If the voltage applied to the mirror is set to 0 V, the capacitance on the mirror slowly discharges and the electrochromic element returns to a transparent, non-colored state. To accelerate the discharge of the capacitive load and reduce the amount of time to reach the transparent state, use a low-side transistor.

This simple open-drain transistor can be turned on by pulling the base high, which provides a direct path to ground for the capacitance on the mirror. Take care to ensure this transistor is only enabled when the output of the DAC has already been set to 0 V to prevent unnecessary current flow through the voltage buffer output and this transistor.

The base of this transistor is tied to a GPIO on the MCU which controls this design. Use a local pullup resistor of 4.7 kΩ with the open-drain output of the MCU GPIO.