ADUC702 AD [Analog Devices], ADUC702 Datasheet - Page 75

• Manufacturer Part Number: ADUC702
• Description: Precision Analog Microcontroller 12-bit Analog I/O, ARM7TDMI MCU
• Manufacturer: AD [Analog Devices]

Preliminary Technical Data
ADUC702X HARDWARE DESIGN
CONSIDERATIONS
POWER SUPPLIES
The ADuC702X operational power supply voltage range is 2.7V
to 3.6V. Separate analog and digital power supply pins (AV
and IOV
of noisy digital signals often present on the system IOV
In this mode, the part can also operate with split supplies; that
is, using different voltage supply levels for each supply. For
example, this means that the system can be designed to operate
with a IOV
at 3 V, or vice versa if required. A typical split supply
configuration is shown in Figure 38.
As an alternative to providing two separate power supplies, the
user can help keep AV
and/or ferrite bead between it and IOV
AV
shown in Figure 39. With this configuration other analog
circuitry (such as op amps, voltage reference, and so on) can be
powered from the AV
Notice that in both Figure 38 and Figure 39, a large value (10
µF) reservoir capacitor sits on IOV
capacitor sits on AV
capacitors are located at each AV
As per standard design practice, be sure to include all of these
capacitors, and ensure the smaller capacitors are close to each
DIGITAL SUPPLY
DIGITAL SUPPLY
DD
0.1µF
+
+
-
-
separately to ground. An example of this configuration is
10uF
DD
0.1uF
10µF
DD
, respectively) allow AV
Figure 39: external single supply connections
Figure 38: External dual supply connections
voltage level of 3.3 V while the AV
IOGND
DD
IOV
DD
DD
ADuC7026
supply line as well.
DD
quiet by placing a small series resistor
. Also, local small-value (0.1 µF)
IOGND
IOV
ADuC7026
DD
DACGND
REFGND
DACV
GND
BEAD
AGND
AV
DD
REF
DACGND
REFGND
DD
DACV
DD
GND
AGND
DD
AV
and IOV
DD
REF
DD
DD
to be kept relatively free
DD
and a separate 10 µF
, and then decoupling
1.6V
DD
ANALOG SUPPLY
10µF
pin of the chip.
DD
10uF
level can be
0.1µF
DD
+
-
0.1uF
Rev. PrB | Page 75 of 80
line.
DD
AV
ground terminal of each of these capacitors directly to the
underlying ground plane. Finally, it should also be noted that,
at all times, the analog and digital ground pins on the
ADuC702x must be referenced to the same system ground
reference point.
Linear Voltage regulator
The ADuC702x requires a single 3.3V supply but the core logic
requires a 2.5V supply. An on-chip linear regulator generates the
2.5V from IOV
supply for the core logic. An external compensation capacitor of
0.47 µF must be connected between LV
as possible to these pins) to act as a tank of charge as shown
Figure 40.
The LV
recommended that the IOV
decoupling this to help improving line regulation performance
of the on-chip voltage regulator.
GROUNDING
RECOMMENDATIONS
As with all high resolution data converters, special attention
must be paid to grounding and PC board layout of ADuC702x-
based designs in order to achieve optimum performance from
the ADCs and DAC.
Although the ADuC702x has separate pins for analog and
digital ground (AGND and IOGND), the user must not tie
these to two separate ground planes unless the two ground
planes are connected together very close to the ADuC702x, as
illustrated in the simplified example of Figure 41a. In systems
where digital and analog ground planes are connected together
somewhere else (at the system’s power supply for example),
they cannot be connected again near the ADuC702x since a
ground loop would result. In these cases, tie the ADuC702x’s
AGND and IOGND Pins all to the analog ground plane, as
illustrated in Figure 41b. In systems with only one ground
plane, ensure that the digital and analog components are
physically separated onto separate halves of the board such that
digital return currents do not flow near analog circuitry and
vice versa. The ADuC702x can then be placed between the
DD
pin with trace lengths as short as possible. Connect the
DD
pin should not be used for any other chip. It is also
0.47µF
Figure 40: voltage regulator connections
DD
for the core logic. LV
AND
LV
DGND
DD
DD
ADuC7026
has excellent power supply
ADuC702x Series
BOARD
DD
DD
and DGND (as close
pin 21 is the 2.5V
LAYOUT