Transconductance of an STM32F446RC

[DCont.1]

I need to know the Gm value of the STM32F446RC to determine the correct HSE crystal I can use with it.

[Danish1]

The application note AN2867 "Oscillator design guide for STM8AF/AL/S and STM32 microcontrollers" seems to provide the answer.

From Rev 11 (31-May-2017) Table 5 on p22

stm32f446 is f4_g2 LSE oscillators with statically-modifiable transconductance

When Low, gm(min) is 2.8; when High gm(min) is 7.5

When low, Gm_crit_max is 0.56; when high it is 1.5

Hope this helps,

Danish

[Imen GH · Accepted solution]

​Hello @DCont.1​ ,

Welcome to STM32 Community!

I recommend you to refer to Application note AN2867 (Section 5 Recommended resonators for STM32 MCUs/MPUs ( table 6)) available on our website

 

Imen

[DCont.1]

Greetings,

I have come to realize that the transconductance should be found in the datasheet of the external crystal oscillator. Please correct me if I am wrong here.

I have looked at the application note AN2867 and I have checked that the oscillator is within the correct parameters, however there's no recommendations for HSE oscillatos, that being said the steps to check that the oscillator is within the safe parameters requires me to know the transconductance (Gm). The problem is, I can't find this transconductance value anywhere, whether on the crystal's datasheet or the STM32F446RC datasheet. I have been working on the assumption that the transconductance value (Gm) is 25 mA/V.

Thank you in advance,

D.C.

[DCont.1]

Excuse me, the first line was meant to say "...should be found in the datasheet of the STM32F446RC and not the external oscillator"

[LMI2]

And you have to remember that you are talking about external crystals. External crystal oscillators have that crystal and electronics in one package and they give out alternating current at their nominal frequency. And they need a power supply.

[Imen GH]

Hello

You can find the value of Gm_crit_max in datasheet. 

So, you can determine the oscillator transconductance (gm)

Note that the conversion between the oscillator transconductance (gm) and the oscillation loop maximal critical gain (Gm_crit_max) is given by the formula Gm_crit_max = gm / 5.

Imen