AL8807AW5-7 データシートの表示（PDF） - Diodes Incorporated.

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AL8807AW5-7

HIGH EFFICIENCY LOW EMI WIDE ANALOG DIMMING RANGE 36V 1A/1.3A BUCK LED DRIVER

Diodes Incorporated. 

AL8807A

Application Information (cont.)

Fault Condition Operation

Open circuit LEDs

The AL8807A has by default open LED protection. If the LEDs should become open circuit the AL8807A will stop oscillating; the SET pin will rise

to VIN and the SW pin will then fall to GND. No excessive voltages will be seen by the AL8807A.

LED Chain Shorted Together

If the LED chain should become shorted together (the anode of the top LED becomes shorted to the cathode of the bottom LED) the AL8807A will

continue to switch and the current through the AL8807A’s internal switch will still be at the expected current - so no excessive heat will be

generated within the AL8807A. However, the duty cycle at which it operates will change dramatically and the switching frequency will most likely

decrease. See Figure 43 for an example of this behavior at 24V input voltage driving 3 LEDs.

The on-time of the internal power MOSFET switch is significantly reduced because almost all of the input voltage is now developed across the

inductor. The off-time is significantly increased because the reverse voltage across the inductor is now just the Schottky diode voltage (See Figure

43) causing a much slower decay in inductor current.

Figure 43 Switching Characteristics (normal operation to LED chain shorted out)

High Temperature Operation and Protection

The AL8807A is a high efficiency switching LED driver capable of operating junction temperatures up to +125°C. This allows it operate with

ambient temperature in excess of 100°C given the correct thermal impedance to free air. If a fault should occur that leads to increased ambient

temperatures and hence junction temperature then the Over-Temperature Protection (OTP) of the AL8807A will cut in turning the output of the

AL8807A off. This will allow the junction temperature of the AL8807A to cool down and potentially giving an opportunity for the fault to clear itself.

The OTP shutdown junction temperature of the AL8807A is approximately +150°C with a hysteresis of +25°C. This means that the AL8807A will

never switch-off with a junction temperature below +125°C allowing the designer to design the system thermally to fully utilize the wide operating

junction temperature of the AL8807A.

AL8807A

Document number: DS35990 Rev. 2 - 2

16 of 20

www.diodes.com

March 2013

© Diodes Incorporated

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