The 48MHz crystal oscillator for HSE of STM32H743 cannot be realized.

[shaunSHAUN]

Hello sir/miss , 

According to the STM32H7 datasheet, the range of the HSE external crystal oscillator is 4M - 48MHz. However, when we used the STM32H7IIT6-EVAL evaluation board and replaced the original 25MHz surface mount passive crystal oscillator with a 48MHz passive crystal oscillator, we were unable to obtain the corresponding 48MHz frequency from the MCO-PA8 pin.

Summary: All conventional passive crystals from 4M to 40MHz were tried and worked fine. However, for external passive crystals above 40MHz , just like 48MHz, the MCO output waveform frequency was 16MHz, which is 1/3 of the HSE frequency, and it was unable to output 48MHz.

Please provide a solution or suggest areas where we can improve the test. Thank you very much!

[RobK1]

You chose a crystal that works in 3rd overtone mode.

Be sure to select one that works in fundamental mode:

Crystals | Electronic Components Distributor DigiKey

[mƎALLEm]

Hello,

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@shaunSHAUN wrote:

Summary: All conventional passive crystals from 4M to 40MHz were tried and worked fine. However, for external passive crystals above 40MHz , just like 48MHz, the MCO output waveform frequency was 16MHz, which is 1/3 of the HSE frequency, and it was unable to output 48MHz.

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From this statement I suspect a failing HSE oscillation startup.

So when you replaced that crystal, did you check if that crystal is compatible with STM32?

Please read this article: How to select a compatible crystal and load capacitors for STM32 with layout guidelines

+ Refer to the application note AN2867 "Guidelines for oscillator design on STM8AF/AL/S and STM32 MCUs/MPUs"

[AScha.3]

HI,

so for the "48MHz" crystal you picked a third overtone type, that will its fundamental resonate at 16M.

1. try with a crystal thats in fundamental mode or a crystal oscillator (+ HSE bypass setting)

2. why try/using crystal at the given limits ? Never a good idea... Better to stay in middle of possible range.