Datasheet

MAX1142/MAX1143
14-Bit ADC, 200ksps, +5V Single-Supply
with Reference
14 ______________________________________________________________________________________
External reference
An external reference can be placed at either the input
(REFADJ) or the output (REF) of the MAX1142/
MAX1143’s internal buffer amplifier.
When connecting an external reference to REFADJ, the
input impedance is typically 9kΩ. Using the buffered
REFADJ input makes buffering of the external reference
unnecessary. The internal buffer output must be
bypassed at REF with a 2.2µF capacitor.
When connecting an external reference at REF,
REFADJ must be connected to AV
DD
. The input imped-
ance at REF is 16kΩ for DC currents. During conver-
sion, an external reference at REF must deliver 250µA
DC load current and have an output impedance of 10Ω
or less. If the reference has a higher output impedance
or is noisy, bypass it at the REF pin with a 4.7µF capac-
itor.
Analog Input
The MAX1142/MAX1143 use a capacitive DAC that
provides an inherent track/hold function. Drive AIN with
a source impedance less than 10Ω. Any signal condi-
tioning circuitry must settle with 16-bit accuracy in less
than 500ns. Limit the input bandwidth to less than half
the sampling frequency to eliminate aliasing. The
MAX1142/MAX1143 has a complex input impedance
which varies from unipolar to bipolar mode (Figure 1).
Input Range
The analog input range in unipolar mode is 0 to +12V
for the MAX1142, and 0 to +4.096V for the MAX1143. In
bipolar mode, the analog input can be -12V to +12V for
the MAX1142, and -4.096V to +4.096V for the
MAX1143. Unipolar and bipolar mode is programmed
with the UNI/BIP bit of the Control-Byte. When using a
reference other than the MAX1142/MAX1143’s internal
+4.096V reference, the full-scale input range will vary
accordingly. The full-scale input range depends on the
voltage at REF and the sampling mode selected (Tables
3 and 4).
Input Acquisition and Settling
Clocking-in a Control-Byte starts input acquisition. In
bipolar mode, the main capacitor array starts acquiring
the input as soon as a start bit is recognized. If unipolar
mode is selected by the second DIN bit, the part will
immediately switch to unipolar sampling mode and
acquire a sample.
Acquisition can be extended by eight clock cycles by
setting M1 = 1, M0 = 1 (long acquisition mode). The
sampling instant in short acquisition completes on the
falling edge of the sixth clock cycle after the start bit
(Figure 2).
+5V
510kΩ
100kΩ
24kΩ
0.22µF
REFADJ
MAX1142
Figure 7. MAX1142 Reference-Adjust Circuit
Table 3. Unipolar Full Scale and Zero Scale
PART REFERENCE ZERO SCALE FULL SCALE
Internal 0 +12V
MAX1142
External 0 +12(V
REF
/4.096)
Internal 0 +4.096V
MAX1143
External 0 +V
REF
Table 4. Bipolar Full Scale, Zero Scale, and Negative Scale
PART REFERENCE
NEGATIVE FULL
SCALE
ZERO SCALE FULL SCALE
Internal -12V 0 +12V
MAX1142
External -12(V
REF
/4.096) 0 +12(V
REF
/4.096)
Internal -4.096V 0 +4.096V
MAX1143
External -V
REF
0 +V
REF