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TPS65051 VCC RC filter

Mitsuharu Iwasaki55
Intellectual 750 points

Hello

TPS65051 data sheet shows a block diagram has RC at VCC. Maximam R is 10 ohm.

It would be for low pass filer for VCC. Fc is 159KHz. My questions are

1. Is 0 ohm possible?

2. Why is Fc 159KHz?

3. How is R value decided? Is there calculation example?

Regards.,

Mitsuharu iwasaki

  • 0
    TI__Genius 16870 points

    Hi,


    I don't know if there is a calculation or specification of the maximum allowable noise amplitude and frequency that the Vcc pin can tolerate. The goal here is to clean up the input supply for the analog sensitive circuits inside the PMU. I suggest keeping the filter resistor if you can.

    One major aggressor is the DCDCs of the device itself. They operate at 2.25MHz and the input switching current can be even faster. If you filter those to frequencies from the VCC pin then I suppose you should see the greatest performance increase from the filter.

    The input current is minimal as the Vcc pin only supplies the analog and logic control circuits of the device. Thus, a 10 ohm resistor has no problem of Ploss because the current draw is so little. If 10 ohms concerns you too much please note that the EVM and datasheet do recommend 1 ohm with a 1 uF filter.


    The power input pins are the VINDCDC1/2 and VINLDOx pins. These are the only pins with higher current draw that would cause a concern if a 10 ohm series resistor was used on them.