MIC5021_05 Datasheet, PDF (9/10 Pages) Micrel Semiconductor – High-Speed High-Side MOSFET Driver

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
10µF
MIC5021
1
8
V _DD
V _BOOST
TTL Input
2
Input
7
Gate
10k to
100k
74HC04
(example)
3
2QN139044
C_T
Gnd
6
Sense-
5
Sense+
Retry (H)
Maintained (L)
N-Channel
Power
MOSFET
0.01
µF
R_{S E N S E}
Load
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 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.
10µF
TTL Input
Micrel, Inc.
+12V to +36V
MIC5021AJB
1
8
V _DD
V _BOOST
2
Input
7
Gate
3
C_T
4
Gnd
6
Sense-
5
Sense+
add resistor for
–40°C to –55°C
operation
2.7
nF
2.2M
R_SENSE
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
10µF
TTL Input
MIC5021AJB
1
8
V _DD
V _BOOST
2
Input
7
Gate
3
C_T
4
Gnd
6
Sense-
5
Sense+
2.7
nF
R_{S E N S E}
add resistor for
–40°C to –55°C
operation
2.2M
Load
Figure 12b. Gate-to-Ground Pull Down
The gate-to-ground configuration (refer to Figure 12b) is ap-
propriate for resistive, inductive, or capacitive loads. This
configuration will decrease the gate output voltage slightly
more than the circuit shown in Figure 12a.
July 2005
9
MIC5021