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BQ25505EVM Issue

Jerry Tang
Intellectual 440 points
Other Parts Discussed in Thread: BQ25570, BQ25505

Hi,

Now we are using the BQ25505EVM to do some evaluating,we meet some problems as below:

1.The input is solar panel;

2.Connecting 16K resistor and 2000uF capacitor in parallel to the VSTOR pin as system load;

3.Connecting 10F supercapacitor to the VBAT_SEC for charging.

We measuring the VSTOR pin ,the output voltage is only 1.8V.This is not suitable for application.

How to get a normal output voltage from VSTOR pin?

Thanks!

  • 0
    TI__Genius 12475 points

    Jerry,

    to change that voltage use the below page and make sure the resistor values for VBAT_OV are correct. 

    Since you have such a large load, i would recommend that you use the BQ25570 and connect the large capacitor to the VOUT pin.

    The leakage from VSTOR to VBAT will make your system startup time longer if thats okay.

    regards,

    gauthambq25505(70_Design_Help_V1_3.xlsx

  • 0 in reply to Gautham
    Intellectual 440 points

    Hi Gautham,

    Thanks! The BQ25505 works in boost mode,this is suitable for this application,Since the output voltage from solar panel is very low, maybe BQ25570 can't  work

    correctly.I know that the output power from BQ25505 satisfy the system load at first,then charge the supercapacitor.For such a large system load,how to make the BQ25505 operate correctly ?

  • 0 in reply to Jerry Tang
    TI__Genius 12475 points
    Jerry,

    The BQ25505 and the BQ25570 share the same front end. They are similar except that the BQ25570 has an integrated Buck converter from the storage element. The input voltage levels are absolutely the same :)

    regards,
    gautham
  • 0 in reply to Gautham
    Intellectual 440 points

    Hi Gautham,

    Using the BQ25505EVM for testing,the input voltage is from 0.3V-5.1V from solar panel.

    Connecting 2600uF capacitor and 16K resistor in parallel as system load at  VSTOR pin,

    and connecting 10F supercap at VBAT_SEC for charging.We expect to get 5V output  from

    VSTOR for system firstly，other output power from VSTOR for charging the supercap. But

    now,this is impossible.How to solve this problem for this case? If using BQ25570 for this

    application,is it suitable? Do you have testing data for the EVM?

    Thanks!