I am projecting a brushless motor driver that contains a LoRa SX1276 radio and a ESP32-D0WDQ6 chip. The power line then gets really noisy when everything is working. For the RF blocks (SX1276 and ESP32), it needs to be very clean at the 3.3v fixed voltage. There are some power signals on the board, so that the image bellow shows the power tree with it's loads on each branch: enter image description here

That being said, I have some questions:

  1. Is there any problem on using the same LDO(ADM7172) to power both the analog chip lines (i.e. ESP32 and SX1276)? This LDO is going to be used exclusively to these two chips, as it's shown above.
  2. The digital blocks from ESP32 and SX1276 are going to be powered by the "green-one" LDO line, on the diagram above. Add to this, the IMU and the DRV motor driver. Despite this LDO is 1A capable, it is recommended to power multiple ICs with one LDO? The noisy around this configuration is acceptable? (Bellow, the schematics:) enter image description here enter image description here enter image description here enter image description here enter image description here enter image description here
  3. How GPIOs affect the LDO stability in order to not disturb other chips? Considering the fact that some chips have GPIOs and SPI pins to communicate with the microcontroller, how to prevent oscillations on that LDO that powers the ICs?

Basically my doubts are about how to stabilize the digital and the analog circuitry and when to divide the source of power between this two parts, or even when use the same LDO to power all this pins.

I hope you can give me some ideas, and thanks you guys for sharing the knowledge!!


If you want locally_clean VDD, then use a LOCAL_BATTERY, which you make.

Use a 1 ohm resistor in the VDD, with 100uF shunt right at the IC(s).

The 1 ohm is needed, to ensure other distant loads cannot suck charge from your (clean) 100uF capacitor.

And you need to Ground the 100uF directly to the GND pin of the IC.

You cannot replace the 1 ohm with a ferrite bead. FBs do not work at low frequencies.

The combination of 1 ohm and 100uF is 100uS time constant, which 1.6KHz low pass filter. No FB will do that.

You can used lumped inductors in place of the 1 ohm, if the DC_drop across 1 ohm is a problem.

Notice you are spending PCB area, and money, to achieve clean VDD and thus clean measurement. That is life.

  • \$\begingroup\$ Thanks for the explanation, but, If possible, I would like you to answer the 3 asks, just to make sure if am I doing right! \$\endgroup\$ – Emanuel M Aug 11 '20 at 19:59

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