Datasheet

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.
High-frequency noise in the V
DD
power supply may
affect the high-speed comparator in the ADC. Bypass
these supplies to the single-point analog ground with
MAX191
Low-Power, 12-Bit Sampling ADC
with Internal Reference and Power-Down
______________________________________________________________________________________ 21
MAX191
AIN +
AIN -
D0–D11
V
IN
R7
10k
R8
10k
VREF
R6
10k
R5
10k
R1
10k
R2
100
R3
10k
R4
49.9
VREF
R9*
20k
0.1µF*
R10*
49.9
* 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
V
DD
AGND V
SS
DGND
+5V DGND
R* = 10
DIGITAL
CIRCUITRY
*OPTIONAL
MAX191
Figure 23. Power-Supply Grounding Connection