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.

affect the comparator in the ADC. Bypass the supply to

the star ground with 0.1µF and 1µF capacitors close to

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.

+2.7V, Low-Power, Multichannel,

Serial 8-Bit ADCs

18

______________________________________________________________________________________

+3V

GND

SUPPLIES

DGND

+3V

DGND

AGND

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 =

+ COM

2

-FS =

+ COM

2

COM =

2

1LSB =

256

Figure 16. Bipolar Transfer Function

OUTPUT CODE

FULL-SCALE

TRANSITION

11111111

11111110

11111101

00000011

00000010

00000001

00000000

12

3

0

FS

FS - 1LSB

256

INPUT VOLTAGE (LSB)

(COM)

Figure 15. Unipolar Transfer Function