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Original question:

BQ25505: VSTOR output drop issue

BQ25505: VSTOR output drop issue

john ingram
Prodigy 50 points
Part Number: BQ25505
Other Parts Discussed in Thread: TMP102,

I am not sure you can put it down to changing cap and inductor values, why would VSTOR drop to 2.28 and recover back 4.2 if the caps / inductor were at fault why would it recover?

Further testing shows at  temperatures just above 70 C the issue appears from 71  up to 85 degrees temperature that occurs it is variable and not all boards fail. Looking at the caps the rating for X7R caps is  85 degrees or better and the inductor was rating for 125 degrees centigrade.

 

  • 0
    TI__Intellectual 1640 points
    Hello dear John Ingram,

    Thank you for your question.

    I have some questions for you:
    1. What's the VBAT_OK and VBAT_OK_HYST values you have programmed?
    2. Can you please provide a scope capture of the behavior? Also, a schematic you have used for the set-up?
    3. Have to connected the load to VSTOR pin or VBAT_SEC pin?

    Thanks and Best Regards,
    Upal Patel
    Product Marketing Engineer
    Texas Instruments Inc
  • 0 in reply to Upal Patel
    Prodigy 50 points

    TemperatureSensorReport.pdf

    Upal Patel said:
    Hello dear John Ingram,

    Thank you for your question.

    I have some questions for you:
    1. What's the VBAT_OK and VBAT_OK_HYST values you have programmed?
    2. Can you please provide a scope capture of the behavior? Also, a schematic you have used for the set-up?
    3. Have to connected the load to VSTOR pin or VBAT_SEC pin?

    Thanks and Best Regards,
    Upal Patel
    Product Marketing Engineer
    Texas Instruments Inc

    The resistors are 887K,6.98M,5.36M

    I have attached a PDF that includes a schematic , PCB layout and SCOPE capture.

    I have attached it to VSTOR.

  • 0 in reply to john ingram
    TI__Intellectual 1640 points
    Thank you for the schematic and scope captures, John.

    Would it be possible for you to increase the value of CSTOR that is C3 on your schematic to greater than 10.5uF, and check to see if VSTOR still droops?

    Thanks and Best Regards,
    Upal Patel
    Product Marketing Engineer
    Texas Instruments Inc
  • 0 in reply to Upal Patel
    Prodigy 50 points

    Hi Upal

    I have changed C3 too 22uF 10V X5R  VSTOR  drooped at lower temperature around 65 degrees C.

    I have attached some screen shots for you plus details on the cap.

    John

    C3 changed to larger value.docx

    Upal Patel said:
    Thank you for the schematic and scope captures, John.

    Would it be possible for you to increase the value of CSTOR that is C3 on your schematic to greater than 10.5uF, and check to see if VSTOR still droops?

    Thanks and Best Regards,
    Upal Patel
    Product Marketing Engineer
    Texas Instruments Inc

    Upal Patel said:
    Thank you for the schematic and scope captures, John.

    Would it be possible for you to increase the value of CSTOR that is C3 on your schematic to greater than 10.5uF, and check to see if VSTOR still droops?

    Thanks and Best Regards,
    Upal Patel
    Product Marketing Engineer
    Texas Instruments Inc

  • 0 in reply to john ingram
    TI__Intellectual 1640 points
    Hi John,

    Thank you for your feedback.

    Did you observe the same drooping behavior of VSTOR at room temperature?

    From what I noticed from your 2 scope captures is, whenever you turn on the load, the load consumed all the current, and hence VSTOR drooped.
  • 0 in reply to Upal Patel
    Prodigy 50 points

    Hi Upal

    Thank you for reply.

    The droop only occurs at high temperatures, as part of the test the system goes through a temperature cycle from -20 to +85 degrees C.

    Circuit operation

    The circuit is a optically powered Temperature sensor based  on the TMP102. The serial data you see in scope capture drives a MEMS mirror and this sends back data to a DSP for remote temperature sensing. Their is an  MCU that is in a reduced power mode and consumes about 100uA of current, this wakes up every 15 milliseconds until timeout of 45 seconds has occurred and at this point is sends out 96 bits of data each at 15 milliseconds duration and whole period takes about 2 seconds, after this point it repeats the 45 second count.

    If VSTOR droops would it try to switch to VBATSEC ?

  • 0 in reply to john ingram
    TI__Intellectual 1640 points

    Hi John,

    Thank you for the feedback, I'll do some testing on our part to see if the VSTOR droops at higher temperature.

    To answer your question about "If VSTOR droops would it try to switch to VBATSEC?"

    According to the datasheet, if VSTOR is above VBAT_UV, the PFET between VSTOR and VBATSEC turns on. Please refer to the diagram below:-

    When the load on VSTOR changes, VSTOR and VBATSEC both tend to droop.

  • 0 in reply to Upal Patel
    TI__Intellectual 1640 points
    Hello John,
    I did the testing on EVM default configuration for BQ25505, and I did not observe VSTOR Drooping issues.
    Thank you.