ADC peripheral clock configuration

[Orkun]

I am using STM32F429VIT6. Configured SystemCoreClock 168MHz and APB2 clock is 84MHz. I accidentally configured ADC peripheral with "ADC_CommonInitStructure.ADC_Prescaler = ADC_Prescaler_Div2;" but datasheet says max ADC frequency is 36MHz. I am wondering about my ADC peripheral clock:

- Is it running at 42MHz with overclocking? or

- Is it running with max freq. so it is 36MHz? or

- Is it running with typical freq. so it is 30MHz? or

- Is it ignore ADC_Prescaler_Div2 and process it with ADC_Prescaler_Div4 so it is 21MHz?

[Sarra.S · Accepted solution]

Hello @Orkun 

It's generally not recommended to exceed the maximum ratings as specified in the datasheet because it could lead to unpredictable behavior or even damage the peripheral. It's advisable to adjust your clock configuration to ensure that the ADC peripheral is not driven above its maximum rated frequency of 36MHz. We cannot guarantee any values outside our test range.

Hope that helps!

[AScha.3]

If you set div2 , it runs at 84/2 = 42 MHz.

Did you use Cube ?

It limits in such case to: hadc1.Init.ClockPrescaler = ADC_CLOCK_SYNC_PCLK_DIV4; (21MHz here ).

You should not "overclocking" , to be sure, tolerances stay at levels, as in datasheet promised.

[Orkun]

nope I did not use Cube, also used STD lib. In my example; TIM1 CC4 trigger ADC injected conversions.

Compared DIV2 and DIV4 performance with toggled GPIO. DIV2 seems much faster than DIV4.

How can I detect if it is overclocking or not?

[AScha.3]

>How can I detect if it is overclocking or not ?

No need to detect, you set the divider - so you know it .

Usually nothing happens , just from 36M to 42M is about 17%  over "allowed" max.

And all cpu and peripherals need to have some safety margin, to be sure (STM) , the chip will work under all bad conditions (+80° around, low or hi supply voltage ) and keep to the promised precision.