10
The t
PSK
specied optocouplers oer the advantages of
guaranteed specications for propagation delays, pulse-
width distortion and propagation delay skew over the rec-
ommended temperature, and power supply ranges.
Powering Sequence
V
DD
needs to achieve a minimum level of 3.0V before
powering up the output connecting component.
Input Limiting Resistors
ACPL-071L and ACPL-074L are direct current driven (Fig-
ure 8), and thus eliminate the need for input power sup-
ply. To limit the amount of current owing through the
LED, it is recommended that a 210ohm resistor is connect-
ed in series with anode of LED (i.e. Pin 2 for ACPL-071L and
Pin 1 and 4 for ACPL-074L) at 5V input signal. At 3.3V input
signal, it is recommended to connect 80ohm resistor in se-
ries with anode of LED.
The recommended limiting resistors are based on the
assumption that the driver output impedence is 50Ω (as
shown in Figure 11).
Speed Improvement
A peaking capacitor can be placed across the input cur-
rent limit resistor (Figure 11) to achieve enhanced speed
performance. The value of the peaking cap is dependent
to the rise and fall time of the input signal and supply volt-
ages and LED input driving current (I
f
). Figure 12 shows
signicant improvement of propagation delay and pulse
with distortion with added peak capacitor at driving cur-
rent of 14mA and 3.3V or 5V power supply.
Figure 11 Connection of peaking capacitor (Cpeak) in parallel of the input
limiting resistor (Rllimit) to improve speed performance
Figure 12. Improvement of t
p
and PWD with added 100pF peaking capacitor in parallel of input limiting resistor.
T
A
- TEMPERATURE -
o
C
p
- PROPAGATION DELAY; PWD-PULSE WIDTH
DISTORTION -ns
T
A
- TEMPERATURE -
o
C
t
p
- PROPAGATION DELAY; PWD-PULSE WIDTH
DISTORTION -ns
0.00
5.00
10.00
15.00
20.00
25.00
30.00
35.00
-40 -20 0 20 40 60 80 100
t
PHL
t
PLH
PLH
t
PHL
With peaking cap
Without peaking cap
0.00
5.00
10.00
15.00
20.00
25.00
30.00
-40 -20 0 20 40 60 80 100
t
PHL
t
PLH
t
PLH
t
PHL
Without peaking cap
(i) V
DD
=3.3V, C
peak
=100pF, R
limit
=80Ω (ii) V
DD
=5V, C
peak
=100pF, R
limit
=210Ω
GND
2
V
DD2
0.1µF
GND
1
R
limit
SHIELD
V
in
+
-
C
peak
V
O
R
drv
=50Ω
