MAX1111CE Datasheet, PDF (18/20 Pages) Maxim Integrated Products – 2.7V, Low-Power, Multichannel, Serial 8-Bit ADCs

+2.7V, Low-Power, Multichannel,
Serial 8-Bit ADCs
OUTPUT CODE
11111111
11111110
11111101
FULL-SCALE
TRANSITION
00000011
00000010
00000001
00000000
012 3
(COM)
INPUT VOLTAGE (LSB)
FS = V_REFIN + COM
1LSB = V_REFIN
256
FS
FS - 1LSB
+3V
R* = 10Ω
SUPPLIES
GND
V_DD
AGND
* OPTIONAL
MAX1110
MAX1111
DGND
+3V DGND
DIGITAL
CIRCUITRY
Figure 15. Unipolar Transfer Function
OUTPUT CODE
01111111
+FS
=
V_REFIN
2
+
COM
01111110
COM
=
V_REFIN
2
00000010
-FS
=
-V_REFIN
2
+
COM
00000001
00000000
1LSB
=
V_REFIN
256
11111111
11111110
11111101
10000001
10000000
-FS
COM
INPUT VOLTAGE (LSB)
+FS
-
1
2
LSB
Figure 16. Bipolar Transfer Function
Figure 17. Power-Supply Grounding Connections
Layout, Grounding, and Bypassing
For best performance, use printed circuit boards. Wire-
wrap boards are not recommended. Board layout
should ensure that digital and analog signal lines are
separated from each other. Do not run analog and digi-
tal (especially clock) lines parallel to one another, or
digital lines underneath the ADC package.
Figure 17 shows the recommended system ground
connections. A single-point analog ground (star ground
point) should be established at AGND, separate from
the logic ground. Connect all other analog grounds and
DGND to the star ground. No other digital system
ground should be connected to this ground. The
ground return to the power supply for the star ground
should be low impedance and as short as possible for
noise-free operation.
High-frequency noise in the V_DD power supply can
affect the comparator in the ADC. Bypass the supply to
the star ground with 0.1µF and 1µF capacitors close to
the V_DD pin of the MAX1110/MAX1111. Minimize
capacitor lead lengths for best supply-noise rejection. If
the +3V power supply is very noisy, a 10Ω resistor can
be connected to form a lowpass filter.
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