topic PMIC MMPF0100Z inductor selection in i.MX Processors

PMIC MMPF0100Z inductor selection

vinodhodal — Fri, 04 Dec 2015 08:10:52 GMT

Hi,

From MMPF0100Z datasheet section 8.1.2 Bill of material selected inductor saturation current value is 4.5Amp for BUCK, SW1AB - (0.300-1.875 V), 2.5 A.

It seems that this current rating much overrated?

For a buck convertor with VIN = VINSW1x = 3.6 V, VSW1x = 1.2 V, ISW1AB= 2.5A, Eff= 80%, Fsw=2Mhz

is 0.5A. Thus Peak inductor current is 2.5+(0.5/2)=2.75A only.

Considering 30% derating 3.6Amp saturation current inductor should be OK.

Please let us know is this OK to select a inductor part as per above calculation. This is to reduce overall PMIC supply cost as our current requirement is much lesser than current available on each buck converter of PMIC.

Regards

Vinod

Re: PMIC MMPF0100Z inductor selection

david_diaz — Tue, 08 Dec 2015 21:24:54 GMT

Hello Vinod,

As you mentioned, the inductor value is chosen based on the desired ripple current.

Your calculations are right. I do not see any inconvenience if you choose the inductor mentioned at the datasheet in order to reduce costs:

I hope this information will be useful for you.

If I misunderstood your question, feel free to let me know. I will be glad to help.

Have a great day.

David Diaz.

Re: PMIC MMPF0100Z inductor selection

vinodhodal — Wed, 09 Dec 2015 06:47:21 GMT

Hi David,

1.From the datasheet 3.6 Amp inductor is optional and 4.5Amp is required. Why it is so?

2.If we see SABRE-AI_DualLite_CPUcard schematic MCIMX6DLAICPU1.

This schematic uses only 2.65Amp (L7, L6) inductor. From above calculation these inductor will get saturated and also this value is much lesser than recommended values in datasheet.

3. We are using SW2 to power VDD_HIGH_IN only.Since VDD_HIGH_IN have only 125mA requirement thus an inductor of 500mA would be also OK. Please confirm

regards

Vinod Sharma

Re: PMIC MMPF0100Z inductor selection

david_diaz — Thu, 10 Dec 2015 18:27:57 GMT

Hello Vinod,

Please note that SW1/A/B/C are 2.5 to 4.5A buck regulators that can be configured in various phasing schemes, depending on the desired cost/performance trade-offs. The following configurations are available:

• SW1A/B/C single phase with one inductor

• SW1A/B as a single phase with one inductor and SW1C in independent mode with one inductor

• SW1A/B as a dual phase with two inductors and SW1C in independent mode with one inductor

In this case, you pretend to use the buck regulator as follow: SW1AB.

It means that, based on the inductor value calculated, the optional 3.6A inductor is enough for your application.

In the other hand, if you pretend to use the SW1ABC configuration, the 4.5A inductor will be necessary.

In regard with your last question, indeed, the 500mA inductor would be great.

I hope this information will be useful for you.

If I misunderstood your question, feel free to let me know. I will be glad to help.

Have a great day.

David Diaz.

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