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BQ25505 using a low power generator

Vineel Kumar
Prodigy 20 points
Other Parts Discussed in Thread: BQ25505, BQ25570

so I am wanting to use the bq25505 with a low power generator, I have used the recommended circuit as suggested for a piezoelectric driver. I am currently bench testing the board with a DC power supply how ever I am unable to get the boost charger to get up to the right voltage. my input voltage from the power supply is 1V at 1mA which is similar to my generator and my output voltage is supposed to be 4.2v for charging Li ion battery which is what the resistors are set to. Is there something I have missed or something I am doing wrong?

ps I used the excel file thats also used for the bq25570 to determine the resistor values with vbat ov = 4.2, vbat ok = 3, vbat ok hyst = 3.7  

  • 0
    TI__Guru**** 166306 points
    I assume the resistor values above are in the megaohm range?

    /EN is active low. You will need to tie this pin to GND in order for the charger to start switching. Also, when simulating the piezo with a power supply, you will need to add a series resistor between the power supply and VCC connection. This resistor should be equivalent to the piezo generator's output impedance.
  • 0 in reply to Jeff F
    Prodigy 20 points

    Thank you for your reply Jeff, I have got the circuit to work. It was because I didnt ground pin 1, 6, 15, 16 and 17 and yes I realised the enable pin had to be tied to ground, my mistake. Yes, those resistor values are in megaohm.

    I tried the IC with the enable pin to however it still didnt work without those other pins being grounded aswell as per the data sheet, sorry that was my mistake.

    Thank you for that information about putting an equivalent series resistor. Is this referenced from the maximum power transfer theorem and the PMIC circuit doesn't act as a load nor does the mppt work with piezo generator?

    thank you so much for your reply

    Vineel

  • 0 in reply to Vineel Kumar
    TI__Guru**** 166306 points
    The MPP function is assuming that you have high impedance power source. If you test with a low impedance power supply, your test results will be very different than when you attach your piezo source, which is high impedance.