ACSL datasheet(15/17 Pages) AVAGO

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the local temperature of the LED can rise, which in turn may

affect 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

buffer 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-

resolution analog-to-digital (A/D) systems where ground

loop currents due to the switching of the LEDs can cause

distortion in the A/D output.

Figure 18. TTL interface circuit for the ACSL-6xx0.

Application Information

ON and OFF Conditions

The ACSL-6xx0 series has the ON condition defined by

current, and the OFF condition defined 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 sufficient 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 effects 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,

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