MIC5012 Datasheet, PDF (8/9 Pages) Micrel Semiconductor – Dual High- or Low-Side MOSFET Driver Not Recommended for New Designs

MIC5012
Micrel
Applications Information (Continued)
12V
can be paralleled. This reduces the switch drop, and distrib-
utes the switch dissipation into multiple packages.
Half-Bridge Motor Driver (Figure 6). Closed loop control of
motor speed requires a half-bridge driver. This topology
presents an extra challenge since the two output devices
should not cross conduct (shoot-through) when switching.
Cross conduction increases output device power dissipa-
tion. Speed is also important, since PWM control requires
the outputs to switch in the 2 to 20kHz range.
100kΩ
1N4148
+
47µF
10kΩ
+
1/2 MIC5012 ^10µF
V+
Input
Source
Gnd Gate
IRFZ44
The circuit of Figure 6 utilizes fast configurations for both the
100Ω
top- and bottom-side drivers. Delay networks at each input
provide a 2 to 3µs dead time effectively eliminating cross
conduction. Two of these circuits can be connected to-
gether to form an H-bridge for locked antiphase or sign/
magnitude control.
OUTPUT
(Delay=2s)
Figure 7. 30 Ampere
Time-Delay Relay
Time-Delay Relay (Figure 7). The MIC5012 forms the
basis of a simple time-delay relay. As shown, the delay
commences when power is applied, but the 100kΩ/1N4148
could be independently driven from an external source such
as a switch or another high-side driver to give a delay
relative to some other event in the system. Hysteresis has
been added to guarantee clean switching at turn-on.
Electronic Governor (Figure 9). The output of an ac
tachometer can be used to form a PWM loop to maintain the
speed of a motor. The tachometer output is rectified,
partially filtered, and fed back to the input of the MIC5012.
When the motor is stalled there is no tachometer output,
and MIC5012 input is pulled high delivering full power to the
motor. If the motor spins fast enough, the tachometer output
Motor Driver with Stall Shutdown (Figure 8). Tachometer _{is sufficient to pull the MIC5012 input low, shutting the}
feedback can be used to shut down a motor driver circuit _{output off. Since the rectified waveform is only partially}
when a stall condition occurs. The control switch is a 3-way _{filtered, the input oscillates around its threshold causing the}
type; the “START” position is momentary and forces the _{MIC5012 to switch on and off at the frequency of the}
5
driver ON. When released, the switch returns to the “RUN” _{tachometer signal. A PWM action results since the average}
position, and the tachometer's output is used to hold the _{dc voltage at the input decreases as the motor spins faster.}
MIC5012 input ON. If the motor slows down, the tach output _{The 1kΩ potentiometer is used to set the running speed of}
is reduced, and the MIC5012 switches OFF. Resistor “R” _{the motor. Loop gain (and speed regulation) is increased by}
sets the shutdown threshold.
increasing the value of the 100nF filter capacitor.
The performance of such a loop is imprecise, but stable and
inexpensive. A more elaborate loop would consist of a PWM
12V
controller and a half-bridge.
R
330kΩ 330kΩ
1/2 MIC5012 ^10µF
V+
Input
Source
Gnd Gate
+
IRFZ44
1N4148
100nF
T
M
12V
START
RUN
STOP
Figure 8. Motor Stall
Shutdown
15V
330kΩ
330kΩ
1/2 MIC5012 ^10µF
V+
Input
Source
Gnd Gate
+
IRF541
1N4148
100nF
15V
T
M
1kΩ
Figure 9. Electronic Governor
April 1998
5-121