1. Voltage DAC Injection via $R_{margin}$ into Feedback Node:
Applying KCL at the regulator FB node ($V_{fb} = V_{ref}$): $$\frac{V_{out} - V_{ref}}{R_1} = \frac{V_{ref}}{R_2} + \frac{V_{ref} - V_{dac}}{R_{margin}}$$ $$V_{out} = V_{ref} \left(1 + \frac{R_1}{R_2}\right) + (V_{ref} - V_{dac}) \frac{R_1}{R_{margin}}$$

2. Current DAC (IDAC) Injection:
$$V_{out} = V_{ref} \left(1 + \frac{R_1}{R_2}\right) \pm I_{dac} \cdot R_1$$