TM4C1294NCPDT GPIO Issue

pooja trivedi

Other Parts Discussed in Thread: TM4C1290NCPDT, TM4C1294NCPDT

I am using TM4C129NCPDT TIVA microcontroller in our product. Find circuit in below figure which we use to on or off our unit's supply.

ESC_KEY_ON_OFF is GPIO pin of microcontroller. VBAT_CHG is 3.6V which comes from battery so in supply off condition we require ESC_KEY_ON_OFF to 3.6V supply. but when it is connected to any GPIO of microcontroller in off condition due to resistance it will drop down voltage at pin from 3.6V to 1.7V. In our old design we use LM3S5b91 microcontroller but in that there is no such issue.

Is this issue is related to TIVA GPIO pin?

over 11 years ago

0 Amit Ashara over 11 years ago

TI__Guru**** 244440 points

Hello Pooja,

Did you mean that when the uC is in OFF condition and the Pull Up is connected to the GPIO of the uC then the voltage drop is seen. If that is what was the intent then it could be possible as the GPIO's on TM4C129 are not fail safe GPIO's. They can sink in current when uC is powered off.

Regards
Amit

0 pooja trivedi over 11 years ago in reply to Amit Ashara

Intellectual 455 points

Hello Amit,

You understand correctly. there is 47K pull up on GPIO in off condition and voltage drop is seen. Please provide any solution to remove this problem.

0 Amit Ashara over 11 years ago in reply to pooja trivedi

TI__Guru**** 244440 points

Hello Pooja,

The GPIO on TM4C129 device is non-fail safe IO (Please see data sheet). As a result when the device is not powered up, it will sink current via the GPIO to the power rail of the device. If the external source cannot supply current it will droop.

Can you confirm if the 47K is not connected then the voltage drop is not seen?

Regards
Amit

0 pooja trivedi over 11 years ago in reply to Amit Ashara

Intellectual 455 points

Hello Amit,

If i do not connect 47K then port pin is isolated from supply. so there is no voltage drop. If i short 47K then it is possible that port pin will be damaged.???

I can not find non-fail safe IO in datasheet for all GPIO it is only for HIB XOSC pin on page 1581 in datasheet of Tiva™ TM4C1290NCPDT Microcontroller.

0 Amit Ashara over 11 years ago in reply to pooja trivedi

TI__Guru**** 244440 points

Hello Pooja,

Thanks for the confirmation on the fact that removing 47K removes the issue. Please note that from the pad in case of GPIO there is a forward biased diode to VDD power rail So you would end up biasing the rail.

Secondly your port titles TM4C1294NCPDT but you mention TM4C1290NCPDT. Please confirm the device you use as the two devices are not pin-compatible.

Regards
Amit

0 pooja trivedi over 11 years ago in reply to Amit Ashara

Intellectual 455 points

Hello Amit,

i also want to high-low port pins to on and off the supply from above shown circuit.
By using diode it is not possible for me to high low port pin.

0 Amit Ashara over 11 years ago in reply to pooja trivedi

TI__Guru**** 244440 points

Hello Pooja,

Please first confirm the device!!! So that you do not end up in another issue.

Regards
Amit

0 pooja trivedi over 11 years ago in reply to Amit Ashara

Intellectual 455 points

Hello Amit,

My device is TM4C1294NCPDT. and i refer Tiva™ TM4C1294NCPDT Microcontroller datasheet now. n later i plan to use TM4C1290NCPDT.

0 Amit Ashara over 11 years ago in reply to pooja trivedi

TI__Guru**** 244440 points

Hello Pooja,

Please note what I mentioned earlier. They are not direct swappable devices. So don't be surprised if you put a TM4C1290NCPDT later on a TM4C1294NCPDT board.

Coming to issue mentioned here and based on the circuit, I would to remove U3B, R22, C17 and connecting a Pull Down instead to U3C input which is also connected to the GPIO from TM4C.

Regards
Amit

0 pooja trivedi over 11 years ago in reply to Amit Ashara

Intellectual 455 points

Hello Amit,

Thank you for your reply. But i can not use this logic because ESC_KEY_ON_OFF is input pin to the microcontroller which is coming from key and internal pull up is on at that pin.
so when i press the key it will get zero logic so i can not pull down it.

0 Amit Ashara over 11 years ago in reply to pooja trivedi

TI__Guru**** 244440 points

Hello Pooja,

It seems contradictory to the earlier post where you mentioned

"i also want to high-low port pins to on and off the supply from above shown circuit.
By using diode it is not possible for me to high low port pin."

Can you send the complete view of the circuit and the GPIO Pin which is sinking in current.

Regards
Amit

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TM4C1294NCPDT GPIO Issue