MAX1491 Datasheet, PDF (17/25 Pages) Maxim Integrated Products – 3.5- and 4.5-Digit, Single-Chip ADCs with LCD Drivers

3.5- and 4.5-Digit, Single-Chip
ADCs with LCD Drivers
Decimal Point Control
The MAX1491/MAX1493/MAX1495 allow for full deci-
mal-point control and feature leading-zero suppression.
Use DPON, DPSET1, and DPSET2 to set the value of
the decimal point. Tables 2 and 3 show the truth tables
of the DPON, DPSET1, and DPSET2 that determine
which decimal point is used.
Reference
The MAX1491/MAX1493/MAX1495 reference sets the
full-scale range of the ADC transfer function. With a
nominal 2.048V reference, the ADC full-scale range is
±2V with RANGE equal to GND. With RANGE equal to
DV_DD, the full-scale range is ±200mV. A decreased ref-
erence voltage decreases full-scale range (see the
Transfer Functions section).
The MAX1491/MAX1493/MAX1495 accept either an
external reference or an internal reference. The INTREF
input selects the reference mode.
For internal reference operation, connect INTREF to
DV_DD, connect REF- to GND, and bypass REF+ to
GND with a 4.7µF capacitor. The internal reference pro-
vides a nominal 2.048V source between REF+ and
GND. The internal reference temperature coefficient is
typically 40ppm/°C.
Connect INTREF to GND to use the external reference.
The external reference inputs, REF+ and REF-, are fully
differential. For a valid external reference input, V_REF+
must be greater than V_REF-. Bypass REF+ and REF-
with a 0.1µF or greater capacitor to GND in external ref-
erence mode.
Figure 13 shows the MAX1493/MAX1495 operating with
an external differential reference. In this mode, REF- is
connected to the top of the strain gauge and REF+ is
connected to the midpoint of the resistor-divider on the
supply.
Applications Information
Power-On
At power-on, the digital filter and modulator circuits
reset. The MAX1493/MAX1495 allow 6s for the refer-
ence to stabilize before performing enhanced offset
calibration. During these 6s, the MAX1493/MAX1495
display 1.2V to 1.5V when a stable reference is detect-
ed. If a valid reference is not found, the MAX1493/
MAX1495 time out after 6s and begin enhanced offset
calibration. Enhanced offset calibration typically lasts
2s. The MAX1493/MAX1495 begin converting after
enhanced offset calibration.
Offset Calibration
The MAX1491/MAX1493/MAX1495 offer on-chip offset
calibration. The MAX1491/MAX1493/MAX1495 calibrate
offset during every conversion cycle. The MAX1495
offers enhanced offset calibration on demand. Connect
HOLD to DV_DD for 2s to perform enhanced offset cali-
bration.
Table 2. Decimal-Point Control Table (MAX1493/MAX1495)
DPON
0
0
0
0
1
1
1
1
DPSET1
0
0
1
1
0
0
1
1
DPSET2
0
1
0
1
0
1
0
1
DISPLAY OUTPUT
18888
18888
18888
18888
1 8 8 8.8
1 8 8.8 8
1 8.8 8 8
1.8 8 8 8
ZERO INPUT READING
0
0
0
0
0.0
0.00
0.000
0.0000
Table 3. Decimal-Point Control Table (MAX1491)
DPSET1
0
0
1
1
DPSET2
0
1
0
1
DISPLAY OUTPUT
1 8 8.8
1 8.8 8
1.8 8 8
1888
ZERO INPUT READING
0.0
0.00
0.000
000
______________________________________________________________________________________ 17