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WEBENCH® Tools/LM3410: LM3410 damage easily

user3305641
Prodigy 100 points
Part Number: LM3410
Other Parts Discussed in Thread: TPS92692, TPS92691

Tool/software: WEBENCH® Design Tools

I am Eric. I am using LM3410 to debug an LED driver circuit. The circuit diagram is as follows:
LDM1 is composed of 7 LEDs in series. The forward voltage of each LED is 3V, and the forward voltage of LDM1 is 21V.I have two questions to consult:
1. LM3410 is easily damaged
The waveform of SW node is as follows (using 3 serial LEDs):
When I use 7 serial LEDs, LM3410 often breaks down, possibly the internal MOS has be damaged. Does the SW node voltage exceed the voltage withstand (24V) of LM3410 ,which cause damage to LM3410? What can be done to avoid it?
2.DIM (pin 2) pin problem
When the high level of H_DIM is 3.3V, LM3410 does not work. Must use pull-up resistance to pull up to 5V, what is the reason? According to the data sheet, LM3410 can be driven above 1.8V.

  • 0
    TI__Mastermind 28655 points

    Hello,

    1)  If you are exceeding the abs max of the SW pin the device can get damaged.  21V + 5V + VD2 is over abs max.  The waveform using 3 LEDs is more than a 10V voltage delta meaning the Vf of the LED is probably higher than 3V in your design.  To avoid this possible damage, SW should remain below abs max at all times and should have some design margin to prevent damage.  If 7 LEDs are needed you could use the TPS92691 or TPS92692.

    2)  DIM should work pulled up to 3.3V, check the pin voltage to make sure it is at 3.3V.  Also, Voltage should not be applied to DIM unless your 5V is present.  From the pin description in the datasheet:  "Do not allow this pin to float or be greater than VIN + 0.3 V."

    Best Regards,