Datasheet LT1681 (Analog Devices)
| Manufacturer | Analog Devices |
| Description | Dual Transistor Synchronous Forward Controller |
| Pages / Page | 20 / 1 — FEATURES. DESCRIPTIO. High Voltage: Operation Up to 72V. Synchronizable … |
| File Format / Size | PDF / 281 Kb |
| Document Language | English |
FEATURES. DESCRIPTIO. High Voltage: Operation Up to 72V. Synchronizable Operating Frequency and Output
Model Line for this Datasheet
Text Version of Document
LT1681 Dual Transistor Synchronous Forward Controller
U FEATURES DESCRIPTIO
■
High Voltage: Operation Up to 72V
The LT®1681 controller simplifies the design of high power ■
Synchronizable Operating Frequency and Output
synchronous dual transistor forward DC/DC converters. The
Switch Phase for Multiple Controller Systems
part employs fixed frequency current mode control and ■
Fixed Frequency Operation to 350kHz
supports both isolated and nonisolated topologies. The IC ■
Adaptive and Adjustable Blanking
drives external N-channel power MOSFETs and operates with ■ Synchronous Rectifier Driver input voltages up to 72V. ■ Local 1% Voltage Reference The LT1681’s operating frequency is programmable and can ■ Undervoltage Lockout Protection with Hysteresis be synchronized up to 350kHz. Switch phase is also con- ■ Input Overvoltage Protection trolled during synchronized operation to accommodate mul- ■ Programmable Start Inhibit tiple converter systems. Internal logic guarantees 50% maxi- ■ Transformer Primary Saturation Protection mum duty cycle operation to prevent transformer saturation. ■ Optocoupler Feedback Support ■ The LT1681 incorporates a soft-start feature that provides a Soft-Start Control
U
controlled increase in supplied current during start-up and
APPLICATIO S
after an undervoltage lockout or overvoltage/overcurrent event. ■ Isolated Telecommunication Systems ■ The part is available in a 20-lead wide SO package to support Personal Computers and Peripherals ■ high voltage pin-to-pin clearance. Lead Acid Battery Backup Systems ■ Automotive and Heavy Equipment , LTC and LT are registered trademarks of Linear Technology Corporation.
U TYPICAL APPLICATIO 36V-72V DC to 5V/7A Synchronous Forward Converter (Half-Brick Footprint)
L1 L2 VOUT = 5V 4.7µH 4.1µH IOUT = 7A • V + + 6 IN VOUT Q1 1 7 2 10Ω MURS120T3 3 0.25W + C5 + C2 C4 • • MBR- 5 330µF 22µF 1.5µF 1nF 0540T1 MURS120T3 10V 100V 100V 8 100V 10 1nF Q6 • 11 100V 10Ω 4 C3 Q3 0.25W 12 0.025Ω 1.5µF 1/2W 9 100V Q5 4.7Ω T1 V – IN V – OUT C2:SANYO 100MV22AX ZVN3310F C3, C4: VITRAMON VJ1825Y155MXB BAT54 C5: 4X KEMET T510X337KO10AS L1: COILCRAFT DO1608C-472 L2: PANASONIC ETQP6F4R1LF4 1OV 10k Q1,Q3:100V SILICONIX SUD40N10-25 BIAS 1OV 100Ω 2k Q5,Q6: SILICONIX Si4450 0.1µF BIAS FZT690 0.22µF T1:COILTRONICS VP5-1200 MMBD914LT1 330pF 50V 100V Q10: ON SEMI MMBT3906LTI 73.2k CMPZ5242B 4.7µF 1% 12V 270k 5V 16V 0.25W BAS21 20k OUT 20 17 19 18 16 11 12 15 14 V LTC1693-2 CC V BLKSENS TG BSTREF BG SENSE T PGND 3.3Ω BST MAX 13 8 6 CMPZ- 2 SG VCC1 VCC2 CMPZ5248B 5248B OVLO LT1681 0.047µF 3 5 18V 15V 1 9 IN2 OUT2 SHDN 5VREF FSET THERM SYNC SGND SS VC VFB 1 7 IN1 OUT1 1681 TA01 5 6 3 7 4 8 10 3.01k 51Ω 0.1µF 4 2 10k 56k 52.3k 1% 100 Q10 Ω GND2 GND1 + 68µF 1.24k 1nF 24k 1 1% µF 150pF 20V 4.7nF 1k 0.01µF 1% 1681f 1
U FEATURES DESCRIPTIO
■
High Voltage: Operation Up to 72V
The LT®1681 controller simplifies the design of high power ■
Synchronizable Operating Frequency and Output
synchronous dual transistor forward DC/DC converters. The
Switch Phase for Multiple Controller Systems
part employs fixed frequency current mode control and ■
Fixed Frequency Operation to 350kHz
supports both isolated and nonisolated topologies. The IC ■
Adaptive and Adjustable Blanking
drives external N-channel power MOSFETs and operates with ■ Synchronous Rectifier Driver input voltages up to 72V. ■ Local 1% Voltage Reference The LT1681’s operating frequency is programmable and can ■ Undervoltage Lockout Protection with Hysteresis be synchronized up to 350kHz. Switch phase is also con- ■ Input Overvoltage Protection trolled during synchronized operation to accommodate mul- ■ Programmable Start Inhibit tiple converter systems. Internal logic guarantees 50% maxi- ■ Transformer Primary Saturation Protection mum duty cycle operation to prevent transformer saturation. ■ Optocoupler Feedback Support ■ The LT1681 incorporates a soft-start feature that provides a Soft-Start Control
U
controlled increase in supplied current during start-up and
APPLICATIO S
after an undervoltage lockout or overvoltage/overcurrent event. ■ Isolated Telecommunication Systems ■ The part is available in a 20-lead wide SO package to support Personal Computers and Peripherals ■ high voltage pin-to-pin clearance. Lead Acid Battery Backup Systems ■ Automotive and Heavy Equipment , LTC and LT are registered trademarks of Linear Technology Corporation.
U TYPICAL APPLICATIO 36V-72V DC to 5V/7A Synchronous Forward Converter (Half-Brick Footprint)
L1 L2 VOUT = 5V 4.7µH 4.1µH IOUT = 7A • V + + 6 IN VOUT Q1 1 7 2 10Ω MURS120T3 3 0.25W + C5 + C2 C4 • • MBR- 5 330µF 22µF 1.5µF 1nF 0540T1 MURS120T3 10V 100V 100V 8 100V 10 1nF Q6 • 11 100V 10Ω 4 C3 Q3 0.25W 12 0.025Ω 1.5µF 1/2W 9 100V Q5 4.7Ω T1 V – IN V – OUT C2:SANYO 100MV22AX ZVN3310F C3, C4: VITRAMON VJ1825Y155MXB BAT54 C5: 4X KEMET T510X337KO10AS L1: COILCRAFT DO1608C-472 L2: PANASONIC ETQP6F4R1LF4 1OV 10k Q1,Q3:100V SILICONIX SUD40N10-25 BIAS 1OV 100Ω 2k Q5,Q6: SILICONIX Si4450 0.1µF BIAS FZT690 0.22µF T1:COILTRONICS VP5-1200 MMBD914LT1 330pF 50V 100V Q10: ON SEMI MMBT3906LTI 73.2k CMPZ5242B 4.7µF 1% 12V 270k 5V 16V 0.25W BAS21 20k OUT 20 17 19 18 16 11 12 15 14 V LTC1693-2 CC V BLKSENS TG BSTREF BG SENSE T PGND 3.3Ω BST MAX 13 8 6 CMPZ- 2 SG VCC1 VCC2 CMPZ5248B 5248B OVLO LT1681 0.047µF 3 5 18V 15V 1 9 IN2 OUT2 SHDN 5VREF FSET THERM SYNC SGND SS VC VFB 1 7 IN1 OUT1 1681 TA01 5 6 3 7 4 8 10 3.01k 51Ω 0.1µF 4 2 10k 56k 52.3k 1% 100 Q10 Ω GND2 GND1 + 68µF 1.24k 1nF 24k 1 1% µF 150pF 20V 4.7nF 1k 0.01µF 1% 1681f 1
