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BQ25570: Battery charging use BQ25570

Youngman Kim
Prodigy 30 points
Part Number: BQ25570

Hi.

Now I am testing for the Current sensing device. this device is using energy harvest IC(BQ25570) for the device operation.

We use Li-ion 2.7V(3mhA) battery. this battery voltage is used for all active components.

But we have face to some problem.

We expect 2.7V @ full charging voltage  but battery cannot charged  to 2.7V. 

It was charged only up to 2.38V 

CT output is variable from 1mA~50mA (transform ratio is 1:1000) and this current into the bridge diode to rectifier circuit.

I attached schematic.

Please review and advice which is problem.

Thank you.BQ25570_Charging.pdf

  • 0
    TI__Genius 10240 points

    Hi Kim,

    We will get back to you after the July 4th holiday weekend. 

  • 0
    TI__Guru**** 166626 points

    Hi Youngman,

    What is the MPP voltage level that the charger sees at VIN_DC?  The voltage must be lower than 2.7V for the charger to boost the voltage.  Also, the input power times efficiency must be greater than the output power where the output power dc current includes the charger's quiescent current into VSTOR plus dc leakage current into the battery.

    Regards,

    Jeff

  • 0 in reply to Jeff F
    Prodigy 30 points

    Hi. Jeff.

    Thank you for your prompt reply.

    I checked VIN_DC. it is about 600mV~1V.

    because we tested Slide_AC to change the testing current for current sensing.

    Bridge diode input current is variable from 1mA to 20mA

    Our system turn on voltage is 2.5V but we just charge to 2.38V.

    If you more information, please let me know.

    Thank you.

     

  • 0 in reply to Youngman Kim
    TI__Guru**** 166626 points

    Hi Youngman,

    How did you find the CT's maximum power point?  Is it possible that you are not at MPP and therefore not getting enough power?

    Also, please review datasheet section on PCB layout.  It is possible that there is a parasitic resistor from solder flux that is in parallel with one of the high value VBAT_OV resistors.  If so, the regulation voltage could be lower than expected.

    Regards,

    Jeff