LT8253/LT8253A

7

Rev. 0

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OPERATION

The LT8253/LT8253A are current mode DC/DC controllers

that can regulate output voltage from an input voltage

above, below, or equal to the output voltage. The propri-

etary peak-buck peak-boost current mode control scheme

uses a single current sense resistor and provides smooth

transition between buck region, buck-boost region, and

boost region. Its operation is best understood by referring

to the Block Diagram.

Power Switch Control

Figure 1 shows a simplified diagram of how the four

power switches A, B, C, and D are connected to the induc-

inductor current information for both peak current mode

control and reverse current detection in buck region,

buck-boost region, and boost region.

There are total four states: (1) peak-buck current mode

control in buck region, (2) peak-buck current mode con-

trol in buck-boost region, (3) peak-boost current mode

control in buck-boost region, and (4) peak-boost current

mode control in boost region. The following sections

give detailed description for each state with waveforms,

in which the shoot-through protection dead time between

switches A and B, between switches C and D are ignored

for simplification.

D

A

SW1

SW2

TG2

BG2

TG1

BG1

B

C

L

Figure 1. Simplified Diagram of the Power Switches