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LT3840

3840fa

For more information www.linear.com/LT3840

operaTion

OVERVIEW

TheLT3840providesasolutionforahighefficiency,general

purpose DC/DC converter. It is a wide input voltage range

switching regulator controller IC that uses a program-

mable fixed frequency, peak current mode architecture.

An internal switching regulator efficiently provides an

auxiliary bias supply to drive multiple, large N-channel

MOSFET switches.

The LT3840 includes functions such as average output

current control and monitoring, micro-power operation

with low output ripple, soft-start, output voltage tracking,

power good and a handful of protection features.

Voltage Control Loop

The LT3840 uses peak current mode control to regulate

the supply output voltage. The error amplifier (EA) gener-

ates an error voltage (VC) based on the difference between

the feedback (FB) voltage and an internal reference.

The externally compensated VC voltage generates a

threshold for the differential current sense comparator.

During normal operation, the LT3840 internal oscillator

runs at the programmed frequency. At the beginning of

each oscillator cycle, the TG switch drive is turned on. The

TG switch drive stays enabled until the sensed inductor

current exceeds the VC derived threshold of the current

sense comparator.

If the current comparator threshold is not reached for the

entire oscillator cycle, the switch driver stays on for up

to eight cycles. If after eight cycles the TG switch driver

is still on, it is turned off to regenerate the BOOST boot-

strapped supply.

When the load current increases, the FB voltage decreases

relative to the reference causing the EA to increase the VC

voltageuntiltheaverageinductorcurrentmatchesthenew

load current. Refer to Figure 1 for a block diagram of the

LT3840 voltage control loop.

Figure 1. Peak Current Mode Voltage Control Functional Block Diagram

INTVCC

BOOST

VIN

EXTERNAL

COMPONENTS

VOUT

INTVCC

DRIVER

ANTI SHOOT

THRU

BGRTN

SENSE+

SENSE–

VREF

3840 BD

SYNC

OSCILLATOR

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