Datasheet

ADuC836
–68–
ADuC836
–69–
Typical System Conguration
A typical ADuC836 conguration is shown in Figure 66. It sum-
marizes some of the hardware considerations discussed in the
previous paragraphs.
Figure 66 also includes connections for a typical analog mea-
surement application of the ADuC836, namely an interface to an
RTD (Resistive Temperature Device). The arrangement shown is
commonly referred to as a 4-wire RTD conguration.
Here, the on-chip excitation current sources are enabled to
excite the sensor. The excitation current ows directly through
the RTD, generating a voltage across the RTD proportional to
its resistance. This differential voltage is routed directly to the
positive and negative inputs of the primary ADC (AIN1, AIN2,
respectively). The same current that excited the RTD also ows
through a series resistance R
REF
, generating a ratiometric voltage
reference V
REF
. The ratiometric voltage reference ensures that
variations in the excitation current do not affect the measurement
system as the input voltage from the RTD and reference voltage
across R
REF
vary ratiometrically with the excitation current. Resis-
tor R
REF
must, however, have a low temperature coefcient to
avoid errors in the reference voltage over temperature. R
REF
must
also be large enough to generate at least a 1 V voltage reference.
C1+
V+
C1–
C2+
C2–
V–
T2OUT
R2IN
V
CC
GND
T1OUT
R1IN
R1OUT
T1IN
T2IN
R2OUT
ADM3202
DV
DD
27
34
33
31
30
29
28
39
38
37
36
35
32
40
47
46
44
43
42
41
52
51
50
49
48
45
DV
DD
1k
DV
DD
1k
2-PIN HEADER FOR
EMULATION ACCESS
(NORMALLY OPEN
)
DOWNLOAD/DEBUG
ENABLE JUMPER
(NORMALLY OPEN)
32.768kHz
DV
DD
1
2
3
4
5
6
7
8
9
AV
DD
200A/400A
EXCITATION
CURRENT
RTD
R
REF
5.6k
AV
DD
AGND
P1.2/I
EXC
1/DAC
REFIN–
REFIN+
P1.4/AIN1
P1.5/AIN2
DV
DD
DGND
PSEN
EA
DGND
DV
DD
XTAL2
XTAL1
RESET RXD TXD DV
DD
DGND
NOT CONNECTED IN THIS EXAMPLE
ADuC836
P1.3/AIN5/DAC
DV
DD
RS232 INTERFACE*
STANDARD D-TYPE
SERIAL COMMS
CONNECTOR TO
PC HOST
*EXTERNAL UART TRANSCEIVER INTEGRATED IN SYSTEM OR AS
PART OF AN EXTERNAL DONGLE AS DESCRIBED IN uC006.
ALL CAPACITORS IN THIS EXAMPLE ARE
0.1F CERAMIC CAPACITORS.
Figure 66. Typical System Conguration
REV. A
REV. A