EVAL-ADUC831QSZ Datasheet, PDF (63/76 Pages) Analog Devices – MicroConverter®, 12-Bit ADCs and DACs with Embedded 62 kBytes Flash MCU

ADuC831
2.45V TYP
DV_DD
1.0V TYP
128ms TYP
128ms TYP
1.0V TYP
INTERNAL
CORE RESET
a.
PLACE ANALOG
COMPONENTS
HERE
AGND
PLACE DIGITAL
COMPONENTS
HERE
DGND
Figure 62. Internal POR Operation
Grounding and Board Layout Recommendations
As with all high resolution data converters, special attention must
be paid to grounding and PC board layout of ADuC831-based
designs in order to achieve optimum performance from the
ADC and DACs.
Although the ADuC831 has separate pins for analog and digital
ground (AGND and DGND), the user must not tie these to two
separate ground planes unless the two ground planes are con-
nected together very close to the ADuC831, as illustrated in the
simplified example of Figure 63a. In systems where digital and
analog ground planes are connected together somewhere else
(at the system’s power supply for example), they cannot be con-
nected again near the ADuC831 since a ground loop would result.
In these cases, tie the ADuC831’s AGND and DGND pins all
to the analog ground plane, as illustrated in Figure 63b. 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 ADuC831 can then be placed between
the digital and analog sections, as illustrated in Figure 63c.
In all of these scenarios, and in more complicated real-life applica-
tions, keep in mind the flow of current from the supplies and back
to ground. Make sure the return paths for all currents are as
close as possible to the paths the currents took to reach their desti-
nations. For example, do not power components on the analog
side of Figure 63b with DV_DD since that would force return currents
from DV_DD to flow through AGND. Also, try to avoid digital
currents flowing under analog circuitry, which could happen if
the user placed a noisy digital chip on the left half of the board in
Figure 63c. Whenever possible, avoid large discontinuities in the
ground plane(s) (such as are formed by a long trace on the same
layer), since they force return signals to travel a longer path. And
of course, make all connections to the ground plane directly,
with little or no trace separating the pin from its via to ground.
Note that the bottom paddle of the CSP package should not
be connected to ground. It should be left unconnected.
If the user plans to connect fast logic signals (rise/fall time < 5 ns) to
any of the ADuC831’s digital inputs, add a series resistor to each
relevant line to keep rise and fall times longer than 5 ns at the
ADuC831 input pins. A value of 100 Ω or 200 Ω is usually suffi-
cient to prevent high speed signals from coupling capacitively into
the ADuC831 and affecting the accuracy of ADC conversions.
b.
PLACE ANALOG
COMPONENTS
HERE
AGND
PLACE DIGITAL
COMPONENTS
HERE
DGND
c.
PLACE ANALOG
COMPONENTS
HERE
PLACE DIGITAL
COMPONENTS
HERE
GND
Figure 63. System Grounding Schemes
OTHER HARDWARE CONSIDERATIONS
To facilitate in-circuit programming, plus in-circuit debug and
emulation options, users will want to implement some simple
connection points in their hardware that will allow easy access
to download, debug, and emulation modes.
In-Circuit Serial Download Access
Nearly all ADuC831 designs will want to take advantage of the
in-circuit reprogrammability of the chip. This is accomplished by
a connection to the ADuC831’s UART, which requires an exter-
nal RS-232 chip for level translation if downloading code from
a PC. Basic configuration of an RS-232 connection is illustrated
in Figure 66 with a simple ADM202-based circuit. If users would
rather not design an RS-232 chip onto a board, refer to the
application note “uC006–A 4-Wire UART-to-PC Interface”* for
a simple (and zero-cost-per-board) method of gaining in-circuit
serial download access to the ADuC831.
In addition to the basic UART connections, users will also need
a way to trigger the chip into download mode. This is accom-
plished via a 1 kΩ pull-down resistor that can be jumpered onto
the PSEN pin, as shown in Figure 64. To get the ADuC831 into
download mode, simply connect this jumper and power-cycle the
device (or manually reset the device, if a manual reset button is
available) and it will be ready to receive a new program serially.
With the jumper removed, the device will come up in normal
mode (and run the program) whenever power is cycled or RESET
is toggled.
*Application Note uC006 is available at www.analog.com/microconverter
REV. 0
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