Rainbow Electronics MAX12553 - Manual (Page 24)

MAX12553
14-Bit, 65Msps, 3.3V ADC
24 ______________________________________________________________________________________
Unbuffered External
Reference Drives Multiple ADCs
The unbuffered external reference mode allows for pre-
cise control over the MAX12553 reference and allows
multiple converters to use a common reference.
Connecting REFIN to GND disables the internal refer-
ence, allowing REFP, REFN, and COM to be driven
directly by a set of external reference sources.
Figure 14 uses the MAX6029EUK30 precision 3.000V
reference as a common reference for multiple convert-
ers. A seven-component resistive divider chain follows
the MAX6029 voltage reference. The 0.47µF capacitor
along this chain creates a 10Hz lowpass filter. Three
MAX4230 operational amplifiers buffer taps along this
resistor chain providing 2.413V, 1.647V, and 0.880V to
the MAX12553’s REFP, COM, REFN reference inputs,
MAX12553
*PLACE THE 1µF REFP-TO-REFN BYPASS CAPACITOR AS CLOSE TO THE DEVICE AS POSSIBLE.
0.1µF
0.1µF
5
2.413V
+3.3V
1
2
2
4
1
3
5
47Ω
1.47kΩ
+3.3V
10µF
6V 330µF
6V
+3.3V
2.2µF
0.1µF
1µF* 10µF
0.1µF
0.1µF
0.1µF
REFOUT
REFN
REFIN
39
1
2
3
V DD
GND
COM
REFP
38
MAX6029EUK30
MAX4230
0.1µF 0.47µF
1.647V
2
4
1
3
5
47Ω
1.47kΩ
+3.3V
10µF
6V 330µF
6V
MAX4230
0.1µF
0.880V
2
4
1
3
5
47Ω
1.47kΩ
+3.3V
10µF
6V 330µF
6V
MAX4230
MAX12553
+3.3V
2.2µF
0.1µF
1µF* 10µF
0.1µF
0.1µF
0.1µF
REFOUT
REFN
REFIN
39
1
2
3
V DD
GND
COM
REFP
38
3.000V
20kΩ
1%
20kΩ
1%
52.3kΩ
1%
52.3kΩ
1%
20kΩ
1%
20kΩ
1%
20kΩ
1%
0.1µF
2.2µF
2.2µF
Figure 14. External Unbuffered Reference Driving Multiple ADCs