MAX1286–MAX1289
150ksps, 12-Bit, 2-Channel Single-Ended, and
1-Channel True-Differential ADCs
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where R
IN
= 1.5kΩ, R
S
is the source impedance of the
input signal, and t
PWR
= 1µs is the power-up time of the
device.
Note: t
ACQ
is never less than 1.4µs and any source
impedance below 300Ω does not significantly affect the
ADC’s AC performance. A high-impedance source can
be accommodated either by lengthening t
ACQ
or by
placing a 1µF capacitor between the positive and neg-
ative analog inputs.
Selecting AIN1 or AIN2
(MAX1286/MAX1287)
Select one of the MAX1286/MAX1287s’ two positive
input channels using the CNVST pin. If AIN1 is desired
(Figure 5a), drive CNVST high to power up the ADC
and place the T/H in track mode with AIN1 connected
to the positive input capacitor. Hold CNVST high for
t
ACQ
to fully acquire the signal. Drive CNVST low to
place the T/H in hold mode. The ADC then performs a
conversion and shutdown automatically. The MSB is
available at DOUT after 3.7µs. Data can then be
clocked out using SCLK. Clock out all 12 bits of data
before driving CNVST high for the next conversion. If all
12 bits of data are not clocked out before CNVST is dri-
ven high, AIN2 is selected for the next conversion.
If AIN2 is desired (Figure 5b), drive CNVST high for at
least 30ns. Next, drive it low for at least 30ns, and then
high again. This powers up the ADC and places the
T/H in track mode with AIN2 connected to the positive
input capacitor. Now hold CNVST high for t
ACQ
to fully
acquire the signal. Drive CNVST low to place the T/H in
hold mode. The ADC then performs a conversion and
shutdown automatically. The MSB is available at DOUT
after 3.7µs. Data can then be clocked out using SCLK.
If all 12 bits of data are not clocked out before CNVST
is driven high, AIN2 is selected for the next conversion.
Selecting Unipolar or Bipolar Conversions
(MAX1288/MAX1289)
Initiate true-differential conversions with the
MAX1288/MAX1289s’ unipolar and bipolar modes,
using the CNVST pin. AIN+ and AIN- are sampled at
the falling edge of CNVST. In unipolar mode, AIN+ can
exceed AIN- by up to V
REF
. The output format is
straight binary. In bipolar mode, either input can
exceed the other by up to V
REF
/2. The output format is
two’s complement.
Note: In both modes, AIN+ and AIN- must not exceed
V
DD
by more than 50mV or be lower than GND by more
than 50mV.
If unipolar mode is desired (Figure 5a), drive CNVST
high to power up the ADC and place the T/H in track
mode with AIN+ and AIN- connected to the input
capacitors. Hold CNVST high for t
ACQ
to fully acquire
the signal. Drive CNVST low to place the T/H in hold
mode. The ADC then performs a conversion and shut-
down automatically. The MSB is available at DOUT
after 3.7µs. Data can then be clocked out using SCLK.
Clock out all 12 bits of data before driving CNVST high
for the next conversion. If all 12 bits of data are not
clocked out before CNVST is driven high, bipolar mode
is selected for the next conversion.
If bipolar mode is desired (Figure 5b), drive CNVST
high for at least 30ns. Next, drive it low for at least 30ns
and then high again. This places the T/H in track mode
with AIN+ and AIN- connected to the input capacitors.
Now hold CNVST high for t
ACQ
to fully acquire the sig-
nal. Drive CNVST low to place the T/H in hold mode.
The ADC then performs a conversion and shutdown
automatically. The MSB is available at DOUT after
3.7µs. Data can then be clocked out using SCLK. If all
12 bits of data are not clocked out before CNVST is dri-
ven high, bipolar mode is selected for the next conver-
sion.
Input Bandwidth
The ADC’s input tracking circuitry has a 1MHz small-
signal bandwidth, so it is possible to digitize high-
speed transient events and measure periodic signals
with bandwidths exceeding the ADC’s sampling rate by
using undersampling techniques. To avoid high-fre-
quency signals being aliased into the frequency band
of interest, anti-alias filtering is recommended.
