Datasheet
AVSS
16
AINP
AINN
13
14
R
2
301W
1 Fm
-2.5V
AVDD
15
10nF
C0G
1 Fm
R
2
301W
+2.5V
ADS1281
OPA211
-2.5V
OPA211
+2.5V
VREFP
VREFN
DGND
6,12,23
18
17
R
1kW
3
C
0.1 F
2
m
1 Fm
C
1
100 Fm
+6.5V
(REF5050+2.8V)
-2.5V
REF02
REF5050
R
1
200W
49.9W
49.9W
1 Fm
20kW
1nF
C0G
100W
100W
Geophone
G=1+2
R
2
R
1
||2 75k´ W
+2.5V
-2.5V
C0G
10nF
100W
100W
1nF
C0G
20kW
75kW75kW
ADS1281
www.ti.com
SBAS378D –AUGUST 2007–REVISED JUNE 2010
APPLICATION INFORMATION
The ADS1281 is a very high-resolution ADC. Optimal The REF02 +5V reference provides the reference to
device performance requires giving special attention the ADS1281. The reference output is filtered by the
to the support circuitry and printed circuit board optional R
3
and C
1
filter network. The filter requires
(PCB) design. Locate noisy digital components, such several seconds to settle after power-on. Capacitor
as microcontrollers and oscillators, in an area of the C
2
provides high-frequency bypassing of the
PCB away from the converter or front-end reference inputs and should be placed close to the
components. Place the digital components close to ADS1281 pins. Note that R
3
(1kΩ) results in a
the power-entry point to keep the digital current path systematic gain error (1.2%). The filter can be
short and separate from sensitive analog externally buffered to eliminate the gain error.
components.
Alternatively, the REF5050 (5V) or REF5045 (4.5V)
Figure 56 shows a typical geophone interface. This reference can be used. The REF5045 reference has
application circuit shows the ADS1281 and the the advantage of +5V power supply operation. The
OPA211 pre-amplifiers operating with ±2.5V supplies. REF5050 requires +5.2V minimum power supply.
The OPA211s are shown with gain = +4 [G = 1 + 2
As with any precision circuit, use good supply
(R
2
/R
1
)]. This pre-amplifier configuration has
bypassing techniques. Place the capacitors close to
inherently good common-mode rejection. The 49.9Ω
the device pins.
resistors isolate the driver outputs from the bypass
capacitor.
If switching dc/dc supplies are used to power the
device, check for frequency components of the supply
The 20kΩ input resistors provide the common-mode
present within the ADS1281 passband. Voltage ripple
bias for the amplifiers. The optional differential and
should be kept as low as possible.
common-mode input filters attenuate possible
out-of-band interference (such as RFI).
Recommended 75kΩ resistors provide a 20mV
DC
input offset. The offset moves the low-level idle tones
out of the passband.
Figure 56. Geophone Interface, Dual Power-Supply Configuration
Copyright © 2007–2010, Texas Instruments Incorporated Submit Documentation Feedback 37
Product Folder Link(s): ADS1281