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BQ25504: bq25504 query

Star Xu
Genius 9645 points
Part Number: BQ25504

Hi

I used an amorphous silicon solar panel SC2510 with working voltage is 1.5v.

After connecting 25504, when testing under direct sunlight, the cold start phase Vin is about 360mV, Vbat is connected with 30mF 3.3V super capacitor, Vstor is floating, when Vstor reaches 1.8V, it reaches the main booster charging phase.
There is an effect of collecting the open circuit voltage in 256ms, and it can be seen that Vin will gradually rise.
However, I measured the measurement every 14s, and observed that the voltage does not directly reach 80% of the open circuit voltage, but gradually increase, and finally to 80% of the situation, is this phenomenon normal work?
The main boost charging phase just mentioned is that under the condition that Vstor is suspended, the voltages of Vbat and Vstor will gradually rise to OV;

But if I connect a red LED light (operating voltage: 1.7-2.0V) in Vstor, the LED light will flash, Vstor will be pulled down to 1.6V in an instant, Vin will also drop to 360mV, Vbat connect the super capacitor so does not drop.
why does this happen after the load is connected? Does this mean that the chip has returned to the cold start phase? Why did Vstor reach 1.6V?
Thanks
Star
  • 0
    TI__Genius 10385 points

    Star,

    Do you mind sending scope captures of the behaviors you are seeing? Do they not match Figure 15, 16, and 18? I am assuming the supercap is discharged on startup.

    The supercap on VBAT will provide power to VSTOR as long as VBAT > VBAT_OK. When VBAT discharges below VBAT_OK, VSTOR and VBAT are disconnected. It is up to the converter to provide the power to LED. A red LED at 1.6V typically draws about 10 mA. I am having a hard time finding a datasheet for SC-2510, can it provide sufficient power for these operating conditions with the supercap depleted? It seems to me your input source ( SC-2510) is crashing.

    Thanks,

    Ricardo

  • 0 in reply to Ricardo
    TI__Genius 10385 points

    Star,

    i have not heard from you in a while. I will be closing this thread unless you have any further questions.

    Thanks,

    Ricardo

  • 0 in reply to Ricardo
    TI__Genius 9645 points

    LED directly with SC2510, I can light it up.Hi Ricardo

    Thanks for your reply.

    1.6V cannot be turned on after connecting the LED, but the output voltage stabilized to 1.6V after the Vstor terminal is connected to the LED. I have not figured out the reason.
    Did you experience the phenomenon that Vstor stabilized to 1.6V during the test?
    Does this have anything to do with the load of the connection?
     And at this time, the super capacitor is not exhausted, is it because Vstor and Vbat are disconnected, resulting in the super capacitor being unable to supply power to the load.
    The input source is not sure if it crashes, because if I connect the LED directly with SC2510, I can light it up.
    Thanks
    Star
  • 0 in reply to Star Xu
    TI__Genius 10385 points

    Star,

    Your understanding is correct. If VSTOR falls beneath VBAT_UV, then VSTOR and VBAT are disconnected. This means that the supercapacitor cannot provide to the LED. This will occur when you connect the LED from VSTOR to GND as VSTOR will be pulled to 1.6V by the diode. At this point VSTOR is below VBAT_UV (2.2V, min).

    Additionally, it seems you are falling into cold start as the LED causes VSTOR to fall below VSTOR_CHGEN (1.8V typ). The device cannot come out of cold start as it is unable to charge VSTOR to 1.8V.

    Thanks,

    Ricardo