Datasheet

13
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 Avago’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.
V
O
PULSE
GEN.
Z = 50 Ω
t = 5 ns
O
r
I MONITOR
F
I
F
0.1 µF
L
R
* C
L
= 15 pF
R
M
0
t
PHL
t
PLH
O
V
I
F
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)
* C
L
IS APPROXIMATELY 15 pF, WHICH INCLUDES
PROBE AND STRAY WIRING CAPACITANCE.
+5 V
Figure 8. Test Circuit for Transient Immunity and Typical Waveforms.
V
O
I
F
L
R
A
B
PULSE GEN.
V
CM
+
V
FF
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
t
r
t
f
5 V
+5 V
–
7
1
2
3
4
5
6
8
R
CC
(SEE NOTE 7)
10 V
0.1 µF
220 Ω