6 − 117

CMR with Other Drive

Circuits

CMR performance with drive

circuits other than that shown in

Figure 13 may be enhanced by

following these guidelines:

1. Use of drive circuits where

current is shunted from the

LED in the LED off” state (as

shown in Figures 15 and 16).

This is beneficial for good

Figure 15 shows a circuit which

can be used with any totem-pole-

output TTL/LSTTL/HCMOS logic

gate. The buffer PNP transistor

allows the circuit to be used with

logic devices which have low

current-sinking capability. It also

helps maintain the driving-gate

power-supply current at a

constant level to minimize ground

shifting for other devices

connected to the input-supply

ground.

When using an open-collector

TTL or open-drain CMOS logic

gate, the circuit in Figure 16 may

be used. When using a CMOS

gate to drive the optocoupler, the

circuit shown in Figure 17 may

be used. The diode in parallel

of the optocoupler LED.

Figure 15. TTL interface circuit.

Figure 16. TTL open-collector/open drain gate drive circuit.

Figure 17. CMOS gate drive circuit.

420

Ω

(MAX)

1

3

2

4

2N3906

(ANY PNP)

VCC

74L504

(ANY

TTL/CMOS

GATE)

HCPL-260L

LED

R

1

3

2

4

VCC

74HC00

(OR ANY

OPEN-COLLECTOR/

OPEN-DRAIN

LOGIC GATE)

HCPL-260L

LED

220

Ω

1

3

2

4

VCC

74HC04

(OR ANY

TOTEM-POLE

OUTPUT LOGIC

GATE)

HCPL-260L

1N4148

LED

www.semiconductor.agilent.com

Data subject to change.

Copyright © 2000 Agilent Technologies

5980-2523EN (11/00)

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