STM32F446 PA5 output levels at high frequency

[waclawek.jan]

Posted on April 25, 2016 at 10:36

This is one for the ST insiders.

On a Nucleo64 (SB21, SB29, SB44 all disconnected) with STM32F446, the PA5 pin has been configured as AF5 (SPI1_SCK/I2S1_CK), push-pull, OSPEEDR set to 0b11 (and later tried also 0b10), compensation cell tried both on and off, DAC at default (i.e. off). SPI1 set to RXONLY mode with clock set to PCLK/2, which should output cca 40MHz onto PA5. The waveform on PA5 is a cca 500mVp-p 40MHz wave riding on a cca +2V DC offset. Cutting down the speed to PCLK/4 results in sane cca 20MHz waveform. SPI1_SCK at a different pin works as expected at PCLK/2 too. The STM32F446 datasheet (rev.5) lists PA5's type as ''TC'', with no explanation what TC might mean... But even then, Table 58. I/O AC characteristics does not indicate that any pin should behave differently as far as output high-speed capability goes. Does PA5 have a different drive than other pins, or do I overlook something? Thanks, Jan Waclawek

[Nesrine M_O]

Posted on April 28, 2016 at 12:32

Hi Jan Waclawek,

Does PA5 have a different drive than other pins, or do I overlook something?You are right. It’s a data sheet typo. Thank you for bringing this issue to our attention. It is noted and will be fixed in coming release of the document.-Syrine-

[waclawek.jan]

Posted on April 28, 2016 at 12:49

Hi Syrine,

Thanks for the answer. So, does this mean that PA5 (and probably PA4) has a different AC output specification than other pins, or are you talking only about the ''TC'' marking? If PA5 has different AC specification, is this relevant only for the 'F446, or for other 'F4xx too? Thanks, Jan

[waclawek.jan]

Posted on November 02, 2017 at 15:12

After one and a half year and one version later, this is still unexplained in DS:

Comment, please.

Thanks,

JW

[Dana Myers]

Posted on November 08, 2017 at 20:53

Looking at a different STM32 datasheet (STM32F373xx, 

http://www.st.com/content/st_com/en/support/resources/resource-selector.html?querycriteria=productId=LN10$$resourceCategory=technical_literature$$resourceType=datasheet

 ) I'm inclined to believe 'TC' means 'Standard 3.3V I/O'. 

[waclawek.jan]

Posted on November 08, 2017 at 21:20

Thanks, Dana.

However, note, that in 'F373, the pins which have ADC functionality are

TTa 3.3 V tolerant I/O directly connected to ADC

and note, that PA4 and PA5 in 'F446 *do* have ADC (and DAC) functionality.

Also, compare to 'F407 datasheet  - PA4 and PA5 there are marked TTa, with the same explanation, directly connected to ADC.

And it also does not explain the problem presented in opening post.

JW

[Dana Myers]

Posted on November 08, 2017 at 21:54

Indeed; 'TC' doesn't seem to describe what 'F446 PA5 is behaving like, though your description makes it sound like there's more than a datasheet error in play here.