SW

VCON

FB

EN

VIN

PGND

OSCILLATOR

RAMP

GENERATOR

OUTPUT SHORT

PROTECTION

THERMAL

SHUTDOWN

DRIVER

CONTROL LOGIC

PWM

COMP.

Ref3

Ref2

NCP

OVER-VOLTAGE

DETECTOR

DELAY

ERROR

AMP

OLP

Ref4

LIGHT-LOAD

CHECK COMP

ECO COMP

BYPASS

VCON

BPEN

FB

2/5

Ref1

+

+

SGND

STANDBY COMP

Ref5

LM3242

SNOSB48E – OCTOBER 2011 – REVISED AUGUST 2015

www.ti.com

7.2 Functional Block Diagram

7.3 Feature Description

7.3.1 Circuit Operation

Referring to the Typical Application and Functional Block Diagram, the LM3242 operates as follows. During the

first part of each switching cycle, the control block in the LM3242 turns on the internal top-side PFET switch. This

allows current to flow from the input through the inductor to the output filter capacitor and load. The inductor

the second part of each cycle, the controller turns the PFET switch off, blocking current flow from the input, and

then turns the bottom-side NFET synchronous rectifier on. In response, the inductor’s magnetic field collapses,

generating a voltage that forces current from ground through the synchronous rectifier to the output filter

capacitor and load. As the stored energy is transferred back into the circuit and depleted, the inductor current

high, and releases it when low, smoothing the voltage across the load.

The output voltage is regulated by modulating the PFET switch on time to control the average current sent to the

load. The effect is identical to sending a duty-cycle modulated rectangular wave formed by the switch and

synchronous rectifier at SW to a low-pass filter formed by the inductor and output filter capacitor. The output

voltage is equal to the average voltage at the SW pin.

12

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