S i 8 4 x x I S O - E V B U G
6
Rev. 0.3
3.1. Digital Isolator Considerations
The Si84xxISO evaluation board (see Figure 1 on page 2) provides a means to evaluate the Si841x,2x,3x,4x,5x,6x
digital isolator families as well as the Si8400 isolated I
2
C family. After power has been supplied to the board,
connect a digital input signal (5 Vpeak max, with desired clock frequency up to 150 Mbps) to the desired input
channel. To view the isolated channel’s data transmission, connect a scope probe to the output channel of interest.
There are various inputs and outputs on either side of the board depending on the device one chooses to evaluate,
as indicated by the silk screen. The board can be used to measure propagation delay, pulse-width distortion,
channel-channel matching, pulse-width skew, and various other parameters.
The nominal output impedance of an isolator driver channel is approximately 50
, ±40%, which is a combination
of the values of the on-chip series termination resistor and the channel resistance of the output driver FET. When
driving loads where transmission line effects will be a factor, output pins should be terminated with 50
controlled
impedance PCB traces.
Figure 5 illustrates the Si8421 transmitting a 500 kHz (5 Vpeak) signal through the Si8421. VDD1 and VDD2 were
powered from 5 V. Channel 1 illustrates the input, and Channel 2 illustrates the output.
Figure 5. 500 kHz (5 V Peak) Signal
