MIC2310_08 Datasheet, PDF (20/34 Pages) Micrel Semiconductor – Single-FET, Constant Power-Limit Hot Swap Controller

Micrel, Inc.
HW_FLT Digital Output Asserted by MOSFET DS
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 DS
detection scheme whose operation is described in
Figure 8. With the applied V_CC supply high such that
the internal V_REG voltage is above the controller’s
V_VREG(UVLOH) threshold voltage, an elapsed POR timer,
and with the ENABLE input LOW, a voltage monitor
circuit for the controller’s SOURCE pin is enabled. If
there is a DS short on the MOSFET, the external load
on the MOSFET is not capable of holding the voltage
MIC2310
at 0V as the SOURCE voltage tracks the MOSFET’s
DRAIN voltage. The voltage monitor circuit at the
controller’s SOURCE pin will be triggered once the
SOURCE voltage crosses the V_SRCFT(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 source 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 controller’s V_VREG(UVLOL) threshold
voltage.
Figure 8. Hardware Fault Detection of a MOSFET DS Short with ENABLE = LOW
July 2008
20
M9999-070108-A