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ADS1258 Latency Clarification

Corey54691
Prodigy 30 points
Other Parts Discussed in Thread: ADS1258

Hi,

Was reading the technical article on delta-sigma converter latency and would like to clarify something in regards to the ADS1258 - it mentions that the 1258 has zero-latency in auto-scan mode, but has 5 cycle latency in an optional mode. Is this optional mode Fixed-Channel mode, and if so, is it applicable for all data rates in that mode, or just a subset?

Now, whichever mode has 5-cycle latency - does this mean that I must manually wait for 5 DRDY cycles before I have the current data from my start condition? I'm trying to reconcile this with the section of the 1258 documentation that describes initial delay. It says the first conversion from a start condition is delayed for a length of time to allow for fully settled data. Is this true even in the 5-cycle delay mode?

Thanks,

Corey

  • 0
    TI__Mastermind 43915 points

    Hi Corey,

    Take a look at Figured 45 and 46 in the ADS1258 data sheet. Figure 45 shows the zero latency and relates to Auto-Scan mode while Figure 46 deals with the latency when run in Fixed-Channel mode. The chip requires roughly a 5 cycle delay in order to wait for the digital filter to settle. This 5 cycle delay is accounted for internally within the ADC when configured for Auto-scan mode causing the max data rate in Auto-scan mode is about 1/5 the data rate in Fixed-channel mode. The reason being, Auto-scan mode is generally meant to have the internal mux cycle through channels. When cycling, you cannot live with latency as the converter is just taking one conversion from a channel and moving to the next one. Therefore, the chip is designed to wait 5 conversions internally between DRDY pulses in Auto-scan mode to account for the latency.

    Regards,

    Tony Calabria