Datasheet
16
Application Information
ON and OFF Conditions
The ACSL-6xx0 series has the ON condition dened by
current, and the OFF condition dened by voltage. In order
to guarantee that the optocoupler is OFF, the forward
voltage across the LED must be less than or equal to
0.8 volt for the entire operating temperature range. This
has direct implications for the input drive circuit. If the
design uses a TTL gate to drive the input LED, then one has
to ensure that the gate output voltage is sucient to cause
the forward voltage to be less than 0.8 volt. The typical
threshold current for the ACSL-6xx0 series optocouplers is
2.7 mA; however, this threshold could increase over time
due to the aging eects of the LED. Drive circuit arrange-
ments must provide for the ON state LED forward current
of at least 7 mA, or more if faster operation is desired.
Maximum Input Current and Reverse Voltage
The average forward input current should not exceed
the 15 mA Absolute Maximum Rating as stated; however,
peaking circuits with transient input currents up to 50 mA
are allowed provided the average current does not exceed
15 mA. If the input current maximum rating is exceeded,
the local temperature of the LED can rise, which in turn may
aect the long-term reliability of the device. When designing
the input circuit, one must also ensure that the input reverse
voltage does not exceed 5V. If the optocoupler is subjected
to reverse voltage transients or accidental situations that
may cause a reverse voltage to be applied, thus an anti-
parallel diode across the LED is recommended.
Suggested Input Circuits for
Driving the LED
Figures 18, 19, and 20 show some of the several techniques
for driving the ACSL-6xx0 LED. Figure 18 shows the rec-
ommended circuit when using any type of TTL gate. The
buer PNP transistor allows the circuit to be used with
TTL or CMOS gates that have low sinking current capabil-
ity. One advantage of this circuit is that there is very little
variation in power supply current due to the switching of
the optocoupler LED. This can be important in high-reso-
lution analog-to-digital (A/D) systems where ground loop
currents due to the switching of the LEDs can cause distor-
tion in the A/D output.
Figure 18. TTL interface circuit for the ACSL-6xx0.