Rainbow Electronics MAX1089 User Manual

Page 8

MAX1086–MAX1089

150ksps, 10-Bit, 2-Channel Single-Ended, and
1-Channel True-Differential ADCs in SOT23

_______________________________________________________________________________________

where R

= 1.5k

Ω, R

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 300

Ω 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

(MAX1086/MAX1087)

Select between the MAX1086/MAX1087’s 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 will then perform
a conversion and shutdown automatically. The MSB is
available at DOUT after 3.7µs. Data can then be
clocked out using SCLK. Be sure to clock out all 12 bits
of data (the 10-bit result plus two sub-bits) before dri-
ving CNVST high for the next conversion. If all 12 bits of
data are not clocked out before CNVST is driven high,
AIN2 will be 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 will power-up the ADC and place 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 will then perform 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 will be selected for the next
conversion.

Selecting Unipolar or Bipolar Conversions

(MAX1088/MAX1089)

Initiate true-differential conversions with the
MAX1088/MAX1089’s 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

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 will then perform a conversion and
shutdown automatically. The MSB is available at DOUT
after 3.7µs. Data can then be clocked out using SCLK.
Be sure to clock out all 12 bits (the 10-bit result plus
two sub-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 will be
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 will place 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 signal. Drive CNVST low to place the T/H in
hold mode. The ADC will then perform 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, bipolar mode will be selected for
the next conversion.

Input Bandwidth

The ADCs 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.

RIN+

HOLD

RIN-

CIN+

REF

GND

DAC

CIN-

TRACK

COMPARATOR

GND(AIN-)

AIN2

AIN1(AIN+)

HOLD

*( ) APPLIES TO MAX1088/1089

Figure 4. Equivalent Input Circuit