Introduction

• Who

  • Daniel Puratich Architecture & Management

  • Kenny Na EE Designer, Documentation

• What

  • A USB-C PD sink where the output voltage can be selected with resistors

    • DNP and fitted resistors, should be foolproof 0805s

  • Intent for requesting 20V 65W when debugging https://uwarg-docs.atlassian.net/wiki/spaces/EL/pages/2701197313/RPi+Interface+Rev+C?atl_f=content-tree setup without the full drone, but should support 12V and 5V as well for testing other boards

  • Use a USB-C PD chip and the associated required FETs that are required for negotiation

  • Ideally does not require a microcontroller, due to cost constraints

  • USB-C input connector / XT30 output connector

  • don't worry about board area too much but it can be tiny

  • no buck converter

Resources

USB-C Sink | Altium 365

https://www.youtube.com/watch?v=W13HNsoHj7A&t=615s

https://hackaday.io/project/192576-picopd-usb-c-pd-30-pps-trigger-with-rp2040

https://www.ti.com/interface/usb/type-c-and-power-delivery/products.html#1241=PD%20controller&

TI | ESD and Surge Protection for USB Interfaces

https://www.usb.org/usb-charger-pd

Wikipedia | USB-C Debug Accessory Mode

https://e2e.ti.com/support/power-management-group/power-management/f/power-management-forum/1339647/tps25730-excess-load-capacitance

https://en.wikipedia.org/wiki/Field-effect_transistor

https://www.robot-electronics.co.uk/i2c-tutorial

https://microchip.my.site.com/s/article/USB-Type-C-Layout-Recommendations#:~:text=USB%20Type%2DC%20CC%20Signals,traces%20with%2050%CE%A9%20impedance.

Engineering

PD Controller Selection

Main Options

There were a few possible options that were selected from research:

• https://www.digikey.ca/en/products/detail/stmicroelectronics/STUSB4500QTR/9092189

• https://www.digikey.ca/en/products/detail/texas-instruments/TPS25730SRSMR/22147461/https://www.digikey.ca/en/products/detail/texas-instruments/TPS25730DREFR/22147394?s=N4IgTCBcDaIC4AcDOYCsB2AzABgCYgF0BfIA

• https://www.digikey.ca/en/products/detail/infineon-technologies/CYPD3177-24LQXQT/10238323

• Cheap PMIC + RP2040 (ex. https://www.digikey.ca/en/products/detail/onsemi/FUSB302B10MPX/7356099 + https://www.digikey.ca/en/products/detail/raspberry-pi/SC0914-13/14306010?s=N4IgTCBcDaIEoAUwAYAsyQF0C%2BQ)

Decision Matrix

The TPS25730x was selected for its recent release, comprehensive datasheet, relatively low price, and simple implementation.

FET Selection

A typical USB-C PD controller will require a gate to block the USB-C input voltage while arbitration occurs. Once the negotiation is successful, the controller sends voltage to the gate to enable the transport of power.

In the case that PD negotiation fails, there is sometimes a fallback “safe power” rail. These might typically supply 5V @ 900mA, or similar. The TPS25730x includes this feature - however, its open drain output pins do not respond to regular USB power events (only those matching the USB-PD protocol).

The TPS25730S recommends the https://www.digikey.ca/en/products/detail/texas-instruments/CSD87501L/5126233, while the TPS25730D comes with an integrated gate in the package. Given the small price delta between the S and D models, the TPS25730D is a practical choice, and very simply concludes our FET selection.

https://www.digikey.ca/en/products/detail/texas-instruments/TPS25730DREFR/22147394?s=N4IgTCBcDaIC4AcDOYCsB2AzABgCYgF0BfIA

Surge Protection

Inrush Current Protection

Seeing as this board is primarily intended for debugging RPi Interface Rev C, which includes a buck converter with large bulk capacitance, inrush current protection is required, as recommended by USB-IF. This is due to the capacitors on the load device requesting a large amount of current, characterized by I_cap = C_cap x dV/dt.

As shown above, the TPS25730 datasheet states that inrush current limiting is “implemented as described” in the USB3.2 specification. The exact section of the USB 3.2 spec regarding inrush currents is shown below.

Input Voltage Protection

While the source device should do most of the voltage regulation, TI recommends a transient voltage suppressing diode be implemented on the VBUS_IN rail. This is due to the possibility of a voltage surge when a cable with current actively running through it is unplugged, causing inductive ringing (as mentioned here), as well as any electrostatic discharge events. For example, the TVS2200 product is recommended for a 20V spec. The Altium schematic is configured with variants, which will change the TVS diode model to match the negotiated voltage.

Power Configuration

Resistor Dividers

Decoded ADC Values

If the source device cannot supply voltage between the minimum and maximum voltages set by pins ADCIN1 and ADCIN2 OR the operating/maximum current is violated, then the controller will signal a capabilities mismatch and run the CAP_MIS pin high.

Schematic