SI88240ED-IS Datasheet, PDF (19/48 Pages) Silicon Laboratories – QUAD DIGITAL ISOLATORS WITH DC-DC CONVERTER

Si88x4x
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
Preliminary Rev. 0.6
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