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Electronics => Beginners => Topic started by: aix on December 25, 2019, 01:29:14 pm

Title: USB Type-C: capacitors between CC1/CC2 and GND
Post by: aix on December 25, 2019, 01:29:14 pm

I'm looking at the schematic of a breakout board for FUSB302 (https://www.onsemi.com/products/interfaces/usb-type-c/fusb302) (Programmable USB Type-C Controller with PD).

The schematic (attached) has 470pF caps between the CC1/CC2 lines and ground.

The official breakout board (https://www.onsemi.com/pub/Collateral/EVBUM2509-D.PDF, (https://www.onsemi.com/pub/Collateral/EVBUM2509-D.PDF,) page 3) also has caps, only 200pF.

I can't seem to find any docs about the purpose of those caps.  Would appreciate if someone could explain why they're needed.

(I'm designing an FUSB302-based USB-PD sink, for my own amusement/education, and am trying to figure out whether I should include these caps and how to choose them.)

Title: Re: USB Type-C: capacitors between CC1/CC2 and GND
Post by: mvs on December 26, 2019, 01:15:06 pm

This caps are needed to comply with USB PD specification (BMC cReceiver capacitance 200-600pF). According to Datasheet of FUSB302, cReceiver capacitance is just 50pF typ, so there is room for additional cap and/or TVS protection diode.

Title: Re: USB Type-C: capacitors between CC1/CC2 and GND
Post by: aix on December 26, 2019, 11:04:52 pm

Thanks for this.  Now that I know what to look for, I found this note that future readers might find useful:

https://www.onsemi.com/pub/Collateral/AN-5086-D.PDF (https://www.onsemi.com/pub/Collateral/AN-5086-D.PDF)

(ON semi AN-5086/D: USB Type-C, CC Pin Design Considerations)