i.MX28 Detect voltage stabilization

[lategoodbye]

Hi,

i'm currently working on a Mainline Linux driver for the linear regulators of the i.MX28.

I've found out that the driver in the FSL BSP 2.6.35 uses the bit 9 (DC_OK) in HW_POWER_STS register to detect the voltage stabilization of dc control loop. But according to reference manual (page 935) this is only correct for voltage increase not for decrease.

Now i want to know, how to "make it the right way". First i thought of the HW_POWER_CTRL register with DC_OK_IRQ. But i want to be sure, that the interrupt comes for voltage increase AND decrease.

Additionally i need a timeout in milliseconds or microseconds, which defines the maximum time for voltage stabilization with enabled voltage steping. I didn't find any information about that in the datasheet.

Thanks in advance

Stefan

[fabio_estevam]

Hi Stefan,

You should not worry about the voltage stabilization in the decrease path. Only the increase path is critical. For example: you need a minimum voltage level for a certain peripheral to operate. The 'decrease' path is not critical because usually an increased voltage means that you will only consume more power, but the device still operates correctly.

[lategoodbye]

thanks a lot

Stefan

[igorpadykov]

Hi Stefan

you are right, RM (page 935) describes this is as correct for voltage increase not for decrease,

but only for LDO case. For DC-DC it is correct in both directions, below part of  MCIMX28RM  p.935 :

"High when switching DC-DC converter control loop has stabilized after a voltage target change. When linear

regulators are active, this bit goes high when the actual voltage is above the target voltage. Therefore,

DC_OK will go high when changing a linear regulator output to a lower value before the actual voltage

decreases to the new target value."

Regarding timeout for voltage stabilization - this depends on loads (number of capacitors, load current),

that is depends on particular design.

Best regards

igor

-----------------------------------------------------------------------------------------------------------------------

Note: If this post answers your question, please click the Correct Answer button. Thank you!

-----------------------------------------------------------------------------------------------------------------------

[lategoodbye]

Hi igor,

thanks. Regarding timeout it would be necessary to define the value outside in the devicetree.

So DC_OK_IRQ have the same limitation according to LDO like DC_OK in HW_POWER_STS?

Stefan

[igorpadykov · Accepted solution]

Hi Stefan

yes limitation the same.

Best regards

igor