LT3757MPMSE#TRPBF Linear Technology, LT3757MPMSE#TRPBF Datasheet

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LT3757MPMSE#TRPBF

Manufacturer Part Number
LT3757MPMSE#TRPBF
Description
IC DC-DC CTRLR ADJ 10MSOP
Manufacturer
Linear Technology
Type
Step-Up (Boost), Inverting, Flyback, Sepicr
Datasheet

Specifications of LT3757MPMSE#TRPBF

Internal Switch(s)
No
Synchronous Rectifier
No
Number Of Outputs
1
Frequency - Switching
100kHz ~ 1MHz
Voltage - Input
2.9 ~ 40 V
Operating Temperature
-55°C ~ 125°C
Mounting Type
Surface Mount
Package / Case
10-MSOP Exposed Pad, 10-HMSOP, 10-eMSOP
Lead Free Status / RoHS Status
Lead free / RoHS Compliant
Current - Output
-
Voltage - Output
-
Power - Output
-

Available stocks

Company
Part Number
Manufacturer
Quantity
Price
Company:
Part Number:
LT3757MPMSE#TRPBFLT3757MPMSE
Manufacturer:
LINEAR/凌特
Quantity:
20 000
applicaTions
Typical applicaTion
FeaTures
n
n
n
n
n
n
n
n
n
n
n
n
n
8V TO 16V
Wide Input Voltage Range: 2.9V to 40V
Positive or Negative Output Voltage Programming
Current Mode Control Provides Excellent Transient
Programmable Operating Frequency (100kHz to
Synchronizable to an External Clock
Low Shutdown Current < 1µA
Internal 7.2V Low Dropout Voltage Regulator
Programmable Input Undervoltage Lockout with
Programmable Soft-Start
Small 10-Lead DFN (3mm × 3mm) and Thermally
Automotive and Industrial Boost, Flyback, SEPIC and
Telecom Power Supplies
Portable Electronic Equipment
with a Single Feedback Pin
Response
1MHz) with One External Resistor
Hysteresis
Enhanced 10-Pin MSOP Packages
Inverting Converters
300kHz
V
41.2k
IN
10µF
25V
X5R
200k
43.2k
0.1µF
High Efficiency Boost Converter
SHDN/UVLO
SYNC
RT
SS
VC
22k
6.8nF
LT3757
V
IN
GND INTV
SENSE
GATE
FBX
CC
4.7µF
10V
X5R
0.01
10µH
226k
16.2k
+
47µF
35V
2
DescripTion
The LT
controller which is capable of generating either positive or
negative output voltages. It can be configured as either a
boost, flyback, SEPIC or inverting converter. The LT3757
drives a low side external N-channel power MOSFET from
an internal regulated 7.2V supply. 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.
The LT3757 features soft-start and frequency foldback
functions to limit inductor current during start-up and
output short-circuit.
L, LT, LTC, LTM, Linear Technology, the Linear logo and Burst Mode are registered trademarks
and No R
trademarks are the property of their respective owners.
Boost, Flyback, SEPIC and
3757 TA01a
SENSE
10µF
25V
X5R
V
24V
2A
®
OUT
3757 is a wide input range, current mode, DC/DC
and ThinSOT are trademarks of Linear Technology Corporation. All other
Inverting Controller
100
30
90
80
70
60
50
40
0.001
V
IN
= 8V
0.01
OUTPUT CURRENT (A)
Efficiency
V
0.1
IN
= 16V
LT3757
1
3757 TA01b
3757fb

10

Related parts for LT3757MPMSE#TRPBF

LT3757MPMSE#TRPBF Summary of contents

Page 1

FeaTures Wide Input Voltage Range: 2.9V to 40V n Positive or Negative Output Voltage Programming n with a Single Feedback Pin Current Mode Control Provides Excellent Transient n Response Programmable Operating Frequency (100kHz to n 1MHz) with One External Resistor Synchronizable to an External Clock n Low Shutdown Current < 1µA n Internal 7.2V Low Dropout Voltage Regulator n Programmable Input Undervoltage Lockout with n Hysteresis Programmable Soft-Start n Small 10-Lead DFN (3mm × 3mm) and Thermally n ...

Page 2

... LT3757EDD#TRPBF LT3757IDD#PBF LT3757IDD#TRPBF LT3757EMSE#PBF LT3757EMSE#TRPBF LT3757IMSE#PBF LT3757IMSE#TRPBF LT3757HMSE#PBF LT3757HMSE#TRPBF LT3757MPMSE#PBF 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° ...

Page 3

T PARAMETER V Operating Range IN V Shutdown Operating Operating I with Internal LDO Disabled IN Q SENSE Current Limit Threshold SENSE Input Bias Current Error Amplifier FBX Regulation Voltage (V ) FBX(REG) FBX Overvoltage Lockout FBX Pin Input Current Transconductance g (∆I /∆ ...

Page 4

LT3757 elecTrical characTerisTics erature range, otherwise specifications are at T PARAMETER INTV Current in Shutdown CC INTV Voltage to Bypass Internal LDO CC Logic Inputs SHDN/UVLO Threshold Voltage Falling SHDN/UVLO Input Low Voltage SHDN/UVLO Pin Bias Current Low SHDN/UVLO Pin Bias Current High Gate Driver t Gate Driver Output Rise Time r t Gate Driver Output Fall Time f Gate V OL 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. ...

Page 5

Typical perForMance characTerisTics Dynamic Quiescent Current vs Switching Frequency 3300pF 500 600 700 0 100 200 300 400 800 900 SWITCHING FREQUENCY (KHz) 3757 G04 Switching Frequency vs Temperature ...

Page 6

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. ...

Page 7

FuncTions VC (Pin 1): Error Amplifier Compensation Pin. Used to stabilize the voltage loop with an external RC network. FBX (Pin 2): Positive and Negative Feedback Pin. Receives the feedback voltage from the external resistor divider across the output. Also modulates the frequency during start-up and fault conditions when FBX is close to GND. SS (Pin 3): Soft-Start Pin. This pin modulates compensa- tion pin voltage (VC) clamp. The soft-start interval is set with an external capacitor. The pin has a 10µA (typical) pull-up current source to an internal 2.5V rail. The soft- start pin is reset to GND by an undervoltage condition at SHDN/UVLO, an INTV undervoltage or overvoltage CC condition or an internal thermal lockout. RT (Pin 4): Switching Frequency Adjustment Pin. Set the frequency using a resistor to GND. Do not leave this pin open. SYNC (Pin 5): Frequency Synchronization Pin. Used to synchronize the switching frequency to an outside clock. ...

Page 8

LT3757 block DiagraM 2. A11 C1 – 1.72V + G6 A12 – + –0.88V + 1.6V A1 – FBX FBX – –0.8V FREQUENCY FOLDBACK Figure 1. LT3757 Block ...

Page 9

Main Control Loop The LT3757 uses a fixed frequency, current mode control scheme to provide excellent line and load regulation. Op- eration can be best understood by referring to the Block Diagram in Figure 1. The start of each oscillator cycle sets the SR latch (SR1) and turns on the external power MOSFET switch M1 through driver G2. The switch current flows through the external current sensing resistor R and generates a voltage SENSE proportional to the switch current. This current sense voltage V (amplified by A5) is added to a stabilizing ISENSE slope compensation ramp and the resulting sum (SLOPE) is fed into the positive terminal of the PWM comparator A7. When SLOPE exceeds the level at the negative input of A7 (VC pin), SR1 is reset, turning off the power switch. The level at the negative input set by the error amplifier A1 (or A2) and is an amplified version of the difference between the feedback voltage (FBX pin) and the reference voltage (1.6V or –0.8V, depending on the configuration). In this manner, the error amplifier sets the correct peak switch current level to keep the output in regulation. 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 ...

Page 10

LT3757 applicaTions inForMaTion For applications where the SHDN/UVLO pin is only used as a logic input, the SHDN/UVLO pin can be connected directly to the input voltage V for always-on operation. IN INTV Regulator Bypassing and Operation CC An internal, low dropout (LDO) voltage regulator produces the 7.2V INTV supply which powers the gate driver shown in Figure low input voltage operation is ex- pected (e.g., supplying power from a lithium-ion battery or a 3.3V logic supply), low threshold MOSFETs should be used. The LT3757 contains an undervoltage lockout comparator A8 and an overvoltage lockout comparator A9 for the INTV supply. The INTV CC threshold is 2.7V (typical), with 100mV hysteresis, to ensure that the MOSFETs have sufficient gate drive voltage before turning on. The logic circuitry within the LT3757 is also powered from the internal INTV The INTV overvoltage (OV) threshold is set to be 17.5V ...

Page 11

V (V) IN Figure 2. Recommended Maximum Q Frequencies to Ensure INTV Higher Than 4. effective approach to reduce the power consumption of the internal LDO for gate drive is to tie the INTV to an external voltage source high enough to turn off the internal LDO regulator. If the input ...

Page 12

LT3757 applicaTions inForMaTion The operating frequency of the LT3757 can be synchronized to an external clock source. By providing a digital clock signal into the SYNC pin, the LT3757 will operate at the SYNC clock frequency. If this feature is used should be chosen to program a switching frequency 20% slower than SYNC pulse frequency. The SYNC pulse should have a minimum pulse width of 200ns. Tie the SYNC pin to GND if this feature is not used. Duty Cycle Consideration Switching duty cycle is a key variable defining converter operation. As such, its limits must be considered. Minimum on-time is the smallest time duration that the LT3757 is capable of turning on the power MOSFET. This time is generally about 220ns (typical) (see Minimum On-Time in the Electrical Characteristics table). In each switching cycle, the LT3757 keeps the power switch off for at least 220ns (typical) (see Minimum Off-Time in the Electrical Characteristics table). The minimum on-time and minimum off-time and the ...

Page 13

FBX Frequency Foldback When V is very low during start- short-circuit OUT fault on the output, the switching regulator must operate at low duty cycles to maintain the power switch current within the current limit range, since the inductor current decay rate is very low during switch off time. The minimum on-time limitation may prevent the switcher from attaining a sufficiently low duty cycle at the programmed switch- ing frequency. So, the switch current will keep increasing through each switch cycle, exceeding the programmed current limit. To prevent the switch peak currents from exceeding the programmed value, the LT3757 contains a frequency foldback function to reduce the switching frequency when the FBX voltage is low (see the Normal- ized Switching Frequency vs FBX graph in the Typical Performance Characteristics section). The typical frequency foldback waveforms are shown in the Typical Performance Characteristics section. The fre- quency foldback function prevents I ...

Page 14

LT3757 applicaTions inForMaTion Due to the current limit function of the SENSE pin, R should be selected to guarantee that the peak current sense voltage V during steady state normal operation SENSE(PEAK) is lower than the SENSE current limit threshold (see the Electrical Characteristics table). Given a 20% margin set to be 80mV. Then, the maximum SENSE(PEAK) switch ripple current percentage can be calculated using the following equation: ∆ V SENSE − ...

Page 15

Boost Converter: Inductor and Sense Resistor Selection For the boost topology, the maximum average inductor current is • L MAX ( ) O MAX ( ) − MAX Then, the ripple current can be calculated by: ∆ • I • I • ...

Page 16

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. ...

Page 17

For the bulk C component, which also contributes 1% to the total ripple MAX ( ) C ≥ OUT • V • f OUT The output capacitor in a boost regulator experiences high RMS ripple currents, as shown in Figure 6. The RMS ripple current rating of the output capacitor can be determined using the following equation: D MAX ≥ • RMS COUT ( ) O MAX ( ) − ...

Page 18

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 ...

Page 19

Flyback Converter: Transformer Design for Discontinuous Mode Operation The transformer design for discontinuous mode of opera- tion is chosen as presented here. According to Figure 8, the minimum D3 (D3 ) occurs when the converter MIN has the minimum V and the maximum output power Choose equal to or higher than 10% OUT MIN to guarantee the converter is always in discontinuous mode operation (choosing higher D3 allows the use of low inductances, but results in a higher switch peak ...

Page 20

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 ...

Page 21

Flyback Converter: Output Diode Selection The output diode in a flyback converter is subject to large RMS current and peak reverse voltage stresses. A fast switching diode with a low forward drop and a low reverse leakage is desired. Schottky diodes are recommended if the output voltage is below 100V. Approximate the required peak repetitive reverse voltage rating V using: RRM > • RRM IN MAX ( ) OUT N P The power dissipated by the diode is • O(MAX) D ...

Page 22

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 V + ...

Page 23

Given an operating input voltage range, and having chosen the operating frequency and ripple current in the induc- tor, the inductor value (L1 and L2 are independent) of the SEPIC converter can be determined using the following equation MIN ( ) = = • D MAX • ∆ I • For most SEPIC applications, the equal inductor values will fall in the range of 1µH to 100µH. By making L1 = L2, and winding them on the same core, the value of inductance in the preceding equation is replaced by 2L, due to mutual inductance MIN ( ...

Page 24

LT3757 applicaTions inForMaTion SEPIC Converter: Output Diode Selection To maximize efficiency, a fast switching diode with a low forward drop and low reverse leakage is desirable. The average forward current in normal operation is equal to the output current, and the peak current is equal to:   • I •     D PEAK ( ) O MAX ( ) 2 1 − recommended that the peak repetitive reverse voltage rating V ...

Page 25

Inverting Converter: Switch Duty Cycle and Frequency For an inverting converter operating in CCM, the duty cycle of the main switch can be calculated based on the negative output voltage (V ) and the input voltage (V OUT The maximum duty cycle (D ) occurs when the converter MAX has the minimum input voltage: V − V OUT MAX V − V − V OUT D IN MIN ( ) Inverting Converter: ...

Page 26

LT3757 applicaTions inForMaTion Board Layout The high speed operation of the LT3757 demands careful attention to board layout and component placement. The Exposed Pad of the package is the only GND terminal of the IC, and is important for thermal management of the IC. Therefore crucial to achieve a good electrical and thermal contact between the Exposed Pad and the ground plane of the board. For the LT3757 to deliver its full output power imperative that a good thermal path be pro- vided to dissipate the heat generated within the package recommended that multiple vias in the printed circuit board be used to conduct heat away from the IC and into a copper plane with as much area as possible. To prevent radiation and high frequency resonance problems, proper layout of the components connected to the IC is essential, especially the power paths ...

Page 27

Check the stress on the power MOSFET by measuring its drain-to-source voltage directly across the device terminals (reference the ground of a single scope probe directly to the source pad on the PC board). Beware of inductive ringing, which can exceed the maximum specified voltage rating of the MOSFET. If this ringing cannot be avoided, and exceeds the maximum rating of the device, either choose a higher voltage device or specify an avalanche- rated power MOSFET. The small-signal components should be placed away from high frequency switching nodes. For optimum load regula- tion and true remote sensing, the top of the output voltage sensing resistor divider should connect independently to the top of the output capacitor (Kelvin connection), staying away from any high dV/dt traces. Place the divider resis- tors near the LT3757 in order to keep the high impedance FBX node short. Figure 11 shows the suggested layout of the 8V to 16V Input, 24V/2A Output Boost Converter. Recommended Component ...

Page 28

LT3757 Typical applicaTions 22µF 6.3V 2 41.2k 300kHz 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 ...

Page 29

Typical applicaTions 16V R T 41.2k 300kHz OUT2 C : KEMET T495X476K035AS OUT1 D1: ON SEMI MBRS340T3G L1: VISHAY SILICONIX IHLP-5050FD-01 10µH M1: VISHAY SILICONIX Si4840BDP Efficiency vs Output Current 100 90 ...

Page 30

LT3757 Typical applicaTions DANGER! HIGH VOLTAGE OPERATION BY HIGH VOLTAGE TRAINED PERSONNEL ONLY 12V C IN 150µF 105k 6.3V 2 46.4k 140k 100kHz 0.1µ MURATA GRM32DR61C106K TDK C3225X7R2J683K OUT D1: VISHAY ...

Page 31

Typical applicaTions V IN 5.5V TO 36V C IN 4.7µF 50V 2 41.2k 300kHz 0.1µ TAIYO YUDEN UMK316BJ475KL KEMET T495X476K020AS OUT1 C : TAIYO YUDEN TMK432BJ106MM OUT2 D1: ON SEMI MBRS360T3G L1A, ...

Page 32

LT3757 Typical applicaTions 12V IN2 IN1 105k 47µF 1µF 16V 16V, X5R SHDN/UVLO 46.4k SYNC 30.9k 400kHz 0.1µF 100pF D1, D2: MBRS140T3 T1: COILTRONICS VP1-0076 (*PRIMARY = 4 WINDINGS IN ...

Page 33

DescripTion 3.55 0.05 1.65 0.05 2.15 0.05 (2 SIDES) 0.25 0.05 RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS PIN 1 TOP MARK (SEE NOTE 6) 0.200 REF DD Package 10-Lead Plastic DFN (3mm × 3mm) (Reference LTC DWG # 05-08-1699 Rev B) 0.70 0.05 PACKAGE OUTLINE ...

Page 34

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 ...

Page 35

... 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  ...

Page 36

... Limited Only by External Components, 6-Lead ThinSot Package IN OUT V and V Limited Only by External Components, 3mm × 3mm 10-Lead IN OUT DFN, 10-Lead MSOP-E Packages www.linear.com ● Efficiency vs Output Current 100 16V 0.001 0 0.01 OUTPUT CURRENT (A) 3757 TA08b ≤ 36V, Burst Mode Operation at ® IN 3757fb LT 0310 REV B • PRINTED IN USA  LINEAR TECHNOLOGY CORPORATION 2008 ...

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