SC420A
POWER MANAGEMENT
Applications Information (Cont.)
Start-up Sequencing
Proper sequencing of the Combi-Sense
TM
controller and
SC420A 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 issue gate drive
pulses that are not well-controlled.
In general it is recommended that the Vcc’s for the Combi-
Sense Controller and SC420A 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 SC420A maximum
UVLO value is guaranteed to be lower than the Combi-
Sense
TM
Controller minimum UVLO value).
For absolute guarantee of proper sequencing it is recom-
mended that the EN controls be used as shown in the
following block diagram. With this arrangement the de-
layed 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 SC420A.
During power-down de-assertion of VID_PWRGD will en-
sure simultaneous disabling of the Combi-Sense
TM
Control-
ler and SC420A.
Manufacturing Guidlines
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”. Please contact your
local Semtech representative to obtain a copy of this
application note.
V
5
SC1403
SYS_PWRGD
V
3
VR_ON
VccVID Regulator
Combi-
TM
Sense
Controller
EN
CO
SC420A
EN
V
cc
-CORE
VID_PWRGD
VccPWRGD
©
2004 Semtech Corp.
10
United States Patent No. 6,441,597
www.semtech.com
SEMTECH [ SEMTECH CORPORATION ]
