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SBAS418I – SEPTEMBER 2007 – REVISED MARCH 2015
13 Application Information
The ADS1282 is a very high-resolution ADC. Optimal
Optional diode clamps protect the ADS1282 inputs
performance requires giving special attention to the
from voltage transients and overloads. The diodes
support circuitry and printed circuit board (PCB)
provide input protection when possible high-level
design. Locate noisy digital components, such as
transients may exceed the internal ESD diode rating.
microcontrollers, oscillators, etc, in an area of the
The REF02 +5V reference provides the reference to
PCB
away
from
the
converter
or
front-end
the ADS1282. The reference output is filtered by the
components. Locating the digital components close to
optional R
7
and C
5
filter network. The filter requires
the power-entry point keeps the digital current path
several seconds to settle after power-on. Capacitor
short
and
separate
from
sensitive
analog
C
7
provides
high-frequency
bypassing
of
the
components.
reference inputs and should be placed close to the
A typical geophone front-end application is shown in
ADS1282 pins. Note that R
7
(1k
Ω
) results in a
. The application shows the ADS1282
systematic gain error of 1.2%.
operation with dual ±2.5V analog supplies. The
Alternatively, the REF5050 (5V) or REF5045 (4.5V)
ADS1282 can also operate with a 5V analog
reference can be used. The REF5045 reference has
supply.
the advantage of operating from the +5V power
The
geophone
input
signal
is
filtered
both
supply. The REF5050 re5.2V minimum power
differentially, by components C
4
and R
1
to R
4
and
supply.
filtered independently by components C
2
, C
3
and R
1
,
Optional components R
8
, and R
9
provides a 20mV
R
2
. The differential filter removes high-frequency
offset to the ADS1282. The internal 300
Ω
resistors
normal mode components from the input signal. The
form a voltage divider with the external resistors to
independent
filters
remove
high-frequency
provide the offset. The offset moves the low level idle
components that are common to both input signals
tones out of the passband. Note that the offset is
leads (common-mode filter). The recommended input
independent of the PGA setting. The offset resistors
filters may not be required for all applications
also result in a small additional gain error. To
depending on the system requirements.
maintain good CMR performance, R
10
and R
11
should
Resistors R
5
and R
6
bias the signals inputs to
be matched to 0.1%, and the traces routed back
midsupply (ground), and also provide the bias current
directly to the reference.
return path for the ADS1282 inputs. For single-supply
Capacitor C
6
(10nF) filters the PGA output glitches
operation, set the bias to a low imp2.5V
caused by sampling of the modulator. The capacitor
(AVDD/2).
also forms a low-pass filter on the input signal with a
cut-off frequency
≉
25kHz.
40
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