Before jumping into full-scale development, I would like to test some parts with Mockup #1

Features to try:

• STM32 PD controller
• LM51772 Voltage and AVG current manipulation with MCU's DAC

Key requirement: less development, use of the shelf solutions.

• Eval board for LM51772 has ready - to -use GUI and USB-I2C converter USB2ANY. Means no need to implement I2C control in the MCU at this point.
• STM has its own eval for USB PD - X-NUCLEO-SNK1M1 - great, just connect it to the Nucleo board with the MCU. 

The only thing I need to develop here - OpAmp board. It serves to convert DAC signals to the LM51772 levels of ATRK and ISET.

Voltage control

LM51772 gives the ability to control the output voltage in two ways simultaneously: I2C and external(ATRK or DTRK). To be able to achieve a small error, we could set a rough voltage with I2C, then fine-tune it with ATRK. The DAC signal should be attenuated and shifted to near FB, 0.8V

Current control

Average current control has another arcitecture, so we have 10/20mA steps via I2C or external ISET with a resistor. Instead of resistor, we'll use a DAC with a FET, stabilising the current in the ISET net. 

Next step - design of the OpAmp board!