With high sdmmc clock SDIO is not working with nucleo_h743/53

[APand.8]

CASE 1:

I am using  sdmmc for SDIO bulk transfer at 400khz initially then switch to 25 mhz.

1. Its not working with nucleo h743/53 where cpu frequency 480 mhz and sdmmc input clock is 480 mhz.
2. Its working with nucleo h743/53 where cpu frequency 480 mhz and sdmmc input clock is 48 or 50 mhz.
3. Its not working with nucleo h743/53 where cpu frequency 160mhz and sdmmc input clock is 160 mhz.
4. Its is working fine with nucleo_u5 when CPU frequecy is 160mhz and SDMMC input clock is 160 mhz which gets converted to like:26.66 mhz.

• I have not checked upto which max sdmmc frequecy it is working fine with nucleo_h743/53.
• It seems to be working when sdmmc input clock is ~50 mhz with nucleoh743/53.

 

Q1: Is there any recommendation with sdmmc input clock frequency with nucleoh743/53?

 

CASE2:

Along with CASE1, I also found that its not working at all with nucleo h743/53, if I give 3.3V External power to SD card(external power also uses voltage regulator) , but same works when giving 3.3V power from nucleo board.

WRT power case with nucleo_u575: external power or direct power from nucleo board both works.

Q2: what could be the cause for CASE 2?

 

[AScha.3]

SDcard can have max. 50 MHz clock. See SD specification, at 3v3.

 

from H743 rm: