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BQ25731EVM: About RSNS_RAC and RSNS_RSR parameter of "Charge Option 1" window on the EVM GUI.

Part Number: BQ25731EVM
Other Parts Discussed in Thread: BQ25731

Hello guys,

One of my customers is evaluating BQ25731 with BQ25731 EVM and GUI.

At the evaluation, they have the following questions.

Could you please give me your reply?

Q. We changed RSNS_RAC and RSNS_RSR parameters of "Charge Option 1" window on the EVM GUI from 5m ohm to 10 m ohm.

      But the actual charge current was not changed.

      Q1. Is it normal operation of EVM that the current does not change even if these parameters are changed?

      Q2. What are these parameters for? What is the correct usage of these parameters?

Your reply would be much appreciated.

Best regards,

Kazuya.

  • Hi Kazuya-san,

    Charge current not changing could be due to other reasons. For example, they are power limiting the input and that is already the max current available.

    If they are testing the EVM, they should keep the setting align with their hardware sense resistance (either 5 mohm or 10 mohm). It does matter what the software setting is. 

    Thanks and I hope this helps,

    Peng

    *Please press "This Resolved My Issue" on the thread if my answer is satisfactory

  • Hi Peng,

    Thank you very much for your reply.

    Could you please give me your reply for the following question?

    Q1. What are these parameters (RSNS_RAC and RSNS_RSR) for? 

    Q2. What is happened if these parameters value are not same as the resistors value on EVM?

    Thank you again and best regards,

    Kazuya. 

  • Hi Kazuya-san,

    Q1: The charger uses these bits for its current sense settings. Please see below from the datasheet:

    "The charger supports 10 mΩ and 5 mΩ for both input current sensing and charge current sensing. By default 5 mΩ is enabled by POR setting RSNS_RAC=1b and RSNS_RSR=1b, if 10-mΩ sensing is used please configure RSNS_RAC=0b and RSNS_RSR=0b."

    Q2: It is ok if it is not the same as the EVM. However, the software setting has to be the same as the sense resistance on their hardware. Otherwise, the current regulation would not be accurate. 

    Thanks and I hope this helps,

    Peng

    *Please press "This Resolved My Issue" on the thread if my answer is satisfactory

  • Hello Peng,

    Thank you very much for your reply.

    The customer changed the sense resistor on the EVM from 5mohm to 10mohm

    and changed RSNS_RAC and RSNS_RSR parameters of "Charge Option 1" window on the EVM GUI from 5mohm to 10 mohm.

    But the charge current was not changed. 

    Is this result correct?

    Which parameter should be changed for the device charge current setting?

    Thank you again and best regards,

    Kazuya.  

  • Hi Kazuya-san,

    Can they send the register values? They could be current limiting the input through the IINDPM settings or the ILIM_HIZ pin. 

    Please use this button to generate a .txt file.



    What is their input voltage, battery voltage, and the charge current they are attempting to set to?

    Please kindly ask them to go through the user's guide if they have not done so.

    https://www.ti.com/lit/ug/sluucb9a/sluucb9a.pdf?ts=1630075057820&ref_url=https%253A%252F%252Fwww.google.com%252F 

    Thanks and I hope this helps,

    Peng

    *Please press "This Resolved My Issue" on the thread if my answer is satisfactory

  • Hello Peng,

    Thank you very much for your strong supports.

    I attached the saved registers file of their EVM .

    Also their VBUS voltage is 22V, VBAT is 16.6V and the charge current is 1088mA.

    If you need any additional information, could you please let me know?

    Thank you again and best regards,

    Kazuya.

     

    Save Registers20210902.txt
    * Created: Thu Sep 02 15:11:33 JST 2021
    *
    * Format: Register Name  tab Character,\t  Hexadecimal register value.
    * Device: bq2573x
    * BQZ Container: Charger_1_00-bq2573x.bqz
    *
    Charge Option 0	071A
    Charge Current	0200
    Max Charge Voltage	40D8
    OTG Voltage	09C4
    OTG Current	1400
    Input Voltage	3FC0
    Min System Voltage	7B00
    IIN_HOST	2000
    Charger Status	8400
    Prochot Status	B880
    IIN_DPM	2000
    ADC VBUS and PSYS	E500
    ADC IBAT	0800
    ADC IIN and CMPIN	0600
    ADC VSYS and VBAT	9E9C
    Manufacture ID	D640
    Device ID	00D6
    Charge Option 1	BF00
    Charge Option 2	007F
    Charge Option 3	1434
    Prochot Option 0	4A81
    Prochot Option 1	41A0
    ADC Option	A07F
    Charge Option 4	0048
    Vmin Active Protection	006C

  • Hi Kazuya-san,

    I checked. The RSNS_RSR bit doesn't change the charge current, what it does is adjust the compensation for the actual resistance used on the board. The customer observation is normal. RSNS_RAC is similar.

    If 5mohm is used on the board, please leave those bits as "1". If 10 mohm is used on the board, please set those bits as "0".

    Thanks and I hope this helps,

    Peng

    *Please press "This Resolved My Issue" on the thread if my answer is satisfactory

  • Hello Peng,

    Thank you very much for your reply.

    Could I ask you a few additional questions as the follows?

    Q1, You said that

           "... what it does is adjust the compensation for the actual resistance used on the board.".

          What does the compensation cover? Is it phase margin of the current sense amp?

          Or a temperature error of internal circuit? Or so on? 

    Q2. Can the charge current be set by Charge Current Register (I2C address = 03/02h) only?

    Thank you again and best regards,

    Kazuya.

  • Hi Kazuya-san,

    It is compensation for the whole feedback loop.

    Yes, charge current is set by ChargeCurrent register under normal operating conditions.

    Peng

    *Please press "This Resolved My Issue" on the thread if my answer is satisfactory