ADAU1401A Datasheet, PDF (18/52 Pages) Analog Devices – SigmaDSP 28-/56-Bit Audio Processor with Two ADCs and Four DACs

ADAU1401A
VOLTAGE REGULATOR
The digital voltage of the ADAU1401A 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 regu-
lator transistor: the transistor’s current amplification factor
(hFE or 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 ADAU1401A is 40 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 with these specifications available in
small SOT-23 or SOT-223 packages.
10µF
+
3.3V
100nF
1kΩ
ADAU1401A
DVDD VDRIVE
Figure 16. Voltage Regulator Configuration
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