MAX1270ACAI Maxim, MAX1270ACAI Datasheet - Page 16

• Manufacturer Part Number: MAX1270ACAI
• Description: Multirange / +5V / 8-Channel / Serial 12-Bit ADCs
• Manufacturer: Maxim

Figure 14a. Unipolar Transfer Function
Output data coding for the MAX1270/MAX1271 is bina-
ry in unipolar mode with 1LSB = (FS / 4096) and two’s
complement binary in bipolar mode with 1LSB = [(2 ·
| FS | ) / 4096]. Code transitions occur halfway between
successive-integer LSB values. Figures 14a and 14b
show the input/output (I/O) transfer functions for unipo-
lar and bipolar operations, respectively. For full-scale
values, refer to Table 3.
Careful printed circuit board layout is essential for best
system performance. Use a ground plane for best per-
formance. 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
Multirange, +5V, 8-Channel,
Serial 12-Bit ADCs
7-184
00... 011
00... 010
00... 001
00... 000
11... 111
11... 110
11... 101
OUTPUT CODE
DD
0
___________________________________________________________________________________
, as shown in Figure 15.
1
Layout, Grounding, and Bypassing
2
3
INPUT VOLTAGE (LSB)
FULL-SCALE
TRANSITION
Transfer Function
FS -
3
/
2
LSB
1 LSB =
FS
DD
4096
FS
with
Figure 14b. Bipolar Transfer Function
Figure 15. Power-Supply Grounding Connections
011... 111
011... 110
000... 001
000... 000
111... 111
100... 010
100... 001
100... 000
* OPTIONAL
** CONNECT AGND AND DGND WITH A GROUND PLANE OR A SHORT TRACE.
R* = 5Ω
OUTPUT CODE
+5V
V
DD
-FS
4.7µF
0.1µF
AGND
MAX1270
MAX1271
INPUT VOLTAGE (LSB)
**
SUPPLY
0
DGND
+FS - 1 LSB
+5V
CIRCUITRY
DIGITAL
1 LSB =
GND
DGND
2FS
4096