EEVblog Electronics Community Forum
Electronics => Projects, Designs, and Technical Stuff => Topic started by: okw on November 10, 2024, 06:10:27 pm
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I have trouble with a crystal and ESP32-C3 (chip, not module), so I'll inject the clock with a signal generator (UTG962E, I also have a R&S SME03 if the Uni-T performs poor). ESP runs at 3.3V.
Crystal requirements are 40MHz ±10 ppm and recommended that the amplitude of the crystal is greater than 500 mV.
I guess it shouldn't swing around 0V. What's the rule of thumb here? If the MCU runs at 3.3V should it swing around half of this (1.65V) with amplitude that won't exceed 3.3V (or goes below 0V)?
And when the hardware guide says 500mV. Is that Vrms or Vpp?
Would I inject the clock in XTAL_P (pin 30) or XTAL_N (pin 31)?
https://docs.espressif.com/projects/esp-hardware-design-guidelines/en/latest/esp32c3/esp-hardware-design-guidelines-en-master-esp32c3.pdf (https://docs.espressif.com/projects/esp-hardware-design-guidelines/en/latest/esp32c3/esp-hardware-design-guidelines-en-master-esp32c3.pdf)
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If the MCU already supports a crystal, the simplest is to select crystal mode and AC couple (100pF~1nF) the generator into the XTALIN pin.
That lets the xtal amplifier bias to its natural point.
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You mean remove R1, then put a capacitor in series with pin 30 and then feed the clock into the cap?
Which voltage and offset should I set my generator to?
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You mean remove R1, then put a capacitor in series with pin 30 and then feed the clock into the cap?
Is that in input pin of the crystal oscillator circuitry ?
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You mean remove R1, then put a capacitor in series with pin 30 and then feed the clock into the cap?
Is that in input pin of the crystal oscillator circuitry ?
Actually, I think it is the crystal power? I just hoped it wasn't. Cause then I need to desolder the 2x1.6mm crystal which is located super close to the ESP32.
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Crystal requirements are recommended that the amplitude of the crystal is greater than 500 mV.
A crystal has no "amplitude". If you want to use an external clock source the required (sine wave) amplitude is min. 500 mVp (= 1Vpp).
Would I inject the clock in XTAL_P (pin 30) or XTAL_N (pin 31)?
XTAL_N (pin 29) would be the input. Put 1nF in series with pin 29 and a 51 Ohm shunt resistor in front of it to match the impedance of the generator.