I’m designing a custom carrier board based on the TX2 carrier board. I note that USB_VBUS_EN0 is tied directly to the enable pin of the APL3511CBI, which is active high. But on the main IO connector (schematic 4) it looks like that pin is just an open collector output, and there isn’t any pullup to 3.3V or 5V? If it’s really an OC output, how does it work without a pullup? If it’s not an OC output, what logic level is it driven by?
Following from that, I don’t want to add an I2C GPIO expander just to get the 5V enable for the HDMI. Can I use USB_VBUS_EN0 to drive it, or should I tie it high, or to some other enable pin? Will it cause errors in the HDMI driver?
Hi, there is pull-up in module for USB_VBUS_EN0. To use USB_VBUS_EN0 is not a good idea, you can use other GPIO which is not from expander, but the related driver change should be done by yourself.
Can you clarify what you mean by “not a good idea”? The module just turns on the hdmi power during boot, right? There’s a nostuff resistor on the carrier board to pull the hdmi enable directly to 3v3. Is there some issue with the hdmi being powered when the module turns on? Does it need to cycle the enable pin at various times?
I don’t have the board space for the gpio expander, and we want to use the modules without custom driver mods, so I need a legitimate reason for direct control of that pin.
USB_VBUS_EN0 is default low during boot. You can use that 3v3 for this.