Part Number: TMS320F2811
Team,
my customer is facing issues with power sequencing and a certain behavior they see at 80C that is messing with their IOs. The behavior is observed in 2 of their 50 prototype boards.
Problem description
At 80C (or higher ambient temperatures), GPIOA12 is actively driving 3.3V output. This is not just an internal pull-up, but actively driving from the 3.3V supply voltage. There is an external 4.7k pull-down.
Figure 1: Normal power-up
Figure 2: GPIOA12 on 3.3V
Both pictures are taken with the same board at 80C. You can see GPIOA12 rising to 3.3V in figure 2.
The 1.9V are activated when the 3.3V supply surpasses 2.5V -> Power sequencing according to datasheet “option 2”.
The reason why the 1.9V do not rise any further (figure 2) is because it is connected to GPIOA12. That means if during the reset phase, the GPIOA12 signal is not below 1V, the 1.9V are not “released”.
We are sure that the 3.3V is not driven by our peripherals.
According to the datasheet, the IO-Pins are undefined until the 3.3V is below 2.5V and until the 1.9V is below 1V. That means the controller is acting according to datasheet.
Questions
- Is it really true that an IO-Pin drives 3.3V when the core voltage (1.9V) is at 0V?
- Is the temperature dependency of this behavior normal?
- Why do we see this behavior at this pin and not at any other IO-Pin?
- Could this behavior be caused by some influence by another pin?
- Is there something wrong with the power sequencing (too large/small du/dt, too large delay for the core voltage, …)?
Thanks
