MIC2584 Datasheet, PDF (19/28 Pages) Micrel Semiconductor – Dual-Channel Hot Swap Controller/Sequencer

MIC2584/2585
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 MIC2585 is equipped
with an internal MOSFET that allows the discharging of any
load capacitance to ground through a 50Ω to 170Ω path. The
discharge feature is configured by wiring the DIS pin to the
output (source) of the external MOSFET and is enabled if the
TRK pin is below 0.3V after the controller has been disabled
by a logic low signal received at the ON pin of Figure 1. See
the "Typical Application" circuit of Figure 1. A series resistor
is required from DIS to V_OUT so that the maximum current of
25mA for the DIS pin is not exceeded.
Micrel
Output Turn-Off Sequencing - No Tracking
There are many applications where it is necessary or desir-
able for the supply rails to sequence during turn-on and turn-
off, as is the case with some microprocessor requirements.
The MIC2585 can be configured to allow one output to shut
off first, followed by the other output. Figure 8 illustrates an
example circuit that sequences OUT1 and OUT2 in a first on–
last off application. During start-up, capacitor C_DLY allows for
V_OUT1 to turn on followed by V_OUT2 20ms later. Once the ON
pin receives a low signal by removing the PCB from the
backplane, or by an external processor signal, DIS1 and DIS2
will assert low. The external crowbar circuit connected from
the DIS2 pin will immediately bring V_OUT2 to ground while
V_OUT1 will discharge to ground through the 750Ω (680Ω
external, 70Ω internal) series path.
V_IN1
MIC2585
GATE1
EN
ON
OUT1
V_OUT1
V_IN2
ON
/FAULT
GATE2
PG
OUT2
MIC2585
V_IN3
V_OUT2
V_OUT1/V_OUT2
PG
/FAULT
GATE1
ON
OUT1
V_OUT3
V_IN4
V_OUT3/V_OUT4
GATE2
/FAULT
OUT2
V_OUT4
Short Circuit
on V_OUT1
System Timing
Figure 7. Supporting More Than Two Supplies
March 2005
19
MIC2584/2585