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LM3464 Dynamic headroom control

MUHAMMED SHAMVEEL
Prodigy 20 points
Other Parts Discussed in Thread: LM3464

In LM3464 datasheet page no.10 under subsection Operation Principles of DHC, it is written that

when all the output channels are in regulation and the forward voltage of any LED
string decreases due to temperature raise, the drain voltage of the corresponding channel (DRx) increases to
exceed the default 0.9V typical headroom voltage in order to maintain constant output current. As the drain
voltage increases, the voltage of CDHC increases and the current sink into the OutP pin decreases. This will
finally result in decrease of rail voltage (VRAIL) until the corresponding DRx voltage returns to minimum level

If voltage of CDHC increases, actually the current sink into the OutP pin is to be increased? pls give explanation for this

  • 0
    TI__Mastermind 25500 points

    I am not sure who wrote this datasheet, but the wording isn't completely obvious. But I believe it to mean, if you think of it as a linear regulator (which it is) as CDHC increases the linear regulator is turning more "off" so that more of the voltage is absorbed by the linear element to keep current regulation in the LEDs. So the "current sink" (linear regulator) is reducing its drive.

  • 0 in reply to Clinton Jensen
    Prodigy 20 points

    Since voltage at the Outp pin is VCC-VCHDC, as VCHDC increases Outp pin voltage should decrease, so the current sink has to be increased. but it is given that current sink will be decreased