i.MX6 Power LDO bypass

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i.MX6 Power LDO bypass

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王剑翰
Contributor III

I check the table 8 in IMX6SDLCEC.pdf and find there are the different supply operating ranges in different run modes(LDO Enable and LDO Bypassed). I can not find any description about the two modes in other documents but IMX6SDLRM.pdf, but there are 4 different modes : Internal Bypass,External Bypass,Power Gate,Analog regulation mode.

1, How to understand the difference?

2, Which one is the default mode for the core? LDO Enable or LDO Bypassed mode?

3, If the default mode is LDO Bypassed mode, and we need set the LDO Enable mode, how to design the VDD_ARM_IN and VDD_SOC_IN circuit?

I have checked the reference design in [SPF-27516_C3.pdf]. And, I find VDD_ARM_IN = VDD_SOC_IN = 1.375V, which is not fit the LDO Bypassed mode operating range.

4, How to change the run modes?

I find the information as below:

TRAG==0x1F  internal bypass mode

TRAG==0x00  POWER GATE mode

but I don't know what is the TRAG. How to find it?

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igorpadykov
NXP Employee
NXP Employee

Hi 王 剑翰

yes, right. Default is LDO enable mode

Best regards

igor

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1282497337
Contributor II

hi,

I have same problem,could you tell me How to change the run modes .when I boot the system, the uboot print "switch ldo bypass mode ",so what should I do to change the mode to ldo_enable mode.

thanks

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igorpadykov
NXP Employee
NXP Employee

Hi 王 剑翰

LDO Enable or LDO Bypassed mode are changed

with field REGx_TARG (Bypassed mode =

11111 Power FET switched full on. No regulation.

POWER GATE mode =00000 Power gated off, others =LDO Enable - this is default)

sect.50.7.4 Digital Regulator Core Register (PMU_REG_CORE) IMX6DQRM

How this is implemented in software:

https://gitorious.org/u-mobo/uboot-imx/commit/9b8b6f2ac34c795fbb272b31a2d37aea30ba06f6

For yocto use dts files: ldo-bypass dts, ldo-enable dts

Commits · embest-tech/meta-fsl-arm · GitHub

Best regards

igor

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2,729 Views
王剑翰
Contributor III

Hi Igor,

Thank you for your kindly answer.

Someone tell me the Linux BSP will set as LDO Bypassed mode first, and then change to LDO Enable mode.

If we want to always use LDO Enable mode, we need add like "ldo_active=on" in u-boot . Is it right?

Besides, as you said above, the LDO Bypassed mode IS the Internal Bypass mode and the LDO Enable mode IS the other two modes except POWER GATE mode. I don't know why the same mode has different name in different document?

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igorpadykov
NXP Employee
NXP Employee

Hi 王 剑翰

no, linux does not change LDO Bypassed mode first

and then change to LDO Enable mode, in fact this configuration is passed

from uboot to kernel. Linux does not change it.

Regarding different naming, yes this can be noticed in documentation.

You should carefully read documents and fully understand what it is

implied.

Best regards

igor

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王剑翰
Contributor III

Hi Igor,

Thank you for your help.

Then, if I add "ldo_active=on" in kernel command line, the LDO enable mode will be set and if I change it as "ldo_active=off", it will enter the LDO Bypassed mode. Right?

Then, if I don't add "ldo_active=on" or "ldo_active=off" in kernel command line, which mode is the default? Is it the LDO Bypassed mode?

Thank you & Best regards!

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igorpadykov
NXP Employee
NXP Employee

Hi 王 剑翰

yes, right. Default is LDO enable mode

Best regards

igor

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王剑翰
Contributor III

Hi,

Sorry, I check the attached file p.9 and find: it claims the default mode is bypassed mode, not the enable mode you said. But I also think your said is not wrong as I checked the REGx_TARG field and it do show the enable mode is default. I am confused about it. Maybe, I also don't quite understand it. Could you help me again for it ?

Thank you!

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igorpadykov
NXP Employee
NXP Employee

You are corect: REGx_TARG field - it do show the enable mode is default

For software BSP it does not make sense - since it depends on used BSP.

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王剑翰
Contributor III

Hi,

Sorry to trouble you again.

As the attached file p.9 said:

By defaut, LDO bypass is enabled. If you want to use internal LDO, please specify " ldo_active=on" to the kernel command line. LDO bypass can only be enabled on the board that mounted with external PMIC to supply VDDARM_IN/VDDSOC_IN power rail. LDO bypass is not supported on the chips with 1.2Ghz max CPU frequency.

As above said, if there is no PMIC on the board, the LDO bypass feature cannot be supported. So, in this case, the default mode is LDO enable mode? Right?

But why do you say "if don't use PMIC in design, one needs add "ldo_active=on" in kernel command line."

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igorpadykov
NXP Employee
NXP Employee

Hi

from hardware point of view: check REGx_TARG field and it does show the LDO enable mode is default.

Form software point of view this question does not make sense. For example

if you are using Linux L3.0.35_4.1.0_ER_SOURCE - yes here by default, LDO bypass is enabled.

For other BSPs this may be wrong.

So it may be recommended to read carefully BSP dcumentation and find which one is correct.

~igor

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王剑翰
Contributor III

Sorry, igor.

You may mistake my question. My question is for the bold type words.

As it says, if there is no PMIC on the board, the LDO bypass feature cannot be supported. I don't know why? As you said, the modes depends on used BSP. So, I think, if the BSP support LDO bypassed mode, the board will support the LDO bypass feature although there is no PMIC on the board.

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igorpadykov
NXP Employee
NXP Employee

Yes, If there is no PMIC on the board, the LDO bypass feature cannot be supported

because somebody should regulate voltages for processor, since Freescale linux BSP

CPUFREQ device driver changes voltages.

Form software point of view this question does not make sense, since

for some other custom BSPs this may be wrong.

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王剑翰
Contributor III

Hi,

Sorry to trouble you again.

I want to ask you another question:

If we don't use PMIC in our design, whether we need add "ldo_active=on" in kernel command line?

As we don't use PMIC and we set VDD_ARM_IN = VDD_SOC_IN = 1.425V, we don't want it enter LDO Bypassed mode.

Thank you & Best regards!

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igorpadykov
NXP Employee
NXP Employee

yes, if don't use PMIC in design, one needs add "ldo_active=on" in kernel command line.


~igor

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王剑翰
Contributor III

Could you kindly expain this to me ? Why? I don't quite understand it.

As you said, the LDO enable mode is the default mode. Why I need add "ldo_active=on" in kernel command line to set the LDO enable mode?

Thank you!

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igorpadykov
NXP Employee
NXP Employee

I believe actually this depends on specific BSP, for example refer to

attached file p.9 and link below

https://gitorious.org/u-mobo/uboot-imx/commit/9b8b6f2ac34c795fbb272b31a2d37aea30ba06f6

~igor

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王剑翰
Contributor III

Hi Igor,

Thank you for your help!

Best regards.

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