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TPS22965: TPS22965 - Cin and Cl spread across board

Rajaram Mathivanan
Prodigy 70 points
Part Number: TPS22965
Other Parts Discussed in Thread: TPS22975,

Hi, 

I have following questions  on TPS22965

1. With respect to Cin and CL. 

We have total of 930uF capacitor spread across the board on input side and 520uF of capacitors on the output side of the switch. 

There are many thread with respect to total Cin and CL, and how higher CL is mitigated using CT. 

for eg: https://e2e.ti.com/support/power-management/f/196/t/799188?tisearch=e2e-sitesearch&keymatch=TPS22965

My question is, will the TPS22965 has special effect of much higher capacitors closer to output than at the input ?  Or TPS22965 will be considering the total capacitors at input and output side which is spread across the board. 

2. CT and rise time calculation for Vbias and Vin values of 3.3V:

The below thread has measured Tr values (Min, Typical, Max) for different values of Ct, Also specifies formula of  SR= .775 (CT) +107.41

But this thread corresponds to Q1 part, could you please confirm if the same values and formula holds good for normal industrial part also ?

https://e2e.ti.com/support/power-management/f/196/t/680698?tisearch=e2e-sitesearch&keymatch=TPS22965-Q1

Thanks and Regards

Raja

  • 0
    TI__Genius 10855 points

    Hi Raja, 

    Thanks for reaching out on E2E!

    Please find the answers to your questions below:

    1: The TPS22965 won't have a special effect to capacitors closer to the board vs farther away. However, it is recommended to keep the capacitance as close to the device as possible, to prevent any board parasitics from interfering with the signal. 

    Since 520uF is a lot of output capacitance, what slew rate are you expecting to use on the load switch? We need to make sure that the inrush current doesn't cause the thermal junction temperature to exceed the maximum junction rating. Also, I recommend switching to the TPS22975 instead of the TPS22965, which is P2P.

    2: Yes, the rise times apply both the TPS22965 and TPS22965-Q1.

    Thanks,

    Arthur Huang

  • 0 in reply to Alpha H
    Prodigy 70 points

    Hi Arthur Huang, 

    Thanks for your response, We are adding CT of 4700pF. 

    We are targeting for slew rate above 5ms. 

    What is the maximum inrush current this device can tolerate ? 

    In our case, calculated inrush current comes to around 300mA, 

    Thanks and Regards

    Raja

  • 0 in reply to Rajaram Mathivanan
    TI__Mastermind 32650 points

    Hi Raja,

    The maximum inrush current that the device can tolerate is very dependent on temperature and voltage as well as CT capacitor. It is a case by case basis.

    For your use case, with Vin and Vbias at 3.3V and CT of 4700pF resulting in inrush of 300mA, we expect this to be no issue for the part whatsoever.

    I hope this answers all your questions and thank you for choosing TI Power Switches for your designs.