Datasheet

MAX1444
10-Bit, 40Msps, 3.0V, Low-Power
ADC with Internal Reference
16 ______________________________________________________________________________________
Buffered External Reference Drives
Multiple ADCs
Multiple-converter systems based on the MAX1195 are
well suited for use with a common reference voltage.
The REFIN pin of those converters can be connected
directly to an external reference source. A precision
bandgap reference like the MAX6062 generates an
external DC level of 2.048V (Figure 10), and exhibits a
noise voltage density of 150nV/√Hz. Its output passes
through a one-pole lowpass filter (with 10Hz cutoff fre-
quency) to the MAX4250, which buffers the reference
before its output is applied to a second 10Hz lowpass
filter. The MAX4250 provides a low offset voltage (for
high gain accuracy) and a low noise level. The passive
10Hz filter following the buffer attenuates noise pro-
duced in the voltage reference and buffer stages. This
filtered noise density, which decreases for higher fre-
quencies, meets the noise levels specified for precision
ADC operation.
REFOUT
29
N.C.
REFIN
31
REFP
32
REFN
1
COM
2
0.1
μ
F
0.1
μ
F
0.1
μ
F
0.1
μ
F
2.048V
100
μ
F2
5
3
2
3
1
4
1
MAX1444
N = 1
MAX4250
REFOUT
29
N.C.
REFIN
31
REFP
32
REFN
1
COM
2
0.1
μ
F
0.1
μ
F
0.1
μ
F
0.1
μ
F
MAX1444
N = 1000
0.1
μ
F
162
Ω
16.2k
Ω
3.3V
1
μ
F
10Hz LOWPASS
FILTER 10Hz LOWPASS
FILTER
NOTE: ONE FRONT-END REFERENCE CIRCUIT DESIGN MAY BE USED WITH UP TO 1000 ADCs.
2.2
μ
F
10V
0.1
μ
F
0.1
μ
F
3.3V
MAX6062
Figure 10. Buffered External Reference Drives Up to 1000 ADCs