SI88X2X Datasheet, PDF (19/45 Pages) Silicon Laboratories – Isolation of up to 5000 Vrms

Si88x2x
2. Functional Description
2.1. Theory of Operation
The Si88xx family of products is capable of transmitting and receiving digital data signals from an isolated power
domain to a local system power domain with up to 5 kV of isolation. Each part has four unidirectional digital
isolation channels. In addition, Si88xx products include an integrated controller and switches for a dc-dc converter
which regulates output voltage by sensing it on the isolated side.
2.2. Digital Isolation
The operation of an Si88xx digital channel is analogous to that of a digital buffer, except an RF carrier transmits
data across the isolation barrier. This simple architecture provides a robust isolated data path and requires no
special considerations or initialization at start-up. A simplified block diagram for a single Si88xx channel is shown in
Figure 6.
Transmitter
RF
OSCILLATOR
Receiver
Semiconductor-
A
MODULATOR
Based Isolation
DEMODULATOR
B
Barrier
Figure 6. Simplified Si88xx Channel Diagram
A channel consists of an RF Transmitter and RF Receiver separated by a silicon dioxide capacitive isolation
barrier. In the transmitter, input A modulates the carrier provided by an RF oscillator using on/off keying. The
receiver contains a demodulator that decodes the input state according to its RF energy content and applies the
result to output B via the output driver. This RF on/off keying scheme is superior to pulse code schemes as it
provides best-in-class noise immunity, low power consumption, and better immunity to magnetic fields. See
Figure 7 for more details.
Input Signal
Modulation Signal
Output Signal
Figure 7. Modulation Scheme
Rev. 0.5
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