Want to remove 0.1ohm series resistors from PMU.

[hikaruuruno]

Hi Community,

We'd like to ask something about 0.1ohm series resistors of PMU.

There are 0.1ohm series resistors connected to 22uF and 10uF of BATTERY and VDD4P2 pin respectively.

The schematics of the EVK Rev. A mentions that the resistors are "to prevent possible battery charger oscillation."

We are making a custom board which will not connect battery and would like to remove these 0.1ohm resistors.

Did anyone develop a custom board with no-battery configuration and also without these 0.1ohm resistors?

If someone did that, was there any problem?

From the description of the schematics, I suppose there will not be any problem but we would like to make sure of that before making a board.

Thank you in advance,

Hikaru

[igorpadykov]

Hi Hikaru

yes, one can remove them from unused pin: BATTERY or VDD4P2.

You should leave them on used connection to prevent stability issues.

Best regards

igor

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[hikaruuruno]

Hi Igor,

Thank you for replying.

I think I didn't explain our intention correctly.

I mean we won't connect a battery to BATTERY and DCDC_BATT pin, but they will be used to supply 3.3V to i.MX28 from external dcdc converter (DCDC_BATT source only configuration).

So more appropriate question is: Are these series resistors necessary only if the configuration is as described in section 4.2 "Battery-powered allications" of AN4199 and you don't need them in case of "Applications with permanent power supply," section 4.1 of AN4199?

Thank you,

Hikaru

[igorpadykov]

Hi Hikaru

with external dcdc converter (for DCDC_BATT) these resistors are

not needed, they are only for usage with internal LDOs.

Best regards

igor

[hikaruuruno]

Hi Igor,

Thank you for replying again, but I'm not sure I got it right.

On the one hand, the schematics of EVK Rev.A describes the resistors are "to prevent possible battery charger oscillation."

On the other hand, you says "they are only for usage with internal LDOs" and there is no mention about battery.

Which is true?

Are the resistors necessary regardless of the existence of a battery in the system if any of the internal LDOs are used?

Thank you,

Hikaru

[igorpadykov · Accepted solution]

Hi Hikaru

if you connects external power supply to DCDC_BATT pin,

they are not necessary.

Best regards

igor

[hikaruuruno]

Hi Igor,

Well... Even though I do not really get it, I suppose we can just remove the resistors.

Anyway, thank you for your patience and help!

Best regards,

Hikaru