Datasheet
REV. 0
ADuC816
–32–
Auxiliary ADC
The Auxiliary ADC is intended to convert supplementary inputs
such as those from a cold junction diode or thermistor. This ADC
is not buffered and has a fixed input range of 0 V to 2.5 V
MU
X
AIN3
AIN4
AIN5
ON-CHIP
TEMPERATURE
SENSOR
SIGMA-
DELTA
MODULATOR
PROGRAMMABLE
DIGITAL FILTER
SIGMA-DELTA A/D CONVERTER
REFIN(–)
REFIN(+)
CHOP
OUTPUT
AVERAGE
OUTPUT
SCALING
DIGTAL OUTPUT
RESULT WRITTEN
TO ADC1H/L SFRs
CHOP
DIFFERENTIAL REFERENCE
THE EXTERNAL REFERENCE INPUT TO
THE ADuC816 IS DIFFERENTIAL AND
FACILITATES RATIOMETRIC
OPERATION. THE EXTERNAL REFER-
ENCE VOLTAGE IS SELECTED VIA THE
XREF1 BIT IN ADC1CON. REFERENCE
DETECT CIRCUITRY TESTS FOR OPEN
OR SHORTED REFERENcES INPUTS
SEE PAGE 35
THE MODULATOR PROVIDES A
HIGH FREQUENCY 1-BIT DATA
STREAM (THE OUTPUT OF WHICH
IS ALSO CHOPPED) TO THE
DIGITAL FILTER,
THE DUTY CYCLE OF WHICH
REPRESENTS THE SAMPLED
ANALOG INPUT VOLTAGE
SIGMA-DELTA
MODULATOR
SEE PAGE 35
PROGRAMMABLE DIGITAL
FILTER
THE SINC
3
FILTER REMOVES
QUANTIZATION NOISE INTRODUCED
BY THE MODULATOR. THE UPDATE
RATE AND BANDWIDTH OF THIS
FILTER ARE PROGRAMMABLE
VIA THE SF SFR
SEE PAGE 35
OUTPUT AVERAGE
AS PART OF THE CHOPPING
IMPLEMENTATION EACH
DATA WORD OUTPUT
FROM THE FILTER IS
SUMMED AND AVERAGED
WITH ITS PREDECESSOR
TO NULL ADC CHANNEL
OFFSET ERRORS
SEE PAGE 36
SIGMA-DELTA ADC
THE SIGMA-DELTA
ARCHITECTURE ENSURES
16 BITS NO MISSING
CODES. THE ENTIRE
SIGMA-DELTA ADC IS
CHOPPED TO REMOVE DRIFT
ERRORS
SEE PAGE 35
THE OUPUT WORD FROM THE
DIGITAL FILTER IS SCALED BY
THE CALIBRATION
COEFFICIENTS BEFORE
BEING PROVIDED AS
THE CONVERSION RESULT
OUTPUT SCALING
SEE PAGE 37
ANALOG INPUT CHOPPING
THE INPUTS ARE ALTERNATELY
REVERSED THROUGH THE
CONVERSION CYCLE. CHOPPING
YIELDS EXCELLENT ADC
OFFSET AND OFFSET DRIFT
PERFORMANCE
SEE PAGE 36
ANALOG MULTIPLEXER
A DIFFERENTIAL MULTIPLEXER
ALLOWS SELECTION OF THREE
EXTERNAL SINGLE ENDED INPUTS OR
THE ON-CHIP TEMP. SENSOR.
THE MULTIPLEXER IS CONTROLLED VIA
THE CHANNEL SELECTION
BITS IN ADC1CON
SEE PAGE 28 AND 33
MUX
Figure 19. Auxiliary ADC Block Diagram
(assuming an external 2.5 V reference). The single-ended inputs
can be driven from AIN3, AIN4 or AIN5 pins or directly from
the on-chip temperature sensor voltage. A block diagram of the
Auxiliary ADC is shown in Figure 19.
REV. A