MIC5020_05 Datasheet, PDF (7/8 Pages) Micrel Semiconductor – Current-Sensing Low-Side MOSFET Driver

MIC5020
Faster MOSFET Switching
The MIC5020’s GATE current can be multiplied using a pair of
bipolar transistors to permit faster charging and discharging
of the external MOSFET’s gate.
+40V max.
+11V to +50V
10µF
150kHz max.
2N3904
MIC5020
1
8
V_DD
Gate
2
7
Input Sense-
3
6
Fault Sense+
2N3906
4
C_T
5
Gnd
N-Channel
Power MOSFET
(IRF540)
Figure 4. Faster MOSFET Switching Circuit
NPN and PNP transistors are used to respectively charge
and discharge the MOSFET gate. The MIC5020 gate current
is multiplied by the transistor β.
The switched circuit voltage can be increased above 40V by
selecting transistors with higher ratings.
Remote Overcurrent Limiting Reset
In circuit breaker applications where the MIC5020 maintains
an off condition after an overcurrent condition is sensed, the
C_T pin can be used to reset the MIC5020.
V+
Micrel, Inc.
For test 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 MIC5020AJB (extended tempera-
ture 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 MIC5020AJB includes low
temperatures (–40°C to –55°C), add an external 2.2MΩ resis-
tor as shown in Figures 6a or 6b. 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.
V+
+11V to +50V
10µF
MIC5020
1
8
V_DD
Gate
2
7
Input Sense-
3
6
Fault Sense+
4
C_T
5
Gnd
2.2M
R_SENSE
Figure 6a. Gate-to-Source Pull Down
The gate-to-source configuration (refer to Figure 6a) is ap-
propriate for resistive and inductive loads. This also causes
the smallest decrease in gate output voltage.
V+
+11V to +50V
10µF
TTL input
Retry (H)
Maintained (L)
10k to
100k
74HC04
(example)
MIC5020
1
8
V_DD
Gate
2
7
Input Sense-
3
6
Fault Sense+
4
Q1 ^CT
5
Gnd
2N3904
N-Channel
Power MOSFET
R_{S E N S E}
Figure 5. Remote Control Circuit
Switching Q1 on pulls C_T low which keeps the MIC5020 GATE
output off when an overcurrent is sensed. Switching Q1 off
causes C_T to appear open. The MIC5020 retries in about
20µs and continues to retry until the overcurrent condition
is removed.
+11V to +50V
10µF
MIC5020
1
V_DD
8
Gate
2
7
Input Sense-
3
6
Fault Sense+
4
C_T
5
Gnd
2.2M R_{S E N S E}
Figure 6b. Gate-to-Ground Pull Down
The gate-to-ground configuration (refer to Figure 6b) 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 6a.
July 2005
7
MIC5020