Question, i.MX233 power supply 2

[Aemj]

Hi team,

I have some questions on internal power supply feature of i.MX233.

(1)

In my understanding, the pins for output power are different depending on using internal DCDC or Linear regulator.

In the case of using internal DCDC, the DCDC can pupply voltage to the following pins.

- DCDC_VDDA, DCDC_VDDD, DCDC_VDDIO, VDDM

In the case of using internal regulator, not using DCDC, it can supply the voltage to the following pins.

- VDDIO33_1, VDDIO33_3, VDDD1, VDDD3, VDDA1, VDDIO_EIM1, VDDIO_EIM2, VDDM

Am I correct?

(2)

Can you provide the characteristics on the power-on rising of the power supply pins powered by linear regulator?

(3)

My customer does not use internal DCDC of i.MX233.

And they believe the L, seen in the schematic of EVK, located between DCDC_LN1 and DCDC_LP pins can be removed.

Is it correct?

If so, DCDC_LN1 and DCDC_LP can be left unconnected?

(4)

The customer believes that the capacity of the decoupling capacitors ,used in i.MX233EVK, connected to DCDC_VDDIO, DCDC_VDDA and DCDC_VDDD pins is too large in the case of not using DCDC.

Could you give me your suggestion what the capacity number should be fine for those decoupling capacitor?

Thanks,

Miyamoto

[tobiasdiendorfe]

We are also want to use the linear regulators only.

DC-DC produces to much EMI noise.

Our u-boot is base on 2015-10 which has DCDC enabled.

I have read through the Power supply section in datasheet and have found out the following:

• In function mxs_power_set_linreg() the linear regs will be set to 25mV under the dcdc voltages.
  Is it correct to set the offset of the linear regs to "0"?
• I havent found the rightregister to NOT switch from lin to dcdc regs. Any sugestions here?
  What i have found is the register "DC_STOPCLK" but like the issue above ill think its to late to stop the clock after the following procedure:

• setup lin to 25mv under dcdc
• switch from lin to dcdc / start dcdc     <-- where does this happen
• stop dcdc with register  "DC_STOPCLK"    <-- ill think its to late here because the cpu shortly runs on the dcdc and we cant remove the L

Thank you

Tobias

[tobiasdiendorfe]

I have made an u-boot patch which doesnt enable the dcdc converter.

You can download it here: https://cloud.pascom.at/index.php/s/5kPAg8Y4Mz43VyY

Tobias

[igorpadykov · Accepted solution]

Hi AVNET JAPAN FAE

1. shortly, pins for output power should not be changed for

cases DC-DC vs Linear regulator only. Reason is that internally there

is connection between outputs of dc-dc and linregs.

Attached is recommended schematic.

2. could not understand

3. yes L can be removed

4. capacity depicted on attached schematic is not recommended to change,

    since this may affect linreg stability.

Best regards

chip

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[Aemj]

Hi Chip,

The customer tested with removing L1 located between DCDC_LN1 and DCDC_LP pins, then he saw i.MX233 did not work.

The firmware seemed not to work.

Do you have any ideas on that?

BR,

Miyamoto

[igorpadykov]

Hi Miyamoto

please check that processor really does not use internal DCDC.

Because it may use it when running only from 5V, using

VDD4P2 node.

Best regards

chip

[Aemj]

Hi Chip,

Thank you for your support.

As for (2);

The customer is worrying that the AC characteristics of the power supplies powered by linear regulator can be different from the DCDC powered case.

Especially, power-on rise time of the supplies.

Does it make sense?

(3)

Can DCDC_LN1 and DCDC_LP pins be left unconnected?

[Aemj]

Hi Chip,

I mean AC timing for the power supply pins.

I understand that the rise time  depends on capacitors connected to the supply pins.

If the capacitors are not changed, the rise/fall time will not be changed depending on DCDC and linreg cases.

Correct?

BR,

Miyamoto

[igorpadykov]

Hi Miyamoto

yes correct.

Best regards

chip

[igorpadykov]

Hi AVNET JAPAN FAE

2.  I do not fully understand what "AC characteristics of the power supplies"

are you refering since all available characteristics are given in IMX28CEC

i.MX28 Consumer Datasheet - IMX28CEC, Table 13 Power Supply Characteristics

Regarding capacitors at output, they should have the same value in case dcdc and

linreg cases.

3. yes

Best regards

chip