FB

SW

RTN

BST

1.225V

VILIM

LM25019

ILIM

COMPARATOR

+

-

V UVLO

ON/OFF

TIMERS

COT CONTROL

LOGIC

1.225V

START-UP

REGULATOR

FEEDBACK

DISABLE

THERMAL

SHUTDOWN

UVLO

OVER-VOLTAGE

1.62V

UVLO

4.5V

SD

SHUTDOWN

VDD REG

BG REF

0.66V

20 µA

CURRENT

LIMIT

ONE-SHOT

LM25019

www.ti.com

SNVS952 – DECEMBER 2012

Block Diagram

Figure 12. Functional Block Diagram

Functional Description

The LM25019 step-down switching regulator features all the functions needed to implement a low cost, efficient,

buck converter capable of supplying up to 100mA to the load. This high voltage regulator contains 48V, N-

channel buck and synchronous switches, is easy to implement, and is provided in thermally enhanced PSOP-8

and LLP-8 packages. The regulator operation is based on a constant on-time control scheme using an on-time

while providing minimum foldback. The simplified block diagram of the LM25019 is shown in Figure 12,

Functional Block Diagram.

The LM25019 can be applied in numerous applications to efficiently regulate down higher voltages. This

regulator is well suited for 12V and 24V rails. Protection features include: thermal shutdown, undervoltage

lockout, minimum forced off-time, and an intelligent current limit.

Control Overview

The LM25019 buck regulator employs a control principle based on a comparator and a one-shot on-timer, with

the output voltage feedback (FB) compared to an internal reference (1.225V). If the FB voltage is below the

reference the internal buck switch is turned on for the one-shot timer period, which is a function of the input

falls below the reference, but never before the minimum off-time forced by the minimum off-time one-shot timer.

When the FB pin voltage falls below the reference and the minimum off-time one-shot period expires, the buck

switch is turned on for another on-time one-shot period. This will continue until regulation is achieved and the FB

voltage is approximately equal to 1.225V (typ).

Copyright © 2012, Texas Instruments Incorporated

Submit Documentation Feedback

7

Product Folder Links: LM25019