PGA4311

SBOS230A – MARCH 2002 – REVISED JUNE 2002

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DAISY-CHAINING MULTIPLE PGA4311 DEVICES

In order to reduce the number of control signals re-

quired to support multiple PGA4311 devices on a

printed circuit board, the serial control port supports

daisy-chaining of multiple PGA4311 devices. Figure 4

shows the connection requirements for daisy-chain

operation. This arrangement allows a 3-wire serial in-

terface to control many PGA4311 devices.

As shown in Figure 4, the SDO pin from device #1 is con-

nected to the SDI input of device #2, and is repeated for

additional devices. This in turn forms a large shift regis-

ter, in which gain data may be written for all PGA4311s

connected to the serial bus. The length of the shift regis-

ter is 32

• N bits, where N is equal to the number of

PGA4311 devices included in the chain. The CS input

must remain LOW for 32

• 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 PGA4311 includes a zero crossing detection func-

tion that can provide for noise-free level transitions.

The concept is to change gain settings on a zero cross-

ing of the input signal, thus minimizing audible glitches.

This function is enabled or disabled using the ZCEN in-

put. When ZCEN is LOW, zero crossing detection is

disabled. When ZCEN is HIGH, zero crossing detec-

tion 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 implemented until either positive

slope zero crossing is detected or a time-out period of

16ms has elapsed. In the case of a time-out, the new

gain setting takes effect with no attempt to minimize

audible artifacts.

Figure 4. Daisy-Chaining Multiple PGA4311 Devices.