Datasheet MIC5021 (Microchip) - 10

MIC5021
5.0 FUNCTIONAL DESCRIPTION Refer to the MIC5021 Functional Block Diagram. 5.1 Input A signal greater than 1.4V (nominal) applied to the
MIC5021 INPUT causes gate enhancement on an
external MOSFET turning the MOSFET on.
An internal pull-down resistor ensures that an open
input remains low, keeping the external MOSFET
turned off. 5.2 When the gate output turns the MOSFET off, the overcurrent signal is removed from the sense inputs which
deactivates current sink 2I1.This allows CINT and the
optional capacitor connected to CT to recharge. A
Schmitt trigger delays the retry while the capacitor(s)
recharge. Retry delay is increased by connecting a
capacitor to CT (optional).
The retry cycle will continue until the fault is removed or
the input is changed to TTL low.
If CT is connected to ground, the circuit will not retry
upon a fault condition. Gate Output Rapid rise and fall times on the gate output are possible
because each input state change triggers a one-shot
which activates a high-value current sink (10I2) for a
short time. This draws a high current though a current
mirror circuit causing the output transistors to quickly
charge or discharge the external MOSFET’s gate.
A second current sink continuously draws the lower
value of current used to maintain the gate voltage for
the selected state.
An internal charge pump utilizes an external “boost”
capacitor connected between VBOOST and the source
of the external MOSFET (Refer to the Typical Application Circuit). The boost capacitor stores charge when
the MOSFET is off. As the MOSFET turns on, its
source to ground voltage increases and is added to the
voltage across the capacitor, raising the VBOOST pin
voltage. The boost capacitor charge is directed through
the gate pin to quickly charge the MOSFET’s gate to
16V maximum above VDD. The internal charge pump
maintains the gate voltage.
An internal Zener diode protects the external MOSFET
by limiting the gate to source voltage. 5.3 SENSE Inputs The MIC5021’s 50 mV (nominal) trip voltage is created
by internal current sources that force approximately
5 μA out of SENSE+ and approximately 15 μA (at trip)
out of SENSE–. When SENSE– is 50mV or more below
SENSE+, SENSE– steals base current from an internal
drive transistor shutting off the external MOSFET. 5.4 Overcurrent Limiting Current source I1 charges CINT upon power up. An
optional external capacitor connected to CT is kept discharged through a MOSFET Q1.
A fault condition (>50 mV from SENSE+ to SENSE–)
causes the overcurrent comparator to enable current
sink 2I1 which overcomes current source I1 to discharge CINT in a short time. When CINT is discharged,
the input is disabled, which turns off the gate output,
and CINT and CT are ready to be charged. DS20005677A-page 10  2016 Microchip Technology Inc.