MIC5021 Micrel Semiconductor, MIC5021 Datasheet - Page 6

• Manufacturer Part Number: MIC5021
• Description: High-Speed High-Side MOSFET Driver
• Manufacturer: Micrel Semiconductor

MIC5021
Logic-Level MOSFET Precautions
Logic-level MOSFETs have lower maximum gate-to-source
voltage ratings (typically
(typically 20V). When an external MOSFET is turned on, the
doubling effect of the boost capacitor can cause the gate-to-
source voltage to momentarily exceed 10V. Internal zener
diodes clamp this voltage to 16V maximum which is too high
for logic-level MOSFETs. To protect logic-level MOSFETs,
connect a zener diode (5V V
Overcurrent Limiting
A 50mV comparator is provided for current sensing. The low
level trip point minimizes I
used for current sensing.
The adjustable retry feature can be used to handle loads with
high initial currents, such as lamps or heating elements, and
can be adjusted from the C
C
overcurrent condition.
C
The default duty cycle (C
to the electrical characteristics when selecting a capacitor for
reduced duty cycle.
C
Increasing the duty cycle increases the power dissipation in
the load and MOSFET under a “fault” condition. Circuits may
become unstable at a duty cycle of about 75% or higher,
depending on conditions. Caution: The MIC5021 may be
damaged if the voltage applied to C
maximum voltage rating.
Boost Capacitor Selection
The boost capacitor value will vary depending on the supply
voltage range.
T
T
T
through a pull-up resistor to V
open, or a capacitor to ground, causes automatic retry.
to ground maintains gate drive shutdown following an
10µF
TTL Input
Figure 1. 12V to 20V Configuration
1
2
3
4
V
Input
C
Gnd
DD
T
T
MIC5021
2
open) is approximately 20%. Refer
R losses when a power resistor is
Sense
Sense
T
10V) than standard MOSFETs
V
Zener
BOOST
Gate
connection.
DD
<10V) from gate to source.
8
7
6
5
increases the duty cycle.
T
exceeds the absolute
+12V to +20V
0.01
µF
5-174
A 0.01 F boost capacitor is recommended for best perfor-
mance in the 12V to 20V range. Refer to figure 1. Larger
capacitors may damage the MIC5021.
If the full 12V to 36V voltage range is required, the boost
capacitor value must be reduced to 2.7nF. Refer to Figure 2.
The recommended configuration for the 20V to 36V range is
to place the capacitor is placed between V
shown in Figure 3.
Do not use both boost capacitor between V
MOSFET source and V
Current Sense Resistors
Lead length can be significant when using low value (< 1 )
resistors for current sensing. Errors caused by lead length
can be avoided by using four-teminal current sensing resis-
tors.
manufacturers.
Figure 3. Preferred 20V to 36V Configuration
Four-terminal resistors are available from several
10µF
10µF
TTL Input
TTL Input
Figure 2. 12V to 36V Configuration
1
2
3
4
1
2
3
4
V
Input
C
Gnd
V
Input
C
Gnd
DD
DD
T
T
BOOST
MIC5021
MIC5021
Sense
Sense
Sense
Sense
V
V
BOOST
BOOST
Gate
Gate
and V
8
7
6
5
8
7
6
5
DD
+12V to +36V
+12V to +36V
at the same time.
2.7
nF
0.1
µF
DD
and V
BOOST
October 1998
BOOST
and the
Micrel
as