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AS3421 AS3422

Datasheet - D e t a i l e d D e s c r i p t i o n

9.5.4

ANC_CSDA Switching

For Bluetooth applications it is sometimes a requirement to switch off the ANC function while listening to music or having a phone call. Because

the fully differential audio outputs of the Bluetooth chip are directly connected to the line input of the AS3421/22 it is not possible to simply switch

off the ANC chip to do music playback without ANC.In order to avoid an expensive bypass path with mechanical or electrical switches the

AS3421/22 features a special low power audio playback mode. In this mode the device enters a low power mode where the ANC function is

disabled and the blocks which are not necessary in this mode are automatically switched off to safe system power. This audio playback mode

can be entered by simply pulling the ANC_SCDA pin to low.

Figure 24. ANC / CSDA Switching

device should enter the low power playback mode the pin is pulled low with the switch S1. Once the pin is pulled low the device enters after

200ms the playback mode. As long as the pin is low the device stays in the playback only mode. If the feature is for some reason not required it

can also be disabled by setting the bit NO_PB_MODE_OTP in register 0x33. Once this bit is set to ‘1’ the status of pin ANC_CSDA has no

influence on the device any more.

Besides the low power playback mode the ANC_CSDA pin supports also volume control via push buttons. In order to enable this feature the

corresponding bit VOL_BUTTON_MODE_OTP is register 0x33 has to be set to ‘1’. Once this bit is set, the device can not support the low power

push buttons S2 and S3.

Table 11. ANC_CSDA Operation Modes

NO_PB_MODE_OTP

Bit

VOL_BUTTON_MODE_OTP

Bit

ANC_CSDA

Pin

Description

0

0

high

Normal ANC operation

0

0

high -> low

Device enters low power playback mode

0

0

low -> high

Device returns to normal ANC operation

1

0

X

Normal ANC operation. No influence on operation via

ANC_CSDA pin.

X

1

high

Volume Control Mode via Button - Volume up

X

1

High Imp.

Volume Control Mode via Button - No Volume change

X

1

low

Volume Control Mode via Button - Volume down