MAX1492 Datasheet, PDF (29/35 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
best performance, ground the MAX1492/MAX1494 to
the analog ground plane of the circuit board.
Avoid running digital lines under the device because
they can couple noise onto the device. Run the analog
ground plane under the MAX1492/MAX1494 to mini-
mize coupling of digital noise. Make the power-supply
lines to the MAX1492/MAX1494 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 0.1µF and 4.7µF
ceramic capacitors to GND. Place these components as
close to the device as possible to achieve the best
decoupling.
See the MAX1494 evaluation kit manual for the recom-
mended layout. The evaluation kit 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 endpoints of the transfer function,
once offset and gain errors have been nullified. INL for
the MAX1492/MAX1494 is measured using the end-
point method.
DNL
Differential nonlinearity (DNL) is the difference between
an actual step width and the ideal value of 1 LSB. A
DNL error specification of less than 1 LSB guarantees
no missing codes 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 near full-scale positive voltage, swapping
AIN+ and AIN-, and then adding the results.
Zero Input Reading
Ideally, with AIN+ connected to AIN- the MAX1492/
MAX1494 LCD is 0 or -0. Zero input reading is the mea-
sured deviation from the ideal 0 and the actual mea-
sured point.
Gain Error
Gain error is the amount of deviation between the mea-
sured full-scale transition point and the ideal full-scale
transition point.
Common-Mode Rejection
Common-mode rejection (CMR) is the ability of a
device to reject a signal that is common to both input
terminals. The common-mode signal can be either an
AC or a DC signal or a combination of the two. CMR is
often expressed in decibels.
Normal-Mode 50Hz and 60Hz Rejection
(Simultaneously)
Normal-mode rejection is a measure of how much out-
put changes when a 50Hz and 60Hz signal is injected
into only one of the differential inputs. The MAX1492/
MAX1494 sigma-delta converter uses its internal digital
filter to provide normal-mode rejection to both 50Hz
and 60Hz power-line frequencies simultaneously.
Power-Supply Rejection Ratio
Power-supply rejection ratio (PSRR) is the ratio of the
input-supply change (in volts) to the change in the con-
verter output (in volts). It is typically measured in decibels.
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