ADUC702 AD [Analog Devices], ADUC702 Datasheet - Page 26

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

ADuC702x Series
ADC CIRCUIT INFORMATION
GENERAL OVERVIEW
The Analog Digital Converter (ADC) incorporates a fast, multi-
channel, 12-bit ADC. It can operate from 2.7V to 3.6V supplies
and is capable of providing a throughput of up to 1MSPS when
the clock source is 45MHz. This block provides the user with
multi-channel multiplexer, differential track-and-hold, on-chip
reference and ADC.
The ADC consists of a 12-bit successive-approximation
converter based around two capacitor DACs. It can operate in
one of three different modes, depending on the input signal
configuration :
The converter accepts an analog input range of 0 to V
operating in single-ended mode or pseudo-differential mode. In
fully differential mode, the input signal must be balanced
around a common mode voltage V
and with a maximum amplitude of 2 V
A high precision, low drift, and factory calibrated 2.5 V
reference is provided on-chip. An external reference can also be
connected as described later.
Single or continuous conversion modes can be initiated in
software. An external CONV
the on-chip PLA or a Timer1 or a Timer2 overflow can also be
used to generate a repetitive trigger for ADC conversions.
A voltage output from an on-chip bandgap reference
proportional to absolute temperature can also be routed
through the front end ADC multiplexer (effectively an
additional ADC channel input) facilitating an internal
temperature sensor channel, measuring die temperature to an
accuracy of ±3°C.
•
•
•
Figure 7: examples of balanced signals for fully differential mode
fully differential mode, for small and balanced signals
single-ended mode, for any single-ended signals
pseudo-differential mode, for any single-ended signals,
taking advantage of the common mode rejection
offered by the pseudo differential input.
AV
V
CM
DD
0
V
CM
START
2V
V
CM
REF
pin, an output generated from
CM
, in the range 0V to AV
REF
(see Figure 7).
2V
REF
2V
REF
REF
when
Rev. PrB | Page 26 of 80
DD
ADC TRANSFER FUNCTION
Pseudo-differential and single-ended modes
In pseudo-differential or single-ended mode, the input range is
0 V to V
differential and single-ended modes with 1 LSB = FS/4096 or
2.5 V/4096 = 0.61 mV or 610 µV when V
code transitions occur midway between successive integer LSB
values (i.e. 1/2 LSB, 3/2 LSBs, 5/2 LSBs, . . ., FS –3/2 LSBs). The
ideal input/output transfer characteristic is shown in Figure 8.
Fully differential mode
The amplitude of the differential signal is the difference
between the signals applied to the V
V
therefore –V
the common mode (CM). The common mode is the average of
the two signals, i.e. (V
that the two inputs are centred on. This results in the span of
each input being CM ± V
externally and its range varies with V
The output coding is two’s complement in fully differential
mode with 1 LSB = 2V
when V
between successive integer LSB values (i.e., 1/2 LSB, 3/2 LSBs,
5/2 LSBs, . . ., FS –3/2 LSBs). The ideal input/output transfer
characteristic is shown in Figure 9.
1111 1111 1111
1111 1111 1110
1111 1111 1101
1111 1111 1100
0000 0000 0011
0000 0000 0010
0000 0000 0001
0000 0000 0000
Figure 8: ADC transfer function in pseudo differential mode or single-ended
IN–
). The maximum amplitude of the differential signal is
OUTPUT
CODE
REF
REF
= 2.5 V. The designed code transitions occur midway
0V 1LSB
. The output coding is straight binary in pseudo
REF
to +V
1LSB =
Preliminary Technical Data
REF
IN+
4096
FS
REF
p-p (i.e. 2 X V
VOLTAGE INPUT
+ V
REF
/4096 or 2x2.5 V/4096 = 1.22 mV
mode
IN–
/2. This voltage has to be set up
)/2 and is therefore the voltage
IN+
REF
and V
REF
, (see driving the ADC).
). This is regardless of
REF
+FS - 1LSB
IN–
= 2.5 V. The ideal
pins (i.e., V
IN+
–