7.3.7 Settling Time

After changing the input multiplexer, the first data are fully settled. In both ADS123x devices, the digital filter is

allowed to settle after toggling either the A1 or A0 pin. Toggling any of these digital pins holds the DRDY/DOUT

line high until the digital filter is fully settled. For example, if A0 changes from low to high, selecting a different

input channel, DRDY/DOUT immediately goes high, and DRDY/DOUT goes low when fully settled data are

ready for retrieval. There is no need to discard any data. Figure 7-7 shows the timing of the DRDY/DOUT line as

the input multiplexer changes.

In certain instances, large or abrupt input changes require four data cycles to settle. One example of such a

change is an external multiplexer in front of the ADS123x, which can cause large changes in input voltage simply

by switching input channels. Another example is toggling the TEMP pin, which switches the internal AINP, AINN

signals to connect to either the external AINPx, AINNx pins or to the TEMP diode (see Figure 7-1).

To acquire fully settled data after an input step change, five readings are required. Five readings are required

because if the change in input occurs in the middle of the first conversion, four additional full conversions of the

fully settled input are required to get fully settled data. Discard the first four readings because they contain only

partially settled data. Figure 7-8 illustrates the settling time for the ADS123x in continuous conversion mode.

A1orA0

t

1

DRDY/DOUT

t

S

Figure 7-7. Example of Settling Time After Changing the Input Multiplexer

Table 7-5. Timing Requirements for Figure 7-7

PARAMETER(1)

MIN

MAX

UNIT

tS

Setup time for changing the A1 or A0 pins

40

50

μs

t1

Settling time (DRDY/DOUT

held high)

SPEED = 1

51

51

ms

SPEED = 0

401

401

ms

(1)

Values given for fCLK = 4.9152 MHz. For different fCLK frequencies, scale proportional to CLK period. Expect a ±3% variation when an

internal oscillator is used.

ToggledTEMPPinor AbruptChangeinExternalV

IN

V

IN

DRDY/DOUT

Startof

conversion.

1stconversion;

includes

unsettledV .

IN

2ndconversion;

V

settled,but

IN

digitalfilter

unsettled.

3rdconversion;

V

settled,but

IN

digitalfilter

unsettled.

4thconversion;

V

settled,but

IN

digitalfilter

unsettled.

5thconversion;

V

anddigital

IN

filterboth

settled.

Conversion

Time

Figure 7-8. Settling Time in Continuous Conversion Mode

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SBAS350H – JUNE 2005 – REVISED JUNE 2025

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