Datasheet

ManualsBrandsLINEAR TECHNOLOGY ManualsPMICsPMIC - voltage regulators - DC DC switch controllers TSSOP 20 EP

LT3741/LT3741-1

37411fe

For more information www.linear.com/LT3741

Typical applicaTion

DescripTion

High Power, Constant

Current, Constant Voltage,

Step-Down Controller

The LT

3741 and LT3741-1 are ﬁxed frequency synchro-

nous step-down DC/DC controllers designed to accurately

regulate the output current at up to 20A. The average current-

mode controller will maintain inductor current regulation

over a wide output voltage range of 0V to (V

– 2V). The

regulated current is set by an analog voltage on the CTRL

pins and an external sense resistor. Due to its unique

topology, the LT3741 is capable of sourcing and sinking

current. If sinking current is not required, or for parallel

applications, use the LT3741-1. The regulated voltage and

overvoltage protection are set with a voltage divider from

the output to the FB pin. Soft-Start is provided to allow a

gradual increase in the regulated current during startup.

The switching frequency is programmable from 200kHz to

1MHz through an external resistor on the RT pin or through

the use of the SYNC pin and an external clock signal.

Additional Features include an accurate external reference

voltage for use with the CTRL pins, an accurate UVLO/EN

pin that allows for programmable UVLO hysteresis, and

thermal shutdown.

10V/20A Constant Current, Constant Voltage Step-Down Converter

FeaTures

applicaTions

Control Pin Provides Accurate Control of Regulated

Output Current

±1.5% Voltage Regulation Accuracy

±6% Current Regulation Accuracy

6V to 36V Input Voltage Range

Wide Output Voltage Range Up to (V

– 2V)

Average Current Mode Control

<1µA Shutdown Current

Up to 94% Efﬁciency

Additional Pin for Thermal Control of Load Current

Thermally Enhanced 4mm × 4mm QFN and 20-Pin

FE Package

General Purpose Industrial

Super-Cap Charging

Applications Needing Extreme Short-Circuit

Protection and/or Accurate Output Current Limit

Constant Current or Constant Voltage Source

EN/UVLOEN/UVLO

CBOOT

REF

CTRL1

CTRL2

LT3741

SYNC

GND

SENSE

–

CC_INT

220nF

2.2µH

22µF

2.5mΩ

10nF

39.2k

5.6nF

82.5k

88.7k

3741 TA01a

12.1k

150µF

×2

10nF

NTC

100µF

14V TO 36V

OUT

10V

20A

1µF

HOT

45.3k

OUT

(A)

0 2 4 6 8 10 12 14 16 18

OUT

(V)

3741 TA01b

= 18V

OUT

= 10V

LIMIT

= 20A

OUT

vs I

OUT

L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of Linear

Technology Corporation. All other trademarks are the property of their respective owners.

Protected by U.S. Patents including 7199560, 7321203 and others pending.

Summary of content (24 pages)

PAGE 1
LT3741/LT3741-1 High Power, Constant Current, Constant Voltage, Step-Down Controller Features n n n n n n n n n n Description Control Pin Provides Accurate Control of Regulated Output Current ±1.
PAGE 2
LT3741/LT3741-1 Absolute Maximum Ratings (Note 1) VIN Voltage.................................................................40V EN/UVLO Voltage.........................................................6V VREF Voltage.................................................................3V CTRL1 and CTRL2 Voltage...........................................3V SENSE+ Voltage.........................................................40V SENSE– Voltage.........................................................
PAGE 3
LT3741/LT3741-1 Electrical Characteristics The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VIN = 12V, VEN/UVLO = 5V, VSYNC = 0V unless otherwise noted. PARAMETER CONDITIONS Input Voltage Range VIN Pin Quiescent Current (Note 2) Non-Switching Operation Shutdown Mode MIN l Not Switching VEN/UVLO = 0V, RT = 40kΩ 6 l EN/UVLO Pin Falling Threshold 1.49 EN/UVLO Hysteresis EN/UVLO Pin Current VIN = 6V, EN/UVLO = 1.
PAGE 4
LT3741/LT3741-1 Electrical Characteristics The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VIN = 12V, VEN/UVLO = 5V, VSYNC = 0V unless otherwise noted. PARAMETER CONDITIONS MIN TYP MAX –3 0 3 UNITS Current Control Loop gm Amp Offset Voltage VCM =4V Input Common Mode Range VCM(LOW) VCM(HIGH) VCM(HIGH) Measured from VIN to VCM l 0 2 Output Impedance V V 3.5 375 gm Differential Gain MΩ 475 625 1.
PAGE 5
LT3741/LT3741-1 Typical Performance Characteristics VREF Pin Voltage VREF Current Limit 2.06 RT Pin Current Limit 90 1.6 2.05 VIN = 6V 2.02 2.01 2.00 TA = 25°C ILIMIT (µA) 2.03 80 1.4 VIN = 36V ILIMIT (mA) VREF VOLTAGE (V) 2.04 TA = 130°C 1.2 TA = –50°C 1.0 70 60 50 1.99 1.98 –50 –15 55 20 TEMPERATURE (°C) 90 0.8 125 18 3741 G05 24 VIN (V) 30 40 –50 36 90 125 Internal UVLO 5.0 5 4.5 VIN = 36V VCC_INT (V) 11 4 VIN = 6V 10 9 VIN (V) 12 3 4.0 2 8 3.
PAGE 6
LT3741/LT3741-1 Typical Performance Characteristics Overvoltage Threshold OVERVOLTAGE THRESHOLD (V) 50 0 LT3741-1 –50 –100 19 1.65 17 1.55 1.45 1.35 1.15 1.20 1.25 VFB (V) 1.30 1.25 –50 1.35 Regulated Sense Voltage 0 25 75 50 TEMPERATURE (°C) 100 9 –50 125 40 30 20 0 0.5 1.0 1.5 VCTRL (V) 4 1.
PAGE 7
LT3741/LT3741-1 Typical Performance Characteristics Minimum On-Time Oscillator Frequency 150 1.5 120 1.2 Overcurrent Threshold 120 90 HG 60 LG 900kHz 0.9 0.6 0.3 30 0 –50 –15 55 20 TEMPERATURE (°C) 90 60 40 –15 20 55 20 TEMPERATURE (°C) 90 3741 G24 0 125 2 4 5 1 2 4 –2 0 25°C –2 2.5 5.0 7.5 OUTPUT VOLTAGE (V) –6 10 2.5 5.0 7.5 OUTPUT VOLTAGE (V) 0 3741 G26 25 3.
PAGE 8
LT3741/LT3741-1 Typical Performance Characteristics Efficiency and Power Loss vs Load Current Efficiency and Power Loss vs Load Current LT3741 LT3741 95 60 90 85 VIN = 20V VOUT = 5V 10 1 LOAD CURRENT (A) 100 LT3741-1 LT3741 80 70 60 80 50 40 0.1 EFFICIENCY (%) 70 90 LT3741-1 LT3741-1 EFFICIENCY (%) EFFICIENCY (%) 80 100 100 100 90 Efficiency and Power Loss vs Load Current 75 0.1 VIN = 25V VOUT = 20V 1 LOAD CURRENT (A) 10 50 0.
PAGE 9
LT3741/LT3741-1 Pin Functions (QFN/TSSOP) EN/UVLO (Pin 1/Pin 4): Enable Pin. The EN/UVLO pin acts as an enable pin and turns on the internal current bias core and subregulators at 1.55V. The pin does not have any pull-up or pull-down, requiring a voltage bias for normal part operation. Full shutdown occurs at approximately 0.5V. VREF (Pin 2/Pin 5): Buffered 2V reference capable of 0.5mA drive. CTRL2 (Pin 3/Pin 6): Thermal control input used to reduce the regulated current level.
PAGE 10
LT3741/LT3741-1 Block Diagram (QFN Package) VIN VIN 402k 1 INTERNAL REGULATOR AND UVLO 133k 100nF SYNC 2 13 12 VREF 2V REFERENCE SYNC OSCILLATOR RT 82.5k – R + S Q PWM COMPARATOR LOW SIDE DRIVER 11µA gm AMP gm = 475µA/V RO = 3.5M IOUT = 40µA 3k + CTRL1 CURRENT MIRROR + + – 3 10 SENSE– CTRL2 VC 47µF 19 VIN 10µF 0.1µF 2.4µH 8 RS 5mΩ VOUT 150µF ×2 9 40.
PAGE 11
LT3741/LT3741-1 Block Diagram (QFN Package) VIN VIN 402k 1 INTERNAL REGULATOR AND UVLO 133k 100nF SYNC 2 13 12 20 EN/UVLO VREF 2V REFERENCE SYNC OSCILLATOR RT 82.5k + S Q PWM COMPARATOR 47µF VIN 19 10µF HIGH SIDE CBOOT DRIVER 17 HG 15 SW SYNCRONOUS 16 CONTROLLER LG 18 – R VCC_INT 1µF 0.1µF 2.4µH LOW SIDE DRIVER ZERO CROSS COMPARATOR + – SENSE+ – 5 CTRL1 CURRENT MIRROR + + 11µA gm AMP gm = 475µA/V RO = 3.5M IOUT = 40µA 3k + 1.
PAGE 12
LT3741/LT3741-1 Operation The LT3741 utilizes fixed-frequency, average current mode control to accurately regulate the inductor current, independently from the output voltage. This is an ideal solution for applications requiring a regulated current source. The control loop will regulate the current in the inductor at an accuracy of ±6%.
PAGE 13
LT3741/LT3741-1 Applications Information Programming Inductor Current Inductor Selection The analog voltage at the CTRL1 pin is buffered and produces a reference voltage, VCTRL, across an internal resistor. The regulated average inductor current is determined by: Size the inductor to have approximately 30% peak-topeak ripple. The overcurrent set point is equal to the high level regulated current level set by the CTRL1 pin with an additional 23mV offset between the SENSE+ and SENSE– pins.
PAGE 14
LT3741/LT3741-1 Applications Information (RDS(ON)), gate to drain charge (QGD), gate-to-source charge (QGS), gate resistance (RG), breakdown voltages (maximum VGS and VDS) and drain current (maximum ID). The following guidelines provide information to make the selection process easier. where rT is a temperature-dependant term of the MOSFET’s on-resistance. Using 70°C as the maximum ambient operating temperature, rT is roughly equal to 1.3.
PAGE 15
LT3741/LT3741-1 Applications Information 2.5 7 MOSFET POWER LOSS (W) MOSFET POWER LOSS (W) 6 5 TOTAL 4 TRANSITIONAL 3 2 1 0 2.0 1.5 TOTAL 1.0 TRANSITIONAL 0.5 OHMIC OHMIC 0 10 20 30 0 40 0 20 10 30 40 INPUT VOLTAGE (V) INPUT VOLTAGE (V) 3741 F04a 3741 F04b Figure 4a. Power Loss Example for M1 Figure 4b. Power Loss Example for M2 Figure 4 Table 3.
PAGE 16
LT3741/LT3741-1 Applications Information Output Current Regulation To adjust the regulated load current, an analog voltage is applied to the CTRL1 pin. Figure 5 shows the regulated voltage across the sense resistor for control voltages up to 2V. Figure 6 shows the CTRL1 voltage created by a voltage divider from VREF to ground. When sizing the resistor divider, please be aware that the VREF pin is current limited to 500µA. Above 1.5V, the control voltage has no effect on the regulated inductor current.
PAGE 17
LT3741/LT3741-1 Applications Information Thermal Shutdown VIN The internal thermal shutdown within the LT3741 engages at 163°C and terminates switching and resets soft-start. When the part has cooled to 155°C, the internal reset is cleared and soft-start is allowed to charge. VIN LT3741 R2 EN/UVLO R1 3741 F09 Switching Frequency Synchronization Figure 9.
PAGE 18
LT3741/LT3741-1 Applications Information Average Current Mode Control Compensation The use of average current mode control allows for precise regulation of the inductor and load currents. Figure 11 shows the average current mode control loop used in the LT3741, where the regulation current is programmed by a current source and a 3k resistor. MODULATOR VCTRL • 11µA/V 3k L RS gm ERROR AMP fS •L •1000V 0.
PAGE 19
LT3741/LT3741-1 Typical Applications 20A Super Capacitor Charger with 5V Regulated Output EN/UVLO EN/UVLO VIN 1µF RT SYNC 82.5k HG 100nF CBOOT VREF 2.2µF RHOT 45.3k 50k 100µF M1 L1 1.0µH SW LT3741 VCC_INT CTRL1 LG CTRL2 SENSE+ SS SENSE– FB 22µF 10nF VC 10Ω 4.7nF 10Ω 33nF 38.
PAGE 20
LT3741/LT3741-1 Typical Applications 20A LED Driver EN/UVLO VIN EN/UVLO 1µF 82.5k RT SYNC HG 100µF 2.2µF RHOT 45.3k CONTROL INPUT L1 1.1µH CTRL2 10nF 22µF LG SENSE VOUT 6V, 20A MAXIMUM 0.75V 20A ILED 5A/DIV 680µF 10A M2 10Ω 10Ω 1ms/DIV + 3741 TA03b 33nF SENSE– SS 1.5V CTRL1 1V/DIV D1 GND RNTC 470k R1 2.5mΩ SW LT3741 VCC_INT CTRL1 VIN 12V TO 36V M1 150nF CBOOT VREF LED Current Waveforms 10A to 20A Current Step 47.
PAGE 21
LT3741/LT3741-1 Package Description Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings. UF Package 20-Lead Plastic QFN (4mm × 4mm) (Reference LTC DWG # 05-08-1710 Rev A) 0.70 ±0.05 4.50 ±0.05 3.10 ±0.05 2.00 REF 2.45 ±0.05 2.45 ±0.05 PACKAGE OUTLINE 0.25 ±0.05 0.50 BSC RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED 4.00 ±0.10 0.75 ±0.05 R = 0.05 TYP R = 0.115 TYP 19 20 0.40 ±0.
PAGE 22
LT3741/LT3741-1 Package Description Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings. FE Package 20-Lead Plastic TSSOP (4.4mm) (Reference LTC DWG # 05-08-1663 Rev J) Exposed Pad Variation CB 6.40 – 6.60* (.252 – .260) 3.86 (.152) 3.86 (.152) 20 1918 17 16 15 14 13 12 11 6.60 ±0.10 2.74 (.108) 4.50 ±0.10 6.40 2.74 (.252) (.108) BSC SEE NOTE 4 0.45 ±0.05 1.05 ±0.10 0.65 BSC 1 2 3 4 5 6 7 8 9 10 RECOMMENDED SOLDER PAD LAYOUT 4.30 – 4.50* (.169 – .
PAGE 23
LT3741/LT3741-1 Revision History REV DATE DESCRIPTION PAGE NUMBER A 8/10 Revised to ±1.
PAGE 24
LT3741/LT3741-1 Typical Application 20V Regulated Output with 5A Current Limit EN/UVLO EN/UVLO VIN 1µF 82.5k RT SYNC HG 100nF CBOOT VREF 2.2µF RHOT 45.3k RNTC 470k 10nF CTRL1 GND CTRL2 SENSE+ SS SENSE– FB VC 30.1k 3.9nF EN/UVLO M1 L1 8.2µH SW LT3741-1 VCC_INT LG CONTROL INPUT 22µF EN/UVLO RT SYNC 22µF 10Ω 10nF 187k 2.2µF RHOT 45.3k 100nF CONTROL INPUT RNTC 470k 10nF 22µF L1 8.2µH LT3741-1 VCC_INT CTRL1 GND CTRL2 SENSE+ SS SENSE– FB VC 30.1k 3.