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ADS131M08: conversion time

David Park
Expert 7240 points

Part Number: ADS131M08

Hi,

Could you let me know calculation of conversion time is correct?

In the continuous conversion mode,

1. startup(0.5ms)+3*OSR/fmod(filter settling time)

2. /DRDY low

3. /CS

4. 32k samples * 8 chs in 1 second under 4.096MHz and 128 OSR

In the GC mode,

1. startup(0.5ms)+tgc_dly + 3*OSR/fmod

2. /DRDY low

3. /CS

4. 1 sample * 8 ch

5. tgc_dly + 3*OSR/fmod

6. /DRDY low

7. 1 sample * 8 ch

8. tgc_dly + 3*OSR/fmod

9. /DRDY low

10. 1 sample * 8 ch

.....repeat

Thanks.

  • 0
    TI__Guru** 100695 points

    David,


    For the two cases that you mention, the startup only applies for starting up the device when power is first applied. This startup is 0.25ms for the power-on-reset (POR) to take place after the supplies reach 90% of the nominal operation. Another 0.25ms is needed for the first data at 4kSPS, which is the default data rate at startup.

    The device can be programmed to read data at 32kSPS (for each of 8 channels) but it cannot startup at that data rate.

    So after powering up the device, I think you would need to:
    1. Start up the device (0.5ms)
    2. Program the device to run at 32kSPS - program the CLOCK register for OSR(~10-30us)
    3. Time to settle (2 data periods, but not completely necessary because the first two data use the fast settling filter)
    4. Read 32k of data * 8 channels (1 second)

    /DRDY goes low before each new conversion (at the data rate). Then /CS is set low, and you would clock out 10*24 bits for each communication frame. /CS then returns high and the master waits again for /DRDY to go low.

    For the case of using the global chop mode, again the device can be programmed to run in global chop mode, but it cannot be set to start up in global chop mode. Again, you would have a similar sequence:

    1. Start up the device (0.5ms)
    2. Program the device to run at 32kSPS and in global chop mode (~10-30us this may take a little longer because you need to program multiple registers)
    3. Time for tgc_dly
    4. Time to settle (6 data periods, but not completely necessary because the first two data use the fast settling filter)
    5. Read 32k of data * 8 channels (3 seconds)

    These are approximate timings. You could probably start programming the device sometime after the POR, so there's an extra 250us that could be variable.


    Joseph Wu