Datasheet

Voltage Reference Congurations
The MAX11903 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
MAX11903. 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
MAX11903.
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 3. MAX11903 External Reference Recommendations
Table 2. Voltage Reference Configurations
PART V
OUT
(V)
TEMPERATURE
COEFFICIENT
(ppm/°C, max)
INITIAL
ACCURACY
(%)
NOISE
(0.1Hz TO 10Hz)
(µV
P-P
)
PACKAGE
MAX6126 2.5, 3 3 0.02 1.45 µMAX-8, SO-8
MAX6325 2.5 1 0.04 1.5 SO-8
REFERENCE
CONFIGURATION
INTERNAL
REFERENCE BUFFERS
REFIN V
REF
V
REFVDD
Internal Reference Buffer ON 2.5V to V
REFVDD
- 0.2V 2.5V to V
REFVDD
- 0.2V 2.7V to 3.6V
External Reference
Buffer
OFF
Tie to 0V or disable
through serial interface
2.5V to V
REFVDD
2.5V to 3.6V
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MAX11903 18-Bit, 1.6Msps, Low-Power,
Fully Differential SAR ADC