Datasheet

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LTC3723-1/LTC3723-2

372312f

, LTC and LT are registered trademarks of Linear Technology Corporation.

All other trademarks are the property of their respective owners.

APPLICATIO S

FEATURES

TYPICAL APPLICATIO

DESCRIPTIO

The LTC

3723-1/LTC3723-2 synchronous push-pull PWM

controllers provide all of the control and protection func-

tions necessary for compact and highly efficient, isolated

power converters. High integration minimizes external

component count, while preserving design flexibility.

The robust push-pull output stages switch at half the

oscillator frequency. Dead-time is independently pro-

grammed with an external resistor. Synchronous rectifier

timing is adjustable to optimize efficiency. A UVLO pro-

gram input provides precise system turn-on and turn off

voltages. The LTC3723-1 features peak current mode

control with programmable slope compensation and lead-

ing edge blanking, while the LTC3723-2 employs voltage

mode control with voltage feedforward capability.

The LTC3723-1/LTC3723-2 feature extremely low operat-

ing and start-up currents. Both devices provide reliable

short-circuit and overtemperature protection. The

LTC3723-1/LTC3723-2 are offered in a 16-pin SSOP

package.

■

Telecommunications, Infrastructure Power Systems

■

Distributed Power Architectures

■

High Efficiency Synchronous Push-Pull PWM

■

1.5A Sink, 1A Source Output Drivers

■

Supports Push-Pull, Full-Bridge, Half-Bridge, and

Forward Topologies

■

Adjustable Push-Pull Dead-Time and Synchronous

Timing

■

Adjustable System Undervoltage Lockout and

Hysteresis

■

Adjustable Leading Edge Blanking

■

Low Start-Up and Quiescent Currents

■

Current Mode (LTC3723-1) or Voltage Mode

(LTC3723-2) Operation

■

Single Resistor Slope Compensation

■

UVLO and 25mA Shunt Regulator

■

Programmable Fixed Frequency Operation to 1MHz

■

50mA Synchronous Output Drivers

■

Soft-Start, Cycle-by-Cycle Current Limiting and

Hiccup Mode Short-Circuit Protection

■

5V, 15mA Low Dropout Regulator

■

Available in 16-Pin SSOP Package

Synchronous Push-Pull

PWM Controllers

•

OUT

GND-F

LT1431

GND-S

COLL R

REF

372312 TA01

REF

FROM

AUXILIARY

WINDING

REF

DRVA

DRVB

CSV

DPRG

LTC3723-1

SDRA

SDRB

REF

COMP

UVLO

SPRG

LEB

FB GND

LTC3901

SYNC

Isolated Push-Pull Converter

Summary of content (20 pages)

PAGE 1
LTC3723-1/LTC3723-2 Synchronous Push-Pull PWM Controllers DESCRIPTIO U FEATURES ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ High Efficiency Synchronous Push-Pull PWM 1.
PAGE 2
LTC3723-1/LTC3723-2 W W U W ABSOLUTE AXI U RATI GS (Note 1) VCC to GND (Low Impedance Source) .......– 0.3V to 10V (Chip Self-Regulates at 10.3V) UVLO to GND ............................................. – 0.3V to VCC All Other Pins to GND (Low Impedance Source) .........................– 0.3V to 5.5V VCC (Current Fed) ................................................. 40mA VREF Output Current ............................... Self-Regulated Operating Temperature (Notes 5,6) LTC3723E ..................
PAGE 3
LTC3723-1/LTC3723-2 ELECTRICAL CHARACTERISTICS The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VCC = 9.5V unless otherwise noted. SYMBOL PARAMETER CONDITIONS ISLP Slope Compensation Current Measured on CS, CT = 1V, 3723-1 Only CT = 2.25V MIN DCMAX Maximum Duty Cycle COMP = 4.5V ● DCMIN Minimum Duty Cycle COMP = 0V ● DTADJ Dead-Time TYP MAX 47 48.
PAGE 4
LTC3723-1/LTC3723-2 ELECTRICAL CHARACTERISTICS The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VCC = 9.5V unless otherwise noted. SYMBOL PARAMETER CONDITIONS SSI Soft-Start Current SS = 2.5V SSR Soft-Start Reset Threshold Measured on SS 0.7 0.4 0.1 V FLT Fault Reset Threshold Measured on SS 4.5 4.2 3.5 V U W TYPICAL PERFOR A CE CHARACTERISTICS 150 10.
PAGE 5
LTC3723-1/LTC3723-2 U W TYPICAL PERFOR A CE CHARACTERISTICS PHASE (DEG) 100 80 60 40 20 0 190 275 180 250 170 225 160 200 DELAY (ns) 200k PREBIAS 150 140 –180 175 150 130 125 –270 120 100 –360 110 75 10 100 1k 10k 100k FREQUENCY (Hz) 1M 100 –55 10M 50 –25 5 35 65 TEMPERATURE (°C) 95 372312 G07 125 900 ICC = 10mA 80 800 10.4 CT = 2.25V 50 40 CT = 1V 10.3 600 DELAY (ns) SHUNT VOLTAGE (V) 700 60 10.2 10.1 500 400 300 10.0 200 20 9.
PAGE 6
LTC3723-1/LTC3723-2 U U PI DESCRIPTIO S (LTC3723-1/LTC3723-2) VREF (Pin 1/Pin 1): Output of the 5.0V Reference. VREF is capable of supplying up to 18mA to external circuitry. VREF should be decoupled to GND with a 0.47µF ceramic capacitor. SDRB (Pin 2/Pin 2): 50mA Driver for Synchronous Rectifier associated with DRVB. SDRA (Pin 3/Pin 3): 50mA Driver for Synchronous Rectifier associated with DRVA. DRVB (Pin 4/Pin 4): High Speed 1.5A Sink, 1A Source Totem Pole MOSFET Driver.
PAGE 7
LTC3723-1/LTC3723-2 U U PI DESCRIPTIO S (LTC3723-1/LTC3723-2) SS (Pin 14/Pin 14): Soft-Start/Restart Delay Circuitry Timing Capacitor. A capacitor from SS to GND provides a controlled ramp of the current command (LTC3723-1) or duty cycle (LTC3723-2). During overload conditions, SS is discharged to ground initiating a soft-start cycle. SS charging current is approximately 13µA. SS will charge up to approximately 5V in normal operation.
PAGE 8
LTC3723-1/LTC3723-2 W BLOCK DIAGRA S LTC3723-1 Block Diagram VCC UVLO VREF CT DPRG SPRG 5 15 1 8 9 16 VCC UVLO REF, LDO 1.2V 10µA 10.25V “ON” 6V “OFF” – FB 13 1.2V 5V VCC REF GOOD ERROR AMPLIFIER + + 5V SYSTEM UVLO VCC GOOD 3 SDRA – 50k PULSE WIDTH MODULATOR – COMP 11 SYNC RECTIFIER DRIVE LOGIC 2 SDRB 14.9k + + OSCILLATOR 650mV – 1A SOURCE Q R 6 DRVA Q + S – R Q 1.5A SINK T Q S VREF 1A SOURCE 13µA SS 14 4 DRVB + 600mV SHUTDOWN CURRENT LIMIT 1.
PAGE 9
LTC3723-1/LTC3723-2 W BLOCK DIAGRA S LTC3723-2 Block Diagram VCC UVLO VREF CT SPRG 5 15 1 8 16 VCC UVLO – FB 13 1.2V REF, LDO 1.2V 10µA 10.25V “ON” 6V “OFF” 5V VCC REF GOOD ERROR AMPLIFIER SYSTEM UVLO + + 5V 50k 3 SDRA – + + SYNC RECTIFIER DRIVE LOGIC PULSE WIDTH MODULATOR – COMP 11 VCC GOOD 2 SDRB OSCILLATOR 650mV – RAMP 9 1A SOURCE Q R 6 DRVA Q S + – R Q Q S VREF 1.5A SINK T OUTPUT DRIVE LOGIC 1A SOURCE 4 DRVB 13µA SS 14 1.
PAGE 10
LTC3723-1/LTC3723-2 U OPERATIO Please refer to the detailed Block Diagrams for this discussion. The LTC3723-1 and LTC3723-2 are synchronous PWM push-pull controllers. The LTC3723-1 operates with peak pulse-by-pulse current mode control while the LTC3723-2 offers voltage mode control operation. They are best suited for moderate to high power isolated power systems where small size and high efficiency are required.
PAGE 11
LTC3723-1/LTC3723-2 U OPERATIO very low (145µA typ) start-up current that allows the use of 1/8W to 1/4W trickle charge start-up resistors. The trickle charge resistor should be selected as follows: RSTART(MAX) = VIN(MIN) – 10.7V/250µA Adding a small safety margin and choosing standard values yields: APPLICATION VIN RANGE RSTART DC/DC 36V to 72V 100k Off-Line 85V to 270VRMS 430k 390VDC 1.4M PFC Preregulator VCC should be bypassed with a 0.
PAGE 12
LTC3723-1/LTC3723-2 U OPERATIO VIN VOUT LOUT RSTART ISO BARRIER 1µF + CHOLD VCC 372312 F04b Figure 4b. Output Inductor Bias Supply Programming the LTC3723-1/LTC3723-2 Oscillator The high accuracy LTC3723-1/LTC3723-2 oscillator circuit provides flexibility to program the switching frequency and slope compensation required for current mode control (LTC3723-1). The oscillator circuit produces a 2.35V peak-to-peak amplitude ramp waveform on CT. Typical maximum duty cycles of 49% are possible.
PAGE 13
LTC3723-1/LTC3723-2 U OPERATIO The 50% duty-cycle limit is overcome with the circuit shown in Figure 7. Operation is similar to external synchronization, except DRVA output is used to terminate its own clock cycle early. Switching period is now equal to the oscillator period plus programmable driver dead time. Maximum on time is equal to oscillator period minus driver dead time.
PAGE 14
LTC3723-1/LTC3723-2 U OPERATIO The LTC3723-1 derives a compensating slope current from the oscillator ramp waveform and sources this current out of CS. This function is disabled in the LTC3723-2. The desired level of slope compensation is selected with an external resistor connected between CS and the external current sense resistor, (Figure 11). Current Sensing and Overcurrent Protection Current sensing provides feedback for the current mode control loop and protection from overload conditions.
PAGE 15
LTC3723-1/LTC3723-2 U OPERATIO High Current Drivers The LTC3723-1/LTC3723-2 high current, high speed drivers provide direct drive of external power N-channel MOSFET switches. The drivers swing from rail to rail. Due to the high pulsed current nature of these drivers (1.5A sink, 1A source), care must be taken with the board layout to obtain advertised performance. Bypass VCC with a 1µF minimum, low ESR, ESL ceramic capacitor. Connect this capacitor with minimal length PCB leads to both VCC and GND.
PAGE 16
1µF 15 5 220pF 100Ω 1/4W 10 8 10k 16 33k 12 7 13 4 DRVB 14 2 11 0.47µF 5V 1 820Ω COMP VREF SDRB 3 SDRA 150k 68nF 9 SS DPRG LTC3723EGN-1 CS UVLO CT SPRG RLEB GND FB VCC 6 DRVA 330pF 470Ω 6 5 C6 2.2nF 250V D5 D4 6 5 8 • 47nF • 5 T2 1(1.5mH):0.5 1 4 100k 2 1 1k 0.1µF C5 68µF 20V L4 1mH MOC207 22Ω + 10V 4 1 • 66.5k 383k 30k 5V 75k R2 0.06Ω 1.5W Si7450DP 80Ω 1W 3 2 • R1 0.06Ω 1.5W Si7450DP 80Ω 1W 100pF 200V 9 10 7 8 11 12 3 8.
PAGE 17
–VIN 66.5k A 50k 5 CT 8.66k 10nF 14 CT MMBT2369 7 UVLO GND SS VCC 1µF VREF 6 DRVA A 8 CT DRVB 4 120pF 220pF 10k 33k 16 12 13 0.47µF 1 22nF VREF VREF COMP SDRB 158K VREF 10 CS 9 174k SPRG RLEB FB DPRG LTC3723EGN-1 80 11 2 + 10V 6 4 1 5 24Ω 1/4W 6 1 T2 4 220pF 24Ω 1/4W 8 7 220pF MOC207 220pF 2.2nF 250V BAS21 BAS21 750Ω VREF L4 1mH 1.5nF 200V 3 5 2 1 8 1k 4.7nF 5 • 15 10V 50 60 70 OUTPUT POWER (W) 68µF 20V 0.03Ω 1W 1.
PAGE 18
VIN 93 94 95 96 97 –VIN 6 8 66.5k 1.5nF 1µF 15 5 13 7 8 UVLO FB GND CT 10k 270pF 33k 16 12 14 68nF 0.47µF 1 VREF 9 150k SPRG RLEB SS DPRG SDRB VCC DRVB ISNS DRVA LTC3723EGN-1 R2 0.03Ω 1.5W 1.5k 2 B R1 0.03Ω 1.5W Si7852DP 4 4 A 2 B 243k 330pF 11 22nF 6 6 1 T2 1(1.5mH):0.5 1 4 D6 D5 Si7852DP 5 3 4 2 8 5 C4 2.2nF 250V MOC207 665Ω 5 9 CSF+ 22nF D8 10V 11 1k 6.19k 1/4W SYNC 220pF 100Ω 100k 2 1 866Ω 1k 1/4W 12 1 0.1µF 14 15 6 CSE+ L6 1.
PAGE 19
LTC3723-1/LTC3723-2 U TYPICAL APPLICATIO S LTC3723-1 300W 42VIN to 56VIN to 12V/25A Isolated Bus Converter VIN BAS21 T1 29.46mm × 25.4mm × 10.2mm PLANAR 1 VCC 6 INP BOOST LTC4440ES6 5 4.7Ω TG GND TS 2 4 3 A VCC 6 INP BOOST LTC4440ES6 5 4.7Ω TG GND TS 2 4 Si7370DP 0.1µF Si7370DP A 4 Si7370DP 0.1µF 3 11 9 7 VE VF HAT2169 ×2 –VOUT 68µF 20V –VOUT VE +VOUT L3 1mH 4.53k BAS21 1 + 4.53k • 12V ISNS 2.67k 2.67k 1.27k 1.
PAGE 20
LTC3723-1/LTC3723-2 U TYPICAL APPLICATIO LTC3723-1 100W, 36VIN to 72VIN to 3.3V/30A Isolated Forward Converter VIN –VIN 2 4 • • 1µF 100V ×2 1µF 100V 3 5 48VIN VOUT 2.2nF 8 VX 100µF 6.3V ×2 10 Si7336ADP ×2 5.1Ω 1/2W 11 2.2nF 2.2nF 630V 93 VOUT 7 Si7450DP 94 L2 0.85µH T1 23.4mm × 20.1mm × 9.4mm PLANAR • • L1 0.33µH VIN Si7336ADP ×2 + 470µF 6.3V 5.1Ω 1/2W –VOUT 0.03Ω 1W 10V 91 90 89 88 68µF 20V 820Ω –VOUT L3 1mH BAS21 845Ω 1 + BAS21 • EFFICIENCY (%) 92 VX 1.