July 2005

11

MIC5013

MIC5013

Micrel, Inc.

Fault

V+

Gate

1

2

3

4

8

MIC5013

Gnd

7

6

5

Thresh

Sense

Source

Input

IRFP250

100µF

6.2kΩ

+

10mΩ

1N4003

90V

100kΩ

1kΩ

100kΩ

4N35

33kΩ

33pF

MPSA05

10mA

Control Input

M

15V

1N4003 (2)

15Vp-p, 20kHz

Squarewave

1N4746

100nF

200V

KC1000-4T

(Kelvin)

1/4 HP, 90V

5BPB56HAA100

(GE)

Since the supply current in the “OFF” state is only a small

leakage, the 100nF bypass capacitor tends to remain

charged for several seconds after the MIC5013 is turned

off. In a PWM application the chip supply is actually much

higher than the system supply, which improves switching

time.

Electronic Circuit Breaker (Figure 7).The MIC5013 forms

the basis of a high-performance, fast-acting circuit breaker.

By adding feedback from FAULT to INPUT the breaker can

be made to automatically reset. If an over-current condition

occurs, the circuit breaker shuts off. The breaker tests the

load every 18ms until the short is removed, at which time

the circuit latches ON. No reset button is necessary.

Opto-Isolated Interface (Figure 8).Although the MIC5013

has no special input slew rate requirement, the lethargic

transitions provided by an opto-isolator may cause oscil-

lations on the rise and fall of the output. The circuit shown

accelerates the input transitions from a 4N35 opto-isolator

by adding hysteresis. Opto-isolators are used where the

control circuitry cannot share a common ground with the

MIC5013 and high-current power supply, or where the

control circuitry is located remotely. This implementation is

intrinsically safe; if the control line is severed the MIC5013

will turn OFF.

Fault-Protected Industrial Switch (Figure 9). The most

common manual control for industrial loads is a push but-

ton on/off switch. The “on” button is physically arranged in

a recess so that in a panic situation the “off” button, which

extends out from the control box, is more easily pressed.

This circuit is compatible with control boxes such as the

CR2943 series (GE). The circuit is configured so that if

both switches close simultaneously, the “off” button has

precedence. If there is a fault condition the circuit will latch

off, and it can be reset by pushing the “ON” button.

This application also illustrates how two (or more) MOS-

FETs can be paralleled. This reduces the switch drop, and

distributes the switch dissipation into multiple packages.

High-VoltageBootstrap(Figure10).AlthoughtheMIC5013

is limited to operation on 7 to 32V supplies, a floating boot-

strap arrangement can be used to build a high-side switch

that operates on much higher voltages. The MIC5013 and

MOSFET are configured as a low-side driver, but the load is

connected in series with ground. The high speed normally

associated with low-side drivers is retained in this circuit.

Power for the MIC5013 is supplied by a charge pump. A

20kHz square wave (15Vp-p) drives the pump capacitor

and delivers current to a 100µF storage capacitor. A zener

diode limits the supply to 18V. When the MIC5013 is off,

power is supplied by a diode connected to a 15V supply.The

circuit of Figure 8 is put to good use as a barrier between

low voltage control circuitry and the 90V motor supply.

Half-Bridge Motor Driver (Figure 11). 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.

Crossconductionincreasesoutputdevicepowerdissipation

and, in the case of the MIC5013, could trip the over-current

comparator. Speed is also important, since PWM control

requires the outputs to switch in the 2 to 20kHz range.

The circuit of Figure 11 utilizes fast configurations for both

the top- and bottom-side drivers. Delay networks at each

input provide a 2 to 3µs dead time effectively eliminating

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

are protected, so the output can be shorted to either rail

without damage.

Figure 10. High-Voltage

Bootstrapped Driver