Datasheet

Transfer Function
Output data coding for the MAX127/MAX128 is binary
in unipolar mode with 1 LSB = (FS/4096) and two’s
complement binary in bipolar mode with 1 LSB = [(2 x
|FS|)/4096]. Code transitions occur halfway between
successive-integer LSB values. Figures 13a and 13b
show the input/output (I/O) transfer functions for unipolar
and bipolar operations, respectively. For full-scale (FS)
values, refer to Table 3.
Layout, Grounding, and Bypassing
Careful PCB layout is essential for best system perfor-
mance. For best performance, use a ground plane. To
reduce crosstalk and noise injection, keep analog and
digital signals separate. Connect analog grounds and
DGND in a star configuration to AGND. For noise-free
operation, ensure the ground return from AGND to the
supply ground is low impedance and as short as possible.
Connect the logic grounds directly to the supply ground.
Bypass V
DD
with 0.1μF and 4.7μF capacitors to AGND to
minimize highand low-frequency fluctuations. If the supply
is excessively noisy, connect a 5Ω resistor between the
supply and V
DD
, as shown in Figure 14.
Figure 13a. Unipolar Transfer Function
Figure 13b. Bipolar Transfer Function
Figure 14. Power-Supply Grounding Connection
OUTPUT CODE
INPUT VOLTAGE (LSB)
0
FS
FS -
3
/
2
LSB
1 LSB =
FULL-SCALE
TRANSITION
1 2 3
11... 111
11... 110
11... 101
00... 011
00... 010
00... 001
00... 000
FS
4096
OUTPUT CODE
INPUT VOLTAGE (LSB)
0 +FS - 1 LSB
1 LSB =
-FS
011... 111
011... 110
000... 001
000... 000
111... 111
100... 010
100... 001
100... 000
2 FS
4096
V
DD
GND
DGND
DGNDAGND
+5V
+5V
SUPPLY
R* = 5Ω
DIGITAL
CIRCUITRY
**
* OPTIONAL
** CONNECT AGND AND DGND WITH A GROUND PLANE OR A SHORT TRACE.
0.1µF
4.7µF
MAX127
MAX128
MAX127/MAX128 Multirange, +5V, 12-Bit DAS with
2-Wire Serial Interface
www.maximintegrated.com
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