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BQ25504EVM-674: Trying to get eval kit to work with an external power supply

raulcl93
Prodigy 110 points

Part Number: BQ25504EVM-674

I have a Tekpower TP3005N Regulated DC Variable Power Supply which is capable of 0 to 30 V at 0 to 5 A. So I'm connecting this power power supply to the input of BQ25504EVM-674 (as if it was a solar panel) and trying to see if the values stated in the datasheet work ("Can be started with VIN as low as 330 mV, and once started, can continue to harvest energy down to VIN = 80 mV")  This is where I'm having issues.

After leaving the board (connected to the LiPo battery and load, which is two other TI regulators and the Cypress PSoC 6) overnight without a V in, I was getting around 1.5 V at both VSTOR and VBAT. So I connected the power supply to the input at 0.330 V and powered it in and the output values stayed the same. I then started slowly increasing the output of my power supply and it wasn't until I got the voltage high enough for the output current reading of the power supply to read 0.10 A that VBAT got to the expected value and began charging. 

My understanding is that I shouldn't be needing to get my external power supply that high since this IC is supposed to work at microwatts of power. Any ideas as to why this is happening would be greatly appreciated.

  • 0
    TI__Mastermind 20570 points
    Can you please show scope capture on your test? The solar panel is essentially a current source. Thus, you will need to use a current source at the input instead of a voltage source for testing.
  • 0 in reply to Jing Zou
    Prodigy 110 points
    Thank you for the reply.

    Unfortunately, I won't have access to a current source until maybe this coming weekend but in the meantime we do have a hypothetical question based on what we are kinda experiencing with our current set up...

    Say the harvester gets powered on and VSTOR and VBAT are equal to the LiPo batteries set max.... If we then place the device in a completely dark cabinet for an infinite amount of time (thus making the input current like 0 right?, as if nothing was connected at V in)... We would imagine the VSTOR=VBAT would discharge until the battery is completely dead, is this assumption correct or are we missing something?

    Thank you!
  • 0 in reply to raulcl93
    Prodigy 110 points

    Any idea as to what would happen in that completely dark cabinet?

    At the very least if you have other solar harvesters you think are worth a shot, we are open to that too.

  • 0 in reply to raulcl93
    TI__Guru**** 167066 points
    Raul,

    The boost charger has undervoltage lockout that turns off the PFET between VBAT and VSTOR below the VBAT_UV threshold. Assuming the system load is attached to VSTOR, below that threshold, the battery would only self discharge.
  • 0 in reply to raulcl93
    TI__Mastermind 20570 points

    Hello raulcl93,

    I apologize for the delay in response. Your assumption is correct. With no input, VBAT is going to get discharged eventually below VBAT_OK. and the FET between VSTOR and VBAT will open disconnecting VSTOR from VBAT.

    Unfortunately, the BQ25504/05/70 are the only low power energy harvesting device we have. For higher power solar charger, you can have a look at BQ24650.