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LM3433SQ-36AEV evaluation board, some transistors seem to be strange

Hansuk Kim
Prodigy 30 points

I am interested in LM3433 LED driver because of its common anode capability.

I want to drive maximum 28A on LED, so I thoroughly reviewed LM3433SQ-36AEV evaluation board. (up to 40A current drive)

But I found weird thing on the board layout. Q10~Q12 transistors (MMBT3904-7) seems to be flipped on bottom layer layout (fig. 8) MMBT3904-7 pin 1 is base and pin 2 is emitter, but I think that Q10 ~ Q12 on the layout are pin 1 emitter and pin 2 base.

So I think that this board works unexpected way about ENA node. If ENA pin is drove externally, it will work okay. But without external ENA signal, Q10~Q12 should make ENA signal when enough negative voltage is applied on -12V, but it will not work as expected, I think.

I don't have that evaluation board in my hand, so I just guess. Is there anyone who can check my finding is right or wrong??

  • 0
    TI__Mastermind 25500 points
    It looks like you have found an error in the layout. I guess it wasn't caught because it's just a non-functional addition as it is connected. You could easily remove that circuit (or leave it) and test the functionality otherwise. It is only there to help with brownout conditions. You don't want to have the input voltage dip to a level where the error amp will not function correctly when you have that much current flowing. So that is set up to pull the enable low if the input voltage dips to an unacceptable level. The schematic is correct but I guess there was some error translating that to the layout.