AN2810

Getting started

Doc ID 14893 Rev 1

13/17

9.2

Open and shorted WLEDs fault testing

1.

Set the input voltage to 12 V

2.

Set the dimming duty-cycle to 20%

3.

Set SW1 and SW2 in the “up” position

4.

Turn-on the PWM generator and the supply in sequence

5.

Disconnect the rows in sequence and compare the behavior of the LED7707 to Table 4

6.

Restore all row connections and press the SW3 pushbutton on the LED7707 board to

reset the device

7.

Short one or more WLEDs and compare the LED7707 behavior to Table 4

8.

Press the SW3 pushbutton on the LED7707 board

9.

Turn-off the power supply and set the SW2 selector to the “up” position (MODE to

ground)

10. Turn-on the power supply and repeat steps 5 through 8

11. Remove all shorted WLEDs and leave ROW1 and ROW2 floating

12. Turn-on the power supply. The floating rows are ignored

13. Turn-off the PWM generator

14. Turn-off the power supply

9.3

Device synchronization

1.

Set the PWM dimming signal to 100%

2.

Remove the jumper from the SW1 selector to leave the FSW pin floating

3.

Connect an external 700 kHz clock generator (0 V-1 V logic levels, 30% duty-cycle)

between the FSW test point and ground. Refer to Figure 9

4.

Turn-on the PWM generator

5.

Turn-on the power supply. The device remains off until the FSW pin is low

6.

Turn-on the clock generator. The device turns on

7.

Monitor the SYNC output and verify the synchronization (the SYNC output is a replica

of the FSW signal)

8.

Turn-off the PWM generator

9.

Turn-off the clock generator

10. Turn-off the power supply