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LM3404HV, paralleling TTL DIMn inputs

Steven Pigliavento
Prodigy 70 points
Other Parts Discussed in Thread: LM3404HV

Working an application with sixty-four (64) LM3404HV's, driving red Cree XLamps.

I'm currently paralleling the DIMn inputs, (2) devices per PCB (2 strings, 10 LEDs/string), 32 PCBs interconnected via a backplane arrangement.

I didn't see any particular guidance in the datasheet for paralleling or scaling an LM3404HV design, and want to make sure that given adequate PWM signal drive capability, I can get away with paralleling these TTL dimming inputs.  I also have transient suppression devices in front of each LM3404HV DIM input.

One of the points that I could use some clarification on would be running this single-ended DIM control -- of all (64) driver ICs -- vs. perhaps using an RS422 differential receiver on each PCB, then driving a differential dimming control signal into the backplane (for higher noise immunity).

Thanks for any guidance.

-s, ny

  • 0
    TI__Mastermind 25500 points
    There is no problem with paralleling the DIM inputs. The only thing you need to keep in mind is that the current draw could be very high at the input if they are all turned on at the same time. But that is no problem if the supply is capable of it and/or there is enough input capacitance.