MAX1065_09 Datasheet, PDF (10/14 Pages) Maxim Integrated Products – Low-Power, 14-Bit Analog-to-Digital Converters with Parallel Interface

Low-Power, 14-Bit Analog-to-Digital Converters
with Parallel Interface
AIN
C_SWITCH
3pF
TRACK
REF
CAPACITIVE DAC
HOLD
C_DAC = 32pF
AGND
HOLD
ZERO
R_IN
800Ω
TRACK
AUTO-ZERO
RAIL
Figure 4. Equivalent Input Circuit
Standby Mode
While in standby mode, the supply current is reduced
to less than 1mA (typ). The next falling edge of CS with
R/C low causes the MAX1065/MAX1066 to exit standby
mode and begin acquisition. The reference and refer-
ence buffer remain active to allow quick turn-on time.
Standby mode allows significant power savings while
running at the maximum sample rate.
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 falling edge of CS with R/C low
causes the reference and buffer to wake up and enter
acquisition mode. To achieve 14-bit accuracy, allow
10ms (C_REFADJ = 0.1µF, C_REF = 1µF) for the internal
reference to wake up. Increase wakeup time propor-
tionally when using larger values of C_REFADJ and C_REF.
Internal and External Reference
Internal Reference
The internal reference of the MAX1065/MAX1066 is
internally buffered to provide 4.096V (typ) output at
REF. Bypass REF to AGND and REFADJ to AGND with
1µF and 0.1µF respectively. Fine adjustments can be
made to the internal reference voltage by sinking or
sourcing current at REFADJ. The input impedance at
REFADJ is nominally 5kΩ. The internal reference volt-
age is adjustable to ±1.5% with the circuit of Figure 7.
External Reference
An external reference can be placed at either the input
(REFADJ) or the output (REF) of the MAX1065/
MAX1066’s internal buffer amplifier. When connecting
an external reference to REFADJ, the input impedance
is typically 5kΩ. Using the buffered REFADJ input
makes buffering the external reference unnecessary;
however, the internal buffer output must be bypassed
at REF with a 1µF capacitor.
Connect REFADJ to AV_DD to disable the internal buffer.
Directly drive REF using an external reference. During
conversion, the external reference must be able to
drive 100µA of DC load current and have an output
impedance of 10Ω or less. REFADJ’s impedance is typ-
ically 5kΩ. The DC input impedance of REF is 40kΩ
minimum.
For optimal performance, buffer the reference through
an op amp and bypass REF with a 1µF capacitor.
Consider the MAX1065/MAX1066’s equivalent input
noise (80µV_RMS) when choosing a reference.
CS
R/C
EOC
REF
AND
BUFFER
ACQUISITION
REF POWER-
DOWN BIT
CONVERSION
DATA
OUT
ACQUISITION
CS
REF POWER-
DOWN BIT
R/C
EOC
REF
AND
BUFFER
CONVERSION
DATA
OUT
Figure 5. Selecting Standby Mode
Figure 6. Selecting Shutdown Mode
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