LMR61428 - output capacitance

Hirotaka Matsumoto

Other Parts Discussed in Thread: LMR61428

Hi all

Would you mind if we ask LMR61428?

The datasheet shows the following;
While tantalum chip capacitors are recommended for the input and output filter capacitors, ceramic caps can also be used.

Is it possible to use 47uF x 2 ceramic capacitances for output capacitance?
Is there define about ESR for output capacitance? Only "Very high ESR values (>3Ω) should be avoided."?

Kind regards,

Hirotaka Matsumoto

over 8 years ago

0 Hirotaka Matsumoto over 8 years ago

Guru 27585 points

Hi team

We guess that your team is so busy, however could you give us the reply?

Kind regards,

Hirotaka Matsumoto

0 Akshay Mehta over 8 years ago

TI__Genius 15810 points

Hello,
The easiest approach will be to follow Webench's suggestion. The LMR61428 operates on a fixed duty cycle of 70% and has bursts of switching. The VOUT is maintained within an acceptable ripple using internal comparators. Capacitors with too much ESR will cause larger voltage ripples.
Regards,
Akshay

0 Hirotaka Matsumoto over 8 years ago in reply to Akshay Mehta

Guru 27585 points

Akshay san

Thank you for your reply always!
We would like to confrim as follows;

<Point1>
There is no the definition about lower limit ESR on the datasheet, right?

<Point2>
Ceramic capacitance is available for output caps, right?

<Point3>
On Webench simulation, it recommends to use ESR range 0.06ohm to 0.1ohm.
And we simulated with ESR=0.003ohm(using part edits), however there was no problem.
The easiest approach will be to follow Webench's suggestion, right?

We need your help.

Kind regards,

Hirotaka Matsumoto

0 Hirotaka Matsumoto over 8 years ago in reply to Hirotaka Matsumoto

Guru 27585 points

Akshay san

Could you give us some advice?

Kind regards,

Hirotaka Matsumoto

0 Akshay Mehta over 8 years ago in reply to Hirotaka Matsumoto

TI__Genius 15810 points

Hello,
I apologize for the delayed response.
Datasheet doesn't have a lower limit on the ESR. The easiest would be either follow Webench's suggestion or go with the 68uF tantalum cap suggestion from the datasheet.
Regards,
Akshay

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LMR61428 - output capacitance