LPC546XX: SDIO and external pull-ups

[giusloq]

I noticed LPCXpresso54628 EVB mounts external pull-ups resistors on data, CLK and CMD lines. In the examples, during pin configurations, internal pull-ups are disabled.

Is is possible to avoid external pull-ups and activate internall pull-ups on CLK, CMD and data lines? This could save some space on PCB.

[ZhangJennie]

Hi giusloq 

Normally, the internally pull up is week pull up as below pic. We use transistor to simulate resistance as internal pull up. it's tens of KOhm.

According to LPC546xx UM, Ipu is 6-30uA when VDD < VI < 5 V

Weak pull-up is that when the output is high, the current that can be output is very small, and it is easy to be pulled low by other strong pull-up, so it is called weak pull-up. For example, the pull-up current is 30 uA. The pull-up capacity is determined by the size of the pull-up resistance. 

So I suggest you using external pull up as reference design suggested.

Thanks,

Jun Zhang