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TPS2115: About RILIM and Capacitor Selection

Kaji@PAN
Mastermind 7015 points
Part Number: TPS2115

Hi,

I am an FAE of a distributor dealing with TI products.
We have received the following questions from customers.
1) Please teach some minimum value of RILIM of TPS2115. The data sheet states that 0 Ω is not recommended.
If a capacitor is connected to the output side while the IN2 side is selected, the capacitor charge current will cause the OUT voltage to drop.
2) Please teach if there is the maximum value of the capacitor capacity that can be connected to the OUT pin.
Best regards,
  • 0
    TI__Genius 10855 points

    Hi Kaji, 

    Thanks for reaching out on E2E!

    Please find the answers to your questions below:

    1) Please teach some minimum value of RILIM of TPS2115. The data sheet states that 0 Ω is not recommended.
    [AH]: We don't spec a minimum current limit value since this is dependent on the operating conditions. RLIM of 400Ω and 700Ω are the two values that were tested and spec'd in the datasheet, but the device should work at higher RLIM resistor values. Is there a specific range you are trying to reach?
    If a capacitor is connected to the output side while the IN2 side is selected, the capacitor charge current will cause the OUT voltage to drop.
    2) Please teach if there is the maximum value of the capacitor capacity that can be connected to the OUT pin.
    [AH]: There isn't a maximum value for the load capacitance. Actually, the capacitor and VOUT relation is different. With higher output capacitance, VOUT will dip less but there will be more inrush current. With a lower output capacitance, VOUT will dip more since there isn't anything to hold the output voltage high. But, there will be less inrush current. You can read more in our app note, Basics of Power MUX. 
    In general, you can calculate the output voltage dip using the equation: Vout, min = tsw * (Iout / Cout)
    Where:
    tsw = switchover time
    Iout = load current
    Cout= output capacitance

    Thanks,

    Arthur Huang

    To find the latest information on Power Switches, visit www.ti.com/powerswitch

  • 0 in reply to Alpha H
    Mastermind 7015 points
    Thank you for your reply.
    I'm thinking about using R (ILIM) = 180Ω or so.
    This is to prevent the current limit from operating with capacitor charge current.
    The steady state current is about 1A.
    Can I use a 180 ohm resistor?
    Best regads,
  • 0 in reply to Kaji@PAN
    TI__Genius 10855 points
    Hi Kaji,

    Yes, this should be fine. You can use the equation in the datasheet to calculate the resistor value if you're looking for a different value.

    Thanks,
    Arthur