MAX1191 Datasheet, PDF (22/27 Pages) Maxim Integrated Products – Ultra-Low-Power, 7.5Msps, Dual 8-Bit ADC

Ultra-Low-Power, 7.5Msps, Dual 8-Bit ADC
3V
0.1µF
1
2
MAX6066
2.500V
3
1µF
NOTE: ONE FRONT-END
REFERENCE CIRCUIT
SUPPORTS UP TO 160 MAX1191s.
3V
UNCOMMITTED
1MΩ
12
0.1µF
4
1/4
14
1MΩ
13 ^MAX4254
11
1%
30.1kΩ
3
1/4
1
MAX4254
2
10µF
6V
1%
10.0kΩ
5
1/4
7
MAX4254
6
10µF
6V
1%
10.0kΩ
10
1/4
8
MAX4254
9
10µF
6V
1%
49.9kΩ
47Ω
1.47kΩ
47Ω
1.47kΩ
47Ω
1.47kΩ
1.748V
330µF
6V
1.498V
330µF
6V
1.248V
330µF
6V
0.33µF
27 _REFP
V_DD
N=1
0.33µF
26
MAX1191
REFN
REFIN
24
25 _COM
0.33µF
GND
0.1µF
0.33µF
27 _REFP
V_DD
N = 160
0.33µF
26
MAX1191
REFN
REFIN
24
25 _COM
0.33µF
GND
2.2µF
Figure 11. External Unbuffered Reference Driving 160 ADCs with MAX4254 and MAX6066
Figure 11 shows the MAX6066 precision bandgap ref-
erence used as a common reference for multiple con-
verters. The 2.500V output of the MAX6066 is followed
by a 10Hz lowpass filter and precision voltage-divider.
The MAX4254 buffers the taps of this divider to provide
the 1.75V, 1.5V, and 1.25V sources to drive REFP,
REFN, and COM. The MAX4254 provides a low offset
voltage and low noise level. The individual voltage fol-
lowers are connected to 10Hz lowpass filters, which fil-
ter both the reference-voltage and amplifier noise to a
level of 3nV/√Hz. The 1.75V and 1.25V reference volt-
ages set the differential full-scale range of the associat-
ed ADCs at ±0.5V.
The common power supply for all active components
removes any concern regarding power-supply
sequencing when powering up or down.
With the outputs of the MAX4252 matching better than
0.1%, the buffers and subsequent lowpass filters sup-
port as many as 160 MAX1191s.
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