MAX1177 Datasheet, PDF (9/13 Pages) Maxim Integrated Products – 16-Bit, 135ksps, Single-Supply ADC with 0 to 10V Input Range

16-Bit, 135ksps, Single-Supply ADC
with 0 to 10V Input Range
ACQUISITION
CS
R/C
EOC
REF AND
BUFFER
POWER
CONVERSION
DATA
OUT
ACQUISITION
CS
R/C
EOC
REF AND
BUFFER
POWER
CONVERSION
DATA
OUT
Figure 5. Selecting Standby Mode
Figure 6. Selecting Shutdown Mode
Standby Mode
While in standby mode, the supply current is less than
3.7mA (typ). The next falling edge of CS with R/C low
causes the MAX1177 to exit standby mode and begin
acquisition. The reference and reference buffer remain
active to allow quick turn-on time.
Shutdown Mode
In shutdown mode, the reference and reference buffer
are shut down between conversions. Shutdown mode
reduces supply current to 0.5µA (typ) immediately after
the conversion. The next falling edge of CS with R/C
low causes the reference and buffer to wake up and
enter acquisition mode. To achieve 16-bit accuracy,
allow 12ms for the internal reference to wake up
(C_REFADJ = 0.1µF, C_REF = 10µF).
Internal and External Reference
Internal Reference
The internal reference of the MAX1177 is internally
buffered to provide +4.096V output at REF. Bypass
REF to AGND and REFADJ to AGND with 10µF and
0.1µF, respectively. Sink or source current at REFADJ
to make fine adjustments to the internal reference. The
input impedance of REFADJ is nominally 5kΩ. Use the
circuit in Figure 7 to adjust the internal reference to
±1.5%.
External Reference
An external reference can be placed at either the input
(REFADJ) or the output (REF) of the MAX1177’s internal
buffer amplifier. Using the buffered REFADJ input
+5V
100kΩ
68kΩ
150kΩ
0.1µF
MAX1177
REFADJ
Figure 7. MAX1177 Reference Adjust Circuit
makes buffering the external reference unnecessary.
The input impedance of REFADJ is typically 5kΩ. The
internal buffer output must be bypassed at REF with a
10µF capacitor.
Connect REFADJ to AV_DD to disable the internal buffer.
Directly drive REF using an external 3.8V to 4.2V refer-
ence. During conversion, the external reference must
be able to drive 100µA of DC load current and have an
output impedance of 10Ω or less.
For optimal performance, buffer the reference through
an op amp and bypass REF with a 10µF capacitor.
Consider the MAX1177’s equivalent input noise (0.6
LSB) when choosing a reference.
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