STKNX Linear regulator dropout

[AlexandreR]

Hi,

I would like the DC/DC converter of STKNX to make 5V.

Also, I want the Linear regulator to make 3.3V

Because of global efficiency, I wanted to power the linear regulator with the 5V output of DC/DC converter.

I'm surprised that the datasheet specifies VDD_REGIN minimum voltage 6.8V, if VCC_SEL is shorted to ground (in order to make 3.3V linear regulator output).

Same for VDD_REGIN minimum voltage specified 8.5V, if VCC_SEL is shorted to VCC_Core (in order to make 5V linear regulator output).

This makes 3.5V voltage dropout, which seems pretty much to me.

Question: Is there a typography error in Datasheet? Or is the dropout of internal regulator as much as 3.5V ?

Many thanks,

   Alexandre

[Peter BENSCH · Accepted solution]

It is not a typo, but has to do with the fact that it is not an LDO, but a simple linear regulator whose dropout voltage can actually be that high. You will have noticed that VDD_REGIN for 5V is also at least 3.5V higher in table 5 one line below.

Regards
/Peter

[AlexandreR]

Thank you Peter for this reply.

I have noticed it is 3.5V for both working modes.

I wish it was just an error, as it may have saved me space on a dense circuit. Also,I think requiring 5V and 3V3 is quite common.

BR,

   Alexandre