Maxim Integrated MAX12557 - Manual (Page 23)

Buffered External Reference Drives
Multiple ADCs
The buffered external reference mode allows for more
control over the MAX12557 reference voltage and
allows multiple converters to use a common reference.
The REFIN input impedance is >50M
Ω.
Figure 12 shows the MAX6029 precision 2.048V bandgap
reference used as a common reference for multiple con-
verters. The 2.048V output of the MAX6029 passes
through a single-pole 10Hz LP filter to the MAX4230.
The MAX4250 buffers the 2.048V reference and pro-
vides additional 10Hz LP filtering before its output is
applied to the REFIN input of the MAX12557.
Unbuffered External Reference Drives
Multiple ADCs
The unbuffered external reference mode allows for pre-
cise control over the MAX12557 reference and allows
multiple converters to use a common reference.
Connecting REFIN to GND disables the internal refer-
MAX12557
Dual, 65Msps, 14-Bit, IF/Baseband ADC
______________________________________________________________________________________ 23
MAX4230
0.1 µF
1 µF
5
2
3
4
1
1
5
2
REFIN
V DD
GND
0.1 µF
47 Ω
3.3V
2.048V
16.2k Ω
REFOUT
0.1 µF
REF_P
REF_N
COM_
0.1 µF
0.1 µF
0.1 µF
2.2 µF 0.1 µF
3.3V
1.47k Ω
300 µF
6V
NOTE: ONE FRONT-END REFERENCE CIRCUIT IS
CAPABLE OF SOURCING UP TO 15mA AND
SINKING UP TO 30mA OF OUTPUT CURRENT.
10 µF
0.1 µF
REFIN
V DD
GND
REFOUT
0.1 µF
REF_P
REF_N
COM_
0.1 µF
0.1 µF
0.1 µF
2.2 µF 0.1 µF
10 µF 0.1 µF
MAX12557
MAX6029
(EUK21)
MAX12557
Figure 12. External Buffered (MAX4230) Reference Drive Using a MAX6029 Bandgap Reference