SMH4812_09 Datasheet, PDF (10/18 Pages) Summit Microelectronics, Inc. – Distributed Power Hot-Swap Controller

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.
NOTE: THE 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.
12V
VGATE
C
F
0V
1
FAULT#
E
0
50mV
B
CBSENSE
0V
A
D
2055 Fig05a
Figure 5.a. Current Regulation & Shutdown
12V
I
VGATE
L
0V
1
FAULT#
K
0
H
50mV
CBSENSE
J
0V
G
2055 Fig05b
Figure 5.b. Current Regulation & Shutdown
2055 4.1 03/27/09
SUMMIT MICROELECTRONICS, Inc.
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