MAX1447 Datasheet, PDF (16/24 Pages) Maxim Integrated Products – 3.5- and 4.5-Digit, Single-Chip ADCs with LED Drivers

3.5- and 4.5-Digit, Single-Chip ADCs
with LED Drivers
Hold
The MAX1447/MAX1496/MAX1498 feature data-hold
circuitry. When activated (HOLD is set to AV_DD for the
MAX1447/MAX1498 or to V_DD for the MAX1496), the
device holds the current reading on the LED.
Strain-Gauge Measurement
Connect the differential inputs of the MAX1447/
MAX1496/MAX1498 to the bridge network of the strain
gauge. In Figure 8, the analog supply voltage powers
the bridge network and the MAX1447/MAX1496/
MAX1498, along with the reference voltage. The
MAX1447/MAX1496/MAX1498 handle an analog input
voltage range of ±200mV and ±2V full scale. The ana-
log/reference inputs of the parts allow the analog input
range to have an absolute value of anywhere between
-2.2V and +2.2V.
Thermocouple Measurement
Figure 9 shows a connection from a thermocouple to
the MAX1447/MAX1496/MAX1498. In this application,
the MAX1447/MAX1496/MAX1498 take advantage of
the on-chip input buffers that allow large source imped-
ances on the front end. The decoupling capacitors
reduce noise pickup from the thermocouple leads. To
place the differential voltage from the thermocouple at
a suitable common-mode voltage, the AIN- input of the
MAX1447/MAX1496/MAX1498 is biased to GND. Use
an external temperature sensor, such as the DS75, and
a microcontroller to perform cold-junction temperature
compensation.
Transfer Functions
Figures 10–13 show the transfer functions of the
MAX1447/MAX1496/MAX1498.
The transfer function for the MAX1447/MAX1498 with
AIN+ - AIN- ≥ 0, RANGE = GND is:
COUNT
=
1.024


V_AIN+
V_REF+
−
−
V_AIN−
V_{REF −}
×

20, 000_
The transfer function for the MAX1447/MAX1498 with
AIN+ - AIN- < 0, RANGE = GND is:
COUNT
=
1.024


V_AIN+
V_REF+
−
−
V_AIN−
V_{REF −}

× 20,000_ + 1
The transfer function for the MAX1447/MAX1498 with
AIN+ - AIN- ≥ 0, RANGE = DV_DD is:
COUNT
=
1.024


V_AIN+
V_REF+
− V_AIN−
− V_REF−
×

20,000_ × 10
The transfer function for the MAX1447/MAX1498 with
AIN+ - AIN- < 0, RANGE = DV_DD is:
COUNT
=
1.024


V_AIN+
V_REF+
−
−
V_AIN−
V_{REF −}
×

20, 000_
× 10 + 1
LED
1----
19,999
2
1
0
-0
-1
-2
-19,999
-1----
-2V
-100µV 0 100µV
+2V
ANALOG INPUT VOLTAGE
Figure 10. MAX1447/MAX1498 Transfer Function, ±2V Range
LED
1----
19,999
2
1
0
-0
-1
-2
-19,999
-1----
-200mV
-10µV 0 10µV
+200mV
ANALOG INPUT VOLTAGE
Figure 11. MAX1447/MAX1498 Transfer Function, ±200mV Range
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