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Original question:

TPSM82823: Availability

TPSM82823: External Component selection

Shmuel Davis
Expert 2930 points
Part Number: TPSM82823

We are interested in the TPSM8282 family. In Table 9-1. List of Components : Can C3 Ceramic capacitor, 120 pF, 50 V, size (0603) - its size be reduced to 0402 ?

Also for C2 ==> Ceramic capacitor, 1 × 22 μF, 6.3 V, X6S, size (0603), JMK107BC6226MA-T - can this be reduced to 0402 like it is in Table 9-2. List of Components ? If no - what is the difference ?

Could you please also explain how you managed to make a part that is rated @1A, 2A & 3A in the same package AND without changing any of the external components ?

  • 0
    TI__Mastermind 21580 points

    Hi Shmuel,

    The important thing to check is that you have enough effective capacitance when using the 0402 size. C3 and C2 can be in 0402 if the effective capacitance meets the requirement in the datasheet.

    In table 9.2, C2 is already in 0402, since this is the fixed VOUT version, where a small solution size is more important. The 0603 will usually have a higher effective capacitance than 0402 and provide a bit better load transient performance.

    The device was designed to support 3A output current. The different current versions are produced by programming the current limit to different values.

    Best regards,

    Varun

  • 0
    Expert 2930 points

    Dear Varun,

    Thank you for your reply ! 

    I have a TPSM82823EVM-080 evaluation board and noticed it has a large CAP, CERM, 47 µF, 10 V, ±20%, X7R, 1210 ! Are we also going have to use such large Cap also on our design ? I couldn' t find such a requirement in the data sheet ?

    Best regards

    Shmuel 

  • 0 in reply to Shmuel Davis
    TI__Mastermind 21580 points

    Hi Shmuel,

    You don't need that in your design. You just need the minimum input cap described in the datasheet. The large 47 uF cap on the EVM is because the EVM is usually powered on by an external bench top power supply through a cable. The cable inductance can prevent the external power supply from reacting to sudden input voltage dips from regular device switching and specially tests like load transients. That's why the big 47uF cap is kept on the input side of the EVM to keep the supply stable.

    Best regards,

    Varun

  • 0
    Expert 2930 points

    Dear Varun,

    Thanks for getting back to me on this !

    For Vout = 3.3V I have chosen R1 = 162K & R2 = 36K. From the data sheets I calculated that C3 = 333pF. We have a 330pF stocked (0402, 50V, X7R) - Can I assume that this is acceptable ? Is it better to have a higher or lower value for C3 ? Since I checked the effective capacitance of this stocked part and  the lowest drop of capacitance I found was that at 85 degC the capacitance could drop as low as 318pF ? Should I try to get a capacitor with a higher value ? The problem is at  lower temperatures the capacitor will be close to the actual rated value ?

    The next available value that I could get is 390pF is this preferable ?  @85 degC the capacitance will drop to as low as 370pF but @30degC the Cap = 387pF. If neither of these are acceptable I may have to go up in size of package ?! 

    Best regards

    Shmuel 

  • 0 in reply to Shmuel Davis
    TI__Mastermind 21580 points

    Hi Shmuel,

    The 330pF (0402, 50V,X7R) should be fine. The change in capacitance to 318pF at 85C is not that drastic to cause the device to operate wrong.

    Best regards,

    Varun

  • 0 in reply to Varun John
    Expert 2930 points

    Dear Varun,

    Thank you so much for getting back to me on this one ! 

    For our Vout=2.5V supply I have chosen => R2 = 3.16K which calculates ==> C3 = 3.8nF,

    We have in stock a : CL05B472KB5NNNC (4.7nF, 0402, 50V, X7R), the greatest loss of CAP is @ 85DegC => approx. 4.47nF

    Is this acceptable or should I go and buy 

    A CL05B392KB5NNNC (3.9nF, 0402, 50V, X7R) which has the greatest loss of CAP is @ 85DegC => approx. 3.86nF ?

    Best regards

    Shmuel 

  • 0 in reply to Shmuel Davis
    TI__Mastermind 21580 points

    Hi Shmuel,

    Yes I think the 4.7nF is acceptable. You can use that.

    Best regards,

    Varun