Datasheet

MAX1491/MAX1493/MAX1495
Supplies, Layout, and Bypassing
Power up AV
DD
and DV
DD
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. Isolate the digital supply from the analog supply
with a low-value resistor (10Ω) or ferrite bead when the
analog and digital supplies come from the same
source. For best performance, ground the MAX1491/
MAX1493/MAX1495 to the analog ground plane of the
circuit board.
Avoid running digital lines under the device, because
these may couple noise onto the die. Run the analog
ground plane under the MAX1491/MAX1493/MAX1495
to minimize coupling of digital noise. Make the power-
supply lines to the MAX1491/MAX1493/MAX1495 as
wide as possible 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-resolu-
tion ADCs. Decouple the supplies with 4.7µF and 0.1µF
ceramic capacitors to GND. Place these components
as close to the device as possible to achieve the
best decoupling.
Refer to the MAX1494 evaluation kit manual for the rec-
ommended layout. The evaluation board package
includes a fully assembled and tested evaluation board.
Definitions
INL
Integral nonlinearity (INL) is the deviation of the values
on an actual transfer function from a straight line. This
straight line is either a best-straight-line fit or a line
drawn between the end points of the transfer function,
once offset and gain errors have been nullified. INL for
the MAX1491/MAX1493/MAX1495 is measured using
the end-point method.
DNL
Differential nonlinearity (DNL) is the difference between
an actual step width and the ideal value of one count. A
DNL error specification of less than one count guarantees
no missing counts and a monotonic transfer function.
Rollover Error
Rollover error is defined as the absolute value differ-
ence between a near-positive full-scale reading and
near-negative full-scale reading. Rollover error is tested
by applying a full-scale positive voltage, swapping
AIN+ and AIN-, and then adding the results.
Zero Input Reading
Ideally, with AIN+ connected to AIN-, the MAX1491/
MAX1493/MAX1495 display a zero. Zero input reading
is the measured deviation from the ideal zero and the
actual measured point.
3.5- and 4.5-Digit, Single-Chip
ADCs with LCD Drivers
20 ______________________________________________________________________________________
Figure 18. MAX1491 Transfer Function ±2V Range
-2V
0
ANALOG INPUT VOLTAGE
+2V
LCD
1 - - -
1999
2
1
0
- 0
- 1
- 2
-1999
- 1 - - -
-1mV
1mV
Figure 17. MAX1491 Transfer Function ±200mV Range
-200mV
0
ANALOG INPUT VOLTAGE
+200mV
LCD
1 - - -
1999
2
1
0
- 0
- 1
- 2
-1999
- 1 - - -
-100µV
100µV