MAX127 Maxim, MAX127 Datasheet - Page 15

• Manufacturer Part Number: MAX127
• Description: Multirange / +5V / 12-Bit DAS with 2-Wire Serial Interface
• Manufacturer: Maxim

Output data coding for the MAX127/MAX128 is binary
in unipolar mode with 1LSB = (FS/4096) and
two’s complement binary in bipolar mode with 1LSB =
[(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.
Figure 13a. Unipolar Transfer Function
Figure 13b. Bipolar Transfer Function
011... 111
011... 110
000... 001
000... 000
111... 111
100... 010
100... 001
100... 000
00... 011
00... 010
00... 001
00... 000
11... 111
11... 110
11... 101
OUTPUT CODE
OUTPUT CODE
0
-FS
1
2
______________________________________________________________________________________
3
INPUT VOLTAGE (LSB)
INPUT VOLTAGE (LSB)
0
FULL-SCALE
TRANSITION
Transfer Function
Multirange, +5V, 12-Bit DAS with
FS -
+FS - 1 LSB
3
/
2
LSB
1 LSB =
1 LSB =
FS
4096
2 FS
FS
4096
Careful printed circuit board layout is essential for best
system performance. For best performance, use a
ground plane. To reduce crosstalk and noise injection,
keep analog and digital signals separate. Connect ana-
log 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 imped-
ance and as short as possible. Connect the logic
grounds directly to the supply ground. Bypass V
0.1µF and 4.7µF capacitors to AGND to minimize high-
and low-frequency fluctuations. If the supply is exces-
sively noisy, connect a 5Ω resistor between the supply
and V
Figure 14. Power-Supply Grounding Connection
2-Wire Serial Interface
* OPTIONAL
** CONNECT AGND AND DGND WITH A GROUND PLANE OR A SHORT TRACE.
R* = 5
DD
+5V
V
, as shown in Figure 14.
DD
Layout, Grounding, and Bypassing
4.7 F
0.1 F
AGND
MAX127
MAX128
**
SUPPLY
DGND
+5V
CIRCUITRY
DIGITAL
GND
DGND
DD
with
15