Rainbow Electronics MAX1499 - Manual (Page 26)

MAX1497/MAX1499
3.5- and 4.5-Digit, Single-Chip ADCs with LED
Drivers and µC Interface
26 ______________________________________________________________________________________
Thermocouple Measurement
Figure 16 shows a connection from a thermocouple to
the MAX1497/MAX1499. In this application, the
MAX1497/MAX1499 take advantage of the on-chip
input buffers that allow large source impedances on the
front end. The decoupling capacitors reduce noise
pickup from the thermocouple leads. To place the dif-
ferential voltage from the thermocouple at a suitable
common-mode voltage, the AIN- input of the MAX1497/
MAX1499 is biased to GND. Use an external tempera-
ture sensor, such as the DS75, and a µC to perform
cold-junction temperature compensation.
Transfer Functions
Figures 17–20 show the transfer functions of the
MAX1497/MAX1499. The output data is stored in the
ADC data register in two’s complement.
The transfer function for the MAX1499 with AIN+ - AIN-
≥ 0, RANGE = 0 is:
COUNTS
V V
V V
AIN AIN
REF REF
. , =





 ×
+
+
− −
− −
1 024 20 000
7CFh
7CFh
002h
001h
000h
FFFh
FFEh
FFDh
830h
<830h
-200mV 0
ANALOG INPUT VOLTAGE
+200mV
ADC RESULT LED
1 - - -
1999
2
1
0
- 0
- 1
- 2
-1999
- 1 - - -
-100µV 100µV
Figure 19. MAX1497 Transfer Function, ±200mV Range
>7CFh
7CFh
002h
001h
000h
FFFh
FFEh
FFDh
830h
<830h
-2V 0
ANALOG INPUT VOLTAGE
+2V
ADC RESULT LED
1 - - -
1999
2
1
0
- 0
- 1
- 2
-1999
- 1 - - -
-1mV 1mV
Figure 20. MAX1497 Transfer Function, ±2V Range
>4E1Fh
4E1Fh
0002h
0001h
0000h
FFFFh
FFFEh
FFFDh
B1E0h
-2V 0
ANALOG INPUT VOLTAGE
+2V
ADC RESULT LED
1 - - - -
19,999
2
1
0
- 0
- 1
- 2
-19,999
- 1 - - - -
-100µV 100µV
Figure 17. MAX1499 Transfer Function, ±2V Range
4E1Fh
4E1Fh
0002h
00001h
0000h
FFFFh
FFFEh
FFFDh
B1E0h
-200mV 0
ANALOG INPUT VOLTAGE
+200mV
ADC RESULT LED
1 - - - -
19,999
2
1
0
- 0
- 1
- 2
-19,999
- 1 - - - -
-10µV 10µV
Figure 18. MAX1499 Transfer Function, ±200mV Range