MC34151, MC33151

http://onsemi.com

7

LAYOUT CONSIDERATIONS

High frequency printed circuit layout techniques are

imperative to prevent excessive output ringing and overshoot.

Do not attempt to construct the driver circuit on

wire–wrap or plug–in prototype boards. When driving

large capacitive loads, the printed circuit board must contain

a low inductance ground plane to minimize the voltage spikes

induced by the high ground ripple currents. All high current

loops should be kept as short as possible using heavy copper

runs to provide a low impedance high frequency path. For

optimum drive performance, it is recommended that the

initial circuit design contains dual power supply bypass

capacitors connected with short leads as close to the VCC pin

and ground as the layout will permit. Suggested capacitors are

a low inductance 0.1

µF ceramic in parallel with a 4.7 µF

tantalum. Additional bypass capacitors may be required

depending upon Drive Output loading and circuit layout.

Proper printed circuit board layout is extremely

critical and cannot be over emphasized.

The MC34151 greatly enhances the drive capabilities of common switching

regulators and CMOS/TTL logic devices.

Figure 18. Enhanced System Performance with

Common Switching Regulators

Figure 19. MOSFET Parasitic Oscillations

Figure 20. Direct Transformer Drive

Figure 21. Isolated MOSFET Drive

Series gate resistor Rg may be needed to damp high frequency parasitic

oscillations caused by the MOSFET input capacitance and any series

wiring inductance in the gate–source circuit. Rg will decrease the

MOSFET switching speed. Schottky diode D1 can reduce the driver’s

power dissipation due to excessive ringing, by preventing the output pin

from being driven below ground.

Output Schottky diodes are recommended when driving inductive loads at

high frequencies. The diodes reduce the driver’s power dissipation by

preventing the output pins from being driven above VCC and below ground.

+

–

VCC

47

0.1

6

5.7V

TL494

or

TL594

2

4

3

7

5

Vin

+

+

++

+

+

1N5819

D1

Rg

Vin

+

+

3

7

5

4 X

1N5819

+

+

+

+

3

1N

5819

Isolation

Boundary