Minimum external clock requirement for STM32G474CET3

[sag]

Hi I am using below controller in one of our design

STM32G474CET3

i would like to know minimum external clock frequency on which my microcontroller works.

Also my requirement includes 1 SPI, 1 I2C and 4 ADC input sensing.

I would need very minimum external clock frequency on which it can ru,

And ultimate goal is to run 1 SPI, 1 I2C and 4 ADC input sensing at a very low current consumption for 3.3V microcontroller supply,

In datasheet its mentioned from 4 MHz, can this be used in 1 to 3 MHz range too

Also any ball park current consumption can i get for 1 SPI, 1 I2C and 4 ADC input sensing at 3.3V input to Microcontroller.

[STTwo-32 · Accepted solution]

Hello @sag 

This MCU minimum HSE resonator Frequency is 4MHz. You can't use any other value under 4MHz.

For the Current consumption of your MCU, you may can refer to the Table 35 of the DS12288. 

Ps: don't forget to read the description of the Table 35.

Best Regards.

STTwo-32 

[AScha.3]

Hi,

Why not use the HSI ?

No external clock needed at all.

[Andrew Neil]

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@sag wrote:

In datasheet its mentioned from 4 MHz, can this be used in 1 to 3 MHz range too

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The datasheet defines the guaranteed operating conditions - if says 4MHz is the limit, then that is the limit for guaranteed operation.

If you want a lower-speed external clock, there's LSE:

[Andrew Neil]

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@STTwo-32 wrote:

This MCU minimum HSE Frequency is 4 MHz. You can't use any other value under 4MHz.

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But, when operating with an external clock source (so not using the HSE oscillator), there is no minimum limit stated:

[Andrew Neil]

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@sag wrote:

I would need very minimum external clock frequency ... at a very low current consumption

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Note that, for low(est) power consumption, it is often better to run the microcontroller fast - so that it can sleep longer.

[sag]

Our operating temperature is 180 deg C which will cause drift in internal oscillator at higher temperature.

The stability is not good at higher temperature. 

[Andrew Neil]

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@sag wrote:

Our operating temperature is 180 deg C . 

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That's well outside the specified operating limits:

[sag]

So can i connect 1 MHz then if lower is not mentioned at clock generated from an external source.

Same for 2 MHz external clock

[Andrew Neil]

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@sag wrote:

So can i connect 1 MHz then if lower is not mentioned at clock generated from an external source.

Same for 2 MHz external clock

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So it seems.

To be clear, that requires an external, active source - not just a crystal.

But, again, for low(est) power consumption, it is often better to run the microcontroller fast - so that it can sleep longer.

eg, here you can see that even at 100kHz, you'll typically draw 0.22mA:

whereas in the sleep modes that can be a few uA or even nA ...

In other words, sleep modes are more beneficial than running with a slow clock.