PGA2320

SBOS312B − JULY 2004 − REVISED DECEMBER 2004

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10

DAISY-CHAINING MULTIPLE

PGA2320 DEVICES

In order to reduce the number of control signals required

to support multiple PGA2320 devices on a printed circuit

board, the serial control port supports daisy-chaining of

multiple

PGA2320

devices.

Figure

4

shows

the

connection requirements for daisy-chain operation. This

arrangement allows a three-wire serial interface to control

many PGA2320 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 configuration in turn forms a

large shift register, in which gain data may be written for all

PGA2320s connected to the serial bus. The length of the

shift register is 16 x N bits, where N is equal to the number

of PGA2320 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 PGA2320 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

V

SDO

SCLK

CS

V

V

SDI

V

V

SDO

SCLK

CS

V

V

SDI

V

V

SDO

SCLK

CS

V

V

Audio

Input

Audio

Input

Audio

Input

100k

Ω

100k

Ω

Controller

PGA2320

#1

PGA2320

#2

PGA2320

#3

Figure 4. Daisy-Chaining Multiple PGA2320 Devices