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USB EZ-PD™ Type-C

NiPr_4097786
New Contributor II

Hi, I would like clarification on the use of the VDC_OUT pin on CYPD3177. I will be using this in a system where the main VBUS gate is not controlled by CYPD3177. So, VBUS_FET_EN and SAFE_POWER_EN will remain disconnected.

I would like to know the expected operation of CYPD3177 if VDC_OUT is left floating, grounded, tied to VBUS_IN, etc.

I would also like assurance that the D+/D- pins can be placed in parallel with a typical USB2 HS device, as this is not specified in the datasheet and the development board does not break out these pins.

Thank you

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4 Replies
YiZ_31
Moderator
Moderator

Hi,

VDC_OUT has to be connected to the power output of the VBUS gate because CYPD 3177 has OVP(Over voltage protection) which cannot be disabled. I'm not sure if your design can work in which CYPD3177 are responsible for CC negotiation but not VBUS control.

D+/D- cannot be simply placed in parallel with other USB 2.0 device. If you want BC 1.2 Apple charge function at the same time, you'll need a USB 2.0 hub.

Regards,

Eddie

 

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NiPr_4097786
New Contributor II

Hi Eddie

Is OVP the only function of the VDC_OUT pin?

What are the conditions to trigger OVP?

What actions does the chip take when triggered?

Will tying VDC_OUT to ground disable OVP?

What will happen if this pin is connected to VBUS_IN?

If my device requires the use of the USB2 data lines should they not be connected to the D+/D- lines of CYPD3177?

If D+/D- lines are unused should they be tied to ground?

This device is pretty similar to a tablet. On its USB-C port we need power that can be negotiated via USB-PD. However due to the design of the rest of the power supply it would be better for us if we can use CYPD3177 only for PD negotiation and not for power control. Considerations such as the dead battery condition have been taken into account.

The device is also a USB2 data peripheral and so these lines will also be connected and used as USB2-HS.

Thanks!

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YiZ_31
Moderator
Moderator

HI,

The function of VDC_OUT is montoring the VBUS output to the system.

The Over-Voltage Protection Event bit Shall be set when the Sink detects its output voltage exceeds its limits triggering its protection circuitry.

Sinks Should attempt to send a Hard Reset message when over voltage protection engages followed by an Alert Message indicating an OVP event once an Explicit Contract has been established.

When VBUS is out of the (VBUS_MIN, VBUS_MAX) range, the OVP event is triggered. So tying it to gnd will not help.

BCR will detect voltage before the PD contract is estbalished, OVP event will still be triggered.

The D+/D- of BCR can be left floating if you do not want to use it.

If BCR do not control power supply, you still need other EC to read the register status of BCR, then control the VBUS gate.

Regards,
Eddie

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NiPr_4097786
New Contributor II

Hi Eddie,

I have tried reproducing this on hardware, but I am not seeing any Hard Resets being sent from the BCR. Whether VDC_OUT is grounded, floating, or shorted to VBUS, I am seeing the same results: PD negotiation proceeds as normal with the source providing the requested voltage. I have tried this with a few different sources, with different capabilities, and I am using CY4500 to sniff and log PD traffic.

Why am I seeing behaviour different from expected?

Thanks!

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