AN1330

Additional features and protection

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Additional features and protection

3.1

Feedback disconnection

If the feedback is disconnected, the duty cycle increases towards the maximum allowed

value, bringing the output voltage close to the input supply. This condition could destroy the

load.

To avoid this hazardous condition, the device is turned OFF if the feedback pin is left

floating.

3.2

Output overvoltage protection

Overvoltage protection, or OVP, is achieved by using an internal comparator connected to

the feedback, which turns OFF the power stage when the OVP threshold is reached. This

threshold is typically 30% higher than the feedback voltage.

When a voltage divider is required to adjust the output voltage (Figure 14), the OVP

intervention will be set at:

Equation 1

3.3

Zero load

Due to the fact that the internal power is a PDMOS, no bootstrap capacitor is required and

so the device works properly even with no load at the output. In this condition it works in

burst mode, with random burst repetition rate.

V

OVP

1.3

R

1

R

2

+

R

2

----------------------

•

V

FB

•

=