ADUC824 Analog Devices, ADUC824 Datasheet - Page 31

• Manufacturer Part Number: ADUC824
• Description: Precision Analog Microcontroller: 1MIPS 8052 MCU + 8kB Flash + 16/24-Bit ADC + 12-Bit DAC
• Manufacturer: Analog Devices

Specifications of ADUC824

• Mcu Core: 8052
• Mcu Speed (mips): 1
• Sram (bytes): 256Bytes
• Gpio Pins: 34
• Adc # Channels: 4

USER TO EASILY DETECT
CURRENTS ALLOW THE
PRIMARY AND AUXILIARY ADC CIRCUIT DESCRIPTION
Overview
The ADuC824 incorporates two independent sigma-delta ADCs
(Primary and Auxiliary) with on-chip digital filtering intended
for the measurement of wide dynamic range, low frequency
signals, such as those in weigh-scale, strain-gauge, pressure trans-
ducer or temperature measurement applications.
Primary ADC
This ADC is intended to convert the primary sensor input. The
input is buffered and can be programmed for one of 8 input ranges
from ± 20 mV to ± 2.56 V, being driven from one of three differ-
ential input channel options AIN1/2, AIN3/4, or AIN3/2. The
input channel is internally buffered allowing the part to handle
significant source impedances on the analog input, allowing R/C
filtering (for noise rejection or RFI reduction) to be placed on
IF A TRANSDUCER HAS
BURNED OUT OR GONE
BURNOUT CURRENTS
TWO 100nA BURNOUT
SEE PAGES 29 AND 34
OPEN-CIRCUIT
FULLY DIFFERENTIAL PAIR OPTIONS AND
ADDITIONAL INTERNAL SHORT OPTION
(AIN2–AIN2).THE MULTIPLEXER IS
CONTROLLED VIA THE CHANNEL
A DIFFERENTIAL MULTIPLEXER
ALLOWS SELECTION OF THREE
SELECTION BITS IN ADC0CON
ANALOG MULTIPLEXER
SEE PAGES 27 AND 33
AIN1
AIN2
AIN3
AIN4
ANALOG INPUT CHOPPING
ALTERNATELY REVERSED
EXCELLENT ADC OFFSET
CONVERSION CYCLE.
AND OFFSET DRIFT
CHOPPING YIELDS
THE INPUTS ARE
MUX
PERFORMANCE
THROUGH THE
SEE PAGE 36
AGND
AV
DD
CHOP
FOR THE ANALOG INPUTS,
IMPEDANCE INPUT STAGE
GAIN AMPLIFIER ALLOWS
THE BUFFER AMPLIFIER
ALLOWING SIGNIFICANT
RANGES FROM 20mV TO
PROGRAMMABLE GAIN
2.56V (EXT VREF = 2.5V)
THE PROGRAMMABLE
EIGHT BIPOLAR INPUT
EIGHT UNIPOLAR AND
BUFFER
BUFFER AMPLIFIER
EXTERNAL SOURCE
PRESENTS A HIGH
IMPEDANCES
SEE PAGE 33
SEE PAGE 34
AMPLIFIER
REFIN(–) REFIN(+)
PGA
CIRCUITRY TESTS FOR OPEN OR
SHORTED REFERENCES INPUTS
SELECTED VIA THE XREF0 BIT
OPERATION. THE EXTERNAL
THE EXTERNAL REFERENCE
FACILITATES RATIOMETRIC
INPUT TO THE ADuC824 IS
REFERENCE VOLTAGE IS
SIGMA-DELTA
MODULATOR
OF WHICH IS ALSO CHOPPED)
THE MODULATOR PROVIDES
DATA STREAM (THE OUTPUT
REPRESENTS THE SAMPLED
THE DUTY CYCLE OF WHICH
REFERENCE DETECT
ANALOG INPUT VOLTAGE
DIFFERENTIAL AND
A HIGH-FREQUENCY 1-BIT
TO THE DIGITAL FILTER,
SIGMA-DELTA A/D CONVERTER
DIFFERENTIAL
IN ADC0CON.
REFERENCE
SEE PAGE 35
SIGMA-DELTA
the analog inputs if required. On-chip burnout currents can
also be turned on. These currents can be used to check that a
transducer on the selected channel is still operational before
attempting to take measurements.
The ADC employs a sigma-delta conversion technique to realize
up to 24 bits of no missing codes performance. The sigma-delta
modulator converts the sampled input signal into a digital pulse
train whose duty cycle contains the digital information. A Sinc3
programmable low-pass filter is then employed to decimate the
modulator output data stream to give a valid data conversion
result at programmable output rates from 5.35 Hz (186.77 ms)
to 105.03 Hz (9.52 ms). A Chopping scheme is also employed
to minimize ADC offset errors. A block diagram of the Primary
ADC is shown in Figure 18.
MODULATOR
SEE PAGE 35
PROGRAMMABLE
DIGITAL
FILTER
ARCHITECTURE ENSURES
CHOPPED TO REMOVE
SIGMA-DELTA ADC IS
QUANTIZATION NOISE INTRODUCED
24 BITS NO MISSING
CODES. THE ENTIRE
BY THE MODULATOR. THE UPDATE
SIGMA-DELTA ADC
THE SIGMA-DELTA
RATE AND BANDWIDTH OF THIS
FILTER ARE PROGRAMMABLE
THE SINC 3 FILTER REMOVES
DRIFT ERROR
SEE PAGE 35
PROGRAMMABLE
DIGITAL FILTER
VIA THE SF SFR
CHOP
SEE PAGE 35
AVERAGE
OUTPUT
AS PART OF THE CHOPPING
SUMMED AND AVERAGED
WITH ITS PREDECESSOR
IMPLEMENTATION, EACH
TO NULL ADC CHANNEL
DATA WORD OUTPUT
FROM THE FILTER IS
OUTPUT AVERAGE
OFFSET ERRORS
SEE PAGE 36
DIGITAL FILTER IS SCALED BY
THE OUPUT WORD FROM THE
THE CONVERSION RESULT
ADuC824
COEFFICIENTS BEFORE
BEING PROVIDED AS
THE CALIBRATION
OUTPUT SCALING
SCALING
OUTPUT
SEE PAGE 37
RESULT WRITTEN
DIGTAL OUTPUT
TO ADC0H/M/L
SFRs