ADS1244

9

SBAS273

www.ti.com

To help see the response at lower frequencies, Figure 7

illustrates the response out to 180Hz. Notice that both 50Hz

and 60Hz signals are rejected. This feature is very useful for

eliminating power line cycle interference during measure-

ments. Figure 8 shows the ADS1244’s response around

these frequencies.

The ADS1244’s data rate and frequency response scale

from 2.4576MHz to 4.9152MHz, the data rate increases from

15sps to 30sps while the notches in the response at 50Hz

and 60Hz move out to 100Hz and 120Hz.

SETTLING TIME

The ADS1244 has single-cycle settling. That is, the output

data is fully settled after a single conversion—there is no

need to wait for additional conversions before retrieving the

data when there is a change on the analog inputs.

In order to realize single-cycle settling, synchronize changes

on the analog inputs to the conversion beginning, which is

when using a multiplexer in front of the ADS1244, change the

ing the time between the conversion beginning and the

error in the conversion data, as shown in Figure 9. The

settling error versus delay time is shown in Figure 10. If the

input change is delayed to the point where the settling error

is too high, simply ignore the first data result and wait for the

second conversion which will be fully-settled.

FIGURE 9. Analog Input Change Timing.

Begin New Conversion,

Complete Previous Conversion

New Conversion Complete

t

DELAY

DRDY/DOUT

V

IN

Previous Conversion Data

FIGURE 10. Settling Error vs Delay Time.

SETTLING ERROR vs DELAY TIME

f

Delay Time, t

2

4

6

8

10

12

14

16

0

10.000000

1.000000

0.100000

0.010000

0.001000

0.000100

0.000010

0.000001

FIGURE 7. Frequency Response to 180Hz.

FIGURE 8. Frequency Response Near 50Hz and 60Hz.

FREQUENCY RESPONSE TO 180Hz

f

Frequency (Hz)

0

–20

–40

–60

–80

–100

–120

–140

–160

–180

FREQUENCY RESPONSE NEAR 50Hz AND 60Hz

f

Frequency (Hz)

50

55

60

65

45

–40

–50

–60

–70

–80

–90

–100

–110

–120