SC420
POWER MANAGEMENT
Applications Information (Cont.)
Start-up Sequencing
Manufacturing Guidelines
Proper sequencing of the Combi-SenseTM Controller and
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.
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.
In general it is recommended that the Vcc’s for theCombi-
SenseTM Controller and SC420 be connected to the same
(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-
SenseTM Controller minimum UVLO value).
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
Combi-SenseTM Controller and SC420.
V5
SYS_PWRGD
SC1403
V3
VR_ON
Vcc-CORE
CO
SC400
EN
SC420
EN
VccVID Regulator
VID_PWRGD
VccPWRGD
2003 Semtech Corp.
9
United States Patent No. 6,441,597
www.semtech.com
SEMTECH [ SEMTECH CORPORATION ]
