STUSB4500 is a USB-C PD controller which supports a 5V fixed power profile, and two customizable power profiles. This library allows for flashing the non-volatile memory of the STUSB4500 to change the default power profiles on boot as well as the capability to dynamically program the high priority power profile with the optimal power profile that the currently plugged in PD charger can supply. Optimal is defined as the highest wattage profile that satisfies a user-defined set of constraints. This code assumes a little endian architecture.
This library can easily be ported to a custom platform. The only requirements are a function to get the current tick in ms (if using timeouts, recommended) and an i2c implementation. Simply implement the read and write functions of the device handle with your i2c implementation. If there are additional requirements for porting the code to your own platform, please submit an issue so that compatibility can be improved. A CMake library is included for convenience. It is strongly recommended to use i2c in fast mode when using dynamic power profiles.
To take advantage of dynamic power profiles, include stusb4500.h and simply call stusb_negotiate to read the capabilities from the PD source and update/load the high priority power profile. stusb_negotiate() expects two parameters: a stusb4500_config_t configuration and a boolean on_interrupt which describes whether the function is being called on cable attachment interrupt or not.
stusb4500_config_thas three adjustable parameters: minimum current, minimum voltage, maximum voltage. The optimal negotiated profile will satisfy these parameters.stusb4500_config_talso expects a function which returns the current tick in ms to handle timeout logic. If one is not provided, the timeout logic will not be used, which may cause the code to hang if something goes wrong.- If
on_interruptistrue,stusb4500_negotiatewill instantly start waiting to intercept the source capabilities message. Ifon_interruptisfalse,stusb4500_negotiatewill transmit a PD soft reset command to force a new transmission of source capabilities. If usingon_interrupt, it may be desirable to callstusb4500_negotiatewithon_interruptset tofalseon boot to perform negotiation if a cable is already attached on boot.
STUSB4500 has a user controllable open-drain GPIO pin. The NVM can set whether the GPIO is controlled by the user or the STUSB4500. In the case of user control, the GPIO pin can be driven low or set to high-z by including stusb4500.h and calling stusb4500_set_gpio_state.
The STUSB4500's non-volatile memory (NVM) determines what power profiles are configured at boot, along with some additional settings. Flashing the NVM is recommended if the circuit using the STUSB4500 cannot handle 20V, as the default NVM configuration contains a 20V profile. An NVM flash is required only once per chip. Currently, the following parameters can be adjusted via the stusb4500_nvm_config_t struct.
| Parameter | Description |
|---|---|
| I_SNK_PDO1 | PDO1 current (mA) |
| V_SNK_PDO2 | PDO2 voltage (mV) |
| I_SNK_PDO2 | PDO2 current (mA) |
| V_SNK_PDO3 | PDO3 voltage (mV) |
| I_SNK_PDO3 | PDO3 current (mA) |
| I_SNK_PDO_FLEX | Global PDO current if PDO = 0 |
| SNK_PDO_NUM | Number of valid PDOs (1, 2, or 3) |
| REQ_SRC_CURRENT | Accept as much current as src provides |
| POWER_ONLY_ABOVE_5V | Only output if negotiation above 5V |
| GPIO_CFG | Configures the behavior of the GPIO pin |
To program the NVM, include stusb4500.h and run stusb4500_nvm_flash with your config. stusb4500_nvm_flash returns true after writing and validating the flash.