• State Resolved
  • Locked Locked
  • Replies 3 replies
  • Subscribers 63 subscribers
  • Views 214 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

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.

TPS3619-33-EP: Having problems in driving p-channel mosfet with PFO pin

Omar Sultan1
Prodigy 40 points
Part Number: TPS3619-33-EP
Other Parts Discussed in Thread: TPS3619

Hello,

In our design the TPS3619 would easily get fried/broken if a malfunction in firmware occurs where the load (microcontroller) would draw around 100+mA continous between ( VBAT - VOUT ), in that case the TPS3619 would always get fried/broken and as an indication for us it starts to overdraw current ~ 120mA up to 400mA and overheat on it's own and when circuit is off the resistances across pins are near short. We thought as a solution that in case that malfunction in firmware would happen we would have a p-channel mosfet be wired in parallel between ( VBAT - VOUT )  where it would be activated by the PFO so as to carry any execessive current , basicly this circuit as a safety mechanism kinda works but unfortunately our microcontroller would have trouble in starting up or shuttingdown/going to sleep mode from VBAT in terms of time ; it takes an additional 4-5 seconds more to startup or shutdown. 

Kindly note that the pulldown resistor at the gate of mosfet is not used as we are aware that the PFO is push-pull.

I would really appreciate it if someone would help us find a solution.

BR

OS

  • +1
    TI__Expert 7180 points

    Hi Omar,

    Due to the low Vbat current capability, the microcontroller might need to be switched to a low power mode when using the battery backup in order to draw less current. It might help to put a large capacitor on VDDSYS to keep the MCU powered while the transistor switches. 

    Best,

    Walter

  • 0 in reply to Walter Zollinger
    Prodigy 40 points

    Hi Walter,

    Thank you for taking the time. We are aware that the microcontroller needs to switch to a lower current consumption (sleep mode) and that is what is happening . We are wondering if we could have any insight on how/if we can integrate the mosfet to operate correctly along with TPS3619 through the (VBAT - VOUT) line , in case the microcontroller malfunctions thus saving the TPS3619 from burning out. 

    BR

    Omar

  • +1 in reply to Omar Sultan1
    TI__Expert 7180 points

    Hi Omar,

    Can R91 and R99 be adjusted so that the transistor switches on at the same voltage as VBat? Also, it may be possible to remove VBCAP from VBAT and instead use a schmitt trigger comparator to compare between 3V3 and VBCAP and use the output of the trigger to switch the mosfet.

    Here is an rough example of what I mean