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LM2936: Output Capacitor Selection

David Schanin
Intellectual 270 points
Part Number: LM2936
Other Parts Discussed in Thread: DRV8313EVM, , DRV8313

The data sheet for this part on Page 15, paragraph 8.2.2.2 spec's that the output cap needs to be tantalum (based on requirements) but it goes on to say a ceramic MLCC can be used with a series resistor of 500mOhm to 1Ohm.  However, the development board DRV8313EVM, which appears to be the only eval board with this part, shows in the schematic DRV8313EVM_SCH the use of a TDK ceramic cap C2012X7R1A106M without such a series resistor.  Is this in fact a proper application of a ceramic capacitor, and in specific this TDK cap?  Reason for this question is that as we all know tantalum cap prices are sky high and this ceramic cap is much cheaper, and the PCB is lay'd out without this series resistor.  So I am looking for guidance here as to whether I need to change the PCB layout.  The tantalum based application has worked flawlessly in fielded units.  Thanks in advance.

  • 0
    TI__Mastermind 23361 points

    Hi David, 

    I checked the ESR for the TDK cap that is used in DRV8313EVM, the ESR is not meeting the requirement from the LM2936 datasheet. Please allow 2 business days for me to investigate if you really need to change your design. 

    Regards, 
    Jason Song

  • 0 in reply to Jason Song
    Intellectual 270 points

    Jason - thank you very much.  I look forward to your input.

  • 0 in reply to David Schanin
    TI__Mastermind 23361 points

    Hi David, 

    We had a discussion here about this issue. LM2936 does require to have a series resistor with the output capacitor to make sure it meets the stability requirement at all conditions. The DRV8313 Evaluation Module does not meet this requirement and should be used as an example. 

    For stability related issues,  it's normally marginal and may only happen at certain conditions. If you already have your boards built, you can validate the part to see without a series resistor if the LDO can still meet your application requirement. Here is an app note that covers the topic of how to conduct LDO stability checks using load transients. 

    We would recommend revising the boards to add the series resistor as datasheet suggested. Hope this helps. 

    Regards, 

    Jason Song