Overshoot at start-up
During the start-up, i.e. while the input voltage is powered on, the linear voltage regulator is driving the maximum output current to charge the output capacitor and raise the output voltage to the nominal value. When the nominal output voltage is reached, the control loop of the linear voltage regulator needs a few microseconds to react. During these few microseconds, the regulator is still charging the output cap, leading to a further increase of the output voltage. After those few microseconds, the regulator starts regulating the output voltage to the nominal voltage.
The overshoot level during the start-up is dependent on the load current and the output capacitor.
The effect of the output capacitor on the voltage overshoot is shown in the following graphs:
TLF42754 output voltage deviation at load transient with a 22µF output capacitor
TLF42754 output voltage deviation at load transient with a 100µF output capacitor
To smooth out voltage overshoot on start-up, two measures are recommended:
- Increase the capacitor value at the input to slow down the slope of the input voltage.
- Increase the output capacitor value to slow down the slope of the output voltage.