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Original question:

ADS131M02-Q1: Root cause of the offset issue

ADS131M02-Q1: conversion time with the global-chop mode enabled

Yoshikazu Kawasaki
Intellectual 575 points
Part Number: ADS131M02-Q1

Tool/software:

Hello,

I have a couple of additional questions from my thread shown below.  It seems the thread seems to be too old to continue adding my comments or even close that anymore, so please let me open a related thread here.

https://e2e.ti.com/support/data-converters-group/data-converters/f/data-converters-forum/1365770/ads131m02-q1-root-cause-of-the-offset-issue/5224840#5224840

My customer asks several questions after that, but I was able to answer those by myself.  They think the offset should be lower, so the global-chop mode should be enabled in default, but they understand the reason why it's not from the figure shown below.

Now, they'd like to calculate how long the conversion time would be when global-chop mode is enabled.  The datasheet says tgc_conversion and tgc_first_conversion are calculated by these equation.

The tMOD is shown below as table 8-5 and the actual data can be configured by the PHASEn[9:0] bits in the CHn_CFG register.

If the PHASEn[9:0] uses the default value, which is 0x000, it also means tMOD should be 0.  Therefore the actual conversion time in default can be calculated as shown below.

tgc_conversion = tGC_DLY + 3 x OSR x tMOD(=0) = tGC_DLY

tgc_first_conversion = tGC_DLY + 3 x OSR x tMOD(=0) + tGC_DLY + 3 x OSR x tMOD(=0) + 44 x tMOD(=0) = 2 x tGC_DLY

Questions

1. Is my understanding shown above correct?

2. If it is yes, it doesn't take 3 times longer when tMOD=0 even if the global-chop mode is enabled.  Am I correct?

Best Regards,

Yoshikazu Kawasaki

  • +1
    TI__Mastermind 37140 points

    Hi Yoshikazu-san,

    The number in the table 8-5 means how much phase adjustment (the number of tMOD) between channels. When you set the Phase Calibration limit to 0 by programming PHASEn[9:0] =0, it means no phase adjustment between these channels, but it does not mean tMOD=0, the tMOD is still 1/fmod (fmod is the modulator frequency).

    BR,

    Dale

  • 0 in reply to Dale Li
    Intellectual 575 points

    Hello Dale-san,

    Thank you for your quick reply.

    Now I understand, but the tMOD shown as "PHASE OFFSET RANGE(tMOD)" in table 8-5 is confusing us since it looks as if PHASE OFFSET RANGE = tMOD which can be configured by the PHASEn[9:0] bits.

    Best Regards,

    Yoshikazu Kawasaki