S&H

VPC

Thresh

Ramp

Enable

S

Q

Q

R

VPC

TBLK

VDD

+

SR_On

Detect

SRon

DRV

Enable

DRV

GND

VSC

UVLO

4.0/3.6 V

SR Control Bias

Fsw Detect

Stand By

Thermal

SD

VPC

Bias

Stand By

VPC

Blanking

Timer

VPC Ramp

VSC Ramp

One

Shot

+

+

+

+

+

9

UCC24636

www.ti.com

SLUSCG2A – MARCH 2016 – REVISED MARCH 2016

Product Folder Links: UCC24636

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Copyright © 2016, Texas Instruments Incorporated

8 Detailed Description

8.1 Overview

The UCC24636 SR controller is targeted for flyback converters operating in DCM and TM modes of operation.

The control method to determine SR on time is based on the volt-second balance principle of primary and

secondary conduction volt-second product. In converters operating in DCM and TM, the secondary current

always returns to zero in each cycle. The inductor charge voltage and time product is equal to the discharge

voltage and time product. The device uses internal current ramp emulators to predict the proper SR on time

based on voltage and time information on the VPC and VSC pins.

To achieve very low standby power in the converter, the UCC24636 has a standby mode of operation that

switching frequency of the converter to enter and exit the standby mode of operation, and is compatible with

converters operating in burst mode or constant frequency in light-load mode.

8.2 Functional Block Diagram