MIC2085 Datasheet, PDF (19/29 Pages) Micrel Semiconductor – Single Channel Hot Swap Controllers

Micrel, Inc.
Higher UVLO Setting
Once a PCB is inserted into a backplane (power supply),
the internal UVLO circuit of the MIC2085/86 holds the
GATE output charge pump off until V_CC exceeds 2.18V.
If VCC falls below 2V, the UVLO circuit pulls the GATE
output to ground and clears the overvoltage and/or
current limit faults. For a higher UVLO threshold, the
circuit in Figure 7 can be used to delay the output
MOSFET from switching on until the desired input
voltage is achieved. The circuit allows the charge pump
to remain off until VIN exceeds ⎜⎛1 + ^R1 ⎟⎞ × 1.24V . The
⎝ ^R2 ⎠
MIC2085/2086
GATE drive output will be shut down when V_IN falls
below ⎜⎛1 + ^R1 ⎟⎞ × 1.14V . In the example circuit (Figure
⎝ ^R2 ⎠
7), the rising UVLO threshold is set at approximately 11V
and the falling UVLO threshold is established as 10.1V.
The circuit consists of an external resistor divider at the
ON pin that keeps the GATE output charge pump off
until the voltage at the ON pin exceeds its threshold
(V_ON) and after the start-up time relapses.
Figure 7. Higher UVLO Setting
May 2006
19
M9999-050406
[phone]