TMC2208 Standalone Mode: Just don't do it.
TMC2208 UART Mode: VREF is set to a max value here, but Klipper decides what to actually use based on the current you specify in printer.cfg Note: in Klipper you do not need to add the second pin with the resistor. (tx_pin) You may use one pin on the board, the UART_Pin
Here is an Instructables page for those who want everything in print.