Rainbow Electronics MAX1111 - Manual (Page 18)

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 may
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 10
Ω
resistor can
be connected to form a lowpass filter.
MAX1110/MAX1111
+2.7V, Low-Power, Multichannel,
Serial 8-Bit ADCs
18 ______________________________________________________________________________________
+3V GND
SUPPLIES
DGND +3V DGND AGND V DD
DIGITAL
CIRCUITRY
MAX1110
MAX1111
R* = 10 Ω
* OPTIONAL
Figure 17. Power-Supply Grounding Connections
01111111
OUTPUT CODE
01111110
00000010
00000001
00000000
11111111
11111110
11111101
10000001
10000000
-FS
COM
INPUT VOLTAGE (LSB)
+FS -
1
LSB
2
+FS =
V REFIN
+ COM
2
-FS =
-V REFIN
+ COM
2
COM =
V
REFIN
2
1LSB =
V
REFIN
256
Figure 16. Bipolar Transfer Function
OUTPUT CODE
FULL-SCALE
TRANSITION
11111111
11111110
11111101
00000011
00000010
00000001
00000000
1 2 3 0 FS
FS - 1LSB
FS = V REFIN + COM
1LSB = V REFIN
256
INPUT VOLTAGE (LSB) (COM)
Figure 15. Unipolar Transfer Function