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TPS22930A: About usage and RCP(Reverse current protection)

Atsushi Takahashi
Expert 1415 points
Part Number: TPS22930A
Other Parts Discussed in Thread: TPS2116

Hi Team,

The customer is planning to use the three TPS22930 to design a circuit that selects any one of the three power supplies(See attached).

Since the TPS22930 has internal RCP(Reverse current protection), I think this circuit is no problem under certain conditions.
I would like to have the following questions.

1) When RCP is on, how much reverse voltage (reverse current) to Vout-pin can withstand?
2) Are there any precautions for this usage circuit?

Best Regards,

TPS22930_Circuit.pdf

  • 0
    TI__Genius 16085 points

    Hello, 

    I would not recommend this implementation as the TPS22930 device has reverse current blocking only when disabled. This would require significant control logic to ensure neither of the other two load switches are enabled when one of the load switches is enabled. 

    Instead, depending on your loading conditions, we do have a more integrated solution in the TPS2116. I would recommend using two of these power mux devices in series to select between 3 different voltage rails. This additionally allows you to achieve priority switching by connect MODE to VIN1 and set the proper threshold through a resistor divider from VIN1 to PR1. 

    TPS2116 Product page: https://www.ti.com/product/TPS2116

    Best Regards, 

    Elizabeth 

  • 0 in reply to Elizabeth Higgins
    Expert 1415 points

    Hello,

    Thank you for your reply.

    I will certainly consider your proposal but I would also like to consider whether the TPS22930 can be used.

    Is it no problem to use this product if I can design high-precision logic?

    For example, disallow the other two load switches from being enabled when one of the load switches is enabled.

  • 0 in reply to Atsushi Takahashi
    TI__Genius 16085 points

    Hi Atsushi-san, 

    If you could be certain only one load switch is enabled (VON>1.1V) at a time and the other two load switches are certainly disabled (VON<0.6V), I do not see why the three switches could not be used to mux between 3 supplies. 

    The disadvantages to a load switch power muxing configuration however are

    • you will always see reverse current when switching
    • there will be a large output voltage drop when no switches are enabled
    • there will be a larger switchover time than with an integrated solution. 

    An integrated solution such as the TPS2116 would provide: 

    • fast switchover: t_SW=8us
    • low IQ =1.32uA
    • low ISD=50nA
    • low Ron=40mΩ
    • Thermal shutdown 
    • Prevents excessive power supply dip
    • Integrated reverse current blocking

    To summarize the difference in reverse protection between load switch muxing and power mux muxing: 

    In load switches, reverse current has to flow in some amount for it to trigger; this is the same for powerMUX reverse current protection.
    The difference is:
    in load switch muxing, you use the reverse current protection to turn off the device during switching
    in pmux muxing, there is a separate switching circuit that handles these cases and protects against the backflow of current by waiting for the output to drop below the input before turning on the channel. so you are not depending on the reverse current protection to turn on and turn off the device. The rev current protection in pmuxes is solely for the event when the channel is ON and is meant to conduct but the output goes high for some fault reason
    In conclusion,
    if you MUX with load switches, you will always see a reverse current flow everytime you switch between the inputs; in a power mux, you will not. 

    Best Regards, 

    Elizabeth