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TPS63031: Inductor selection recommendation

MAURICIO VIDAL
Intellectual 260 points
Part Number: TPS63031
Other Parts Discussed in Thread: TPS63051, TPS63802

Hi guys:

I'm making a final revision of a design where ( with the help of @Milos ) the TPS63031 has been selected to regulate the voltage of the device whose purpose is to be as efficient as possible when operating on batteries with nominal voltage of 3.25 to 3.3V. When the device is charging from USB we are not that much interested on efficiency.

From the conversor datasheet, to calculate the "minimum saturation current of the inductor needed" according to the formula presented there, I selected 3V (almost depleted battery), as the minimum input voltage at the conversor, even most of the time it operates at 3.25V. I also selected Iout 500mA as this is the biggest current draw from the conversor (compared to just a couple of mA most of the time, when the circuit is idle).

Then having VIN: 3, VOUT: 3.3, Iout: 500mA, f: 2.500.000, L: 0.0000015 and n: 75% (the conversor efficiency from the graph when providing about 500mA). I get a about 0.92A for the iPEAK (which includes the extra 20% that TI recommends).

Naturally the LPS3015-152MR that the datasheet mentions (I wasn't able to find the LPS3015-1R5, maybe it is a typo), serves here.

However, I have compared it to others I found on the forum and other places, including factors like price and the "DC resistance", which the lower, the better efficiency according to the stated on the datasheet (even I have no clue about the amount of improvement it can provide).

Here is a preliminar selection:

LPS3015-152MR: Coilcraft, DCR: 0.100 ohms, 1.7A, Price: USD 1.14 (The recommended on the datasheet)

XFL4020-152ME: Coilcraft, DCR: 0.014 ohms. 9.1A, Price: USD 1.99

LQH3NPN1R5MJRL: Murata, DCR: 0.049 ohms, 1.1A, Price: USD 0.42

LQH3NPZ1R5MGRL: Murata, DCR: 0.074 ohms, 2.04A, Price: USD 0.44

CIGW252010GL1R5MNE: Samsung, DCR: 0.054 ohms, 3.2A, Price: USD 0.21

1269AS-H-1R5M=P2: Murata, DCR: 0.108 ohm, 2.1A, Price: USD 0.42 (Recommended on the datasheet of the TPS63051)

Then, all being able to provide that iPEAK 0.92 of my circuit, it seems the best choice is the 2nd in the list for having the lowest DCR. But it is quite expensive compared the the cheapest, the one from Samsung, which has almost half of the DRC of the recommended on the datasheet. Sadly, I don't know how to determine the impact of that DRC and if it's worth the price difference. However the Samsung and the last on the list, are "encapsulated chips" (their form factor is different from the others), and I don't know if that's something that should be considered on this selection or if there other factors I'm not aware of.

Could you please give me a recommendation on the inductor selection (even from other sources) based mainly for the best efficiency when operating on batteries at 3.25 to 3.3V and the described consumption?

I appreciate your help.

Thank you!

  • 0
    TI__Mastermind 20900 points

    Hello Mauricio,

    the inductor from Samsung is good. You won't loose a lot on efficiency as the switches have a much higher DCR.

    Here are some alternatives:

    Murata 1226AS-H-1R5N=P2

    Murata 1227AS-H-1R5N=P2, i would recommend this one.

    Abracon ASPI-0628-3R0N-T1

    Regards,

    Julian

  • 0 in reply to Julian Hagedorn
    Intellectual 260 points

    Julian,

    Thank you for your response.

    Comparing the DCR of the switches to the DCR of the inductors gave me a good reference. From the datasheet, and assuming the "High-side switch ON-resistance" and "Low-side switch ON-resistance" are the specs that are the ones to look at, both are 200 mOhms for this conversor.

    Regarding the 1227AS-H-1R5N=P2 I would like to learn in which way it could be more appealing than the others. I've found that its 1.5uH inductance is tested at a frequency of 100Khz while the others on my original selection have that inductance, but tested at 1Mhz. (To note they have inductance tolerances of +-30% and +-20% respectively). Can be the reason that your recommended this inductor that - regulating 3.25 to 3.3 - the "duty" of the conversor is closer to 100Khz than to 1Mhz?. I say this, assuming that the conversor dutty at 3.25V would be about 1.5% of the 2.5 Mhz which is about 37 Khz. Am I correct?

    One last question. The last one part on your list is a 3 uH inductance device. Is there a reason for preferring a higher inductance in my case?

    Thank you again Julian.

  • 0 in reply to MAURICIO VIDAL
    TI__Mastermind 20900 points

    Hello Mauricio,

    you picked the correct datasheet parameter.

    I recommended the 1227AS-H-1R5N=P2 as it fulfills the needs. It has low DCR, comes in small size, has good enough current ratings and it is low cost.

    If efficiency is of concern then the TPS63051 has a better efficiency compared to TPS63031. Another high efficiency part is TPS63802.

    regards,

    Julian

  • 0 in reply to Julian Hagedorn
    Intellectual 260 points

    Thank you for your response Julian.

    Best regards,

    Mauricio