LM4120: Output Capacitor ESR

Victor Miranda1

Part Number: LM4120
Other Parts Discussed in Thread: PMP21629, REF3112, ADC128S102

Hi,

I've selected LM4120 for my application and I have a question regarding the output capacitor ESR.

The datasheet for this device states the following:

The PMP21629 reference design is using a 0.047uF GRM155R71E473KA88D capacitor from Murata, and its ESR characteristic is depicted in the picture below.

(refer to Murata SimSurfing tool at https://www.murata.com/support/faqs/products/capacitor/mlcc/char/0016)

Is this part selection correct per LM4120 datasheet advise, where "these capacitors typically have an ESR of about 0.1 Ω to 0.5 Ω. Smaller ESR can be tolerated, but larger ESR cannot be tolerated."?

Which frequency range should be taken into account?

Thanks in advance.

Regards,

Victor

over 4 years ago

0 Victor Miranda1 over 4 years ago

Prodigy 60 points

Resending the broken attachments

1) ESR info from LM4120 datasheet

2) GRM155R71E473KA88D ESR

0 Marcoo Z over 4 years ago in reply to Victor Miranda1

TI__Mastermind 19550 points

Hi Victor,

Most of the time the frequency of interest is at the resonance point for this type of application since it is the worst case.

The LM4120 was designed to be stable with a ESR range of 0.1 Ω to 0.5 Ω. I would recommend to use a MLCC or a MLCC + 0.1 ESR resistor.

I would stay away from capacitors with high internal ESR.

0 Victor Miranda1 over 4 years ago in reply to Marcoo Z

Prodigy 60 points

Hi Marcoo

What I didn't get was how GRM155R71E473KA88D (an MLCC capacitor used in TI's PMP21629 reference design) meets the ESR requirement as I have no clue what the resonance point is for a voltage reference like LM4120 (hope it is >100kHz)?

Thanks,

Victor

0 Marcoo Z over 4 years ago in reply to Victor Miranda1

TI__Mastermind 19550 points

Hi Victor,

The datasheet mentions a smaller ESR can be tolerated. It could be for this TI design the LM4120 works with that capacitor + parasitic resistances.

I would still recommend to add ESR to meet the datasheet standards.

What is your driving motive to use the LM4120?

It is a solid device but the capacitor limitation can be restrictive for designs that need larger output capacitors.

Have you considered recommend using a REF3112 for better performance and not have to deal with the ESR of the capacitors.

0 Victor Miranda1 over 4 years ago in reply to Marcoo Z

Prodigy 60 points

Hi Marcoo,

Great. Actually, the ADC128S102 reference design uses LM4120. I'll look into REF3112 as well.

Thanks,

Victor

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LM4120: Output Capacitor ESR