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TPS23753 Oring Power OFF

Frederic Jutras
Prodigy 100 points
Other Parts Discussed in Thread: TPS23753, TPS23753A, TPS23754

Hi, 

I was reading the application report SLVA306A about the advanced adapter Oring solution using the TPS23753 and I can't seem to find an option where the gate drive continue switching while the adapter is plug/unplug. It seem there is always a time period, the PSE turn ON and the ADP shut OFF, where the gate drive stop.

It seem possible reducing that time OFF by using DVDD, a diode between the VDD and VDD1 as option 2 describe but not keeping the gate running. 

Is there a possibility to load with 10mA the input so the MPS is maintain, use an external supply and when that external supply is removed, the gate drive doesn't stop.

Thanks

Frederic Jutras

  • 0
    TI__Expert 7990 points

    ORing issues and some considerations are also discussed at a high level in the TPS23753A datasheet and the TPS23754A datasheet.  There are a few fundamental limitations that you might run into in trying to create a seamless switch, and in general they are concerned with the bounds on the problem.  One of the concerns is the physics of the required switcher current given the (potential) difference in adapter and PSE voltages (e.g. a full power load from a 24V adapter requires 2x the current required from the PSE) and the internal sequencing/protection of the internal hotswap that can come into play during the attempt to charge a bulk capacitor from 24V to 48V while also supplying load power.  If the right set of constraints and assumptions are used (e.g. 1W load), there may be solutions with cleaner switchover.  

    Your best chance to getting a seamless switchover is provided in the TPS23754 datasheet under "Advanced ORing Techniques" (Figure 34) where a solution with a 48V adapter and PoE voltage are seamlessly (to the load) switched.  The TPS23754 had a subtle hotswap control change to enable this functionality, so it most likely will not work with the TPS23753A.  The TPS23754 can be configured/used in any circuit the TPS23753A can be used in.

  • 0 in reply to Martin Patoka
    Prodigy 100 points

    Thanks for your help Martin, 

    I was just suggested that we have a seamless output. I will look what I can do to limited the effect and roll with it.

    Thanks again

    Frederic