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TPSM831D31: TPSM831D31

Kevin Huang67
Intellectual 410 points
Part Number: TPSM831D31
Other Parts Discussed in Thread: TPS53681

Tool/software:

Hi Sir
We would like to measure current in TPSM831D31 PMIC with the following command.
(8Ch) READ_IOUT :The READ_IOUT command returns the output current in amperes.

How to get more precise current value in TPSM831D31 ?
Does it related the following register to get the precise current ?
(38h) IOUT_CAL_GAIN :The IOUT_CAL_GAIN command is used to set the ratio of the voltage at the current sense pins to the sensed current, in mΩ.

  • 0
    TI__Expert 4295 points

    Hi,

    IOUT_CAL_GAIN (38h) sets the gain used by the controller to calculate output current from the current sense voltage. The current sense voltage provided by the power stages is expected to increase by 5mV for every additional Amp of current, so IOUT_CAL_GAIN should be left at 5mohm (hex value of D140h) in most cases. In the case that the current sense voltage gain and the controller gain is slightly mismatched, IOUT_CAL_GAIN can be used to tune the controller gain.

    You can also use the IOUT_CAL_OFFSET (39h) command to set a fixed offset in reported current, to compensate any offset errors.

    You can find additional information on using IOUT_CAL_GAIN and IOUT_CAL_OFFSET to tune current reporting in the datasheet for TPS53681, which is the controller used internal to TPSM831D31, available on TI.com: https://www.ti.com/product/TPS53681 

    Regards,

    Troy

  • 0 in reply to Troy Johnson
    Intellectual 410 points

    Hi Johnson,

    What's the average current error scope(0< current error < ? mA)when using TPSM831D31 to measure current and using your method to add offset ?

  • 0 in reply to Kevin Huang67
    TI__Expert 4970 points

    Hi Kevin,

    Troy is away on business travel so response may be delayed.

    Thank you for your patience.

    Regards,

    Maha

  • 0 in reply to Maha Noor
    TI__Expert 4295 points

    Hi,

    The current error for TPSM831D31 under full load is typically within +/-3%. You can find this in section 6.7 of the TPSM831D31 datasheet. https://www.ti.com/product/TPSM831D31 

    This error value is for when IOUT_CAL_OFFSET and IOUT_CAL_GAIN are their default values. The offset and gain should only be adjusted if a consistent error is found during testing.

    You can also refer to section 6.8 in the datasheet for TPS53681, for information about the accuracy of the module's internal controller.

    Regards,

    Troy

  • 0 in reply to Troy Johnson
    Intellectual 410 points

    Hi Johnson,

    1.The channel A(120A) of TPSM831D31 is 3-phase, so I need to check the 3-phase of TPS53681 section 6.8?

    2.The channel B(40A) of TPSM831D31 is single phase, but the TPS53681 section 6.8 has no single phase current accuracy and which can I check ?

    3. Is the current value of TPSM831D31 RMS(root mean square) value ?

  • 0 in reply to Kevin Huang67
    TI__Expert 4295 points

    Hi,

    1. For channel A, you should check the 3-phase section.

    2. For channel B, you can use the Rail B 2-phase section. Since the current listed in this section is total current, you should relate the error to the per phase current for comparison to the one phase Rail B on TPSM831D31. For example, the Rail B 2-phase section gives +/-1.8% error at 82A load, or 41A per phase. So the error for single phase would be +/-1.8% at 41A load.

    3. Are you referring to the 120A for channel A and 40A for channel B current values? These values are max continuous output current.

    Regards,

    Troy

  • 0 in reply to Troy Johnson
    Intellectual 410 points

    Hi Sir,

    We follow the datasheet of TPS53681 to adjust the current value, but it still has the 6A or 2A current value been found when the measured load current is 4A. Do you have any formula(how many times to record&average and cut which value +-?% offset) or experience to calculate the average current to be close to accurate current ? Thanks a lot.

  • 0 in reply to Kevin Huang67
    TI__Expert 4295 points

    Hi Kevin,

    I do not have any procedure for adjusting IOUT_CAL_GAIN and IOUT_CAL_OFFSET beyond what is given in the datasheet. 

    The current sense accuracy improves at higher loads, so for making adjustments to gain and offset I would recommend testing at the highest current you are expecting your system to pull.

    Regards,

    Troy