SW

FB

BGND

PGND

PVIN

BP

MODE

EN

ACB

SGND

VDD

CONTROL LOGIC

DRIVER

ACB

CTL

CURRENT

SENSE

+

-

+

-

+

-

SGND

ERROR AMP.

PFM COMP.

PWM COMP.

VCON

LM3243

SNVS782C – OCTOBER 2010 – REVISED AUGUST 2015

www.ti.com

7.2 Functional Block Diagram

7.3 Feature Description

7.3.1 ACB

The 3GPP time mask requirement for 2G requires high current to be sourced by the LM3243. These high

currents are required for a small time during transients or under a heavy load. Over-rating the switching inductor

for these higher currents would increase the solution size and will not be an optimum solution. Thus, to allow an

optimal inductor size for such a load, an alternate current path is provided from the input supply through the ACB

current required to support the load. The ACB circuit also minimizes the dropout voltage by having the analog

a 4-A (maximum) peak current limit.

7.3.2 Bypass Operation

typical). When BP = LOW the part will be in automatic bypass mode which will automatically determine the

amount of bypass needed to maintain voltage regulation. When the input supply voltage to the LM3243 is

lowered to a level where the commanded duty cycle is higher than what the converter is capable of providing, the

part will go into pulse-skipping mode. The switching frequency will be reduced to maintain a low and well-

behaved output voltage ripple. The analog bypass circuit will allow the converter to stay in regulation until full

bypass is reached (100% duty cycle operation). The converter comes out of full bypass and back into analog

bypass regulation mode with a similar reverse process.

12

Submit Documentation Feedback

Copyright © 2010–2015, Texas Instruments Incorporated

Product Folder Links: LM3243