FB

SW

RT

BST

SD

5V

S

R

Q

Q

AGND

IS

CLK

+

SS

PRE

3

2

10

6

5

4

7

8

11

9

12

1

SD

Ir

LM25574

SHUTDOWN

STANDBY

7V

REGULATOR

SYNC

SYNC

OSCILLATOR

RAMP

OUT

PGND

CLK

CLK

COMP

ERROR

AMP

R3

21k

C3

470p

C9

22

R6

1.65k

R5

5.11k

L1

100 PH

C7

0.022

C8

0.47

D1

CMSH2-60M

13

15

14

16

THERMAL

SHUTDOWN

UVLO

UVLO

CLK

DIS

VCC

LEVEL

SHIFT

DRIVER

1.225V

1.225V

0.7V

0.7V

R4

24.9k

C5

0.022

C6

open

R2

OPEN

C2

OPEN

C4

0.01

C1

1.0

R1

OPEN

7V ± 42V

VIN

1.4V

PWM

C_LIMIT

10 PA

5 PA

TRACK

SAMPLE

and

HOLD

2V/A

RAMP GENERATOR

+ 50 PA

0.1

0.2

0.3

0.4

0.5

0

10

20

30

40

50

60

70

80

90

100

LM25574

SNVS483F – JANUARY 2007 – REVISED FEBRUARY 2009

www.ti.com

Typical Performance Characteristics (continued)

Demoboard Efficiency

vs

Typical Application Circuit and Block Diagram

Detailed Operating Description

The LM25574 switching regulator features all of the functions necessary to implement an efficient high voltage

buck regulator using a minimum of external components. This easy to use regulator integrates a 42V N-Channel

buck switch with an output current capability of 0.5 Amps. The regulator control method is based on current

mode control utilizing an emulated current ramp. Peak current mode control provides inherent line voltage feed-

forward, cycle-by-cycle current limiting, and ease of loop compensation. The use of an emulated control ramp

reduces noise sensitivity of the pulse-width modulation circuit, allowing reliable processing of very small duty

cycles necessary in high input voltage applications. The operating frequency is user programmable from 50kHz

to 1MHz. An oscillator synchronization pin allows multiple LM25574 regulators to self synchronize or be

synchronized to an external clock. The output voltage can be set as low as 1.225V. Fault protection features

include, current limiting, thermal shutdown and remote shutdown capability. The device is available in the

TSSOP-16 package.

8

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