• State Resolved
  • Locked Locked
  • Replies 3 replies
  • Subscribers 63 subscribers
  • Views 280 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

BQ25505: a couple question on VBAT_SEC

Kevin Lai
Intellectual 2916 points
Part Number: BQ25505

Hi team,

please help with the questions below.

1. Since it is a boost charger, what happens internally when VIN is greater than VBAT_SEC? Does it perform as a shunt regulator to provide a constant voltage?

2. if we use a Li-ion battery (3-4.2V) what would be the ideal solar panel voltage to connect to VIN?

3. Is it recomended to connect a 5V USB voltage to VIN in parallel to charge the battery since VBAT_SEC will always be much lower in voltage?

Thanks,

Kevin

  • 0
    TI__Guru**** 165886 points

    Hi Kevin,

    Regarding 1, if VN_DC>VBAT_OV setting, the charger turns on a pull down FET at VIN_DC in order to prevent the input power source from over-voltaging the battery.  Keep in mind the input is connected to the VBAT_SEC through 2 body diodes at all times.

    Regarding 2, based on datasheet efficiency curve fig 4 on page 9, I suggest a panel with MPP close to 3.0V (so VOC = 3.0V/0.8) and ISC no higher than 20mA.  This charger gets less efficient will high current input source.

    Regarding 3, no. As explained in 1, a low impedance source could damage the pull down FET or overvoltage the battery.

    Regards,

    Jeff 

  • 0 in reply to Jeff F
    TI__Intellectual 2916 points

    Hi Jeff,

    thanks for the input! a quick follow up on this below.

    1. what would you recommend as an alternative to the BQ25505 that could handle 1W solar panel with MPPT?

    Thanks,

    Kevin 

  • 0 in reply to Kevin Lai
    TI__Guru**** 165886 points

    Kevin,

    What is the panel's VOC and ISC?  What is the regulation voltage for the battery being charged?  Does the customer want a stand alone charger or do they have a host to communicate via I2C?

    Regards,

    Jeff