ADAU1445 Analog Devices, ADAU1445 Datasheet - Page 25

• Manufacturer Part Number: ADAU1445
• Manufacturer: Analog Devices

Specifications of ADAU1445

• Instructions/cycles: 3584
• Digital I/o Channels: 24/24
• Analog I/o Channels: 0/0
• Product Description: Digital audio processor with flexible audio routing matrix, 8 × 2-channel ASRC

VOLTAGE REGULATOR
The digital supply voltage of the ADAU1442/ADAU1445/
ADAU1446 must be set to 1.8 V. The chip includes an on-board
voltage regulator that allows the device to be used in systems
where a 1.8 V supply is not available but a 3.3 V supply is. The
only external components needed for this are a PNP transistor
and one resistor. Only one pin, VDRIVE, is necessary to
support the regulator.
The recommended design for the voltage regulator is shown
in Figure 12. The 10 μF and 100 nF capacitors shown in this
schematic 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) is needed
for all pins. In this design, 3.3 V is the main system voltage; 1.8 V
is generated at the collector of the transistor, 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.
Figure 12. Voltage Regulator Design
100nF
10µF
+
DVDD
VDRIVE
ADAU1442/
ADAU1445/
ADAU1446
3.3V
1kΩ
Rev. C | Page 25 of 92
Two specifications must be considered when choosing a regulator
transistor: the current amplification factor (h
be at least 200, and the collector must be able to dissipate the heat
generated when regulating from 3.3 V to 1.8 V. The maximum
digital current draw of the ADAU1442 and ADAU1445, which
use ASRCs, is 310 mA. The equation to determine the minimum
power dissipation specifications of the transistor is as follows:
Many transistors fit these specifications. Analog Devices
recommends the NJT4030P from On Semiconductor. For
projects with stringent size constraints, an FMMT734 from
Zetex can be used.
The ADAU1446, which does not contain ASRCs, has a lower
maximum digital current draw of approximately 235 mA. The
maximum power dissipation of the transistor in this case should
be around 355 mW.
SRC GROUP DELAY
The group delay of the sample rate converter is dependent on
the input and output sampling frequencies as described in the
following equations.
For f
For f
where GDS is the group delay in seconds.
(3.3 V − 1.8 V) × 310 mA = 465 mW
S_OUT
S_OUT
GDS
GDS
< f
> f
=
=
ADAU1442/ADAU1445/ADAU1446
S_IN
S_IN
f
f
S
S
16
16
_
_
,
,
IN
IN
+
+
⎛
⎜
⎜
⎝
f
S
32
f
_
S
32
IN
_
IN
⎞
⎟
⎟
⎠
×
⎛
⎜
⎜
⎝
f
f
S
S
_
_
OUT
IN
⎞
⎟
⎟
⎠
FE
or beta) should