MIC2310_08 Datasheet, PDF (21/34 Pages) Micrel Semiconductor – Single-FET, Constant Power-Limit Hot Swap Controller

Micrel, Inc.
HW_FLT Asserted by MOSFET DS Short after
Steady-state Operation then ENABLE = HIGH-to-
LOW
Figure 9 illustrates the behavior of the controller to a
shorted DS MOSFET condition after steady-state
operation is achieved via a nominal start-up. Note that
the load capacitor at start-up was charged in a
controlled dI_D/dt mode and assertion of the controller’s
PWRGD digital output occurs when the output load
voltage profile is higher than the controller’s V_PGH
threshold voltage and the V_GS of the external
MOSFET is higher than the controller’s V_GSPGH
threshold voltage. Upon the application of a HIGH-to-
LOW transition on ENABLE by the service processor,
the GATE drive circuit is disabled, the weak GATE
MIC2310
current sink is enabled, the DISCH output goes high,
and the t_DS-SSFAULT timer is started. With the ENABLE
input LOW, a voltage monitor circuit for the controller’s
SOURCE pin (i.e., V_OUT) is enabled. If there is a DS
short, the voltage at the source will not drop to 0V
even though the GATE is OFF. If the output voltage at
the SOURCE pin remains higher than the controller’s
V_SRCFT(EXT) threshold voltage when the t_DS-SSFAULT timer
terminates, the HW_FLT digital output is asserted. To
repair the damaged MOSFET and to reset the
HW_FLT digital output and the controller, the service
processor instructs the main supply to turn off the V_CC
supply voltage to the controller such that V_REG falls
below the controller’s V_VREG(UVLOL) threshold voltage.
Figure 9. Hardware Fault by a MOSFET DS Short after Steady-State Operation
(ENABLE = HIGH-to-LOW)
July 2008
21
M9999-070108-A