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TPS2663: inrush current solution using Cdvdt or Cout calculation options?

Hen Lange
Prodigy 220 points
Part Number: TPS2663
Other Parts Discussed in Thread: TPS55340, DRV10987

hi,

we connected the TPS2663 as shown in the schematics below:

we enter 12V IN to the main power. we started the operation and measured 4A in rush current.

we removed C42 of 22uF and the inrush has decreased to under 1 A.

as I understand from the datasheet, we can connect the C42 back and change the Cdvdt to control the inrush.

I would appreciate your assistance with the calculations of the correct value for the capacitors.

thank you

Hen Lange  

  • 0
    TI__Expert 5575 points

    Hello Hen Lange

    You can refer to section 9.3.1 to  understand relation between inrush current, CdVdT capacitor and output capacitor.

    Alternately you can use TPS2663 design calculator available to get component values as per your design requirements.

    http://www.ti.com/product/TPS2663/technicaldocuments

    However inrush current of 4A with just 22uF output capacitor looks too high. Do you have C34 populated on board?

    Thanks & Regards

    Abhijeet

  • 0 in reply to Abhijeet Godbole
    Prodigy 220 points

    Hi

    C34 is connected with 0.1uF

    this component is connected to the power management of the circuit. as shown below. the overall capacity is around 44uF

  • 0 in reply to Hen Lange
    TI__Expert 5575 points

    Hi Hen Lange

    With 100nF on CdVdT pin and with 44uF of output capacitor, expected inrush current is around 20mA. Please refer to datasheet section 9.3.1 for the equation of the inrush current.

    Can you share VIN, VOUT, Input current (12V bus) and FLT waveforms. Is there any load on U15 or U4 output during startup?

    Thanks & Regards

    Abhijeet

  • 0 in reply to Abhijeet Godbole
    Prodigy 220 points

    Hi Abhijeet

    the output capacitors are C1, C42, C44 which adds up to 66uF.

    Vin is 12V  nominal Vmax 16V, Vmin 4.5V.

    Vout from TPS55340 is up to 24V.

    Input current is maximum 1A.

    U4 is connected to a microcontroller, the load is minimal.

    U15 is connected to DRV10987 which is connected to a circular engine that has about 3ohm load and 1mH impedance.

    the maximum current during startup and normal operation must be under 1A.

    thank you

    Hen

     

  • 0 in reply to Hen Lange
    TI__Expert 5575 points

    Hello Hen

    Even with 66uF output capacitor, we expect inrush current lesser than 100mA or soe as per the equation. 

    Is DRV10987 load is ON at the time of startup or it is applied once all the rails are stable (Main_Power and V_Motor_30V is ramped up and stable).

    If you are still seeing an issue with 100nF cdVdT cpacitor then I need to look at the input current waveform on Main_PWR_B in order to comment more.

    Alternate option is increasing CdVdT capacitor to 330nF and see if you see reduced inrush current. That will give us some pointers on exact issue

    Thanks & Regards

    Abhijeet