Diodes AP8802 Manuel d'utilisateur télécharger pdf (Page 14)

AP8802

1A LED STEP-DOWN CONVERTER

AP8802

Document number: DS31766 Rev. 9 - 2

14 of 19

www.diodes.com

May 2012

Applications Information (cont.)

Fault Condition Operation

The AP8802 has by default open LED protection. If the LEDs should become open circuit the AP8802 will stop oscillating; the SET pin will

rise to V

and the SW pin will then fall to GND. No excessive voltages will be seen by the AP8802.

If the LEDs should become shorted together the AP8802 will continue to switch however the duty cycle at which it will operate will change

dramatically and the switching frequency will most likely decrease. The on-time of the internal power MOSFET switch will be significantly

reduced because almost all of the input voltage is now developed across the inductor. The off-time will be significantly increased because the

reverse voltage across the inductor is now just the Schottky diode voltage (See Figure 20) causing a much slower decay in inductor current.

During this condition the inductor current will remain within its controlled levels and so no excessive heat will be generated within the

AP8802.

Figure. 24 Switching Characteristics (normal open to short LED chain)

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Diodes AP8802 Manuel d'utilisateur Page 14