Datasheet

DIN
DBACK
PRIMARY SIDE
A
B
DAC161P997
V
O
to SWIF
decoder
ACKB
SECONDARY SIDE
C
S
C
P
+
-
V
P
V
P
Tx
FET OFF
COMD
8k
A
B
C
DIN
DBACK
to SWIF
decoder
DAC161P997
ACKB
COMD
DAC161P997
SNAS515E –JULY 2011–REVISED OCTOBER 2013 www.ti.com
Figure 21. SWIF Front End
Transformer Coupled Interface - Data Flow to the DAC
In systems requiring galvanic isolation between the transmitter (micro-controller) and the receiver, the commonly
used coupling element is a pulse transformer. Transformer passes only the AC components of the square input
waveform resulting in an impulse train across the secondary winding. Buffers A and B form a latch circuit around
the secondary winding that recovers the square waveform from the impulse train.
Figure 22 shows the details of the square waveform transmission from the primary side and recovery of the
signal on the secondary side. Transmitter’s DC component is blocked by the capacitor CP. The transmitter’s
output waveform VO results in the impulse train VP across the primary winding. Similar impulse train then
appears across the secondary winding. If the magnitude of the impulse exceeds the threshold on the A buffer,
the latch formed by A and B buffers will change state. The new latch state will persist until an opposite polarity
impulse appears across the secondary winding.
Note that in Figure 22 the capacitor CS bottom plate floats, and thus does not affect the operation of this circuit.
Figure 22. Transformer coupled SWIF link with the DAC161P997 as Receiver
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