topic Re: Internal LDO usage of FRDM in Kinetis Microcontrollers

Internal LDO usage of FRDM

kai_liu — Thu, 13 Feb 2014 02:02:15 GMT

I found most of the FRDM boards leave internal LDO of KL25Z/K20D50M as is. Is there any considerations to prevent the designers from using the internal LDO as main power supply for MCU itself ?

Usually I simply copy the power supply design for my own board. But using internal LDO may reduce PCB area in some designs.

Re: Internal LDO usage of FRDM

kai_liu — Fri, 14 Feb 2014 23:27:11 GMT

Well, after reading reference manaual of K20. I found the LDO is enabled after reset by default value in SIM_OPT1.

In general, the firmware will leave it as is, aka as enabled. UNLESS the firmware close it on purpose for low-power consumption or by fault, like copy a value instead of logcial OR/AND operations. So if we consider the internal LDO is stable enough under 120mA, which is enough for most of applications. The final decision is firmware.

If the firmware is fully under our control, we can use internal LDO. If there is some firmware out of our control, use the external LDO as back up.

I hope any FSL employee can confirm that conclusion.

Re: Internal LDO usage of FRDM

Jorge_Gonzalez — Sat, 15 Feb 2014 19:43:36 GMT

Hello Kai:

Your understanding is correct. You can use the internal regulator as long as you respect the 120 mA current limit.

Just do not forget to include an external capacitor in Vout33. Datasheet suggests a 2.2 uF cap.

Hope this helps!

Jorge Gonzalez

Re: Internal LDO usage of FRDM

kai_liu — Sun, 16 Feb 2014 12:29:14 GMT

Thanks Jorge