Datasheet

ADuC7060/ADuC7061 Data Sheet
Rev. D | Page 104 of 108
HARDWARE DESIGN CONSIDERATIONS
POWER SUPPLIES
The ADuC706x operational power supply voltage range is
2.375 V to 2.625 V. Separate analog and digital power supply
pins (AVDD and DVDD, respectively) allow AVDD
to be kept
relatively free of noisy digital signals often present on the
system DVDD line. In this mode, the part can also operate with
split supplies; that is, it can use different voltage levels for each
supply. For example, the system can be designed to operate
with a DVDD voltage level of 2.6 V, whereas the AVDD level
can be at 2.5 V or vice versa. A typical split supply
configuration is shown in Figure 28.
ADuC7060/
ADuC7061
0.1µF
ANALOG
SUPPLY
10µF
AVDD
DVDD
DGND
AGND
0.1µF
+
–
DIGITAL
SUPPLY
10µF
+
–
07079-022
Figure 28. External Dual Supply Connections
As an alternative to providing two separate power supplies, the
user can reduce noise on AVDD by placing a small series
resistor and/or ferrite bead between AVDD and DVDD, and then
decoupling AVDD separately to ground. An example of this
configuration is shown in Figure 29. With this configuration,
other analog circuitry (such as op amps, voltage reference, and
others) can be powered from the AV DD supply line as well.
ADuC7060/
ADuC7061
0.1µF
ANALOG
SUPPLY
10µF
AVDD
DVDD
DGND
AGND
0.1µF
DIGITAL
SUPPLY
BEAD
10µF
+
–
07079-023
Figure 29. External Single Supply Connections
Notice that in both Figure 28 and Figure 29, a large value (10 µF)
reservoir capacitor sits on DVDD, and a separate 10 µF
capacitor sits on AVDD. In addition, local, small value (0.1 µF)
capacitors are located at each AVDD and DVDD pin of the chip.
As per standard design practice, be sure to include all of these
capacitors and ensure that the smaller capacitors are close to the
AVDD pin with trace lengths as short as possible. Connect the
ground terminal of each of these capacitors directly to the
underlying ground plane.
Note that the analog and digital ground pins on the ADuC706x
must be referenced to the same system ground reference point
at all times.
Finally, note that, when the DVDD supply reaches 1.8 V, it must
ramp to 2.25 V in less than 128 ms. This is a requirement of the
internal power-on reset circuitry.