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© 2003 Semtech Corp.

POWER MANAGEMENT

SC420

United States Patent No. 6,441,597

www.semtech.com

Start-up Sequencing

SC420 driver during both start-up and shut-down is very

important. In general, the design must ensure that the

driver powers up (during start-up) before the controller

does, and that the driver powers down last during shut-

down. This ensures that the driver will never puts out

gate drive pulses which are not well-controlled, a situation

that can lead to MOSFET damage.

In general it is recommended that the Vcc’s for the Combi-

(5V) supply. If the EN controls are not used (tied high)

then the UVLO settings for the controller and driver will

guarantee the proper sequencing (the SC420 maximum

UVLO value is guaranteed to be lower than the Combi-

For absolute guarantee of proper sequencing it is rec-

ommended that the EN controls be used as shown in

the following block diagram. With this arrangement the

delayed PWRGD signal from the VccVID regulator is

used to enable both ICs. The Soft-Start time established

for the controller ensures it will come up well after the

SC420.

During

power-down

de-assertion

of

VID_PWRGD will ensure simultaneous disabling of the

VccVID Regulator

SYS_PWRGD

VR_ON

SC1403

VID_PWRGD

CO

SC400

EN

SC420

EN

VccPWRGD

Applications Information (Cont.)

Detailed information on manufacturing and rework

of PCBs using the MLP package can be found in

the MLP application note “Comprehensive User’s

Guide - Micro Lead Frame Package” dated April

2002.

Please contact your local Semtech

representative to obtain a copy of this application

note.

Manufacturing Guidelines