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TPS25942A: TPS25942A Power Mux

Part Number: TPS25942A

Hi,

I am going to mux power supplied to a PCIE card.

1. Main power supply : ATX power connector ,5.0A current limit

2. AUX power supply: PCIE connector,2.0A current limit(to comply with PCIE standard)

My Problem is,

1. Both the power supplies will be same 12V.Is it possible to use this in the given configuration?

2. Will the auto try feature of one efuse interupt the output supply by the other efuse?

3. When external power is not available output power should come from PCIE connector.My issue in that case main power efuse is not powered up. In a priority power configuration aux power is activated by PGOOD signal. Won't that be an issue?

  • Hi Hasith,

    It is understood that you want to limit current to 2A from PCIE connector to comply with PCIE standard. What is the board power (current at 12v)? Is it less than 2A? In that case why you want to set 5A current limit for main power supply?


    1. Both the power supplies will be same 12V. Is it possible to use this in the given configuration?
    1A) Yes, you can configure as per Figure 79 or Figure 84 in the datasheet and use in your system

    2. Will the auto try feature of one efuse interrupt the output supply by the other eFuse?
    2A) No. It would not affect the operation.

    3. When external power is not available output power should come from PCIE connector.My issue in that case main power efuse is not powered up. In a priority power configuration aux power is activated by PGOOD signal. Won't that be an issue?
    3A) Can you please elaborate what issue you foresee? During change over from external power to aux power the output capacitor acts as buffer to the load (i.e., output capacitor provides the load current)

    Regards,
    Rakesh
  • Hi,
    Thank you for the reply.
    This custom PCB design is used in few applications with different applications. There are some application which may have power consumption more than 2A. Where the board consumtion is less than 2A ,user have the freedom of disconnecting the power connector.
    1. In the datasheet it says that there is a difference of 0.3V . I don't think there will be any difference in the power rails in my application.
    thank you
  • Hi,
    Thanks. Understood your intention behind that.

    0.3V difference is not necessarily required to use as per Figure 84 configuration. You can connect equal voltage rails.

    Best Regards,
    Rakesh
  • Hi,

    According to the figure 84, aux power supply is always ON in non-ideal diode mode even when the Main power is available .It says that it will operate with 50% of ILIM. I guess this means that both supplies will work in a load sharing manner where none of the power supplies are failed. This happens when the PGOOD pin of Main power supply is connected to DMODE of aux power.Can't we use the OVP pin instead? 

    Other thing I have noticed is that pins like PGTH,OVP are not used in the aux power circuit. Can we program it with the same values as main power supply IC?

    thank you

  • Hi Hasith,

    Below is the equivalent circuit for Figure 84, when both power supplies are available. The diode path does not conduct load current unless there is a variation in main supply voltage which makes diode to forward bias. If you foresee such scenario in your system, please use OVP pin as per Figure 79 configuration.

    You can use other pins PGTH, PGOOD in aux power circuit to supervise aux supply voltage or output voltage or any other voltage in your system. Similarly OVP pin can be configured for over voltage protection of Aux supply voltage.

    Regards,

    Rakesh