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TPS3813-Q1: Window time (typcal) value

Yusuke Mukuno
Expert 7395 points
Part Number: TPS3813-Q1

Hi expert,

Customer is testing t_window as thier production test. 

Use case : Programable window time,  external capacitor 180pF +/-5%

From datasheet  calculation for typical value is 78.6ms.

From datasheet calculation for minimum value is 56.2ms.

The avarage of tested data is 68.2ms 

the tested data are near minimum calculation limit than typical calculation value

(From datasheet)

Could you please give me your advice for the reason of thie shifted value?

- it come from device variation? originally tends to be biased toward the lower limit?

- if they use small capacitance, the typical value from datasheet will shift, due to internal characteristic?

- or, capacitor characteristics for acutual capacitance?

etc

Thanks

Muk

  • 0
    TI__Genius 13140 points

    Hi Muk,

    How much do you estimate that the capacitor's value is derating? The nominal value is always a bit higher than capacitance seen in the application unless you are using a stable type capacitor (C0G/NP0).

    Thanks,

    Andrew  

  • 0 in reply to Andrew Kutzler
    TI__Expert 7395 points

    Andrew-san,

    Thank you for your supporting.

    Customer checked capacitor characteristic. From datasheet, it will be +/- 5% even if they consider temp characteristic and DC bias etc.

    Also,  if they calculate with -5% capacitor, the typ value will be 75ms. 

    They believe, this issue is not affected from capacitor characteristic.

    Do you have any other possible factors or your experience?

    .

    Thanks

    muk

  • 0 in reply to Yusuke Mukuno
    TI__Genius 13140 points

    Hi Mukuno-san,

    The spec you see in the DS only pertains to an ideal capacitor. Even if the nominal value is only varying ± 5%, there's other factors you have to consider like the capacitor parasitics, resistance of the trace on the PCB, how close the capacitor is the TPS3813-Q1, temperature, etc. Because of this we cannot guarantee the spec in the DS with an external capacitor.

    From your data, it looks like though the device is behaving as expected.

    Thanks,

    Andrew