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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

9.6 VNEG Charge Pump

The VNEG charge pump uses one external 1uF capacitor to generate a negative supply voltage out of the battery input voltage to supply all

audio related blocks. This allows a true-ground headphone output with no more need of external dc-decoupling capacitors.

9.6.1

Parameter

VBAT=1.5V, TA= 25ºC, unless otherwise specified.

9.7 OTP Memory & Internal Registers

The OTP memory consists of OTP register and the OTP fuses.The OTP register can be written as often as wanted but will lose the content on

power off. The OTP fuses are intended to store basic chip configurations as well as the microphone gain settings to optimize the ANC

performance and get rid of sensitivity variations of different microphones. Burning the fuses can only be done once and is a permanent change,

which means the fuses keep the content even if the chip is powered down. This AS3421/22 offers 4 register set for storing the microphone gain

making it possible to change the gain 3 times for re-calibration or other purposes.

When the chip is controlled by a microcontroller via I2C, the OTP memory don’t has to be used. The chip configuration can be stored in the flash

memory of the Bluetooth- or wireless chipset.

9.7.1

Figure 25 is showing the principal register interaction.

Figure 25. Register Access

Registers 0x8, 0x9, 0xA, 0xB, 0xC and 0x21 have only effect when the corresponding “REG_ON” bit is set, otherwise the chip operates with the

OTP Register settings which are loaded from the OTP fuses at every start-up.

All registers settings can be changed several times, but will loose the content on power off. When using the I2C mode, the chip configuration has

to be loaded from the micro controller after every start-up. In stand alone mode the OTP fuses have to be programmed for a permanent change

of the chip configuration.

A single OTP cell can be programmed only once. Per default, the cell is “0”; a programmed cell will contain a “1”. While it is not possible to reset

a programmed bit from “1” to “0”, multiple OTP writes are possible, but only additional unprogrammed “0”-bits can be programmed to “1”.

Independent of the OTP programming, it is possible to overwrite the OTP register temporarily with an OTP write command at any time. This

setting will be cleared and overwritten with the hard programmed OTP settings at each power-up sequence or by a LOAD operation.

Table 12. Headphone Output Parameter

Symbol

Parameter

Condition

Min

Typ

Max

Unit

VIN

Input voltage

VBAT

1.0

1.5

1.8

VOUT

Output voltage

VNEG

-0.7

-1.5

-1.8

CEXT

External flying capacitor

OTP Register

10h...16h; 30h...35h

OTP

Fuses

BURN

LOAD

0x8,0x9,0xA

0xB, 0xC, 0x21

OTP WRITE

OTP READ

normal I2C write

normal I2C read

8h...21h

OTP path is default

but can be switched

by register setting

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