Datasheet

CalibrationTime=
50
f
OSC
32
f
MOD
16
f
DATA
+
+
ADS1146
ADS1147
ADS1148
SBAS453F –JULY 2009–REVISED APRIL 2012 www.ti.com
Calibration Commands
calibrations the offset calibration register (OFC) is
updated afterwards. When either offset calibration
The ADS1146/7/8 provide commands for three types
command is issued, the ADS1146/7/8 stop the
of calibration: system gain calibration, system offset
current conversion and start the calibration procedure
calibration and self offset calibration. Where absolute
immediately.
accuracy is needed, it is recommended that
calibration be performed after power on, a change in
Calibration Timing
temperature, a change of PGA and in some cases a
change in channel. At the completion of calibration,
When calibration is initiated, the device performs 16
the DRDY signal goes low indicating the calibration is
consecutive data conversions and averages the
finished. The first data after calibration are always
results to calculate the calibration value. This
valid. If the START pin is taken low or a SLEEP
provides a more accurate calibration value. The time
command is issued after any calibration command,
required for calibration is shown in Table 10 and can
the devices goes to sleep after completing calibration.
be calculated using Equation 9:
It is important to allow a pending system calibration to
complete before issuing any other commands.
(9)
Issuing commands during a calibration can result in
corrupted data. If this occurs either resend the
Table 10. Calibration Time versus Data Rate
calibration command that was aborted or issue a
DATA RATE (SPS) CALIBRATION TIME (ms)
device reset.
5 3201.01
System Gain Calibration 10 1601.01
20 801.012
System gain calibration corrects for gain error in the
40 400.26
signal path. The system gain calibration is initiated by
sending the SYSGCAL command while applying a
80 200.26
full-scale input to the selected analog inputs.
160 100.14
Afterwards the full-scale calibration register (FSC) is
320 50.14
updated. When a system gain calibration command is
640 25.14
issued, the ADS1146/7/8 stop the current conversion
1000 16.14
and start the calibration procedure immediately.
2000 8.07
System Offset and Self Offset Calibration
1. For f
OSC
= 4.096MHz.
System offset calibration corrects both internal and
external offset errors. The system offset calibration is
ADC SLEEP MODE
initiated by sending the SYSOCAL command while
Power consumption can be dramatically reduced by
applying a zero differential input (V
IN
= 0) to the
placing the ADS1146/7/8 into sleep mode. There are
selected analog inputs. The self offset calibration is
two ways to put the device into sleep mode: the sleep
initiated by sending the SELFOCAL command.
command (SLEEP) and through the START pin.
During self offset calibration, the selected inputs are
disconnected from the internal circuitry and a zero
During sleep mode, the internal reference status
differential signal is applied internally. With both offset
depends on the setting of the VREFCON bits in the
MUX1 register; see the Register Descriptions section
for details.
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