12
V
CM
10 V
10%
t
r
90%
90%
10%
t
f
I
F
B
1
2
A
3
8
7
6
5
R
CC
(SEE NOTE 7)
+5 V
220
Ω
0.1 µF
R
L
V
O
0V
V
O
SWITCH AT A: I
F
= 0 mA
V
O
SWITCH AT B: I
F
= 0.5 mA
5V
V
FF
4
V
OL
+
V
CM
–
PULSE GEN.
Figure 8. Test Circuit for Transient Immunity and Typical Waveforms.
I
F
0
V
O
(SATURATED
RESPONSE)
t
PHL
1.5 V
1.5 V
V
OL
t
PLH
I
F
MONITOR
R
M
* C
L
IS APPROXIMATELY 15 pF, WHICH INCLUDES
PROBE AND STRAY WIRING CAPACITANCE.
4
5
5V
PULSE
GEN.
Z
O
= 50
Ω
t
r
= 5 ns
I
F
1
2
3
8
7
6
0.1 µF
* C
L
= 15 pF
R
L
V
O
+5 V
10% DUTY CYCLE
1/f < 100 µs
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
worst-case total output (I
ol
) and
power supply current (I
ccl
) of two
and a half milliamperes. Typically,
the HCPL-47XX can control a
total output and supply current of
15 mA. The output current, I
O
is
determined by the LED forward
current multiplied by the current
gain of the optocoupler,
I
O
= I
F
(CTR)/100%. In particular
with the HCPL-47XX opto-
couplers, the LED can be driven
with a very small I
F
of 40
µA
to
control a maximum I
O
of 320
µA
with a worst case design Current
Transfer Ratio (CTR) of 800%.
Typically, the CTR and the
corresponding I
ol
, are 4 times
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
output V
CC
and for the open-
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.
AGILENT [ AGILENT TECHNOLOGIES, LTD. ]
