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Original question:

BQ25570 VOUT Problem

BQ25570: Vout is very low

Mason_123
Prodigy 50 points
Part Number: BQ25570

Hi there,

When I use the BQ25570, I always get a low Vout problem.

  • The schematic is as follows:



  • When VBAT_OK rises to 1.5V, Vout should be 3.3V, but it is actually only 0.29V, and sometimes it rises irregularly to about 0.5V, but never reaches the desired 3.3V.

 

I am thinking about whether it is a schematic design problem, or a capacitor problem, because my capacitor for C+ is a common electrolytic capacitor, and I didnt use a supercapacitor.


I hope to get your reply soon :)

Much thanks !

 

Mason

  • 0
    Prodigy 50 points

    I made a very stupid mistake when I was drawing that schematic.

    This is the corrected one. Vout still shows very low output. Sometimes it will gradually drop from 1.4V to around 0.2V, even VBAT_OK has already reached 1.5V

  • 0 in reply to Mason_123
    TI__Genius 10385 points

    Mason,

     

    I am not seeing anything wrong with your schematic. In terms of layout I suggest you have C4 (CSTOR) as close to the IC as possible. Could you please give me more details about your test setup?

    • What are you using as an input voltage source?
    • What is your battery voltage before you begin charging?

     

    Thanks,

    Ricardo

  • 0 in reply to Ricardo
    Prodigy 50 points

    Hi Ricardo,

    Very happy to hear from you !

    regarding to the question 1,

    • The input voltage source is 4.5Vdc and it is supplied by our lab power generator

    and regarding to the question 2,

    • After the power supply is stopped, the battery will continue to discharge until the preset voltage (3.4V) is reached, then stop discharging

    It seems that VBAT_OK_HYST and VBAT_UV are working properly.

    Thanks  :)

    Mason

  • 0 in reply to Mason_123
    TI__Genius 10385 points

    Mason,

     

    I am concerned your input voltage(4.5 V) is higher than your VBAT_OV setting (4.2 V). The BQ25570 is a boost charger. Assuming your IIN is a typical 100 uA, the voltage drop across R1 would be 10 mV resulting in VIN_DC being 4.49 V. This voltage is higher than the output and the device would not allow charging to occur. What is your IIN value?

     

    Thanks,

    Ricardo

  • 0 in reply to Ricardo
    Prodigy 50 points

    Hi Ricardo,

    As our lab is now closed and I will test IIN tomorrow. Once I finished I will let u know.

    But i just concerned about that,

    • I tried to change the input voltage range from 4.5 to 3.3 Vdc, but this does not make Vout work

    • When I remove the input voltage after VBAT_OK rises to 1.5Vdc, the C +, 47000uf capacitor should start to discharge to supply the output, but  Vout also doesn't work 

     

    Much thanks,

    Maosn

  • 0 in reply to Ricardo
    Prodigy 50 points

    Hi Ricardo,

    IIN is 120 uA, and the current for pin 13 (VBAT_OK) is 100 uA

    Vout started to stabilize at around 1.5V, but it was still not the expected 3.3V. I suspect that there is a problem with the layout. is it possible?

    I'm using a breadboard, and when I try to follow the layout recommendations in the datasheet, it doesn't work when I even changed the layout today.

    Thanks,

    Mason

  • 0 in reply to Mason_123
    TI__Genius 10385 points

    Mason,

    Would it be possible for you to try using our EVM to troubleshoot further? This could clear up if it is a layout issue. 

    Thanks,

    Ricardo

  • 0 in reply to Ricardo
    TI__Genius 10385 points

    Mason,

    I have not heard back from you in a while. I am going to mark this thread as resolved. Otherwise, let me know if there are any further updates.

    Thanks,

    Ricardo