Datasheet

MAX1196
Dual 8-Bit, 40Msps, 3V, Low-Power ADC with
Internal Reference and Multiplexed Parallel Outputs
18 ______________________________________________________________________________________
produced in the voltage-reference and buffer stages.
This filtered noise density, which decreases for higher
frequencies, meets the noise levels specified for preci-
sion-ADC operation.
Unbuffered External Reference Drives
Multiple ADCs
Connecting each REFIN to analog ground disables the
internal reference of each device, allowing the internal
reference ladders to be driven directly by a set of exter-
nal reference sources. Followed by a 10Hz lowpass fil-
ter and precision voltage-divider, the MAX6066
generates a DC level of 2.500V. The buffered outputs of
this divider are set to 2.0V, 1.5V, and 1.0V, with an
accuracy that depends on the tolerance of the divider
resistors.
Those three voltages are buffered by the MAX4252,
which provides low noise and low DC offset. The individ-
ual voltage followers are connected to 10Hz lowpass fil-
ters, which filter both the reference-voltage and amplifier
noise to a level of 3nV/√Hz. The 2.0V and 1.0V reference
voltages set the differential full-scale range of the asso-
ciated ADCs at 2V
P-P
. The 2.0V and 1.0V buffers drive
the ADCs’ internal ladder resistances between them.
Note that the common power supply for all active com-
ponents 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 can
be replicated to support as many as 32 ADCs. For
applications requiring more than 32 matched ADCs, a
voltage-reference and divider string common to all con-
verters is highly recommended.
MAX4250
MAX6062
16.2kΩ
162Ω
3.3V
2
4
2
3
5
10Hz LOWPASS
FILTER
10Hz LOWPASS
FILTER
1
1
REFOUT
REFP
REFIN
1µF
MAX1196
N = 1
REFN
29N.C.
2.048V
N.C.
31
32
1
2
29
31
32
1
2
COM
REFOUT
NOTE: ONE FRONT-END REFERENCE CIRCUIT DESIGN CAN BE USED WITH UP TO 1000 ADCs.
REFP
REFIN
MAX1196
N = 1000
REFN
COM
3
0.1µF
0.1µF
3.3V
0.1µF0.1µF0.1µF
0.1µF
0.1µF
2.2µF
10V
0.1µF0.1µF
0.1µF
100µF
0.1µF
Figure 8. External Buffered (MAX4250) Reference Drive Using a MAX6062 Bandgap Reference