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BQ25504EVM not working

Ashim Gurung
Intellectual 330 points
Other Parts Discussed in Thread: BQ25504

Hello

Q1. I have a dc power supply feeding the BQ25504EVM. There is no load attached to Vstor pin and no storage on Vbatt pin.

I supplied a 1 V with a current limit of 50 mA on the dc power supply.

However current drawn by the BQ25504EVM is 0 mA.

I can see the Vstor voltage fluctuating repeatedly from 1.8V to 3V. Is that normal?

Q2. Now I attached a battery with 2.3 V and observed the Vstor voltage becomes 2.3 V and again no current is drawn from the dc supply.

        Is this normal?

       I want to charge the battery to 3 V using the bq25504 EVM.

Any help will be greatly appreciated.

Any help will be greatly appreciated.

 

  • 0
    TI__Guru**** 166626 points
    Regarding 1, no. With no battery and on the capacitors on the EVM, I would have expected the charger to first enter cold start, clamp VIN_DC to 0.350V, charge VSTOR 1.8V then enter main boost and charge VSTOR up to 3.0V. You reached 3.0V at some point so the boost charger appears to be working. But, as the board capacitors discharge, the boost charger should occasionally switch (as seen on the LBOOST pin) in order to keep VSTOR at 3.0V, not droop back to 1.8V. Your power supply meter will likely not report the correct current because the IC pulls current spikes instead of steady DC pulses. If you have a current meter in series between power supply and EVM, remove it and try again. You might also try inceasing PS current limit and inserting a series resistor.
    Regarding 2, no. the charger should charge the battery up to 3.0V and stop. Using an oscope, check the LBOOST pin. Is there activity on that pin?
  • 0 in reply to Jeff F
    Intellectual 330 points
    Thank you Jeff for your reply.
    There was a current meter in series between power supply and EVM, I removed it but still the Vstor repeatedly changes from 1.8 V to 3 V.
    I tried increasing the PS current limit, but there was no change.
    However,
    1. when I changed the power supply voltage from 1V to 2 V for 200 mA current limit , the Vstor repeatedly changes from 1.8 V to 5 V
    2. with 2 V power supply with 100 ohm in series, 200 mA current limit, the Vstor repeatedly changes from 1.8 V to 4.2 V.
    I checked the voltage at Lboost pin, it was a steady 1 V for 1 V power supply, 2 V for 2 V power supply.
  • 0 in reply to Ashim Gurung
    TI__Guru**** 166626 points
    If VSTOR is ever > your applied power, you have to switching so there should be switching pulses in the 1Mhz range for brief periods at LBOOST. Can you follow the EVM users' guide example exactly (you can use a real battery instead) and report back?
  • 0 in reply to Jeff F
    Intellectual 330 points

    Fig 1. start up with no battery and with 10 kohm load

    Fig 2. powering up with a battery above uv

    Hi Jeff,

    I followed the EVM users' guide test procedures mentioned in section 3.3.1. Power-up With No Battery and 10kΩ Load on STOR

    and 3.3.3. Power-up with Battery more than UV (2.3V to 3V), BAT FET ON 

    Fig 1. is the measurement i got for 3.3.1 and Fig 2. is the measurement i got for 3.3.3

    the blue line is for Vstor, green line is for Vbatt, pink is for Vphase (LBST pin) and yellow line is for Vindc.

    In Fig. 1, I can see the switching LBST pulses but Vstor continuously charges and discharges and doesnot reach saturation as indicated in the user guide.

    In Fig. 2, the LBST voltage switching doesnot look like the one in the user guide.

    Do you think the EVM is working ok?

    Your help is highly appreciated.