ADS1255IDB Burr-Brown Corporation, ADS1255IDB Datasheet - Page 24

• Manufacturer Part Number: ADS1255IDB
• Description: Very Low Noise/ 24-Bit Analog-to-Digital Converter
• Manufacturer: Burr-Brown Corporation

ADS1255
ADS1256
SBAS288D − JUNE 2003 − REVISED AUGUST 2004
CALIBRATION
Offset and gain errors can be minimized using the
ADS1255/6 onboard calibration circuitry. Figure 23 shows
the calibration block diagram. Offset errors are corrected
with the Offset Calibration (OFC) register and, likewise,
full-scale errors are corrected with the Full-Scale
Calibration (FSC) register. Each of these registers is
24-bits and can be read from or written to.
The output of the ADS1255/6 after calibration is shown in
Equation 3.
24
AIN
AIN
N
P
DATA RATE
Figure 23. Calibration Block Diagram
PGA
30,000
15,000
(SPS)
7500
3750
2000
1000
500
100
2.5
60
50
30
25
15
10
5
VREFP
Modulator
Analog
VREFN
Table 18. Calibration Values for Different Data Rate Settings
Digital
Filter
5DC000 H
5DC000 H
5DC000 H
3C0000 H
3C0000 H
3C0000 H
4B0000 H
3E8000 H
4B0000 H
3E8000 H
4B0000 H
3E8000 H
400000 H
400000 H
400000 H
400000 H
Register
OFC
Register
FSC
X
Output
1.8639
1.8639
1.8639
1.8639
1.7474
1.7474
1.7474
2.1843
1.8202
2.1843
1.8202
2.1843
1.8202
2.7304
2.7304
2.7304
where
Table 18 along with the ideal values (assumes perfect
analog performance) for OFC and FSC. OFC is a Binary
Two’s Complement number that can range from
−8,388,608 to 8,388,607, while FSC is unipolar ranging
from 0 to 16,777,215.
The ADS1255/6 supports both self-calibration and system
calibration for any PGA setting using a set of five
commands:
SYSOCAL, and SYSGCAL. Calibration can be done at
any time, though in many applications the ADS1255/6 drift
performance is low enough that a single calibration is all
that is needed. DRDY goes high when calibration begins
and remains so until settled data is ready afterwards.
There is no need to discard data after a calibration. It is
strongly recommended to issue a self-calibration
command after power-up when the reference has
stabilized. After a reset, the ADS1255/6 performs
self-calibration. Calibration must be performed whenever
the data rate changes and should be performed when the
buffer configuration or PGA changes.
Output +
and
SELFOCAL,
PGA
IDEAL OFC
vary with data rate settings shown in
000000 H
000000 H
000000 H
000000 H
000000 H
000000 H
000000 H
000000 H
000000 H
000000 H
000000 H
000000 H
000000 H
000000 H
000000 H
000000 H
2V
REF
·
V
IN
* OFC
SELFGCAL,
a
FSC
IDEAL FSC
2EE14C H
2EE14C H
2EE14C H
44AC08 H
44AC08 H
44AC08 H
44AC08 H
3A99A0 H
3A99A0 H
3A99A0 H
494008 H
494008 H
494008 H
4651F3 H
4651F3 H
4651F3 H
·
b
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SELFCAL,
(3)