stm32f373 adc ftrig

[othane]

Posted on October 30, 2017 at 05:13

Hi,

Looking at the other stm32 MCU's like the stm32f407 I see in their datasheet a spec fTRIG (aka the External trigger frequency) ... however I cannot see the same spec for the 16bit SDADC on the stm32f373 datasheet ... indeed it is even there for the stm32f373 12 bit ADC.

It seems I can trigger an ADC via the JEXTSEL bits from an EXTI11 line or a TIM TRGO output etc just like for all the other ADC's. What is the max trigger frequency for this please (or did I miss it)?

Thanks

#stm32f373-adc-trigger #stm32f373 #synchronize

[S.Ma]

Posted on October 30, 2017 at 08:26

Sigma Delta ADC is an analog IP which is present only in specific STM32 families.

Look at the datasheet and reference manual, then board examples for this SDADC in cube.

[othane]

Posted on October 31, 2017 at 00:59

Thanks, but this is not a question of how to do this, I have code to do it (almost).

I am instead looking for a specification for the fTRIG rate on the SDADC so that I know if I trigger the ADC at a rate of say 20kHz or 50kHz etc, and it will work reliably across all the stm32f373 chips I get. I am just about to start testing the code I have to see what I can actually achieve, but a guaranteed spec is really required here (especially since it is a published spec for the other 12 bit ADCs).

That is unless I am miss understanding the design and the chip does not support this feature?

Thanks.

[othane]

Posted on November 01, 2017 at 02:41

So i have done some testing by triggering the Injected mode on SDADC1 using TIM19_CH2's rising edge.

The SDADC_CLK is at 6MHz (SYSCLK @72MHz prescaled by 12), JCONT is 0, CR2->FAST is 0 (it seems to be irrelevant anyway), and the CR1->SLOWCK bit is 0.

I find that I get reliable triggering up to about 12kHz, after this I think I am dropping samples from the ADC. To test this I have the TIM19_CH2 mapped to pc11 which I monitor on the scope. Then I have the ADC populating a buffer via a DMA with 100 samples, when I get the DMA complete ISR for all 100 samples I hit a break point and I count the number of edges on pc11 using the scope .... I get 100 edges reliably up to about 12kHz, but after this I start to see many more edges as I believe the ADC cannot service all the triggers.

Since I am converting a single channel I was expecting fTRIG to be closer to at least the 16.66kHz of the fast mode with multiplexed channels (ideally closer to the full 50kHz for the non multiplexed, but I could understand why using an external trigger might make this drop back to multiplexed mode) .... But it seems I am getting a response closer to the 12.5kHz of the one channel slow mode which I was not expecting.

Can anyone confirm the fTRIG spec or tell me how I might increase this sample rate please ?

Thanks.