i.MX6UL LDO bypass

[samchinnery]

I am designing a board with the i.MX6 UltraLite processor. I want to power the CPU using a 1.2V regulator, bypassing the internal LDO_ARM and LDO_SOC regulators. However, the reference manual states that the internal POR module will hold the CPU in reset until the VDD_SOC_CAP supply is "valid." The LDO_SOC regulator is set to 1.15 volts by default, which does not give the LDO enough overhead given a 1.2V input: the dropout voltage is 150mV. The datasheet states an operating VDD_SOC_IN voltage of 1.15-1.3V, with the internal LDO bypassed.

My question is, if I supply 1.2V to the VDD_SOC_IN, with intent to bypass the internal regulator, will the internal POR module ever bring the CPU out of reset?

Additionally, if it does, what is the easiest way to bypass the internal LDO?

[jamesbone]

Hello Sam,

What version are you reviewing of the Reference Manual,?  because in the latest available on the web site REV 0, 08/2015. It states :

"If the external SRC_POR_B signal is used to control the processor POR, SRC_POR_B

must remain low (asserted) until the VDD_ARM_CAP and VDD_SOC_CAP supplies

are stable."

"If the internal POR function is used, the following power supply requirements must be

met:

• VDD_ARM_IN and VDD_SOC_IN may be supplied from the same source, or

• VDD_SOC_IN can be supplied before VDD_ARM_IN with a maximum delay of 1ms"

So yes if you supply 1.2V to the VDD_SOC_IN and VDD_ARM_IN then device should be working correctly!. and out of reset.

Have a great day,
Jaime

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[samchinnery]

Thanks!

Also, if it's not too much trouble, what is the best way to disable the LDO_ARM regulator? Is it possible to disable it early in the boot prcess, or must the program image be loaded first?

[jamesbone]

From my experience it is better at the boot process.

Have a great day,
Jaime

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