MAX1447 Datasheet, PDF (17/24 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
The transfer function for the MAX1496 with AIN+ - AIN-
≥ 0, RANGE = GND is:
COUNT
=
1.024


V_AIN+
V_REF+
−
−
V_AIN−
V_{REF −}
×

2000_
The transfer function for the MAX1496 with AIN+ - AIN-
< 0, RANGE = GND is:
COUNT
=
1.024


V_AIN+
V_REF+
−
−
V_AIN−
V_{REF −}

× 2000_
+1
The transfer function for the MAX1496 with AIN+ - AIN-
≥ 0, RANGE = V_DD is:
COUNT
=
1.024


V_AIN+
V_REF+
−
−
V_AIN−
V_{REF −}
×

2000_
× 10
The transfer function for the MAX1496 with AIN+ - AIN-
< 0, RANGE = V_DD is:
COUNT
=
1.024


V_AIN+
V_REF+
−
−
V_AIN−
V_{REF −}
×

2000_ × 10 + 1
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.
LED
1---
1999
2
1
0
-0
-1
-2
-1999
-1---
-200mV
-100µV 0 100µV
+200mV
ANALOG INPUT VOLTAGE
Figure 12. MAX1496 Transfer Function, ±200mV Range
LED
1---
1999
2
1
0
-0
-1
-2
-1999
-1---
-2V
-1mV 0 1mV
+2V
ANALOG INPUT VOLTAGE
Figure 13. MAX1496 Transfer Function, ±2V Range
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