MAX1447 Datasheet, PDF (15/24 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
For external-reference operation, set INTREF to GND.
REF+ and REF- are fully differential. For a valid exter-
nal-reference input, V_REF+ must be greater than V_REF-.
Bypass REF+ and REF- with a 0.1µF or greater capaci-
tor to GND in external-reference mode.
Figure 8 shows the MAX1447/MAX1496/MAX1498 oper-
ating with an external differential reference. In this fig-
ure, REF- is connected to the top of the strain gauge
and REF+ is connected to the midpoint of the resistor-
divider of the supply.
Figure 9 shows the MAX1447/MAX1496/MAX1498 oper-
ating with an external single-ended reference. In this
figure, REF- is connected to GND and REF+ is driven
with an external 2.048V reference. Bypass REF+ to
GND with a 0.47µF capacitor.
Applications Information
Power-On Reset
At power-up, the digital filter and modulator circuits reset.
The MAX1447/MAX1498 allows 6s for the reference to
stabilize before performing enhanced offset calibration.
During these 6s, the MAX1447/MAX1498 display 1.2V
to 1.5V when a stable reference is detected. If a valid
reference is not found, the MAX1447/MAX1498 time out
after 6s and begin enhanced offset calibration.
Enhanced offset calibration typically lasts 2s. The
MAX1447/MAX1498 begin converting after enhanced
offset calibration.
Offset Calibration
The MAX1447/MAX1496/MAX1498 offer on-chip offset
calibration. The device offset calibrates during every con-
version cycle.
Enhanced Offset Calibration
(MAX1447 Only)
Enhanced offset calibration is a more accurate calibra-
tion method that is needed in the case of the ±200mV
range and 4.5-digit resolution. In addition to enhanced
offset calibration at power-up, the MAX1447 performs
enhanced calibration on demand by connecting HOLD
to AV_DD for > 2s.
Peak
The MAX1447/MAX1496/MAX1498 feature peak-detec-
tion circuitry. When activated (PEAK connected to
AV_DD for the MAX1498/MAX1447 or to V_DD for the
MAX1496), the devices display only the highest voltage
measured to the LED.
First, the current ADC result is displayed. The new ADC
conversion result is compared to the current result. If the
new value is larger than the previous peak value, the
new value is displayed. If the new value is less than the
previous peak value, the display remains unchanged.
Connect PEAK to GND to clear the peak value and dis-
able the peak function.
0.1µF
0.1µF
R_REF
ACTIVE
GAUGE
0.1µF
R
0.1µF
DUMMY
GAUGE
0.1µF
R
ANALOG SUPPLY
4.7µF
FERRITE
BEAD
0.1µF
AV_DD
REF+
DV_DD
MAX1447
MAX1496
REF- _MAX1498
AIN+
AIN-
GND
4.7µF
THERMOCOUPLE
JUNCTION
MAX1447
MAX1496
AIN+ _MAX1498
AIN-
0.1µF
+5V
MAX6062
+2.048V
REF+
REF-
GND
0.47µF
Figure 8. Strain-Gauge Application with the MAX1447/MAX1496/
MAX1498
Figure 9. Thermocouple Application with the MAX1447/MAX1496/
MAX1498
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