4.2 KiB
USB-C Dual TCPC Example
This board configuration implements a USB-C TCPC for two ports.
The design uses a microcontroller running code from the Chromium EC codebase to implement the TCPC. The code tries to follow the "USB Type-C Port Controller Interface Specification" that is released as part of the USB 3.1 Specification.
Building
Chromium OS chroot
All the following instructions have been verified in a Chromium OS chroot. You can find how to set one up on the Chromium development wiki.
Build the TCPM code
cd src/platform/ec
make BOARD=glados_pd
Schematic
Note that you may need to zoom in the browser to read the image if
reading this through the git source tree browser. A
pdf of this schematic is in the
board/glados_pd directory. It shows three main areas.
The two (identical) sections on the left provide the analog interface to the CC line. Each CC line is identical. Resistors are used in combination to set the resistor applied to CC:
| Resistor | USB_Cx_CCy_DEVICE_ODL |
USB_Cx_CCy_HOST_HIGH |
Value |
|---|---|---|---|
| 1.5A Rp | high impedance | high 3.3V | 5.11k+6.98k pullup |
| 3A Rp | high 3.3V | high impedance | 5.11k pullup |
| Rd | low 0V | high impedance | 5.11k pulldown |
When USB-PD transmission is required the USB_Cx_CCy_MCU is set low
and the data transmitted on USB_Cx_CCy_TX_DATA. The two resistors
form a divider that sets the level to match the BMC
specification. These resistors and the capacitor on the pulldown may
need tuning for a given application to meet the required TX eye mask.
The EN_PP3300_USB_PD is a critical enable output from the MCU. It
must be pulled down when power is off (not shown here, it is done as
part of the load switch on the power supply page) and remains low
until the microcontroller is ready for operation. It:
- Enables the
PP3300_USB_PDpower supply that powers all the USB-C port related components (eg the low speed muxU24shown here and the high speed mux that is not part of this example page) - Controls the isolation FET (two parts of
Q1,two parts ofQ6) to disconnet the CC lines when power is off or the MCU is intializing. When power is enabled the enable will put the gate at 3.3V and ensure no higher voltage on CC will reach the MCU. - Disables the Dead Battery pulldown once the MCU is ready for
operation. The Dead Battery Rd pulldown is provided by a FET (two
parts of
Q24andQ12) and resistor. When there is no power, the gate is pulled down to ground. A DFP application of Rp will pull up the source and provide the required Vgs=-0.7 (Vgsth max should be 1V) to turn on the FET and connect the Rd pulldown. Once there is power and the MCU is running it will driveEN_PP3300_USB_PDhigh and disable the FET.
There is a load switch (U9,U10,U11,U12) to provide current
limited Vconn.
The main area of the schematic is the STM32F051 microcontroller that
runs the glados_pd code.
There is a quirk in U24. For port C0 the transmit data is provided
by the SPI1 controller as SPI1_MISO. The internal I/O multiplex
allows this to be driven on either pin PB4 or PA6 and thus support
driving whichever CC line is needed. Port C1 uses the SPI2
controller which (on this package) can only use pin PB14, so an
external mux is used to direct this to the appropriate port.
Replacement with Two TCPC parts
This schematic page can be replaced by two TCPC parts.
Flashing and Running
Flashing the firmware binary
The microcontroller can be pre-programmed or is programmed in the
factory by pulling USB_PD_BOOT0 high and resetting the part to
initiate a firmware update over UART. During development the
Servo board can be used
for this.
Once programmed for the first time, the part supports secure update of the Read/Write copy.
Known Issues
- This is the first version of the documentation...