MAX1446_08 Datasheet, PDF (16/20 Pages) Maxim Integrated Products – 10-Bit, 60Msps, 3.0V, Low-Power ADC with Internal Reference

10-Bit, 60Msps, 3.0V, Low-Power
ADC with Internal Reference
3.3V
0.1μF
3.3V
0.1μF
2.048V
1
MAX6062
3
16.2kΩ
2
1μF
10Hz LOWPASS
FILTER
0.1μF
3
5
MAX4250
4
2
162Ω
1
100μF
10Hz LOWPASS
FILTER
0.1μF
N.C. 29 _REFOUT
31 _REFIN
32 _{REFP MAX1446}
1 _REFN ^{N = 1}
2 _COM
0.1μF 0.1μF
0.1μF
0.1μF
0.1μF
N.C. 29 _REFOUT
31 _REFIN
32 _{REFP MAX1446}
1
N = 1000
REFN
2 _COM
0.1μF 0.1μF
2.2μF
10V
NOTE: ONE FRONT-END REFERENCE CIRCUIT DESIGN MAY BE USED WITH UP TO 1000 ADCs.
Figure 10. Buffered External Reference Drives Up to 1000 ADCs
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.
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 (Figure 11), 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. The three voltages are buffered by the
MAX4252, which provides low noise and low DC offset.
The individual voltage followers are connected to 10Hz
lowpass filters, which filter both the reference voltage
and amplifier noise to a level of 3n√Hz. The 2.0V and
1.0V reference voltages set the differential full-scale
range of the associated ADCs at 2V_P-P. The 2.0V and
1.0V buffers drive the ADC’s internal ladder resistances
between them. Note that 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 can
be replicated to support as many as 32 ADCs. For
applications that require more than 32 matched ADCs,
a voltage reference and divider string common to all
converters is highly recommended.
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