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TPS543820E: Bulk capacitor requirement for multiple ICs

Abhishek Parikh
Prodigy 205 points
Part Number: TPS543820E

Tool/software:

Dear TI E2E team,

For one of the FPGA based Project we're developing power supply using multiple TPS543820E ICs with power supply sequencing.

Can anyone help to understand total requirement of bulk capacitor at input as Datasheet mentions " A 100-µF bulk capacitance is also used to bypass long leads when connected a lab bench top power supply."

Does this requirement remains for each regulator or effective requirement will comedown if 8 ICs used in parallel.

Regards,

Abhishek

  • +1
    TI__Mastermind 22595 points

    The input capacitors must support the input rms current and be sized for the preferred input voltage ripple (typically ~1%).   

    Equation 16 and 17 in datasheet give guidance on the rms current and capacitance values. 

    If all 8 devices are free running, the rms currents is the summation of all the devices for the worse case estimation.       

    The TPS543820E has a sync pin and hw developers sometimes use a system clock  and run the devices out of phase with the same frequency. 

    The advantage of using the sync pin is the reduction of Cin needed for a given input ripple requirement by "increasing" the effective switching frequency. 

    The 100uF bulk capacitance is needed because of the long trace leads from the lab

    bench to the evm board input increase the parasitic resistance and inductance in line to input supply.     

    Typically, the evm board is used to test various specs and functionally such as the overcurrent.       

    If overcurrent is tested without the 100uF,  the input rail can oscillate and potentially swing greater than the input voltage abs max. 

    The proximity of the upstream supply and its output capacitors to the TPS543820E devices will factor in the amount of bulk cap needed. 

    For applications where the upstream supply is on the same board  will be lower than if using a wall adapter.   

    Also, if ferrite beads are used on the inputs of the dc dc to minimize switching noise on the adjacent supplies can impact the Bulk Cin amount