Open And Shorted Wleds Fault Testing; Device Synchronization - STMicroelectronics LED7707 Application Note

AN2810
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
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
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
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
Doc ID 14893 Rev 1
Getting started
Table 4
Figure 9
Table 4
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