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BQ28Z610EVM-532: BQ28Z610 Charge overtemperature control opens charge MOSFET during discharge

Ekaterina Samartseva
Prodigy 50 points
Part Number: BQ28Z610EVM-532
Other Parts Discussed in Thread: BQ28Z610

Hi,

I am having a problem with charge and discharge overtemperature control with BQ28Z610. I have different thresholds for charge and discharge overtemperature alert, where charge overtemperature is lower than discharge, let say charge should not be allowed at temperatures more than 45 degrees C, discharge should not be allowed at temperatures more than 60 degrees C.

First i tried to use only OTFET option to perform FET action in overtemperature.When temperature passes 45 degrees the device alerts charge overtemperature OTC and closes charge MOSFET even in case the device is in discharge mode. In this case current flows through charge mosfet body diode, what is not desirable as body diode cannot withstand high currents and has high forward voltage.

Secondly, I tried to use charge suspend CHGSU and  charge inhibit CHGIN settings to solve this problem, but it didn't help. When i start discharging in overtemperature region, the charge suspend flag SU is cleared, however inhibit the start of charge flag IN is set. At this moment charging MOSFET opens again leading to the same problem as before, discharge is performed through charge MOSFET body diode.

I also tried to use CHGSU without CHGIN, but it didn't work for me as well. Although CHGIN bit is set to 0, the flag IN was still set during discharge in high temperature region. No action was performed at this moment, both mosfets were still closed. Charging was also allowed, but unfortunately charge suspend cannot be set as long as charge inhibit is set. As a result the charge was not prevented in charge overtemperature region.

It there any way to prevent ChargingStatus()[IN] = 1 from happening?

Or is there any way to turn off charge temperature control during discharge?

Thank you in advance!

  • 0
    TI__Guru* 76230 points
    when you have OTD - overtemperature in discharge the discharge fet turns off. When you have overtemperature in charge, the charge fet turns off , but discharge would still be posibble. You will have to set you OTD thresholds properly to turn off the discharge fets.

    thanks
    Onyx
  • 0 in reply to Onyx Ahiakwo
    Prodigy 50 points

    Onyx Ahiakwo said:
    when you have OTD - overtemperature in discharge the discharge fet turns off. When you have overtemperature in charge, the charge fet turns off , but discharge would still be posibble. You will have to set you OTD thresholds properly to turn off the discharge fets.

    thanks
    Onyx

    Hi Onix,

    thank you for your response.

    I set OTC threshold at 45, OTD at 60.

    My problem is when i am in discharge mode and the OTC threshold is reached everything is fine. Next when in charge mode and OTC is reached the charge mosfet turns off. At this moment if discharge is starged the charge mosfet is still closed. I attach a pic of the registers, you can see that although in discharge mode both CHG and DSC are allowed, OTC flag is still there and XCHG status is set to 1, meaning charge transistor is closed.

    Yes, discharge is still possible, but through charge mosfet body diode, which has high dropout voltage.

    Is there any possibility to turn off the OTC function during discharge?

    Regards,

    Ekaterina

  • 0 in reply to Ekaterina Samartseva
    Prodigy 50 points
    Connecting oscilloscope cleared the things to me. I saw that BQ actually opens the charge mosfet despite of XCHG being 1 as soon as it detects discharge current.