SMH4812
Preliminary
Current Regulation
12V
The current regulation mode is an optional feature that
provides a means to regulate current through the MOS-
FET for a programmable period of time. See Figures 5a
and 5b. If enabled the device will start the internal timer
whenthevoltageatCBSENSEexceeds50mV(A&G, H).
Also, it attempts to limit the voltage at CBSENSE to 60mV
by regulating the VGATE output (B & C vs. I). The circuit
breaker will trip if the over-current condition remains after
the time-out (D, E, F; & J, K, L). However, if CBSENSE
dropsbelow50mVbeforethetimerends,thetimerisreset
and VGATE resumes normal operation. If the Quick-Trip
level is exceeded then the device will bypass the current
regulation timer and shut down immediately. The Current
Regulationfeatureisdisabledinthedefaultconfiguration.
VGATE
FAULT#
C
F
E
0V
1
0
B
50mV
0V
D
CBSENSE
A
2055 Fig05a
Non-Volatile Fault Latch
Figure 5.a. Current Regulation & Shutdown
The SMH4812 also provides an optional nonvolatile fault
latch (NVFL) circuit breaker feature. The nonvolatile fault
latch essentially provides a programmable fuse on the
circuit breaker. When enabled the nonvolatile fault latch
will be set whenever the circuit breaker trips. Once set, it
cannot be reset by cycling power.
12V
I
VGATE
L
NOTE: THE DEVICE REMAINS PERMANENTLY DISABLED
UNTIL IT IS REPROGRAMMED AT THE FACTORY.
0V
1
FAULT#
K
As long as the NVFL is set, the FAULT# output will be
driven active. The Non-Volatile Fault Latch feature is
disabled in the default configuration.
0
H
50mV
J
CBSENSE
G
Resetting FAULT#
0V
When the circuit breaker trips the VGATE output is turned
off and FAULT# is driven low. In the default condition the
breaker resets automatically after a time of tCYC. In the
latchedconditioncyclingpowertotheboardortogglingthe
EN/TS input will also reset the circuit breaker. If the over
current condition still exists after the MOSFET switches
back on, the circuit breaker will re-trip.
2055 Fig05b
Figure 5.b. Current Regulation & Shutdown
SUMMIT MICROELECTRONICS, Inc.
2055 4.0 12/22/00
10
SUMMIT [ SUMMIT MICROELECTRONICS, INC. ]
