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TPS22915: Input and Output Capacitors selection

shiwei luan63
Prodigy 140 points
Part Number: TPS22915

From the TPS22915 datahseet (www.ti.com/.../tps22915.pdf), description 9.3.3 on page  16, "A CL greater thant CIN can cause VOUT to exceed VIN when the system supply is removed". Why this would happen?  Why "A CIN to CL ratio of 10 to 1 is recommended for minizing VIN dip caused by inrush currents during startup"?


Thank you.

  • 0
    TI__Genius 15770 points

    Hi Shiwei,

    If the load capacitance is greater than the input capacitance, then reverse current may be possible if VIN is removed. This is because the voltage on the smaller capacitor (CIN) will decay faster than the voltage on the output capacitor (CL). When this happens, the voltage on VOUT will be larger than the voltage on VIN, and current can flow from VOUT to VIN.

    As for the 10:1 ratio, this is mainly due to the power supply on VIN and its ability to handle the current transient during device startup. If a small amount of inrush current is expected or the power supply is very strong, then a 10:1 ratio is not needed.

    Let me know if you have any questions.

    Thanks,

    Alek Kaknevicius