MIC5021
Remote Overcurrent Limiting Reset
In circuit breaker applications where the MIC5021 maintains
an off condition after an overcurrent condition is sensed, the
C
T
pin can be used to reset the MIC5021.
+12V to +20V
MIC5021AJB
10µF
TTL Input
1
2
3
MIC5021
10µF
TTL Input
10k to
100k
74HC04
(example)
Retry (H)
Maintained (L)
Micrel
+12V to +36V
V
DD
Input
C
T
Gnd
V
BOOST
Gate
Sense
Sense
8
7
6
5
2.7
nF
2.2M
R
SENSE
4
8
7
6
5
0.01
µF
R
SENSE
N-Channel
Power
MOSFET
1
2
3
V
DD
Input
V
BOOST
Gate
Sense
Sense
C
T
2N3904
4
Q1
Gnd
Load
Figure 12a. Gate-to-Source Pull Down
The gate-to-source configuration (refer to Figure 12a) is
appropriate for resistive and inductive loads. This also
causes the smallest decrease in gate output voltage.
+12V to +36V
Figure 11. Remote Control Circuit
Switching Q1 on pulls C
T
low which keeps the MIC5021
GATE
output off when an overcurrent is sensed. Switching Q1 off
causes C
T
to appear open. The MIC5021 retries in about
20µs and continues to retry until the overcurrent condition is
removed.
For demonstration purposes, a 680Ω load resistor and 3Ω
sense resistor will produce an overcurrent condition when the
load’s supply (V+) is approximately 12V or greater.
Low-Temperature Operation
As the temperature of the MIC5021AJB (extended tempera-
ture range version—no longer available) approaches –55°C,
the driver’s off-state, gate-output offset from ground in-
creases. If the operating environment of the MIC5021AJB
includes low temperatures (–40°C to –55°C), add an external
2.2MΩ resistor as shown in Figures 12a or 12b. This assures
that the driver’s gate-to-source voltage is far below the
external MOSFET’s gate threshold voltage, forcing the
MOSFET fully off.
MIC5021AJB
10µF
TTL Input
1
2
3
4
V
DD
Input
C
T
Gnd
V
BOOST
Gate
Sense
Sense
8
7
6
5
2.7
nF
R
SENSE
Load
add resistor for
–40
°
C to –55
°
C
operation
5
add resistor for
–40
°
C to –55
°
C
operation
2.2M
Figure 12b. Gate-to-Ground Pull Down
The gate-to-ground configuration (refer to Figure 12b) is
appropriate for resistive, inductive, or capacitive loads. This
configuration will decrease the gate output voltage slightly
more than the circuit shown in Figure 12a.
October 1998
5-177
Load
MICREL [ MICREL SEMICONDUCTOR ]
