Electronic – Charge Pump Inverter Noise

charge-pump

I'm using an Charge Pump Inverter,MAX899R in free run mode with switching frequency of 500kHz like in the circuit attached. The problem is that I'm seeing a lot of switching noise in the output, much more than i expected as it is visible in the figure attached. Moreover the noise has a frequency of 1MHz, and not 500 KHz, is this normal ? How could i fix the problem ?

Switching Noise

Circuit

Update
After a suggestion of AndyAka, I checked the ground and it has the noise I'm seeing in the output, I read it would improve to use a ferrite bead after GND and after VCC but no improvements. I'm adding 3 more pictures with the noise at the ground(fig1), noise in the VCC with osciloscoppe earth probe closer to C11(fig2) and the noise in VCC with earth probe closer to C20.

Ground Signal
Noise At GND

VCC with with osciloscope earth probe closer to C20
enter image description here

VCC with with osciloscope earth probe closer to C11
enter image description here

Best Answer

Background: -

If you short the probe tip to probe earth and leave the probe earth still connected what do you see? - Andyaka

@Andyaka I shorted and i see the same noise I'm seeing at the output.

The basic problem here is your scope is picking up a signal in the loop formed with its ground connection. You need to use a better probe or a differential measurement. Here's apicture from TI that explains the problem: -

enter image description here

The picture was taken from Understanding, Measuring, and Reducing Output Voltage Ripple by Texas Instruments and covers the issue of good scope probing techniques.

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