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TPS7A90: Input and Output capacitors value

Oba
Genius 15750 points
Part Number: TPS7A90

Hello,

TPS7A90 datasheet(SBVS324) recommends to use ceramic capacitors of 10uF or greater at the input and output.

And there is also the below description on 8.1.3 Capacitor Recommendation.
 

“The TPS7A90 is designed to be stable using low equivalent series resistance (ESR) ceramic capacitors at the

input, output, and noise-reduction pin. Multilayer ceramic capacitors are the industry standard for these types of

applications and are recommended, but must be used with good understanding of their limitations. Ceramic

capacitors that employ X7R-, X5R-, and COG-rated dielectric materials provide relatively good capacitive stability

across temperature, whereas the use of Y5V-rated capacitors is discouraged precisely because the capacitance

varies so widely. In all cases, ceramic capacitors vary a great deal with operating voltage and temperature and

the design engineer must be aware of these characteristics. As a rule of thumb, ceramic capacitors are

recommended to be derated by 50%. The input and output capacitors recommended herein account for a

capacitance derating of 50%.”

 

So does that mean user can use 10uF with X7R, X5R or COG rated?

Or does that mean user should use 15uF with X7R, X5R or COG rated?

I also have another question.
Where does this 10uF for both input and output come from? My customer feels it is a little bit large capacitor.
Would it cause unstable issue if using less than 10uF? 

Regards,
Oba

  • 0
    TI__Mastermind 23361 points

    Hi Oba,

    TPS7A90 requires to have input and output capacitors with 10uF or greater to be stable. The following statement in the datasheet is trying to explain the difference between capacitors and capacitance: "The input and output capacitors recommended herein account for a capacitance derating of 50%." For example, one capacitor being labeled for "10uF" but in the application, the capacitor may only provide 50% of 10uF which is 5uF capacitance with the derating at different voltage and temperature conditions. X7R, X5R and COG are the common ones that have relative stable capacitance value across different conditions and the minimum values required for those capacitors are 10uF. In term of effective capacitance, TPS7A90 requires a minimum 5uF capacitance to make it stable across conditions in the application.

    Different designs have different requirements for input and output capacitors. In LDO designs, there are multiple control loops and certain loops may require compensations. Usually, those recommended input and output capacitor values are decided at design and then being verified and tested during validation across different conditions and temperatures. We would always suggest customers use the devices under the recommended conditions. Having less than required capacitance may make the devices unstable during certain load/line transients conditions. If you share more details on your customer's application, we may find you an LDO that requires less capacitance on input and output to be stable. 

    you can find more information on capacitors vs capacitance here:

    Regards,
    Jason Song