• State Resolved
  • Locked Locked
  • Replies 3 replies
  • Subscribers 63 subscribers
  • Views 870 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

BQ25504 Questions

Luke Morton
Prodigy 50 points
Other Parts Discussed in Thread: BQ25504

Hi, I have some questions about the BQ25504 chip.

1. I have the chip set up to operate with a low impedance source, disabling MPPT and the battery-good signal, and using the VBAT_OV and UV resistors used in the datasheet. Is there anything that would cause the chip to clamp the input voltage to 170mV, or have I likely just soldered it incorrectly?

2. The datasheet claims I can implement my own MPPT algorithm, but how would I do that? I assume applying a voltage on VREF_SAMP will modulate the input resistance of the converter, but how exactly will it do that?

  • 0
    TI__Guru**** 166996 points
    Regarding 1, the chip clamps the input voltage in 2 instances. When in cold start (i.e., VSTOR < 1.8V) the input will be clamped to ~350mV. When VIN > VSTOR=VBAT, an internal high resistance FET pulls VIN down to prevent it from overcharging the battery. This charger can only boost from a low input voltage to the battery voltage.
    Regarding 2, the converter performs MPPT by stopping the boost converter if the input voltage starts to droop below the voltage at VREF_SAMP. If you disable the MPPT sampling by tying VOC_SAMP to VSTOR and then apply your own voltage to VREF_SAMP, the regulator will then "regulate" the boost charger's input voltage (=output voltage of highZ source) to that voltage.
  • 0 in reply to Jeff F
    Prodigy 50 points
    Does the MPPT only work for high impedance sources, then?
  • 0 in reply to Luke Morton
    TI__Guru**** 166996 points

    MPPT is only necessary for hiZ sources, otherwise, the charger will pull peak currents up to its current limit (~200mA) and crash the source.