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BQ76952: Temperature limits

Patrick Visser
Prodigy 70 points
Part Number: BQ76952

The question i have is about the temperature limits OTC and OTD. 

The Technical Reference Manual states that for the OTC treshold

When the maximum cell temperature is greater than or equal to this threshold for Protections:OTC:Delay seconds, the protection is
triggered. Note that charging does not need to be occurring for this protection to trigger. I

And with automatic FET control we can switch of the charge fet via the OTC. 

But When the OTC and OTD thresholds are at different values, we can have a situation that the discharge FET is on and the charge FET is disabled. 
This will result in the charge FET being possibly  damaged, as we will discharge over the body diode of the charge FET. 

My problem is why can the OTC trigger when we are discharging. 

  • 0
    TI__Guru* 81034 points

    Hi Patrick,

    This device also includes a body diode protection feature which is enabled by default. This allows the device to enable the FET that is off to prevent damage - so if a discharge current is detected above Settings:Protection:Body Diode Threshold, the CHG FET will be enabled to protect it from damage.

    Best regards,

    Matt

  • 0 in reply to Matt Sunna
    Prodigy 70 points

    yes i know about the body diode protection. 

    but what will have precedence the disable (OTC) of the reenable (body diode protection) 
    also I cant use it reliable as a input for a process on a microcontroller as it will trigger always. 
    we want to only allow charging in a specific temperature range and discharge is a specific temperature range. 

  • 0 in reply to Patrick Visser
    TI__Guru* 81034 points

    Body diode protection will always have precedence. So when a large enough discharge current is sensed, it will enable the CHG FET, but the CHG FET will return to its previous state once the discharging stops, so it will still be disabled until the OTC fault is cleared.