MIC2085 Datasheet, PDF (18/29 Pages) Micrel Semiconductor – Single Channel Hot Swap Controllers

Micrel, Inc.
PCB Connection Sense
There are several configuration options for the
MIC2085/86’sON pin to detect if the PCB has been fully
seated in the backplane before initiating a start-up cycle.
In the typical applications circuit, the MIC2085/86 is
mounted on the PCB with a resistive divider network
connected to the ON pin. R2is connected to a short pin
on the PCB edge connector. Until the connectors mate,
the ON pin is held low which keeps the GATE output
charge pump off. Once the connectors mate, the resistor
network is pulled up to the input supply, 12V in this
example, and the ON pin voltage exceeds its threshold
(V_ON) of 1.24V and the MIC2085/86 initiates a start-up
MIC2085/2086
cycle. In Figure 6, the connection sense consisting of a
logic-level discrete MOSFET and a few resistors allows
for interrupt control from the processor or other signal
controller to shut off the output of the MIC2085/86. R4
keeps the GATE of Q2 at V_IN until the connectors are
fully mated. A logic LOW at the/ON_OFF signal turns Q2
off and allows the ON pin to pull up above its threshold
and initiate a start-up cycle. Applying a logic HIGH at the
/ON_OFF signal will turn Q2 on and short the ON pin of
the MIC2085/86 to ground which turns off the GATE
output charge pump.
Figure 6. PCB Connection Sense with ON/OFF Control
May 2006
18
M9999-050406
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