• State Resolved
  • Locked Locked
  • Replies 7 replies
  • Answers 1 answer
  • Subscribers 49 subscribers
  • Views 369 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.

LM319-N: Slew Rate

ttd
Mastermind 7900 points
Part Number: LM319-N
Dear Technical Support Team,
Could you check if LM319 has a slew rate that works with a 10MHz input?
The input voltage is about -1 to 5.0V and output connects to FPGA with pullup.
Best Regards,
ttd
  • +1
    Guru 140200 points

    Hi TTD,

    have you had a look at the response time figures in the datasheet of LM319-N? From these I would say that the LM319-N cannot safely handle 10MHz.

    Kai

  • 0 in reply to kai klaas69
    TI__Genius 11701 points

    Thanks Kai.

    TTD,

    LM319 does not have the speed capability to handle a 10 MHz input. Sorry we do not currently have a device that have a similar output structure as LM319 with better speed. We have reached out to your FAE offline regarding a new development, however. 

    -Chi

  • 0 in reply to Chi Nguyen1
    Mastermind 7900 points

    Hi Kai and Chi,

    Thank you for your reply. 

    In fact, how is the speed capability with OC? Response times of rising and falling edge input are max 80ns. it seems yo be under 6.25MHz（totally 160ns）from simple math. I guess that it would be under 5MHz.

    Chi, I got new information from FAE. Thank you for your support.

    Best Regards

    ttd

  • +1 in reply to ttd
    TI__Genius 11701 points

    Hi TTD,

    Thanks for the follow up. Max toggle frequency is 1/(tpdlh + trise + tpdhl + tfall) so yes under 4-5 MHz is a good estimate.

    -Chi

  • +1 in reply to ttd
    Guru 140200 points

    Hi TTD,

    if your pull-up is high ohmic, another time constant being formed by parasitic capacitances (input capacitance of FPGA, output capacitance of LM319-N and board stray capacitance) comes into play furtherly decreasing the speed. With a 10k and 10pF parasitic capacitance this time constant would be 10k x 10pF = 100ns. That's the reason why the pull-up resistor should be chosen rather small and why the timing specs of LM319-N are given in the datasheet for a 500R pull-up.

    Furtherly decreasing the pull-up resistance, on the other hand, can again decrease the speed because the output stage has to switch a much higher current then - and, of course, would unwantedly increase the supply current.

    Kai

  • 0 in reply to Chi Nguyen1
    Mastermind 7900 points

    Hi,

    How is the response time to be satisfied  with 10MHz?

    tpdlh + trise + tpdhl + tfall < 100ns is required for 10MHz. 

    I guess that it should be 30～40ns(plus trise/tfall and pullup).

    Best Regards,

    ttd

  • +1 in reply to ttd
    TI__Genius 11701 points

    Hi TTD, 

    Yes around 30 ns would be a fair estimate but that is also dependent on the trise/tfall and the size of your pullup as you and kai mentioned. Though I would refrain from using a device at its max toggle frequency and choose a device with a tpd << 30 ns to be safe.

    -Chi