MAX1245 Datasheet, PDF (17/20 Pages) Maxim Integrated Products – +2.375V, Low-Power, 8-Channel, Serial 12-Bit ADC

+2.375V, Low-Power, 8-Channel,
Serial 12-Bit ADC
OUTPUT CODE
11 . . . 111
11 . . . 110
11 . . . 101
FULL-SCALE
TRANSITION
FS = VREF + COM
00 . . . 011
ZS = COM
1LSB = ^VREF
4096
00 . . . 010
00 . . . 001
00 . . . 000
012 3
(COM)
FS
FS - 3/2LSB
INPUT VOLTAGE (LSBs)
Figure 14. Unipolar Transfer Function, Full Scale (FS) = VREF
+ COM, Zero Scale (ZS) = COM
ground should be low impedance and as short as pos-
sible for noise-free operation.
High-frequency noise in the VDD power supply may
affect the high-speed comparator in the ADC. Bypass
the supply to the star ground with 0.1µF and 4.7µF
capacitors close to pin 20 of the MAX1245. Minimize
capacitor lead lengths for best supply-noise rejection. If
the +2.5V power supply is very noisy, a 10Ω resistor
can be connected as a lowpass filter (Figure 16).
OUTPUT CODE
011 . . . 111
011 . . . 110
000 . . . 010
000 . . . 001
000 . . . 000
111 . . . 111
111 . . . 110
111 . . . 101
FS = ^VREF + COM
2
ZS = COM
-FS = ^-VREF + COM
2
1LSB = ^VREF
4096
100 . . . 001
100 . . . 000
- FS
COM
( VREF/2)
INPUT VOLTAGE (LSBs)
+FS - 1LSB
Figure 15. Bipolar Transfer Function, Full Scale (FS) = VREF /
2 + COM, Zero Scale (ZS) = COM
+2.5V
SUPPLIES
+2.5V GND
R* = 10Ω
VDD
AGND
COM DGND
+2.5V DGND
MAX1245
DIGITAL
CIRCUITRY
* OPTIONAL
Figure 16. Power-Supply Grounding Connection
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