AN681

Rev. 0.3

3

3. Device Application

3.1. Si87xx Device Transfer Characteristics

The Si87xx is offered in three different grades, allowing the user to optimize input forward current versus CMTI.

The Si87xx “A” grade and “C” grade have an optimum input diode current of 3 mA resulting in a minimum CMTI of

20 kV/µs(min), (35 kV/µs typical), while the “B” grade has an optimum input diode current of 6 mA resulting in a

minimum CMTI of 35 kV/µs(min), (50 kV/µs typical).

Referring to the “A” grade and “C” grade devices in Figure 3A, an open-collector output low event begins when the

input current crosses the 1.2 mA current threshold, and input current must continue rising to 3.0 mA for the Si87xx

to achieve rated CMTI performance. An open-collector output high event begins when the input current falls below

the 1.1 mA threshold and must continue falling to zero for the Si87xx to achieve rated CMTI performance. The “B”

grade device (Figure 3B) exhibits similar operation, with the exceptions of a low-going current threshold of 2.3 mA

rising to 6 mA and a high-going input current turn-off threshold of 2.0 mA falling to zero.

Note: All device grades must have a voltage drop of 1.7 to 2.8 V across the input during those periods where the open-collec-

tor output voltage is low. In addition, all device grades must operate at the optimum ON current to achieve rated perfor-

mance.

Figure 3. Device Transfer Characteristics

AB

Minimum Current Required for Turn‐On

(A and C Grade) 

Output High

Output Low

Minimum Current Required for Turn‐On 

(B Grade)

Output High

Output Low