Using internal pullups for SDIO interface

[sincoon]

Posted on December 11, 2017 at 13:55

Can I use internal pull-ups for SD card connection with SDIO interface(STM32F4xx)?

#sdio #pull-up #sd-cards

[AvaTar]

Posted on December 11, 2017 at 14:25

For short connections and low clock rates, this might work.

All examples I know use external resistors, with values much lower than the internal pull-up.

The less your resistors match the line impedance, the more distortions, and the lower the possible clock frequency (and data rate).

[Tesla DeLorean]

Posted on December 11, 2017 at 15:11

If the leads/traces are very short. The ideal placement is at the socket, not the IC, the prototype I built for the STM32F4-DISCO used 33K at the socket, I don't recall it being reliable without them.

I'd shot for something in the 33K to 50K range

[sincoon]

Posted on December 11, 2017 at 14:40

But, as I see, for example, Olimex dev board with stm32f407 MCU:

Pullup resistors have value 33k, which is not so far from internal pullup value(~30-40k - am I right?).

[AvaTar]

Posted on December 11, 2017 at 15:02

Ahhh yes, correct. Probably mixed up something with I2C pull-ups.

The F4-Discovery Baseboard has 22R series resistors (before the 47k pull-up), the Mikromedia M4 10k pull-ups.

I think you don't need to restrict to STM32F4 boards for SD card example hardware.