12

Figure 9. Switching Test Circuit.

Applications Information

Low-Power Operation

Current Gain

There are many applications

where low-power isolation is

needed and can be provided by

the single-channel HCPL-4701, or

the dual-channel HCPL-4731 low-

power optocouplers. Either or

both of these two devices are

referred to in this text as HCPL-

47XX product(s). These opto-

couplers are Agilent’s lowest

input current, low-power

optocouplers. Low-power

isolation can be defined as less

than a milliwatt of input power

needed to operate the LED of an

optocoupler (generally less than

500

µA). This level of input

forward current conducting

through the LED can control a

and a half milliamperes. Typically,

the HCPL-47XX can control a

total output and supply current of

determined by the LED forward

current multiplied by the current

gain of the optocoupler,

with the HCPL-47XX opto-

couplers, the LED can be driven

with a worst case design Current

Transfer Ratio (CTR) of 800%.

Typically, the CTR and the

larger. For low-power operation,

Table 1 lists the typical power

dissipations that occur for both

the 3.3 Vdc and 5 Vdc

HCPL-47XX optocoupler applica-

tions. These approximate power

dissipation values are listed

respectively for the LED, for the

collector output transistor. Those

values are summed together for a

comparison of total power dissi-

pation consumed in either the 3.3

Vdc or 5 Vdc applications.

VO

PULSE

GEN.

Z

= 50

Ω

t = 5 ns

O

r

I

MONITOR

F

IF

0.1 µF

L

R

* CL = 15 pF

RM

0

tPHL

tPLH

O

V

IF

OL

V

1.5 V

1.5 V

5 V

7

1

2

3

4

5

6

8

10% DUTY CYCLE

1/f < 100 µs

(SATURATED

RESPONSE)

* CL IS APPROXIMATELY 15 pF, WHICH INCLUDES

PROBE AND STRAY WIRING CAPACITANCE.

+5 V

Figure 8. Test Circuit for Transient Immunity and Typical Waveforms.

VO

IF

L

R

A

B

PULSE GEN.

VCM

+

VFF

O

V

OL

V

O

V

0 V

10%

90%

90%

10%

SWITCH AT A: I = 0 mA

F

SWITCH AT B: I = 0.5 mA

F

CM

V

tr

tf

5 V

+5 V

–

7

1

2

3

4

5

6

8

RCC (SEE NOTE 7)

10 V

0.1 µF

220

Ω