SMH4814
Preliminary Information
APPLICATIONS INFORMATION (CONTINUED)
In the case when Current Regulation is enabled and
CBSENSE exceeds VQCB before the circuitry has time
to modulate VGATE_HS, the Quick-Trip circuit assists
the modulation by pulling down on the gate
immediately. Rather than pull all the way to VSS, the
Quick-Trip circuitry may also be configured to only pull
down to within one, two or three diode of VSS
Resetting FAULT#
When the circuit breaker trips and, in the case in which
current regulation is enabled, tPCR times out, the
VGATE_HS and PUP outputs are turned off and
FAULT# is driven low. Other events may also be
configured to cause a Fault, as determined by
R0D[3:0] and R10[7:4]. Once a Fault has occurred,
the SMH4814 may be configured (using R05[2]) to
either restart on its own after a programmable cooling
off period of tCYC (Figure 13), or it may be configured to
stay latched off until the Fault is manually reset (Figure
14). The duty cycle timeout period tCYC is set using
R03[7:4] and can range from 7ms to 21.5s. The Fault
condition may be manually reset by driving RESET#
low, or through the use of the Command Register.
(R05[7:6]). Once CBSENSE falls back below VQCB
,
the pull-down circuitry will shut off. By this point, the
Current Regulation circuit will have had time to
activate, and VGATE_HS will be modulated to keep
the CBSENSE level at VCR. Figure 11 and Figure 12
illustrate the current regulation function.
<tPCR
VQCB
CBSENSE
VCR
tCBD
tCBD
VCB
VCB
0V
CBSENSE
tCBD
12V
VGATE_HS
tCYC
VGATE_HS
0V
Figure 11 - Current Regulation With Recovery
Figure 13 - Circuit Breaker Duty Cycle Operation
with RESET# High
tPCR
VQCB
tCBD
VCB
CBSENSE
0V
VCR
CBSENSE
VCB
12V
VGATE_HS
tPDD
VGATE_HS
0V
tCBRST
Figure 12 - Current Regulation Without Recovery
RESET#
Figure 14 - Circuit Breaker Reset with RESET#
Summit Microelectronics, Inc
2080 2.0 07/21/05
18
SUMMIT [ SUMMIT MICROELECTRONICS, INC. ]
