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Original question:

BQ24074: Could you review BQ24074 SCH.

BQ24073: Thermal Issues with BQ24073

Marco Beffa
Prodigy 10 points
Part Number: BQ24073

We have a client that uses a lot uf bq24073 charge controllers in his application.

As this a linear controller, thermal considerations need to made.

Seveal hunderd units using this controller are returned with a burned up bq24073, despite its thermal protection features.

The PCB around the controller is charcoal black, so it must have been a quite high temperature.

I checked the schematic they did and it seems to have no errors. It is almost exactly as the application examples.

Ilim = 1.15A

Iset = 0.74A

TMR = 6.2h

Ub = 5V (USB AC Adapter Charger)

Battery = Standard LG 18650 Cell

Question:

What could lead to a complete destruction of the device, despite its thermal protection features?

A little suspicous for me is that, the TD pin is set to high -> Charge Termination is thus disabled.

This would mean, that the controller maintains the cell at 4.2V all the time, but still lets charing current flow?

This does not make sense IMHO.

Any insigts a greatly apreciated.

  • 0
    TI__Mastermind 31420 points

    Hi Marco,

    Thank you for reaching out via E2E. Please see my comments below. 

    Firstly, can you please provide the schematic so we can also review? 

    Marco Beffa said:
    What could lead to a complete destruction of the device, despite its thermal protection features?

    I would not expect the damage described to occur due to an issue with the thermal regulation/shutdown protection feature. My best theory at this time is a short circuit occurred and caused a current surge.

    Marco Beffa said:
    A little suspicous for me is that, the TD pin is set to high -> Charge Termination is thus disabled.

    Even with charge termination disabled charge current to the battery should still be very low once VBAT reaches 4.2V. The device should reach the end of CV (constant voltage) phase of charge and current should be tapered off. 

    Best Regards,

    Garrett