three subintervals occur During on, and D is reverse-biased. During ...
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... MOSFET turn-off. This is increasingly prominent at higher load currents, where more stored energy must be dis- sipated. In some cases a snubber circuit will be required to avoid overvoltage breakdown at the MOSFET’s drain node. There are different snubber circuits, and Application Note good reference on snubber design. An RCD snubber is shown in Figure 7. The snubber resistor value (R following equation LT3757 = • I SW(PEAK) LP(MAX • I D(PEAK) LS(MAX • V • ...
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... LT3757 applicaTions inForMaTion where V is the snubber capacitor voltage. A smaller SN V results in a larger snubber loss. A reasonable 2.5 times of: V • N OUT P N the leakage inductance of the primary winding, LK which is usually specified in the transformer character- istics. L can be obtained by measuring the primary LK inductance with the secondary windings shorted. The ...
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... COUT has the advantage that both the power MOSFET and the output diode voltages are clamped by the capacitors (C C and C DC across the power MOSFET and the output diodes. The SEPIC converter requires much smaller input capacitors 4 − ( • • than those of the flyback converter. This is due to the fact ) • LT3757 P − 4 OUT MAX ( ) ≥ • • • MIN ( ) − 1 ...
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... LT3757 applicaTions inForMaTion that, in the SEPIC converter, the inductor series with the input, and the ripple current flowing through the input capacitor is continuous. SEPIC Converter: Switch Duty Cycle and Frequency For a SEPIC converter operating in CCM, the duty cycle of the main switch can be calculated based on the output voltage (V ), the input voltage (V OUT forward voltage ( The maximum duty cycle (D ) occurs when the converter MAX has the minimum input voltage OUT MAX ...
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... MOSFET, its junction temperature can be obtained using the following equation • θ • (θ FET JA A FET T must not exceed the MOSFET maximum junction J temperature rating recommended to measure the MOSFET temperature in steady state to ensure that absolute maximum ratings are not exceeded. LT3757 ) is SENSE to be the minimum • C • RSS should be RSS + θ 3757fb ...
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... The RMS OUT D > I • MAX ( ) V IN MIN ( ) . DC − − − – C LT3757 OUT M1 GATE SENSE R SENSE GND Figure 10. A Simplified Inverting Converter while OUT IN – OUT + 3757 F09 3757fb ...
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... DC the switch off-time, the current through C approximately –I rating of the coupling capacitor is determined by the fol- lowing equation: I RMS CDC ( A low ESR and ESL, X5R or X7R ceramic capacitor works well for C 8 • • OUT LT3757 > 0.3 • ∆I L2 – V IN(MAX) OUT DC flows during the on-time. The RMS O D MAX > I • MAX ( ) − MAX ...
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... MOSFET and the sensing resistor. The high di/dt secondary loop contains the output capacitor, the secondary winding and the output diode. • In SEPIC configuration, the high di/dt loop contains the power MOSFET, sense resistor, output capacitor, Schottky diode and the coupling capacitor. • In inverting configuration, the high di/dt loop contains power MOSFET, sense resistor, Schottky diode and the coupling capacitor LT3757 VCC ...
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... Inductors Thermalloy Heat Sinks Tokin Capacitors Toko Inductors United Chemicon Capacitors Vishay/Dale Resistors Vishay/Siliconix MOSFETs Vishay/Sprague Capacitors Würth Electronik Inductors Zetex Small-Signal Discretes LT3757 WEB ADDRESS avx.com bhelectronics.com coilcraft.com bussmann.com diodes.com fairchildsemi.com generalsemiconductor.com irf.com irctt.com kemet.com mag-inc.com microsemi.com murata.co.jp nichicon.com onsemi.com panasonic.com sanyo.co.jp sumida.com t-yuden ...
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... OUT1 C OUT2 3.3V Input, 5V/10A Output Boost Converter L1 0.5µ 49.9k C INTV VCC CC 4.7µF SHDN/UVLO 10V X5R 34k LT3757 SYNC GATE FBX 22 RT SENSE SS VC GND 6.8k 0.1µF 22nF 2.2nF : TAIYO YUDEN JMK325BJ226MM D1: MBRB2515L : PANASONIC EEFUEOJ151R L1: VISHAY SILICONIX IHLP-5050FD-01 : TAIYO YUDEN JMK325BJ226MM M1: VISHAY SILICONIX SI4448DY ...
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... R 0. 100pF 22k 1W C VCC C 4.7µ 0.1µF 10V 6.8nF X5R : MURATA GRM31CR61E106KA12 500mV/DIV I OUT 1A/DIV 1 10 3757 TA03b LT3757 D1 V OUT 24V 2A R2 226k OUT1 47µF 35V OUT2 R1 10µF 16.2k 25V 1% X5R 3757 TA03a Load Step Response 12V ...
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... D1: VISHAY SILICONIX GSD2004S DUAL DIODE CONNECTED IN SERIES M1: VISHAY SILICONIX Si7850DP T1: TDK DCT15EFD-U44S003 Start-Up Waveforms V OUT 100V/DIV 2ms/DIV 0 High Voltage Flyback Power Supply SHDN/UVLO INTV VCC CC 47µF SYNC 25V LT3757 X5R GATE RT 22 SENSE SS VC GND FBX 10nF 6.8k 22nF 100pF 20V/DIV 3757 TA04b 1:10 ...
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... GND INTV CC 10k 4.7µF 6.8nF 10V X5R V 200mV/DIV 1.6A I OUT 1A/DIV 0. 3757 TA05b Frequency Foldback Waveforms When Output Short-Circuits 10V/DIV 20V/DIV I L1A 3757 TA05d LT3757 C DC 4.7µF 50V, X5R OUT 12V 2A L1B I L1B • 105k OUT1 47µF 20V 2 C OUT2 10µ ...
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... SENSE FBX 0.02 GND INTV CC 22k C VCC 4.7µF 6.8nF 10V X5R Nonisolated Inverting SLIC Supply VP5-0155 (PRIMARY = 3 WINDINGS IN PARALLEL 10µ 50V 1,2,3 SHDN/UVLO X5R LT3757 M1 SYNC GATE Si7850DP SENSE RT FBX SS VC GND INTV CC 0.012 9.1k 0.5W C VCC 4.7µF 10nF 10V, X5R 15.8k 464k D1 1.05k ...
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... ALL DIMENSIONS ARE IN MILLIMETERS 4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.15mm ON ANY SIDE 5. EXPOSED PAD SHALL BE SOLDER PLATED 6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION ON THE TOP AND BOTTOM OF PACKAGE LT3757 R = 0.125 0.40 0.10 TYP 6 10 ...
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... LT3757 package DescripTion 2.794 0.102 (.110 .004) 5.23 (.206) MIN 0.305 0.038 (.0120 .0015) TYP RECOMMENDED SOLDER PAD LAYOUT DETAIL “A” 0.254 (.010) GAUGE PLANE 0.18 (.007) NOTE: 1. DIMENSIONS IN MILLIMETER/(INCH) 2. DRAWING NOT TO SCALE 3. DIMENSION DOES NOT INCLUDE MOLD FLASH, PROTRUSIONS OR GATE BURRS. ...
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... Rev B) REV DATE DESCRIPTION B 3/10 Deleted Bullet from Features and Last Line of Description Updated Entire Page to Add H-Grade and Military Grade Updated Electrical Characteristics Notes and Typical Performance Characteristics for H-Grade and Military Grade Revised TA04a and Replaced TA04c in Typical Applications Updated Related Parts 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 representa- tion that the interconnection of its circuits as described herein will not infringe on existing patent rights. LT3757 PAGE NUMBER 3757fb ...
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... LT3757 Typical applicaTion High Efficiency Inverting Power Supply 15V V 47µF IN 105k 16V SHDN/UVLO X5R R1 46.4k LT3757 SYNC GATE SENSE RT SS FBX VC GND INTV CC 41.2k 9.1k 300kHz 0.1µF 10nF L1, L2: COILTRONICS DRQ127-3R3 (*COUPLED INDUCTORS) relaTeD parTs PART NUMBER DESCRIPTION LT3758 Boost, Flyback, SEPIC and Inverting Controller ...