
MIC5021
Remote Overcurrent Limiting Reset
Micrel, Inc.
+12V to +36V
C T pin can be used to reset the MIC5021.
IncircuitbreakerapplicationswheretheMIC5021maintains
an off condition after an overcurrent condition is sensed, the
+12V to +20V
10μF
TTL Input
1
2
MIC5021AJB
V DD V BOOST
Input Gate
8
7
2N3904
10μF
TTL Input
10k to
100k
74HC04
(example)
1
2
3
Q1 4
MIC5021
V DD V BOOST
Input Gate
C T Sense-
Gnd Sense+
8
7
6
5
0.01
μF
N-Channel
Power
MO S F E T
R S E N S E
3
4
6
C T Sense-
5
Gnd Sense+
add resistor for
–40 ° C to –55 ° C
operation
2.7
nF
2.2M
R S E NS E
Load
Retry (H)
Maintained (L)
Figure 11. Remote Control Circuit
Load
Figure 12a. Gate-to-Source Pull Down
The gate-to-source con?guration (refer to Figure 12a) is
appropriate for resistive and inductive loads. This also causes
the smallest decrease in gate output voltage.
+12V to +36V
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.
10μF
TTL Input
1
2
3
4
MIC5021AJB
V DD V BOOST
Input Gate
C T Sense-
Gnd Sense+
8
7
6
5
2.7
nF
R S E N S E
Low-Temperature Operation
As the temperature of the MIC5021AJB (extended temperature
range version—no longer available) approaches –55°C, the
driver ’s off-state, gate-output offset from ground increases.
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.
add resistor for
°
–40 ° C to –55 C 2.2M Load
operation
Figure 12b. Gate-to-Ground Pull Down
The gate-to-ground con?guration (refer to Figure 12b) is ap-
propriate for resistive, inductive, or capacitive loads. This
con?guration will decrease the gate output voltage slightly
more than the circuit shown in Figure 12a.
July 2005
9
MIC5021