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TPS2115: TPS2115 autoswitching hysterisis

Darius Leckas
Prodigy 50 points
Part Number: TPS2115
Other Parts Discussed in Thread: TPS2121, TPS2120, TPS2113

Hello, here is my setup:

-I use TPS2115 in autoswitching mode

-Two Li-Po batteries are connected at inputs In1 and In2. 

-Load current is 0.8A (constant power).

Problem is that hysterisis between input1 and In2 is small, and output begins to oscilate when batteries both about same level.  I assume this happens becouse of internal rezistance of the . batteries. Voltage drop occurs on battery and  TPS2115  switches to another input. Then situation reapeats..

In my case both inputs must be same priority, but input with higher voltage must be used. Any advice to manually increase hysterisis  or use another device to solve this? 

  • 0
    TI__Genius 10855 points

    Hi Darius, 

    Thanks for reaching out on E2E! Great question and good timing, we actually just started sampling our newest generation of power mux devices, the TPS2120 (WCSP) and TPS2121 (QFN). These new devices use newer technology, smaller package, offer similar or additional functionality (ex., higher voltages & currents, current limit, short circuit protection, etc.), and offers adjustable hysteresis. 

    I have a thread that discusses how the adjustable hysteresis works on the TPS2121, it also goes into additional detail on configuring our new devices: e2e.ti.com/.../734615

    Basically, the ST pin is pulled low when IN2 is the output. If a resistor network is connected to this pin, the voltage will be pulled lower and provide a voltage comparison with hysteresis.

    For reference, could you comment on the application of this design? 

    Thanks,

    Arthur Huang

  • 0 in reply to Alpha H
    Prodigy 50 points

    Thank you for response. Application for this device would be general dual power injector. Where user equipment would be powered from 5V wall adaptor, but in case of power loss, power would be suplied from external removable LIPO battery. In this scenario there is no problem, becouse voltage diferencies between 5V adaptor and batery is high enougth. No oscilations.

    But user also could use this device with two batteries, where oscilation occurs.

    I assume it would be possible to switch to TPS2113, where on of the control inputs is voltage referenced, and combining it with STAT it is possible obtaion hysterisis.

    Sadly TPS2121 is not yet available on digikey :(

  • 0 in reply to Darius Leckas
    TI__Genius 10855 points

    Hi Darius, 

    Thanks for the background information!

    The TPS2121 will be available late Q4 2018, but you can order samples on ti.com right now.

    Thank you,

    Arthur