Using DVFS with external DC-DC power supply

[sureshans]

Hi all,

In i.MX6 processor family, for DVFS to work successfully , is it neccessary that Internal Digital LDOs are for powering on ARM , SoC & PU ?

Is there a method to make DVFS work when the digital LDOs are used in bypass mode ?

My concern here is if we use LDOs , drop across the LDOs itself will result in power consumption .

If we can control the DC-DC converer present externally for DVFS , this voltage drop across LDO can be eliminated.

Please share your thoughts.

Regards,

Suresha.N.S.

[AnsonHuang · Accepted solution]

Hi, Suresha

     As long as we can scale the voltage of ARM/SOC/PU, no matter it is from internal LDO or external DCDC. So, if external DCDC or PMIC can change the output voltage via software, then DVFS is available. For example, we use PMIC(PFuze) on our sabresd board, this is a programmable PMIC, so we bypass the internal LDOs by default to save power. Everytime cpu freq is changed, PMIC's voltage for ARM/SOC/PU are also changed via I2C. Bypass internal digital LDOs can save about 10% power, this is based on our experiment.

[sureshans]

Hi Huang,

Thanks for your quick response.

I have one more doubt.

What is the purpose of these Digital LDOs ? Is there a specific use case where in we should use LDOs instead of directly using PMIC output ?

Regards,

Suresha.N.S.

[AnsonHuang]

Hi, Suresha

     I can NOT tell you all the benefits of internal digital LDOs, as I am only a SW guy. My understanding is that using internal LDOs can simplify hardware design, as you may only need one power rail input to our SOC, then internal LDOs can scale it separately for three power rails. And it also can lower the design cost.