JAJSHL9A June 2019 – January 2021 ADS125H01
PRODUCTION DATA
The digital filter averages data from the modulator to produce the conversion result. The internal stages of the digital filter must be settled to provide fully settled output data. The order and the decimation ratio of the digital filter determine the amount of data averaged that, in turn, affects the latency of the conversion result. The FIR and sinc1 filter modes are zero latency because the ADC provides the conversion result in one conversion cycle. Latency time is an important consideration for overall data throughput in multiplexed applications.
Table 9-6 lists the conversion latency values of the ADC. Conversion latency is defined as the time from the start of the first conversion by taking the START pin high or sending the START command to the time of the first conversion data. The ADC is designed to provide fully settled data under this condition. The conversion latency values listed in Table 9-6 include the programmable start-conversion delay that delays the digital filter start. After the first conversion in continuous-conversion mode, the periods of the following conversions are equal to 1 / fDATA.
DATA RATE (SPS) | CONVERSION LATENCY TIME (t(STDR)(1), ms) | ||||
---|---|---|---|---|---|
SINC1 | SINC3 | SINC4 | SINC5 | FIR | |
2.5 | 400.4 | 1,200 | 1,600 | — | 402.2 |
5 | 200.4 | 600.4 | 800.4 | — | 202.2 |
10 | 100.4 | 300.4 | 400.4 | — | 102.2 |
16.6 | 60.43 | 180.4 | 240.4 | — | — |
20 | 50.43 | 150.4 | 200.4 | — | 52.22 |
50 | 20.43 | 60.43 | 80.43 | — | — |
60 | 17.09 | 50.43 | 67.09 | — | — |
100 | 10.43 | 30.43 | 40.43 | — | — |
400 | 2.925 | 7.925 | 10.43 | — | — |
1200 | 1.258 | 2.925 | 3.758 | — | — |
2400 | 0.841 | 1.675 | 2.091 | — | — |
4800 | 0.633 | 1.050 | 1.258 | — | — |
7200 | 0.564 | 0.841 | 0.980 | — | — |
14400 | — | — | — | 0.423 | — |
19200 | — | — | — | 0.336 | — |
25600 | — | — | — | 0.271 | — |
40000 | — | — | — | 0.179 | — |
As shown in Figure 9-17, if the input-step change occurs during an active conversion, the conversion data are a mix of old and new data. After an input-step change, the number of conversion periods required to provide fully settled output data are determined dividing the conversion latency time by the conversion period plus one additional conversion period.