Getting started

AN2809

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9.2

Open and shorted WLED fault testing

1.

Set the input voltage to 12 V.

2.

Set the dimming duty-cycle to 20%.

3.

Disconnect the rows in sequence and compare the behavior of the LED7706 to

Table 4.

4.

Restore all row connections and force the EN input to ground.

5.

Release the EN input.

6.

Short one or more WLEDs and compare the behavior of the LED7706 to

Table 4.

7.

Press the SW3 push button of the LED7706 board to reset the device.

8.

Turn off the power supply and set the SW2 selector to the upper position (MODE to

ground).

9.

Turn on the power supply and repeat steps 3 to 7.

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

11. Turn on the power supply: the floating rows are ignored.

12. Turn off the PWM generator.

13. 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 600 kHz clock generator (0 to 1 V logic levels, 40% 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.