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USB EZ-PD Type-C

New Contributor II

I’m working with the CYPD3175-24LQXQ_pa_direct_fb project for the CCG3PA, on custom HW. I have a separate supply for the CCG3PA VDDD (3.3V) and the VBUS source regulator. The firmware is somewhat functional on my HW but I see strange behavior. After the controller enables the VBUS source by asserting a GPIO to the regulator’s pin (and VBUS goes to 5V), when I then disable the VBUS source I see 3.3V remaining on the VBUS line. The 3.3V is coming from the CCG3PA somewhere (verified by shutting down the power to the VBUS source regulator).

Any ideas what could cause the 3.3V to show up on the VBUS line? The CCG3PA has pins VBUS_C_MON_DISCHARGE and VBUS_IN_DISCHARGE connected to the VBUS line, per the reference schematic in the CCG3PA datasheet. My guess is that it has something to do with the ability of the CCG3PA to derive VDDD from VBUS_IN_DISCHARGE, that somehow the 3.3V on VDDD is getting fed back to this pin?

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Moderator
Moderator

Hi,

May I see your schematic? Usually VBUS_C_MON_DISCHARGE and VBUS_IN_DISCHARGE would not put power on VBUS.

Regards,

Eddie

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New Contributor II

Also interested in this raised question and root cause.

Very confident we saw this event today in the lab while experimenting with the PWM (CY4532 EVK) to dial up custom voltages onto the USB Type A VBUS line. For sure saw the 3v3 on Vbus but ignored this as a fluke till we are more confident on the code run. After some attempts, did manage to dial up to 6v0, 9v0, 12v0 and also 20v0 on the Type A Vbus rail.

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Moderator
Moderator

Hi,

Can you tell me the steps so I can reproduce 3.3V on VBUS from my side?

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New Contributor II

Hi. Will try to retrace our steps but may be logical - from the CY4532 EVK. In our review, we did not wish to apply any load due to the varying Vbus values (5V..20V) and for now, missing the proper QC3.0 triggers. So we had manually configured the code to output our desired voltage values. During some of these attempts, we saw the 3v3..3v6 range. More details to follow.

cypress_default_vbus_voltage.png

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