Diodes AP8801 - Manual (Page 11)

AP8801
500mA LED STEP-DOWN CONVERTER
AP8801
Document number: DS31765 Rev. 7 - 2
11 of 14
www.diodes.com
June 2012
© Diodes Incorporated
Application Information (cont.)
Package Selection
The device comes with a wide selection of packages. The suggested package is able to provide a case temperature below 70˚C (with an
ambient temperature of +25°C) for the combination of input voltage and load requested.
8 12 16 20 24 28 32 36 40 44 48
8 LEDs
I = 500mA
LED
L = 100µH
SO-8
MSOP-8
SO-8
12 LEDs
10 LEDs
2 LEDs
6 LEDs
4 LEDs
Figure. 21 Package Section
Fault Condition Operation
The AP8801 has by default open LED protection. If the LEDs should become open circuit the AP8801 will stop oscillating; the SET pin will
rise to V
IN
and the SW pin will then fall to GND. No excessive voltages will be seen by the AP8801.
If the LEDs should become shorted together the AP8802H 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
AP8801.
Figure. 22 Switching Characteristics
(normal open to short LED chain)