SI8220 Datasheet, PDF (13/31 Pages) Silicon Laboratories – 0.5 AND 2.5 AMP ISODRIVERS WITH OPTO INPUT (2.5, 3.75, AND 5.0 KVRMS)

Si8220/21
4. Functional Description
4.1. Theory of Operation
The Si8220/21 is a functional upgrade for popular opto-isolated drivers, such as the Avago HPCL-3120, HPCL-
0302, Toshiba TLP350, and others. The operation of an Si8220/21 channel is analogous to that of an opto coupler,
except an RF carrier is modulated instead of light. This simple architecture provides a robust isolated data path and
requires no special considerations or initialization at start-up. A simplified block diagram for the Si8220/21 is shown
in Figure 6.
Transmitter
RF
OSCILLATOR
Receiver
V_DD
Semiconductor-
A
LED
Emulator
MODULATOR
Based Isolation
Barrier
DEMODULATOR
B
0.5 to 2.5 A
peak
Gnd
Figure 6. Simplified Channel Diagram
A channel consists of an RF Transmitter and RF Receiver separated by a semiconductor-based isolation barrier.
Referring to 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. 1.5
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