SMH4812
Preliminary
Current Regulation
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
when the voltage at CBSENSE exceeds 50mV (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
drops below 50mV before the timer ends, the timer is reset
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
Regulation feature is disabled in the default configuration.
Non-Volatile Fault Latch
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.
Figure 5.a. Current Regulation & Shutdown
12V
VGATE
0V
1
C
F
FAULT#
0
50mV
0V
E
B
CBSENSE
A
D
2055 Fig05a
12V
VGATE
0V
1
I
L
N
OTE
: T
HE
DEVICE REMAINS PERMANENTLY DISABLED
UNTIL IT IS REPROGRAMMED AT THE FACTORY
.
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.
Resetting FAULT#
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 t
CYC
. In the
latched condition cycling power to the board or toggling the
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.
FAULT#
0
K
H
50mV
CBSENSE
0V
G
J
2055 Fig05b
Figure 5.b. Current Regulation & Shutdown
10
2055 4.1 03/27/09
SUMMIT MICROELECTRONICS, Inc.
SUMMIT [ SUMMIT MICROELECTRONICS, INC. ]
