Datasheet LT1725 (Analog Devices)
| Manufacturer | Analog Devices |
| Description | General Purpose Isolated Flyback Controller |
| Pages / Page | 28 / 1 — FEATURES. DESCRIPTIO. Drives External Power MOSFET with External. SENSE … |
| File Format / Size | PDF / 265 Kb |
| Document Language | English |
FEATURES. DESCRIPTIO. Drives External Power MOSFET with External. SENSE Resistor. Application Input Voltage Limited Only by
Model Line for this Datasheet
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LT1725 General Purpose Isolated Flyback Controller
U FEATURES DESCRIPTIO
■
Drives External Power MOSFET with External
The LT®1725 is a monolithic switching regulator control-
I
ler specifically designed for the isolated flyback topology.
SENSE Resistor
■
Application Input Voltage Limited Only by
It drives the gate of an external MOSFET and is generally
External Power Components
powered from a third transformer winding. These features ■
Senses Output Voltage Directly from Primary Side
allow for an application input voltage limited only by
Winding—No Optoisolator Required
external power path components. The third transformer ■ Accurate Regulation Without User Trims winding also provides output voltage feedback informa- ■ Regulation Maintained Well into Discontinuous Mode tion, such that an optoisolator is not required. Its gate ■ Switching Frequency from 50kHz to 250kHz with drive capability coupled with a suitable external MOSFET External Capacitor can deliver load power up to tens of watts. ■ Optional Load Compensation The LT1725 has a number of features not found on most ■ Optional Undervoltage Lockout other switching regulator ICs. By utilizing current mode ■ Available in 16-Pin SO and SSOP Packages switching techniques, it provides excellent AC and DC line regulation. Its unique control circuitry can maintain regu-
U
lation well into discontinuous mode in most applications.
APPLICATIO S
Optional load compensation circuitry allows for improved ■ Telecom Isolated Converters load regulation. An optional undervoltage lockout pin ■ Offline Isolated Power Supplies halts operation when the application input voltage is too ■ Instrumentation Power Supplies low. An optional external capacitor implements a soft- start function. A 3V output is available at up to several mA , LTC and LT are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners. for powering primary side application circuitry.
U TYPICAL APPLICATIO 48V to Isolated 5V Converter
CTX02-14989
Output Load Regulation
6 470pF LT1725 5.25 18Ω 35.7k VIN 36V TO 72V 3VOUT BAS16 1% 1 VIN = 48V FB 22Ω VIN = 36V 47k 3.01k V SFST V OUT = 5V CC 1% V 1nF + 2 9 IOUT = 0 to 2A IN = 72V 15µF 1µF 12CWQ06 (V) VC 51Ω 5.00 47pF 68Ω OUT 1W V OSCAP 11 820k 150pF tON UVLO 51k 10 + 100pF 33k 1.5µF 150µF ENDLY 51k 4 12 4.75 MENAB 0 0.5 1.0 1.5 2.0 51k ILOAD (A) ROCMP GATE IRF620 2.7k 1725 F10b RCMPC ISENSE 0.1µF SGND PGND 0.18Ω 1725 TA01a 1725fa 1
U FEATURES DESCRIPTIO
■
Drives External Power MOSFET with External
The LT®1725 is a monolithic switching regulator control-
I
ler specifically designed for the isolated flyback topology.
SENSE Resistor
■
Application Input Voltage Limited Only by
It drives the gate of an external MOSFET and is generally
External Power Components
powered from a third transformer winding. These features ■
Senses Output Voltage Directly from Primary Side
allow for an application input voltage limited only by
Winding—No Optoisolator Required
external power path components. The third transformer ■ Accurate Regulation Without User Trims winding also provides output voltage feedback informa- ■ Regulation Maintained Well into Discontinuous Mode tion, such that an optoisolator is not required. Its gate ■ Switching Frequency from 50kHz to 250kHz with drive capability coupled with a suitable external MOSFET External Capacitor can deliver load power up to tens of watts. ■ Optional Load Compensation The LT1725 has a number of features not found on most ■ Optional Undervoltage Lockout other switching regulator ICs. By utilizing current mode ■ Available in 16-Pin SO and SSOP Packages switching techniques, it provides excellent AC and DC line regulation. Its unique control circuitry can maintain regu-
U
lation well into discontinuous mode in most applications.
APPLICATIO S
Optional load compensation circuitry allows for improved ■ Telecom Isolated Converters load regulation. An optional undervoltage lockout pin ■ Offline Isolated Power Supplies halts operation when the application input voltage is too ■ Instrumentation Power Supplies low. An optional external capacitor implements a soft- start function. A 3V output is available at up to several mA , LTC and LT are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners. for powering primary side application circuitry.
U TYPICAL APPLICATIO 48V to Isolated 5V Converter
CTX02-14989
Output Load Regulation
6 470pF LT1725 5.25 18Ω 35.7k VIN 36V TO 72V 3VOUT BAS16 1% 1 VIN = 48V FB 22Ω VIN = 36V 47k 3.01k V SFST V OUT = 5V CC 1% V 1nF + 2 9 IOUT = 0 to 2A IN = 72V 15µF 1µF 12CWQ06 (V) VC 51Ω 5.00 47pF 68Ω OUT 1W V OSCAP 11 820k 150pF tON UVLO 51k 10 + 100pF 33k 1.5µF 150µF ENDLY 51k 4 12 4.75 MENAB 0 0.5 1.0 1.5 2.0 51k ILOAD (A) ROCMP GATE IRF620 2.7k 1725 F10b RCMPC ISENSE 0.1µF SGND PGND 0.18Ω 1725 TA01a 1725fa 1
