7

(EQ. 3)

(EQ. 4)

Since the CA3272A do not have on-chip diodes to clamp

voltage spikes which may be generated during inductive

switching of the load circuit, an external Zener diode (30V or

less is recommended) should be connected between the

output terminal and ground. Only those outputs used to

switch inductive loads require this protection. Note that since

the rate of change of output current is very high, even small

values of inductance can generate voltage spikes of consid-

erable amplitude on the output terminals which may require

clamping. External free-wheeling diodes returned to the sup-

ply voltage are generally not acceptable as inductive clamps

if the supply voltage exceeds 30V during transients. Typical

loads for either the CA3272A or CA3292A are shown in the

application circuit of Figure 4A. Where inductive loads are

driven from outputs A and B, no external Zener diode clamp

is needed for the CA3292A but is required for the CA3272A

as shown in Figure 4B.

The CA3272A and CA3292A are supplied in specially con-

figured power packages to conduct heat from the junction

through the mounting structure and device leads to the PC

Board. The ground leads are directly connected to the

mounting pad of the chip. The junction-to-air thermal resis-

tance,

design of the PC board to which the package is soldered.

Two or more square inches of PC Board ground area next to

the device ground pins is recommended. The PC Board

ground layer should be on the device side of the board with

open space for heat radiation.

Refer to Application Note AN9416 for additional thermal

information. Further information is provided on pulse energy

calculation methods for inductive load applications with

detail explaining the Safe Operating Area shown in Figure 5.

The SOA area for single energy transients is below the dot-

ted lines for the given ambient temperature conditions. The

energy locus plots of the three inductive coils were made for

arbitrarily chosen values of inductance and are shown here

for reference information. The RL time constant, ambient

temperature, clamp voltage and the stored energy in the coil

determine the SOA limits.

NOTE: The internal drive circuit with self protection and fault output

is the CA3292A with the over voltage Zener diode clamp.

FIGURE 4A. TYPICAL APPLICATION CIRCUIT SHOWING OUT-

PUT LOAD CONTROL CAPABILITY OF THE

CA3272A OR CA3292A

load switching.

FIGURE 4B. CA3272A OVER-VOLTAGE PROTECTION IS AN

EXTERNAL ZENER DIODE CLAMP WHERE

FAULT

OUT A

FAULT

OUT B

FAULT

OUT C

FAULT

OUT D

HIGH CURRENT

HIGH SIDE DR

LAMP

RELAY

SOLENOID

CA3292A

MOTOR

FAULT

OUT A

EXTERNAL ZENER DIODE CLAMP

PROTECTION FROM POSITIVE VOLTAGE

SPIKE (INDUCTIVE KICK PULSE) AT TURN-OFF

INDUCTIVE

LOAD

CA3272A

(1 OF 4 CHANNELS)

CA3272A, CA3292A