MIC2085 Datasheet, PDF (20/29 Pages) Micrel Semiconductor – Single Channel Hot Swap Controllers

Micrel, Inc.
Fast Output Discharge for Capacitive Loads
In many applications where a switch controller is turned
off by either removing the PCB from the backplane or
the ON pin is reset, capacitive loading will cause the
output to retain voltage unless a ‘bleed’ (low impedance)
path is in place in order to discharge the capacitance.
The MIC2086 is equipped with an internal MOSFET that
allows the discharging of any load capacitance to ground
through a 550Ω path. The discharge feature is
configured by wiring the DIS pin to the output (source) of
the external MOSFET and becomes active (DIS pin
MIC2085/2086
output is low) once the ON pin is deasserted. Figure 8(a)
illustrates the use of the discharge feature with an
optional resistor (R5) that can be used to provide added
resistance in the output discharge path. For an even
faster discharge response of capacitive loads, the
configuration of Figure 8(b) can be utilized to apply a
crowbar to ground through an external SCR (Q3) that is
triggered when the DIS pin goes low which turns on the
PNP transistor (Q2). See the different “Functional
Characteristic” curves for a comparison of the discharge
response configurations.
May 2006
Figure 8. MIC2086 Fast Discharge of Capacitive Load
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M9999-050406
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