MAX1402 Datasheet, PDF (36/40 Pages) Maxim Integrated Products – +5V, 18-Bit, Low-Power, Multichannel, Oversampling Sigma-Delta ADC

+5V, 18-Bit, Low-Power, Multichannel,
Oversampling (Sigma-Delta) ADC
R_L1
RTD
R_L2
R_L3
V+
OUT1
V_DD
200µA
REFIN- REFIN+
12.5k
AIN1
AIN2
OUT2
AGND
PGA
A = 1 TO 128
MODULATOR
200µA
MAX1402
DGND
Figure 19. 3-Wire RTD Application
perature drift of the RTD current source and compen-
sated for by the variation in the reference voltage. A
common resistance value for the RTD is 100Ω generat-
ing a 20mV signal directly handled at the analog input
of the MAX1402. The voltage at OUT1 and OUT2 can
go to within 1.0V of the V+ supply.
Grounding and Layout
For best performance, use printed circuit boards with
separate analog and digital ground planes. Wire-wrap
boards are not recommended.
Design the printed circuit board so that the analog and
digital sections are separated and confined to different
areas of the board. Join the digital and analog ground
planes at only one point. If the MAX1402 is the only
device requiring an AGND to DGND connection, then
the ground planes should be connected at the AGND
and DGND pins of the MAX1402. In systems where mul-
tiple devices require AGND to DGND connections, the
connection should still be made at only one point. Make
the star ground as close to the MAX1402 as possible.
Avoid running digital lines under the device, because
these may couple noise onto the die. Run the analog
ground plane under the MAX1402 to minimize coupling
of digital noise. Make the power-supply lines to the
MAX1402 as wide as possible to provide low-imped-
ance paths and reduce the effects of glitches on the
power-supply line.
Shield fast switching signals, such as clocks, with digi-
tal 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.
Traces on opposite sides of the board should run at
right angles to each other. This will reduce the effects
of feedthrough on the board. A microstrip technique is
best, but is not always possible with double-sided
boards. In this technique, the component side of the
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