Datasheet
8k
A
C
DIN
R
IN
to SWIF
decoder
DAC161P997
Tx
Handshake pulse
(Acknowledge)
DIN
DBACK
A
B
DAC161P997
ACKB
COMD
N.C.
PRIMARY SIDE SECONDARY SIDE
C
S
(Tx)
FET ON
DAC161P997
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SNAS515E –JULY 2011–REVISED OCTOBER 2013
Transformer Coupled Interface - Acknowledge Pulse
Since the transformer is a symmetrical device (particularly one with 1:1 winding ratio), it is simple to reverse the
data flow through it.
Figure 23 shows the SWIF interface circuit during the transmission of the Acknowledge pulse from the
DAC161P997 on the secondary side back to the micro-controller on the primary side.
On the secondary side buffer B drives the square waveform across the transformer. Capacitor CS, whose bottom
plate is now grounded via the ACKB pin, blocks the DC component of the square waveform. Buffer A is inactive.
On the primary side a square waveform recovery is performed by the now familiar latch.
Figure 23. Transformer coupled SWIF link with the DAC161P997 as transmitter
DC-Coupled Interface
DC coupled signal path between the transmitter and the receiver is shown in Figure 24. Such circuit as the
internal buffer A is sufficient for the signal recovery as the signal presented at the DIN input is a square CMOS
level waveform.
In noisy environments it may be necessary to implement a Hysteresis loop around the DIN input to improve noise
immunity of the input circuit. Presence of the buffer C and its output resistor facilitate this. The Hysteresis can be
easily realized by inserting R
IN
between the transmitter and DIN input.
Note that when R
IN
= 0 the presence of the buffer C can be ignored.
Figure 24. DC-Coupled SWIF Input
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