MAX1132 Datasheet, PDF (14/19 Pages) Maxim Integrated Products – 16-Bit ADC, 200ksps, 5V Single-Supply with Reference

16-Bit ADC, 200ksps, 5V Single-Supply
with Reference
Table 3. Unipolar Full Scale and Zero Scale
PART
MAX1132
MAX1133
REFERENCE
Internal
External
Internal
External
ZERO SCALE
0
0
0
0
FULL SCALE
+12V
+12(V_REF/4.096)
+4.096V
+V_REF
Table 4. Bipolar Full Scale, Zero Scale, and Negative Scale
PART
MAX1132
MAX1133
REFERENCE
Internal
External
Internal
External
NEGATIVE FULL
SCALE
-12V
-12(V_REF/4.096)
-4.096V
-V_REF
ZERO SCALE
0
0
0
0
FULL SCALE
+12V
+12(V_REF/4.096)
+4.096V
+V_REF
Most applications require an input buffer amplifier. If
the input signal is multiplexed, the input channel should
be switched immediately after acquistion, rather than
near the end of or after a conversion. This allows more
time for the input buffer amplifier to respond to a large
step-change in input signal. The input amplifier must
have a high enough slew-rate to complete the required
output voltage change before the beginning of the
acquisition time. At the beginning of acquisition, the
capacitive DAC is connected to the amplifier output,
causing some output disturbance. Ensure that the sam-
pled voltage has settled to within the required limits
before the end of the acquisition time. If the frequency
of interest is low, AIN can be bypassed with a large
enough capacitor to charge the capacitive DAC with
very little change in voltage. However, for AC use, AIN
must be driven by a wideband buffer (at least 10MHz),
which must be stable with the DACs capacitive load (in
parallel with any AIN bypass capacitor used) and also
settle quickly (Figures 8 or 9).
Digital Noise
Digital noise can couple to AIN and REF. The conver-
sion clock (SCLK) and other digital signals that are
active during input acquisition contribute noise to the
conversion result. If the noise signal is synchronous to
the sampling interval, an effective input offset is pro-
duced. Asynchronous signals produce random noise
on the input, whose high-frequency components may
be aliased into the frequency band of interest. Minimize
noise by presenting a low impedance (at the frequen-
cies contained in the noise signal) at the inputs. This
requires bypassing AIN to AGND, or buffering the input
with an amplifier that has a small-signal bandwidth of
several MHz, or preferably both. AIN has a bandwidth
of about 4MHz.
Offsets resulting from synchronous noise (such as the
conversion clock) are canceled by the MAX1132/
MAX1133’s calibration scheme. The magnitude of the
offset produced by a synchronous signal depends on
the signal’s shape. Recalibration may be appropriate if
the shape or relative timing of the clock or other digital
signals change, as might occur if more than one clock
signal or frequency is used.
Distortion
Avoid degrading dynamic performance by choosing an
amplifier with distortion much less than the MAX1132/
MAX1133’s THD (-90dB) at frequencies of interest. If
the chosen amplifier has insufficient common-mode
rejection, which results in degraded THD performance,
use the inverting configuration to eliminate errors from
common-mode voltage. Low temperature-coefficient
resistors reduce linearity errors caused by resistance
changes due to self-heating. To reduce linearity errors
due to finite amplifier gain, use an amplifier circuit with
sufficient loop gain at the frequencies of interest.
DC Accuracy
If DC accuracy is important, choose a buffer with an
offset much less than the MAX1132/MAX1133’s maxi-
mum offset (±6mV), or whose offset can be trimmed
while maintaining good stability over the required tem-
perature range.
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