STM32G4 TCXO

CrazyChel · ‎2024-09-20

Please let me know if there are any hardware or sofware specifics for connecting TCXO to the STM32G474 series? What should pay special attention to?

I use FT2MN at 40 MHz. Its output was connected through a 10 pF capacitor and a 220 Ohm resistor, in series, to PF0 RCC_OSC_IN.
I'm running CubeIDE 1.16.0.

Unfortunately this doesn't work, I'll use a primitive for testing:

  while (1)
  {
  HAL_GPIO_TogglePin(GPIOC, LED_G_Pin);
  HAL_Delay(100);
    /* USER CODE END WHILE */

    /* USER CODE BEGIN 3 */
  }

When power is supplied, the LED_G lights up constantly. After pressing the reset button, it turns off and does not turn on again. If I turn the power off and on again, everything repeats itself.

When I change the configuration to the built-in RC generator. The LED_G flashes as specified by the program, the reset button works correctly.

I tried to see what happens at the input PF0 with my DSO2D15 oscilloscope, the declared band is 150 MHz, with the original probe in the 1:10 mode. I am not sure about the reliability of the results, especially regarding the amplitude. There I see a truncated sine wave that goes negative to 200 mV and positive to 220 mV. Accordingly, the full amplitude is 420 mV. Directly at the output of the TCXO, the amplitude is 1.2 V, and it almost does not go to negative. I didn't see a significant DC component there.

Andrew Neil · ‎2024-09-20

Show that code.

Andrew Neil · ‎2024-09-20

@CrazyChel wrote:
whether such a board layout can affect the operation of the generator

It seems that the oscillator is operating as specified - it's just the wrong part for this application?

Andrew Neil · ‎2024-09-20

@CrazyChel wrote:

I use FT2MN at 40 MHz. Its output was connected through a 10 pF capacitor and a 220 Ohm resistor, in series

Please show the actual schematic - far better than trying to describe connections in words.

But it doesn't sound at all like what the datasheet recommends:

CrazyChel · ‎2024-09-20

I am already in contact with Abrakon, as soon as it becomes clear I will share.
It seems to me that the problem is the low amplitude of the signal at the output of the generator. Even if I disconnect the generator from the controller, the amplitude remains low.

TDK · ‎2024-09-20

0.8 Vpp isn't sufficient for the incoming clock signal to the STM32F4.

Should be able to find a different part that outputs a clock with 3.3V logic.

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CrazyChel · ‎2024-09-24

Thanks to everyone who responded.

In this case, it was my mistake with the choice of the generator. I mistakenly perceived 0.8 Vp-p as 0.8 V from the supply voltage of the generator. But it is not so. This is exactly 0.8 Vpp (peak to peak). Abrakon recommended using generators with HСМОS output.
They have a slightly lower accuracy and more consumption, but the output voltage meets the requirements of the STM32 datasheet.
Below is an excerpt from two datasheets of the CSW generator and the HCMOS. I hope this will help you not to repeat my mistakes.