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TPS2113A: vs TPS2115A auto switching.

Adam Dupuis17
Prodigy 150 points
Part Number: TPS2113A
Other Parts Discussed in Thread: TPS2115A, TPS2115

Hi TI,

I have a few questions about the TPS2113A and the TPS2115A.

My product requires me to switch between a local supply and a backup supply to keep an IC powered. Both rails are 3.3V. I also need it to switch back to the local rail when it recovers.

1. TPS2115A

has an auto switch feature that will switch between the greater of the two inputs. From the datasheet it looks like it has a hysteresis of 0.1 to 0.2V on the comparator.

A) Does this mean that the TPS2115A cannot guarantee a switch back to the local rail after it recovers, since both will be at 3.3V?

B) is the hysteresis the value I should be looking at for the initial switch or is that the amount it needs to recover by in order to switch back?

2. TPS2113A

This device has a VSNS pin that can make any rail the priority. However the truth table indicates that in the case where the VSNS is  less than 0.8V then it depends on the Vin2 > Vin1 relationship.

A) In this case when I lose the rail on VSNS will the worst case switch over occur at 3.3V -200mV(hysteresis) ? This is a bit better as at least it will be able to switch back once Vsns is > 0.8V trip point but I still have an issue where it needs to drop 200mV.

What I would like to see happen is that it switches over automatically to INx when pwr drops below 3.2V on InY and go back to InY when it recovers....

thanks,

Adam

  • 0
    TI__Genius 10855 points

    Hi Adam,

    Thanks for your questions! My answers to each of the questions is listed below:

    1: TPS2115

    A) Does this mean that the TPS2115A cannot guarantee a switch back to the local rail after it recovers, since both will be at 3.3V?

    That is correct. We recommend using the TPS2115A for manual switchover configurations instead of automatic switchover; it won't be able to switch back to your primary rail without an additional signal or circuitry. The TPS2113A is the best solution for automatic switchover. 

    B) is the hysteresis the value I should be looking at for the initial switch or is that the amount it needs to recover by in order to switch back?

    For this device, the hysteresis is for the comparator between IN1 and IN2, or used for UVLO. I suggest the TPS2113A for switching back to the main rail. 

    2: TPS2113A

    A)  In this case when I lose the rail on VSNS will the worst case switch over occur at 3.3V -200mV(hysteresis) ? This is a bit better as at least it will be able to switch back once Vsns is > 0.8V trip point but I still have an issue where it needs to drop 200mV.

    Please refer to Figure 14 on page 16. This connection connects VSNS to IN1 via a resistor divider, and gives priority to IN1 if both supplies are present at 3.3V. If IN1 dips below 3.3V - hysteresis, VSNS will also dip and the device will switchover to IN2. If IN1 rises back up, so will VSNS and the device will switchover back to IN1. This allows the automatic switchover configuration. 

     

    Let me know if you have any more questions! I hope I helped clarify the devices.

     

    Thanks,

    Arthur Huang

  • 0 in reply to Alpha H
    Prodigy 150 points

    Hi Arthur,

    Yes that does confirm my questions. Ok so really the worst case value on my 3.3V rail is 3.3V - 0.2V (Max hysteresis) -Vdroop. So below 3.1V...

    thanks,

    Adam