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 23 shows the recommended system ground

connections. Establish a single-point ground (“star”

ground point) at AGND, separate from the logic

ground. Connect all other analog grounds and DGND

to it. No other digital-system ground should be con-

nected to this single-point analog ground. The ground

return to the power supply for this star ground should

be low impedance and as short as possible for noise-

free operation.

affect the high-speed comparator in the ADC. Bypass

these supplies to the single-point analog ground with

Low-Power, 12-Bit Sampling ADC

with Internal Reference and Power-Down

______________________________________________________________________________________

21

MAX191

AIN +

AIN -

D0–D11

R7

10k

R8

10k

VREF

R6

10k

R5

10k

R1

10k

R2

100

Ω

R3

10k

R4

49.9

Ω

VREF

R9*

20k

0.1

µF*

R10*

49.9

Ω

* CONNECT AIN- TO AGND WHEN USING DUAL SUPPLIES

MAX480

Figure 21b. Offset (±10mV) and Gain (±1%) Trim Circuit

01 . . . 111

01 . . . 110

00 . . . 010

00 . . . 001

11 . . . 111

11 . . . 110

00 . . . 000

10 . . . 001

10 . . . 000

11 . . . 101

0V

VREF - 1LSB

VREF

––––

2

0V

SINGLE SUPPLY

VREF

AIN- = ––––

2

(

)

DUAL SUPPLY

AIN- = 0V

VREF

–––– - 1LSB

2

-VREF

––––

2

Figure 22. Bipolar Transfer Function

SUPPLIES

+5V

-5V

GND

AGND

+5V

DGND

R* = 10

Ω

DIGITAL

CIRCUITRY

*OPTIONAL

MAX191

Figure 23. Power-Supply Grounding Connection