TMS320F28379D: min/max values of GPIO pull-ups

HS FAE Germany

Part Number: TMS320F28379D

Hello,
is there any value you can give me for min/max value of the GPIO pull-ups. In the d/s there are only typical values. The customer wants to pull-down the pin (<0.8V) even the pull-up is switched on. Therefor he has to know how much max current he has to pull-down.

Regards, Holger

over 6 years ago

0 Manoj Santha Mohan over 6 years ago

TI__Guru 55700 points

Holger,

I shall check with design and get back with you within next week (upto 5 business days).

Regards,
Manoj

0 Manoj Santha Mohan over 6 years ago

TI__Guru 55700 points

Holger,

I'm puzzled why customer wants to enable the pullup on pins which are going to have pulldown resistors. What is the rational behind it?

Regards,
Manoj

0 HS FAE Germany over 6 years ago in reply to Manoj Santha Mohan

TI__Mastermind 32310 points

Manoj,
the customer has to different HW but only one firmware. This port has the function to decide which HW is connected. It could be that the port is open and the pull-ups pull it to high or the HW is connected and the external pull-down resistor pull it to low (but still the internal pull-ups are switched on). Currently they have a 5.11Kohm resistor on the external HW which means a VIN of 767mV. The question is what is the max pull-up current so customer can decide on the right pull-down resistor to be below the VIL=0.8V.

This requirement is decribed on our wiki:
http://processors.wiki.ti.com/index.php/General_Purpose_IO_(GPIO)_FAQ_for_C2000#Q:_What_is_the_value_of_the_pull-up_and_pull-down_resistors.3F
but we need the max value here because it is an automotive application and the typical value is not acceptable.

Regards, Holger

0 Manoj Santha Mohan over 6 years ago in reply to HS FAE Germany

TI__Guru 55700 points

Holger,

Max pullup current for this device would be 540uA. Ask the customer to chose the pulldown resistor accordingly.

Regards,
Manoj

0 HS FAE Germany over 6 years ago in reply to Manoj Santha Mohan

TI__Mastermind 32310 points

Hello Manoj,
the 540uA is valid for VIO=3.3V+/-10%? Is this over temperature?
In the current devices they used a 5.11kohm pull-down resistor which would be valid for the typical 150uA current. Now the fear they some of the devices which will have a higher pull-up current than 150uA will have a higher VIL then 0.8V. Can you say how the deviation of the pull-up current is? Will the pull-up current increase with higher chip temperature?

Regards, Holger

0 Manoj Santha Mohan over 6 years ago in reply to HS FAE Germany

TI__Guru 55700 points

Yes, 540uA is across VIO and over temperature corner. There will be variation of pull-up current over temperature. But, it will not exceed 540uA pull-up current.

Regards,
Manoj

0 HS FAE Germany over 6 years ago in reply to Manoj Santha Mohan

TI__Mastermind 32310 points

but you can't tell me the disdribution of the values (Gauss distribution?) ?

Further question:
- a 1kohm resisitor is ok? Max current output current ok?
- do you know the temperature influence? Current increases with higher current? Do we have any values?

0 Jason Whiles over 6 years ago in reply to HS FAE Germany

TI__Expert 5550 points

Holger, sorry, it looks like I missed hitting the post button on this yesterday.

----
Holger,

The internal pulls should only be used when there is no other external DC pull down resistance connected to the pin.

If this application requires HW detection for different PCB's, then the internal pull-up should be disabled and external pull-up/pull-down should be used between the different boards.

If the internal pull-up must be kept enabled due to existing software, then for the external pull down case the resistor should be made quite small to provide a very hard 0v. The internal pull-up strength is weak and I can't recommend overdriving it with another weak external resistor in the way you have described.

Best regards,
Jason

0 Manoj Santha Mohan over 6 years ago in reply to HS FAE Germany

TI__Guru 55700 points

Holger,

I'm closing this thread as we were able to discuss this issue over the call.

Regards,
Manoj

C2000™︎ microcontrollers

C2000 microcontrollers forum

TMS320F28379D: min/max values of GPIO pull-ups