Hi,
I am facing some problems using the component TUSB321AI in UFP only mode.
I am prototyping an instrument that is supplied by the USB and I want to know how much current I can draw from the host. Since the only supply is from the USB, I use the 5V for both supplying the TUSB321AI and the open drain outputs (OUT1, OUT2, FAULT); VBUS line is also connected with this 5V by a 887k resistor.
When I connect the USB-C connector I can see that OUT1 line is high while OUT2 is low, meaning 900mA of current capability. I am connecting my board to a 2.5A wall adapter so I am expecting a 1.5A current advertising. On my PC I have the same behavior.
On E2E forum (e2e.ti.com/.../3519981 I red that the problem might be caused by supplying the open drain outputs before VDD is stable, so I tried to connect these output lines to an external supply and activate the supply after connecting the USB cable. At first I saw that both OUT1 and OUT2 where low and I thought I solved the problem but if I see the voltage on the CC line I measure 0.4V that is in the "default current" range.
If I try to supply the open-drain outputs before the TUSB321AI I can see the OUT2 going high for an instant and then going back low and watching CC line with an oscilloscope I can see what reported in the screenshot below
The CC line goes to 1V, that is in the "medium current" range but I can't figure out why is then going low to 0.4V.
What am I doing wrong?
Thank You for your help
Kind regards
Francesco
