LT3154AVPBF datasheet(14/32 Pages) AD

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LT3154

Rev. 0

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OPERATION

Automatic Burst Mode Operation

When the SYNC/MODE pin is held low, the LT3154 is

configured for automatic Burst mode operation. As a

result, the buck‑boost DC/DC converter will operate with

normalcontinuousPWMswitchingaboveapredetermined

average inductor current and will automatically transition

to power saving Burst mode operation below this level.

Refer to the Typical Performance Characteristics section

of this data sheet to determine the Burst mode transition

threshold for various combinations of VIN and VOUT. With

SYNC/MODE low, at light output loads, the LT3154 will

go into a standby or sleep state when the output voltage

achieves its nominal regulation level. The sleep state

halts PWM switching and powers down all non‑essential

functions of the IC, significantly reducing the quiescent

currentoftheLT3154.Thisgreatlyimprovesoverallpower

conversion efficiency when the output load is light. Since

the converter is not operating in sleep, the output voltage

will slowly decay at a rate determined by the output load

resistanceandtheoutputcapacitorvalue.Whentheoutput

voltage has decayed by a small amount, typically less than

1%, the LT3154 will wake up and resume normal PWM

switching operation until the voltage on VOUT is restored

to the previous level. If the load is very light, the LT3154

may only need to switch for a few cycles to restore VOUT

and may sleep for extended periods of time, significantly

improving efficiency.

Average Current Mode Control

The LT3154 utilizes Average Current mode control for the

pulse width modulator as shown inFigure 2. Current mode

control, both average and the better known peak method,

enjoy some benefits compared to other control methods

including: simplified loop compensation, rapid response

to load transients and inherent line voltage rejection.

Referring to Figure 2, an internal high gain transcon‑

ductance error amplifier labeled V_AMP monitors VOUT

through a voltage divider connected to the FB node and

ICOMP

VOUT

CHF

3154 F02

0.99V

RCS

SW2

PWM

DRIVE

LOGIC

SWITCHES

PWM RAMPS/

OSCILLATOR

SW1

V_AMP

I_AMP

INDUCTOR

CURRENT SENSE

0.9V

CLAMP

INTERNAL

CURRENT

AMPLIFIER

Figure 2. Average Current Mode Control Loop

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