MAX11902 Datasheet, PDF (17/29 Pages) Maxim Integrated Products – Fully Differential SAR ADC

MAX11902
18-Bit, 1Msps, Low-Power,
Fully Differential SAR ADC
Voltage Reference Configurations
The MAX11902 features internal reference buffers,
helping to reduce component count and board space.
Alternatively, the user may drive the reference nodes REF
with an external reference. To use the internal reference
buffers, drive the REFIN pin with an external reference
voltage source. It will appear on the REF pin as a buffered
reference output. The internal reference buffers can be
disabled by writing to a register (see the Mode Register
section) or tying REFIN to 0V. Once the on-chip reference
buffers are disabled, REF pins can be directly driven by
external reference buffers. A simplified diagram is shown
to clarify the required connections for external reference.
A low-noise, low-temperature drift reference is required
to achieve high system accuracy. The MAX6126 and
MAX6325 are particularly well suited for use with the
MAX11902. The MAX6126 and MAX6325 offer, respec-
tively, 0.02% and 0.04% initial accuracy and 3ppm/°C and
1ppm/°C (max) temperature coefficient for high-precision
applications. Maxim recommends bypassing REFIN and
REF with a 2.2µF capacitor close to the ADC pins.
Transfer Function
Figure 4 shows the ideal transfer characteristics for the
MAX11902.
The default data format is two’s complement. However,
offset binary format can be chosen by setting mode regis-
ter BIT 1 (see the Mode Register section).
Table 4 shows the codes in terms of input voltage applied.
The data reported is with V_REF of 3.0V, that gives a full-
scale range of 6V.
Table 2. Voltage Reference Configurations
REFERENCE
CONFIGURATION
Internal Reference Buffer
External Reference
Buffer
INTERNAL
REFERENCE BUFFERS
ON
OFF
REFIN
2.5V to V_REFVDD - 0.2V
Tie to 0V or disable
through serial interface
V_REF
2.5V to V_REFVDD - 0.2V
2.5V to V_REFVDD
V_REFVDD
2.7V to 3.6V
2.5V to 3.6V
Table 3. MAX11902 External Reference Recommendations
PART
MAX6126
MAX6325
V_OUT (V)
2.5, 3
2.5
TEMPERATURE
COEFFICIENT
(ppm/°C, max)
3
1
INITIAL
ACCURACY
(%)
0.02
0.04
NOISE
(0.1Hz TO 10Hz)
(µV_P-P)
1.45
1.5
PACKAGE
µMAX-8, SO-8
SO-8
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