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

LM5574

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 2H

C7

0.022

C8

0.47

D1

CMSH2-100M

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 ± 75V

VIN

1.4V

PWM

C_LIMIT

10 2A

5 2A

TRACK

SAMPLE

and

HOLD

2V/A

RAMP GENERATOR

+ 50 2A

LM5574-Q1

www.ti.com

SNOSB22C – OCTOBER 2008 – REVISED OCTOBER 2014

7 Detailed Description

7.1 Overview

The LM5574-Q1 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 75 V 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 50 kHz

to 500 kHz. An oscillator synchronization pin allows multiple LM5574-Q1 regulators to self synchronize or be

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

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

TSSOP-16 package.

The functional block diagram and typical application of the LM5574-Q1 are shown in Figure 16. The LM5574-Q1

can be applied in numerous applications to efficiently step-down a high, unregulated input voltage. The device is

well suited for telecom, industrial and automotive power bus voltage ranges.

7.2 Functional Block Diagram

7.3 Feature Description

7.3.1 Shutdown And Standby

The LM5574-Q1 contains a dual level Shutdown (SD) circuit. When the SD pin voltage is below 0.7 V, the

regulator is in a low current shutdown mode. When the SD pin voltage is greater than 0.7 V but less than 1.225

When the SD pin voltage exceeds 1.225 V, the output switch is enabled and normal operation begins. An internal

5 µA pull-up current source configures the regulator to be fully operational if the SD pin is left open.

Copyright © 2008–2014, Texas Instruments Incorporated

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Product Folder Links: LM5574-Q1