ADUC831BS Analog Devices Inc, ADUC831BS Datasheet - Page 23

• Manufacturer Part Number: ADUC831BS
• Description: IC ADC/DAC 12BIT W/MCU 52-MQFP
• Manufacturer: Analog Devices Inc
• Series: MicroConverter® ADuC8xxr

Specifications of ADUC831BS

• Rohs Status: RoHS non-compliant
• Core Processor: 8052
• Core Size: 8-Bit
• Speed: 16MHz
• Connectivity: EBI/EMI, I²C, SPI, UART/USART
• Peripherals: PSM, Temp Sensor, WDT
• Number Of I /o: 34
• Program Memory Size: 62KB (62K x 8)
• Program Memory Type: FLASH
• Eeprom Size: 4K x 8
• Ram Size: 2.25K x 8
• Voltage - Supply (vcc/vdd): 2.7 V ~ 5.5 V
• Data Converters: A/D 8x12b, D/A 2x12b
• Oscillator Type: Internal
• Operating Temperature: -40°C ~ 125°C
• Package / Case: 52-MQFP, 52-PQFP
• For Use With: EVAL-ADUC831QSZ - KIT DEV FOR ADUC831 QUICK START

Keep in mind that the ADC’s transfer function is 0 to V
any signal range lost to amplifier saturation near ground will
impact dynamic range. Though the op amps in Table VI are
capable of delivering output signals very closely approaching
ground, no amplifier can deliver signals all the way to ground when
powered by a single supply. Therefore, if a negative supply is
available, you might consider using it to power the front end
amplifiers. If you do, however, be sure to include the Schottky
diodes shown in Figure 10 (or at least the lower of the two
diodes) to protect the analog input from undervoltage condi-
tions. To summarize this section, use the circuit of Figure 10 to
drive the analog input pins of the ADuC831.
Voltage Reference Connections
The on-chip 2.5 V band gap voltage reference can be used as the
reference source for the ADC and DACs. To ensure the accu-
racy of the voltage reference, you must decouple the V
ground with a 0.1 µF capacitor and the C
a 0.1 µF capacitor as shown in Figure 11.
If the internal voltage reference is to be used as a reference for
external circuitry, the C
buffer must be used in this case to ensure that no current is
drawn from the C
that of an internal node within the buffer block, and its voltage
is critical to ADC and DAC accuracy. On the ADuC812 V
was the recommended output for the external reference; this
can be used but it should be noted that there will be a gain error
between this reference and that of the ADC.
The ADuC831 powers up with its internal voltage reference in
the “on” state. This is available at the V
before there will be a gain error between this and that of the
ADC. The C
powered up.
If an external voltage reference is preferred, it should be
connected to the V
Bit 6 of the ADCCON1 SFR must be set to 1 to switch in the
external reference voltage.
REV. 0
BUFFER
Figure 11. Decoupling V
REF
output becomes available when the ADC is
V
REF
REF
REF
0.1 F
0.1 F
C
REF
pin itself. The voltage on the C
and C
REF
output should be used. However, a
REF
51
BUFFER
pins as shown in Figure 12.
REFERENCE
ADuC831
BAND GAP
REF
2.5V
REF
REF
and C
pin, but as noted
pin to ground with
REF
REF
REF
REF
pin is
pin to
REF
, and
–23–
To ensure accurate ADC operation, the voltage applied to V
must be between 1 V and AV
input signals are proportional to the power supply (such as some
strain gage applications) it may be desirable to connect the C
and V
Operation of the ADC or DACs with a reference voltage below
1 V, however, may incur loss of accuracy eventually resulting in
missing codes or non-monotonicity. For that reason, do not use
a reference voltage less than 1 V.
To maintain compatibility with the ADuC812, the external
reference can also be connected to the V
Figure 13, to overdrive the internal reference. Note this intro-
duces a gain error for the ADC that has to be calibrated out,
thus the previous method is the recommended one for most
users. For this method to work, ADCCON1.6 should be config-
ured to use the internal reference. The external reference will
then overdrive this.
REF
Figure 12. Using an External Voltage Reference
Figure 13. Using an External Voltage Reference
REFERENCE
pins directly to AV
REFERENCE
EXTERNAL
EXTERNAL
VOLTAGE
VOLTAGE
V
V
DD
DD
0.1 F
0.1 F
0.1 F
V
C
0.1 F
REF
REF
V
C
REF
REF
51
"1" =
"0" = INTERNAL
DD
DD
.
ADCCON1.6
EXTERNAL
. In situations where analog
51
REFERENCE
BAND GAP
BUFFER
ADuC831
2.5V
ADuC831
REF
REFERENCE
BAND GAP
pin as shown in
2.5V
ADuC831
BUFFER
REF
REF