Unbuffered external reference drives multiple adcs – Rainbow Electronics MAX1209 User Manual
Page 23
Unbuffered External
Reference Drives Multiple ADCs
The unbuffered external reference mode allows for pre-
cise control over the MAX1209 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 five-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
MAX1209
12-Bit, 80Msps, 3.3V IF-Sampling ADC
______________________________________________________________________________________
23
MAX1209
*PLACE THE 1
µF REFP-TO-REFN BYPASS CAPACITOR AS CLOSE TO THE DEVICE AS POSSIBLE.
0.1
µF
0.1
µF
5
2.157V
+3.3V
1
2
2
4
1
3
5
47
Ω
1.47k
Ω
+3.3V
10
µF
6V
330
µF
6V
+3.3V
2.2
µF
0.1
µF
1
µF*
10
µF
0.1
µF
0.1
µF
0.1
µF
REFOUT
REFN
REFIN
39
1
2
3
V
DD
GND
COM
REFP
38
MAX6066
MAX4230
0.1
µF
0.47
µF
1.649V
2
4
1
3
5
47
Ω
1.47k
Ω
+3.3V
10
µF
6V
330
µF
6V
MAX4230
0.1
µF
1.141V
2
4
1
3
5
47
Ω
1.47k
Ω
+3.3V
10
µF
6V
330
µF
6V
MAX4230
MAX1209
+3.3V
2.2
µF
0.1
µF
1
µF*
10
µF
0.1
µF
0.1
µF
0.1
µF
REFOUT
REFN
REFIN
39
1
2
3
V
DD
GND
COM
REFP
38
3.000V
24.3k
Ω
1%
20k
Ω
1%
26.7k
Ω
1%
26.7k
Ω
1%
20k
Ω
1%
20k
Ω
1%
20k
Ω
1%
2.2
µF
2.2
µF
Figure 14. External Unbuffered Reference Driving Multiple ADCs