Datasheet

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SBOS207B − OCTOBER 2001 − REVISED JUNE 2004
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10
DAISY-CHAINING MULTIPLE
PGA2310 DEVICES
In order to reduce the number of control signals required
to support multiple PGA2310 devices on a printed circuit
board, the serial control port supports daisy-chaining of
multiple PGA2310 devices. Figure 4 shows the
connection requirements for daisy-chain operation. This
arrangement allows a three-wire serial interface to control
many PGA2310 devices.
As shown in Figure 4, the SDO pin from device #1 is
connected to the SDI input of device #2, and is repeated
for additional devices. This in turn forms a large shift
register, in which gain data may be written for all
PGA2310s connected to the serial bus. The length of the
shift register is 16 x N bits, where N is equal to the number
of PGA2310 devices included in the chain. The CS
input
must remain low for 16 x N SCLK periods, where N is the
number of devices connected in the chain, in order to allow
enough SCLK cycles to load all devices.
ZERO CROSSING DETECTION
The PGA2310 includes a zero crossing detection function
that can provide for noise-free level transitions. The
concept is to change gain settings on a zero crossing of the
input signal, thus minimizing audible glitches. This
function is enabled or disabled using the ZCEN input
(pin 1). When ZCEN is low, zero crossing detection is
disabled. When ZCEN is high, zero crossing detection will
be enabled.
The zero crossing detection takes effect with a change in
gain setting for a corresponding channel. The new gain
setting will not be latched until either two zero crossings
are detected, or a timeout period of 16ms has elapsed
without detecting two zero crossings. In the case of a
timeout, the new gain setting takes effect with no attempt
to minimize audible artifacts.
SDI
V
IN
L
V
IN
R
SDO
SCLK
CS
V
OUT
L
V
OUT
R
PGA2310
#1
SDI
V
IN
L
V
IN
R
SDO
SCLK
CS
V
OUT
L
V
OUT
R
PGA2310
#2
SDI
V
IN
L
V
IN
R
SDO
SCLK
CS
V
OUT
L
V
OUT
R
PGA2310
#3
Audio
Input
Audio
Input
Audio
Input
100k
Ω
100k
Ω
Controller
Figure 4. Daisy-Chaining Multiple PGA2310 Devices