Introduction
VCONN is a dedicated power supply pin in the USB Type-C® connector. It provides power to the cables electronics, such as e-markers (EMC), long cables with data repeaters, and VCONN-powered USB devices. It ensures proper power supply to these components in specific scenarios.
On the connector, one CC line performs the attachment, orientation, and power delivery communication, the other CC line can be used to power the attached cable. The valid VCONN voltage range is 3.0 V – 5.5 V.
It is a USB Power Delivery communication with Start of Packet (SOP) for source to sink signaling and SOP’/SOP ’' for cable addressing.
USB-IF: USB Power Delivery Specification, Revision 3.2, Version 1.1, 2024-10, page 58
1. VCONN activation
VCONN activation is required only when a 1kΩ pull-down resistor (Ra) is detected on the CC line of the cable. This resistor indicates that VCONN power can be turned on.
A full-featured USB Type-C® cable must assert Ra pull-down resistors on the VCONN pin.
Note: USB data capability as well as the capability to provide VCONN are not mandatory.
2. VCONN in STM32 USB Type-C® port design
STM32 microcontrollers detects Ra and manages power delivery timings and state machine.
2.1. External power supply
STM32 cannot provide VCONN power internally because of limited I/O current capability to provide 100 mW (33 mA with 3.3 V Vdd). An external power supply, power switch, LDO, or dedicated IC is required.
Proper power management is crucial to ensure that VCONN is supplied only when needed and that the power supply can handle the required current. This involves detecting the connection and managing the power delivery accordingly with correct timings, discharge profile etc.
2.3. Circuit design
The design should include components such as MOSFETs, resistors, capacitors, and OCP to manage the VCONN power supply effectively. The circuit should ensure that VCONN is only supplied to the correct pin and that the power is stable and within the required specifications.
3. TCPP for VCONN management
TCPP devices offer an integrated solution for managing VCONN power as a companion chip of the STM32 UCPD peripheral. These devices embed a power switch that closes the power path between the CC line (with Ra) and the VCC_VCONN pin, simplifying the design and providing needed protection.
3.1. Integrated switch with discharge
The STM32 with UCPD detects of Ra on the CC line and drives TCPP to close the internal switch. This switch connects the VCC_VCONN pin to the CC line which supplies VCONN power to the cable or device.
To avoid residual voltage on the CC line at disconnect, a VCONN discharge is required. TCPP embeds a VCONN discharge resistor that grants accurate timings managed by STM32.
3.2 OCP protection
Over current protection against defective VCONN powered device on short circuit is needed.
VCONN OCP triggers at 47 mA over the 3.0 V to 5.5 V voltage range.
At startup, a soft start sets the tripping current to about 590 mA within 512 μs min. (1 ms max.) to avoid overcurrent triggering. After this delay, the soft start is ended and the normal OCP threshold occurs (50 mA).
For instance, when using TCPP20, if an OCP event occurs:
- VCONN switches, CC switches, and gate drivers are shut down.
- The OCP alarm is maintained for up to 40 μs, during which no recovery is possible.
- CC switches after this delay are reactivated, but VCONN switches and gate drivers remain OFF. The system can be restarted only with a recovery word sent by the MCU via I2C commands.
- The FLGn signal stays low as long as the recovery word has not been sent.
4. Example design with STM32 and TCPP
X-NUCLEO-SRC1M1 is a Nucleo expansion board design example for SOURCE. As VCONN features are embedded on TCPP02-M18, there is no specific hardware design.
X-NUCLEO-DRP1M1 is a Nucleo expansion board design example for dual role port. As VCONN features are embedded on TCPP03-M18, there is no specific hardware design.
Since VCONN features are embedded into the TCPP02-M18, no additional hardware changes are required.
STM32 UCPD peripheral and associated middleware let the possibility to activate or not VCONN when needed through VCONN_Support.
Note: VCONN is required only for SOURCE and dual role power using USB3.0 and recommended for sink application. For USB4.0, it is mandatory for all configurations.
Conclusion
Implementing VCONN in your USB Type-C® port design ensures compatibility and functionality with a wide range of devices and cables. VCONN is essential in USB Type-C® design. It provides the power and communication for advanced cable functionalities and connected devices. STM32 and TCPP devices offer robust solutions for managing VCONN power.
By understanding the requirements and implementing the necessary components, designers can create efficient and reliable USB Type-C® ports that meet the specifications and provide the necessary power for connected devices.
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