EZ-PD BCR (CYPD3177) external VDDD supply

[ShAk_4697856]

We are interested in including the EZ-PD BCR  (CYPD3177) in our design, to support external power input.

Our design incorporates an internal battery and MCU. We would like to establish communication with the CYPD3177 via HPI, even when the external USB-C power source is not connected and supplying VBUS_IN. The datasheet indicates that the VDDD pin can also be used as a power input:

The EZ-PD BCR device can operate from two possible external supply sources: VBUS_IN (3.0 V–24.5 V) or VDDD (2.7 V–5.5 V).

However, it is not entirely clear what the proper/safe way to power the device is, from both VBUS_IN and VDDD. Can this be safely accomplished by simply supplying VDDD through an external Schottky diode, to prevent the internal LDO from back-driving our own 3.3V power supply when VBUS_IN is present? Is the internal LDO protected from being back-driven when VBUS_IN is not present?

Could you please provide a recommendation for powering the CYPD3177 from both an internal and/or external power source?

[Pablo_EG]

Hello ShAk_4697856,

Thank you for posting on Infineon Community.

We have understood your application needs thanks to your clear explanation.

Unfortunately, this section
->The EZ-PD BCR device can operate from two possible external supply sources: VBUS_IN (3.0 V–24.5 V) or VDDD (2.7 V–5.5 V).
of the datasheet is not completely correct.
The datasheet will be amended shortly.
The reality is that BCR can only be supplied from VBUS_IN.
The reason is that there is no way to disable the internal VBUS LDO  (this is required to avoid damaging the device)unless there is a change in firmware.
And as BCR is fixed firmware, this is not possible.

Therefore, the device will get damaged when using the VDDD supply after there is a voltage on the VBUS.
You could apply 5V on VBUS instead of  VDDD for the same result.
However, this will require the use of a diode (from 5V source such as a microcontroller to VBUS) which can stand the maximum allowed VBUS voltage.

Alternatively, you could consider CCG3PA if powering the controller using VDD is required.
CCG3PA does support these two supply modes, and the switch between them can be performed in the firmware.

Please refer to the following documentation for further understanding of the supply switch requirements.
https://community.infineon.com/t5/Resource-Library/CCGx-Power-SDK-If-system-has-external-VDDD-source...

I apologize for the confusion caused.

Best regards,
Pablo

[ShAk_4697856]

Hi Pablo,

Thank you for the quick reply.

We find the EZ-PD BCR device attractive because of it's standalone operation, as compared to the CCG3-PA.

It would be convenient for us to power the CYPD3177 through a diode via VBUS_IN, since our device already has an internal 5V rail to support this, although we would also need to include a second diode in series with VBUS, as in the attached image, to prevent our internal 5V supply from driving VBUS.

One concern is whether the forward drop of the second diode would interfere appreciably with the VBUS voltage monitoring of the device:

Do you foresee this being an issue?

Thanks,
Shea

[Pablo_EG · Accepted solution]

Hello ShAk,

Thank you for your reply.

Your concern about the forward drop is very valid.
One of the VBUS_IN functions is to detect the bus voltage, and this will be offset due to the diode.

However, BCR has only Over Voltage Protection and there is no Under Voltage Protection.
Therefore, even if there is a voltage drop in the VBUS_IN line, the protections will not be triggered.
Just for safety margins, we recommend you choose a low voltage drop diode, if possible.

Best regards,
Pablo