Datasheet

MAX1447/MAX1496/MAX1498
3.5- and 4.5-Digit, Single-Chip ADCs
with LED Drivers
______________________________________________________________________________________ 17
The transfer function for the MAX1496 with AIN+ - AIN-
≥ 0, RANGE = GND is:
The transfer function for the MAX1496 with AIN+ - AIN-
< 0, RANGE = GND is:
The transfer function for the MAX1496 with AIN+ - AIN-
≥ 0, RANGE = V
DD
is:
The transfer function for the MAX1496 with AIN+ - AIN-
< 0, RANGE = V
DD
is:
Supplies, Layout, and Bypassing
Power up AV
DD
and DV
DD
(MAX1447/MAX1498) and
V
DD
(MAX1496) before applying an analog input and
external-reference voltage to the device. If this is not
possible, limit the current into these inputs to 50mA.
When the analog and digital supplies come from the
same source, isolate the digital supply from the analog
supply with a low-value resistor (10Ω) or ferrite bead.
For best performance, ground the MAX1447/
MAX1496/MAX1498 to the analog ground plane of the
circuit board.
Avoid running digital lines under the device as this can
couple noise onto the IC. Run the analog ground plane
under the MAX1447/MAX1496/MAX1498 to minimize
coupling of digital noise. Make the power-supply lines
to the MAX1447/MAX1496/MAX1498 as wide as possi-
ble to provide low-impedance paths and reduce the
effects of glitches on the power-supply line.
Shield fast-switching signals, such as clocks, with digital
ground to avoid radiating noise to other sections of the
board. Avoid running clock signals near the analog
inputs. Avoid crossover of digital and analog signals.
Running traces that are on opposite sides of the board at
right angles to each other reduces feedthrough effects.
Good decoupling is important when using high-resolution
ADCs. Decouple the supplies with 0.1µF ceramic capaci-
tors to GND. Place these components as close to the
device as possible to achieve the best decoupling.
COUNT
VV
VV
AIN AIN
REF REF
. =×






×+
+
+
−
−
−
−
1 024 2000 10 1
COUNT
VV
VV
AIN AIN
REF REF
. =×






×
+
+
−
−
−
−
1 024 2000 10
COUNT
VV
VV
AIN AIN
REF REF
. =×






+
+
+
−
−
−
−
1 024 2000 1
COUNT
VV
VV
AIN AIN
REF REF
. =×






+
+
−
−
−
−
1 024 2000
-200mV
0
ANALOG INPUT VOLTAGE
+200mV
-100µV
100µV
LED
1 - - -
1999
2
1
0
- 0
- 1
- 2
-1999
- 1 - - -
Figure 12. MAX1496 Transfer Function, ±200mV Range
-2V
0
ANALOG INPUT VOLTAGE
+2V
-1mV
1mV
LED
1 - - -
1999
2
1
0
- 0
- 1
- 2
-1999
- 1 - - -
Figure 13. MAX1496 Transfer Function, ±2V Range