Micrel, Inc.
MIC2310
July 2008
18
M9999-070108-A
VCC = 12V, nominal
VGSPGH
V
GSPGH
V
PGH
VPGL
t
POC
IPOC
VREG = 5V, nominal
t
RETRY
tPOR
CC & VREG
ENABLE
GATE
V
OUT
I
LOAD
CRETRY
PWRGD
I_FLT
DISCH
VVREG(UVLOH)
Figure 6. Primary Overcurrent Fault with Auto-Retry to Reset the Circuit Breaker
HW_FLT Digital Output Asserted by a MOSFET DG
Short with ENABLE = LOW
In order to protect the system from the result of the
installation of a damaged MOSFET on the PCB, the
controller incorporates a MOSFET shorted DG
detection scheme whose operation is described in
Figure 7. With the applied V
CC
supply high such that
the internal V
REG
voltage is above the controllers
V
VREG(UVLOH)
threshold voltage, an elapsed POR timer,
and with the ENABLE input LOW, a weak current sink
at the GATE pin attempts to hold the GATE voltage at
0V. If there is a DG short on the MOSFET, the weak
current sink is not capable of holding the voltage at 0V
as the GATE voltage tracks the MOSFETs DRAIN
voltage. The voltage monitor circuit at the controllers
GATE pin will be triggered once the GATE voltage
crosses the V
GATEFT(EXT)
threshold voltage. The
HW_FLT digital output is subsequently asserted within
a delay approximately equal to the delay in the logic
circuits no additional timing circuit is required. To
clear the latched GATE voltage monitor circuit and to
reset the HW_FLT digital output, the applied V
CC
supply voltage must fall such that V
REG
is below the
controllers V
VREG(UVLOL)
threshold voltage.