ADS1255IDB Burr-Brown Corporation, ADS1255IDB Datasheet - Page 22

• 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
Settling Time Using One-Shot Mode
A dramatic reduction in power consumption can be achieved
in the ADS1255/6 by performing one-shot conversions using
the STANDBY command; the sequence for this is shown in
Figure 20. Issue the WAKEUP command from Standby
mode to begin a one-shot conversion. Following the settling
time (t
complete and data can be read using the RDATA command.
The ADs1255/6 settles in a single cycle—there is no need to
ignore or discard data. Following the data read cycle, issue
another STANDBY command to reduce power consumption.
When ready for the next measurement, repeat the cycle
starting with another WAKEUP command.
Settling Time while Continuously Converting
After a synchronization, input multiplexer change, or
wakeup from Standby mode, the ADS1255/6 will
continuously convert the analog input. The conversions
coincide with the falling edge of DRDY. While continuously
converting, it is often more convenient to consider settling
times in terms of DRDY periods, as shown in Table 15.
The DRDY period equals the inverse of the data rate.
If there is a step change on the input signal while
continuously converting, performing a synchronization
operation to start a new conversion is recommended.
Otherwise, the next data will represent a combination of
22
ADS1255/6
DRDY
DOUT
Status
18
DIN
), DRDY will go low, indicating that the conversion is
Figure 21. Step Change on V
STANDBY
V
IN
= AIN
Figure 20. One-Shot Conversions Using the STANDBY Command
P
DRDY
DOUT
AIN
DIN
N
Standby
Mode
Old V
IN
IN
while Continuously Converting for Data Rates
WAKEUP
Old V
IN
t
Data
18
New V
the previous and current input signal and should therefore
be discarded. Figure 21 shows an example of readback in
this situation.
IN
Mix of
Old and New
V
Performing One− Shot Conversion
Table 15. Data Settling Delay vs Data Rate
IN
Data
DATA RATE
RDATA
30,000
15,000
(SPS)
7500
3750
2000
1000
500
100
2.5
60
50
30
25
15
10
5
RDATA
Fully Settled
New V
Settled
Data
IN
Settled
Data
Data
STANDBY
SETTLING TIME
(DRDY Periods)
3750SPS
5
3
2
1
1
1
1
1
1
1
1
1
1
1
1
1
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Standby
Mode