GPIO Pins connected to Peripherals at Startup

[Beko]

Hi,

We are using the OSD335x C-SIP and have a question regarding the GPIO pins. We are connecting these pins to out-board peripherals and some have separate power supplies. At power-up, the connected peripherals may be on and trying to send data to the GPIO pins of the C-SIP prior to the full power-up. These GPIO data lines may even be pulled up to a Vdd by the peripheral circuitry. So our questions are:

1) Does having a 3.3V voltage at GPIO pins during power-up cause any issues to the C-SIP? (Normally these data lines would be pulled up by the C-SIP after the SYS_VDD1_3P3V rail is powered but since the peripherals are already connected we may already have signals before SYS_VDD1_3P3V rais is up)

2) Are GPIO of C-SIP pins 5V tolerant? So, for example if the UART signal lines are connected to a 5V peripheral device, would it cause any issues?

If it is not permissible to have any kind of voltage at GPIO pins during power-up, how would you suggest we mitigate the issue?

Thank you in advance for your response.

Regards,

Beko

[Neeraj Dantu]

Beko,

Both #1 and #2 are not recommended and will result in operating the SiP and SoC out of spec.

The way to mitigate these issue would be the following:

1. Use buffers(bidirectional if needed) with enable input. You can tie the enable pin to either SYS_VDD3_3P3V(powers the IO domain of the SoC) or a GPIO that you can control based on when you want the device to communicate with off-board peripherals.

2. You should not connect any GPIO to 5V. This poses a risk of permanent damage to the SoC. A voltage translator buffer is the best solution for this issue.

Please let us know if you have more questions.

Best,

Neeraj

[Author]

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