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TPS92518: Synchronous rectification for higher efficiency

Martin Paap
Prodigy 10 points
Part Number: TPS92518
Other Parts Discussed in Thread: TPS92641

Hi,

Is there a similar LED driver with an extra output for driving a low side mosfet to replace the "lossy" schottky diode?

I haven't done any prototyping just yet with TPS92518 dev. boards, but just as a concept adding a half-bridge driver (i.e. IRS2007STRPBF, random functionally equivalent IC) and a mosfet to replace the recirculation diode. This will throw off set current values by somewhat (due to added propagation delays), but could be (?) calibrated out. Also dead time between switching would be needed to avoid shoot-thru. 

This can be useful for battery powered lights, when i.e. a RGBW LED I@2.5A (each) and a diode Vf@0.35V, (not considering duty cycle derating, assume Vin >> Vled) we get ~0.8W. With 4 LED in RGBW this would be a considerable ~3-3.5W.

Shunt dimming must also be part of this design('s considerations).

Regards,

Martin

  • 0
    TI__Mastermind 28655 points

    Hello Martin,

    I would look at the TPS92641 or the TPS92520.  There are always ways to make non-synchronous parts synchronous but it can get involved.  Also have to check with the TPS92518 going synchronous and shunt FET dimming since the recirculating voltage is near zero instead of a diode drop.  If shunted for a long time the current may rise due to minimum on-time of the TPS92518.  This depends a lot on the operating conditions and design.

    Best Regards,