• State TI Thinks Resolved
  • Locked Locked
  • Replies 6 replies
  • Answers 3 answers
  • Subscribers 31 subscribers
  • Views 242 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

TAS5722L: Passive Selection

Daniel De Sousa
Intellectual 580 points
Part Number: TAS5722L

Hi there, we had some questions regarding TAS5722L passive selection:

Input bulk capacitance:

Section 8.2 shows 2 x 100 uF electrolytic capacitors

Section 8.2.2.4 refers to them

The evaluation kit uses 2 x 47 uF electrolytic

Questions:

- How do we find out how much capacitance is needed for our application? Our PVDD is quite low (5V0) and we want to conserve board space as much as possible

- Why are electrolytic capacitors used instead of ceramics? 

Output filter:

The datasheet does not mention the design of any output filters. Section 8.2 demonstrates a filterless design

The evaluation kit uses ferrite beads on the output

Questions:

- How do we know whether a filter is needed or not?

- How should we go ahead on designing this filter? 

  • 0
    TI__Mastermind 36680 points

     Hi Daniel

         The minimum working voltage is 4.5V, actually we don't recommend you to use 5V PVDD, there always ripple voltage when the device start playing.

         The value for input capacitance will influence the ripple voltage, check how much ripple you can accept. Large ripple will also influence the THD performance. As for electrolytic capacitors, I don't think ceramic capacitor can give out a real large value easily, like 100uF, can they? You can compare the cost and decide.

         You can use 4.7uH and 0.68uF as the output filter. If you don't care about the EMC performance, you can also choose a 300Ω@100MHz ferrite beads instead of the inductor.

  • 0 in reply to Shadow He
    Intellectual 580 points

    Hi there,

    Thanks for your response. We would like to use this device at 5V0 and we should never see a voltage below 4.5V anyways as other devices on this rail will also start to have problems. If we can ensure that the voltage does not go below 4.5V, can we use 5V0 PVDD?

    Do you have any formulas or advice on determining a starting value for the needed capacitance? 

    Section 8.2.2.4 refers to the fact that the device has very high PSRR meaning that ripple on the input should not be a problem. Please clarify.

    It looks like Murata manufacturers 1206 ceramic capacitors with 47, 100, 220 uF capacitance. Is there any downsides to using ceramics? Is it just cost?

    How did you come up with the values for the filter?

    Thanks

  • 0 in reply to Daniel De Sousa
    TI__Mastermind 36680 points

     Hi Daniel

    Daniel De Sousa said:
    If we can ensure that the voltage does not go below 4.5V, can we use 5V0 PVDD?

    Yes, you can.

    Daniel De Sousa said:
    Do you have any formulas or advice on determining a starting value for the needed capacitance? 

    No formulas about it.

    Daniel De Sousa said:
    ripple on the input should not be a problem. Please clarify.

    Ripple won't harm the device, only cause THD worse.

    Daniel De Sousa said:
    Is there any downsides to using ceramics? Is it just cost?

    It's OK to use ceramics.

    Daniel De Sousa said:
    How did you come up with the values for the filter?

    It's a filter value we generally use, have a better EMC performance, also won't harm the sound band.

  • 0 in reply to Shadow He
    Intellectual 580 points

    Thank you.

    With regards to your comment "you can also choose a 300Ω@100MHz ferrite beads instead of the inductor." - why did you decide on 300 ohms whereas the eval uses 180 ohms?

    What is the impact of having worse THD in our system?

  • 0 in reply to Daniel De Sousa
    TI__Genius 14480 points

    Hello Daniel,

    300ohm impedance @100MHz is the common recommendation for EMI concerns but using the Ferrite bead we use in the EVM is also suitable. Worse THD  impacts sound quality so you would need to determine if the audio performance is suitable given your system requirements, it might be given your application but that's something you would need to verify in your own system.

    best regards,

    Luis

  • 0 in reply to Luis Fernandes de Pina
    Intellectual 580 points

    Thanks - we will use NFZ2MSM181SN10L for now.