MAX1270BCAI Datasheet, PDF (17/20 Pages) Maxim Integrated Products – Multirange, +5V, 8-Channel, Serial 12-Bit ADCs

Multirange, +5V, 8-Channel,
Serial 12-Bit ADCs
OUTPUT CODE
11... 111
11... 110
11... 101
FULL-SCALE
TRANSITION
1 LSB =
FS
4096
OUTPUT CODE
011... 111
011... 110
000... 001
000... 000
111... 111
1 LSB =
2|FS|
4096
00... 011
00... 010
00... 001
00... 000
01 2 3
INPUT VOLTAGE (LSB)
FS
FS - ³/₂LSB
Figure 14a. Unipolar Transfer Function
100... 010
100... 001
100... 000
-FS
0
INPUT VOLTAGE (LSB)
+FS - 1 LSB
Figure 14b. Bipolar Transfer Function
Transfer Function
Output data coding for the MAX1270/MAX1271 is bina-
ry 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 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.
Layout, Grounding, and Bypassing
Careful PC board layout is essential for best system
performance. Use a ground plane for best perfor-
mance. 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 15.
SUPPLY
+5V
GND
R* = 5Ω
4.7µF
0.1µF
**
V_DD
AGND
MAX1270
MAX1271
DGND
+5V DGND
DIGITAL
CIRCUITRY
*OPTIONAL
**CONNECT AGND AND DGND WITH A GROUND PLANE OR A SHORT TRACE.
Figure 15. Power-Supply Grounding Connections
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