LT8301MP 查看數據表（PDF） - Linear Technology

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LT8301MP

42VIN Micropower No-Opto Isolated Flyback Converter with 65V/1.2A Switch

Linear Technology 

BLOCK DIAGRAM

VIN

CIN

5

VIN

RFB

3

RFB

1:4

M3

M2

25µA

RREF

10kΩ

1.0V

R1

EN/UVLO

1

R2

2.5µA

1.228V

–

A1

+

M4

–

gm

+

OSCILLATOR

–

A3

+

VIN

REFERENCE

REGULATORS

LT8301

BOUNDARY

DETECTOR

T1

NPS:1

DOUT

LPRI

•

•

LSEC

4

SW

VOUT+

COUT

VOUT–

S

RQ

DRIVER

M1

A2

RSENSE

GND

2

8301 BD

OPERATION

The LT8301 is a current mode switching regulator IC de-

signed specially for the isolated flyback topology. The key

problem in isolated topologies is how to communicate the

output voltage information from the isolated secondary

side of the transformer to the primary side for regulation.

Historically, opto-isolators or extra transformer windings

communicate this information across the isolation bound-

ary. Opto-isolator circuits waste output power, and the

extra components increase the cost and physical size of

the power supply. Opto-isolators can also cause system

issues due to limited dynamic response, nonlinearity, unit-

to-unit variation and aging over lifetime. Circuits employing

extra transformer windings also exhibit deficiencies, as

using an extra winding adds to the transformer’s physical

size and cost, and dynamic response is often mediocre.

The LT8301 samples the isolated output voltage through

the primary-side flyback pulse waveform. In this manner,

neither opto-isolator nor extra transformer winding is re-

quired for regulation. Since the LT8301 operates in either

boundary conduction mode or discontinuous conduction

mode, the output voltage is always sampled on the SW

pin when the secondary current is zero. This method im-

proves load regulation without the need of external load

compensation components.

8301f

For more information www.linear.com/LT8301

7

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