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LM3532 / short ILEDx pin to GND

K.Yaita
Guru 29720 points
Other Parts Discussed in Thread: LM3532

Hi Team,

My customer concerns about failure mode of LM3532.
Could you tell me what happens if ILEDx pin short to GND?

The LED structure of his application is triple string 4LEDs(Vf=3.0V x 4) and input voltage is 1cell Li-ion battery(3.6V).
I think LED current increases but output power is clamped within 3.6W(3.6V x 1A) because of NFET current limit.
Is my understand correct?

Best Regards,
Yaita

  • 0
    TI__Intellectual 1040 points

    Yes, that is correct.  When the LED pin gets shorted to GND the boost feedback gets set to 0 which causes the boost to go to max duty cycle, and hit current limit.  There is some delay between the boost cycling in and out of current limit.  This causes the inductor current to drop down when it hits the peak current limit threshold and then gradually build back up over a few switching cycles.  The result is that the average input current is a bit less than what would be predicted with contimuous conduction and the peak current limit value.

    Thanks

    Travis