Questions about power bypass capacitors and explanations when using an external DC power source

[SHMoon]

hello

I am developing a product with two power supply types with nRF52832.

1 - Battery )

When using battery power, in my experience,

the voltage seems to drop a lot as the discharge increases.

Currently, it is configured to detect low voltage at 3.0V, which is the terminal voltage....

When using this battery voltage, is it a good idea to use a larger bypass capacitor on the VDD line? Power drop or... From watching SNR...

2 - external DC Power  )

DC power is supplied from an external SMPS.

However, this SMPS has many loads, especially DC motors.

So, a Pi Filter was configured with Bead and Capacitor on the nRF52 power supply line.

DC POWER ----  Capacitor 1uF  ---- bead  60ohm  --- Capacitor 22uF  ------ VDD 5V  ---- LDO ------ 2.8V

    |                                |                             |                             |                                                            |

    | ------------------------------------------  bead  60ohm  ------------------------------------------------------------------GND

    

However, the question is, generally, the impedance of the Bead must be around 1Mhz to be high, so is it possible to attenuate the inflow of noise from relatively low motors, etc.? This is the part. I'm thinking of adding about 10 ohms as shown below. Are there any recommendations or guides in this regard?

DC POWER ---- Resistor 10 ohm ------  Capacitor 1uF  ---- bead  60ohm  --- Capacitor 22uF  --- VDD 5V  -- LDO ------ 2.8V

    |                                                                                    |                                                              |

    | ------------------------------------------------------------------------  bead  60ohm  ---------------------------------------------------------GND

    

thank.

[Simonr]

Hi

You should not use a series resistor for this purpose at least. From your description it's hard to say what the best setup here would be, as it depends on the battery, the capacitors, and the resistors, etc. so we would recommend that you set up a test rig where you can connect this and do some measurements to find the best setup.

Best regards,

Simon

[SHMoon]

hi, Simonr

As you said, I plan to tune the Power Filter while measuring with an instrument.

Add to,

1) What I would like to ask is... You said not to use a series resistor (small value)... Can you tell me why?

2) If the VDD Bypass is increased to 22uF (Ceramic), will there be a side effect?

3) Is there a good capacitor value to add to the VDD stage to remove power noise (harmonic components, etc.) generated during 2.4Ghz RF operation?

[ketiljo]

SHMoon said:

1) What I would like to ask is... You said not to use a series resistor (small value)... Can you tell me why?

There will be increases rippled because of the voltage drop across the resistor. 

SHMoon said:

2) If the VDD Bypass is increased to 22uF (Ceramic), will there be a side effect?

A large cap is not a problem.

SHMoon said:

3) Is there a good capacitor value to add to the VDD stage to remove power noise (harmonic components, etc.) generated during 2.4Ghz RF operation?

The radio has the highest current draw. There's no RF noise on the VDD pin so you only need to handle the power supply ripple.