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Original question:

TPS3808: Delay Time

TPS3808E: Minimal capacitor at CT pin

Patrick Ruf
Genius 4965 points
Part Number: TPS3808E
Other Parts Discussed in Thread: TPS3808

Tool/software:

Hi,

In the datasheet of the TPS3808E device it is written on page 4 under the CT pin description that a capacitor >= 130pF is needed for a user programmable delay.
On page 12 it is written capacitor >= 100pF is needed for a user programmable delay.
What is the correct value?

If it is 100pF, is the device designed to allow a 100pF capacitor on this pin? Means is there an additional tolerance band calculated for the capacitor device?
Or is the limit strictly 100pF?

Thanks and best regards,
Patrick

  • 0
    TI__Genius 9900 points

    Hi Patrick,

    Thanks for highlighting there are 2 different values in the datasheet. 

    The minimum capacitor for TPS3808E CT pin is 130 pF. 

    Best,

    Sila Atalar  

  • 0 in reply to Sila Atalar
    Genius 4965 points

    Hi Sila,

    If minimum capacitor at CT pin is 130pF it would not make sense that TPS3808E is a drop-in replacement for the TPS3808 that has a minimum capacitor of 100pF as stated on the website. That in fact confuses me quite a lot. Can you please clarify this again with the design specialists of the TPS3808E.

    And this leads to my second question:
    If it is 100pF, is the device designed to allow a 100pF capacitor on this pin? Means is there an additional tolerance band calculated for the capacitor device?
    Or is the limit strictly 100pF?
    Can you please give me an answer to those questions as well. You can also answer those questions for the TPS3808.

    Regards,
    Patrick

  • 0 in reply to Patrick Ruf
    TI__Genius 9900 points

    Hi Patrick, 

    Thanks for your follow up. The datasheet should have enough information for customers/designers to decide if they can use the IC in their system or not. I already checked with my team to see what is the min cap for TPS3808E, and I already reply your question in above. 

    Even if there are minor changes device to device, the timing performance, and overall power consumption are matching for TPS3808E and TPS3808 to P2P. Please feel free to use them if you were using TPS3808 and switch to TPS3808E in your current design. 

    Best,

    Sila