ADAU1977WBCPZ-R7 datasheet(17/68 Pages) AD

17 / 68 page

Data Sheet

ADAU1977

Rev. C | Page 17 of 68

DC-TO-DC BOOST CONVERTER

The boost converter generates a supply voltage for the

microphone bias circuit from a fixed 3.3 V supply. The boost

converter output voltage is programmable using Register 0x03.

The boost converter output voltage is approximately 1 V above

the set microphone bias voltage. The boost converter uses the

clock from the PLL, and the switching frequency is dependent

on the sample rate of the ADC. The FS_RATE bits (Bits[6:5] of

converter switching frequency can be selected to be 1.5 MHz or

3 MHz using Bit 4 of Register 0x02. For the 1.5 MHz switching

frequency, the recommended value for the inductor is 4.7 µH,

whereas for the 3 MHz switching frequency, the recommended

value for the inductor is 2.2 µH.

Table 11 lists the typical switching frequency based on the

sample rates.

Capacitor Selection

The boost converter output is available at the VBOOST_OUT pin

(Pin 25) and must be decoupled to PGND using a 10 µF ceramic

capacitor to remove the ripple at the switching frequency. The

capacitor must have low ESR and good temperature stability.

The MLCC X7R/NPO dielectric type with 25 V is recommended.

Care must be taken to place this capacitor as close as possible to

the VBOOST_OUT pin (Pin 25).

Table 11. Typical Switching Frequency Based on the Sample Rates

Boost Converter Switching Frequency

Base Sample Rate (kHz)

Sample Rates (kHz)

Inductor = 2.2 µH

Inductor = 4.7 µH

8/16/32/64

(1024/12) × fS

(1024/22) × fS

44.1

11.025/22.05/44.1/88.2/176.4

(1024/16) × fS

(1024/30) × fS

12/24/48/96/192

(1024/16) × fS

(1024/32) × fS

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