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AS3490

Datasheet - D e ta i l e d D e s c r i p t i o n

Startup

In order to avoid inrush-current during startup the supplies are smoothly ramped up according to Figure 17 even under

low PWM duty cycle conditions. This allows the easy integration into mobile battery powered systems:

Figure 17. Startup Procedure

Open and short LED detection

After the startup is finished, the AS3490 continuously monitors open and shorted LEDs. If an open or shorted LED

string is detected, this LED string is disabled and the driver continuous its normal operation. The driver is disabled to

keep the efficiency of AS3490 for different LED configurations high. The error is cleared once the AS3490 enters shut-

down

Shorted LED

Open LED

LED outputs (LED1...LED5) which are not used by the application shall be connected permanently to VOUT or GND.

The AS3490 detect this condition upon startup and automatically disables the current sources for these LEDs - see

Figure 18 and Figure 19, immediately after the rising edged of ON.

For LEDs, which are open during operation of the device, following procedure of the AS3490 is used for detection:

Figure 18 shows the waveform for the detection of a single open LED, Figure 19 for all LEDs open.

4. The error is automatically cleared as the open/short LED error might be temporarily (e.g. bouncing of the

connections to the LED)

detected.





 

  

 

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