April 1998

5-99

MIC5010

Micrel

5

cross conduction. Both the top- and bottom-side drivers are

protected, so the output can be shorted to either rail without

damage.

The top-side driver is based on the bootstrapped circuit of

Figure 6, and cannot be switched on indefinitely. The

bootstrap capacitor (1

µF) relies on being pulled to ground

by the bottom-side output to recharge. This limits the

maximum duty cycle to slightly less than 100%.

Two of these circuits can be connected together to form an

H-bridge. If the H-bridge is used for locked antiphase

control, no special considerations are necessary. In the

case of sign/magnitude control, the “sign” leg of the H-

bridge should be held low (PWM input held low) while the

other leg is driven by the magnitude signal.

If current feedback is required for torque control, it is

available in chopped form at the bottom-side driver's 22m

Ω

current-sensing resistor.

Time-Delay Relay (Figure 12). The MIC5010 forms the

basis of a simple time-delay relay. As shown, the delay

commences when power is applied, but the 100k

Ω/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. Note that an over-current condition latches the

relay in a safe, OFF condition. Operation is restored by

either cycling power or by momentarily shorting pin 3 to

ground.

Motor Driver with Stall Shutdown (Figure 13). Tachom-

eter feedback can be used to shut down a motor driver

circuit when a stall condition occurs. The control switch is a

3-way type; the “START” position is momentary and forces

the driver ON. When released, the switch returns to the

“RUN” position, and the tachometer's output is used to hold

the MIC5010 input ON. If the motor slows down, the tach

output is reduced, and the MIC5010 switches OFF. Resis-

tor “R” sets the shutdown threshold. If the output current

exceeds 30A, the MIC5010 shuts down and remains in that

condition until the momentary “RESET” button is pushed.

Control is then returned to the START/RUN/STOP switch.

Inhibit

Input

Thresh

Sense

Source

Gnd

Fault

V+

C1

Com

C2

Gate

1

2

3

4

5

6

78

9

10

11

12

13

14

MIC5010

IRFP250

100µF

6.2k

Ω

Figure 10. High-Voltage

Bootstrapped Driver

+

NC

NC

10m

Ω

1N4003

90V

100k

Ω

1k

Ω

100k

Ω

4N35

33k

Ω

33pF

MPSA05

10mA

Control Input

M

1nF

15V

1N4003 (2)

15Vp-p, 20kHz

Squarewave

1N4746

100nF

200V

KC1000-4T

(Kelvin)

1/4 HP, 90V

5BPB56HAA100

(GE)