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Data Sheet ADAU1701

Rev. C | Page 19 of 52

VOLTAGE REGULATOR

The digital voltage of the ADAU1701 must be set to 1.8 V. The

chip includes an on-board voltage regulator that allows the

device to be used in systems without an available 1.8 V supply

but with an available 3.3 V supply. The only external components

needed in such instances are a PNP transistor, a resistor, and a

few bypass capacitors. Only one pin, VDRIVE, is necessary to

support the regulator.

The recommended design for the voltage regulator is shown

in Figure 16. The 10 µF and 100 nF capacitors shown in this

configuration are recommended for bypassing, but are not

necessary for operation. Each DVDD pin should have its own

100 nF bypass capacitor, but only one bulk capacitor (10 µF to

47 µF) is needed for both DVDD pins. With this configuration,

3.3 V is the main system voltage; 1.8 V is generated at the

transistor’s collector, which is connected to the DVDD pins.

VDRIVE is connected to the base of the PNP transistor. If the

regulator is not used in the design, VDRIVE can be tied to ground.

Two specifications must be considered when choosing a regulator

transistor: The transistor’s current amplification factor (h

beta) should be at least 100, and the transistor’s collector must

be able to dissipate the heat generated when regulating from

3.3 V to 1.8 V. The maximum digital current drawn from the

ADAU1701 is 60 mA. The equation to determine the minimum

power dissipation of the transistor is as follows:

(3.3 V − 1.8 V) × 60 mA = 90 mW

There are many transistors, such as the FZT953 from Zetex

Semiconductors, with these specifications available in small

SOT-23 or SOT-223 packages.

3.3V

1kΩ

VDRIVE

DVDD

10µF

100nF

ADAU1701

06412-016

Figure 16. Voltage Regulator Configuration

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