Slew Rate Control

Discussion in 'General Electronics Chat' started by jmbdr03, Feb 22, 2012.

  1. jmbdr03

    Thread Starter New Member

    Feb 22, 2012
    7
    0
    Why do we need to reduce/control slew rates in ICs? i really don't know why some ICs have that feature. Thanks!
     
  2. hgmjr

    Moderator

    Jan 28, 2005
    9,030
    214
    What particular IC do you have in mind as an example of one that controls the slew-rate?

    hgmjr
     
  3. jmbdr03

    Thread Starter New Member

    Feb 22, 2012
    7
    0
    AD5422, 16bit current/voltage source DAC.
     
  4. hgmjr

    Moderator

    Jan 28, 2005
    9,030
    214
    Interesting device. I suspect the slew rate control is there to minimize ringing on the output of the DAC under certain load conditions. You did notice that the slew-rate control can be turned off.

    I have not had the need to use any devices that offered slew-rate control in my 40 year circuit design career.

    hgmjr
     
  5. jmbdr03

    Thread Starter New Member

    Feb 22, 2012
    7
    0
    default setting is it is turned off, so if you don't do anything it will still be at it's maximum slew rate. Did you suspect that it can affect other devices through EMI?

    Thanks hgmjr
     
  6. Brownout

    Well-Known Member

    Jan 10, 2012
    2,375
    998
    It's possible. A bigger danger is overshoot that might be higher than the voltage rating of connected components. If you have long connecting lines, that danger is greater.
     
  7. hgmjr

    Moderator

    Jan 28, 2005
    9,030
    214
    No, not really. Rather than EMI problems, I would expect that if the slew-rate is not limited then there is likely to be ringing on the output if the load is inductive.

    hgmjr
     
  8. MrChips

    Moderator

    Oct 2, 2009
    12,449
    3,365
    Bus and interface drivers such as RS-232, RS-422, RS-485, USB etc. all have to control the slew rate otherwise you can have excessive ringing which can corrupt the data being transmitted. Similarly, if the output of a video DAC drives a video monitor you do not want ringing on the transitions. It doesn't matter if the load is inductive or not. If the line is not properly terminated you will get reflections.
     
  9. jmbdr03

    Thread Starter New Member

    Feb 22, 2012
    7
    0
    can anybody give me any article i can read about ringing caused by inductive loads? thanks!
     
  10. MrChips

    Moderator

    Oct 2, 2009
    12,449
    3,365
  11. Brownout

    Well-Known Member

    Jan 10, 2012
    2,375
    998
    The problem is both, actually. Reactive loads or connecting members have a natural frequency. Typically the frequency is in the RF spectrum, and fast slew rates can excite the network, causing ringing. Long connecting lines and stray capacitance can cause ringing. Careful layout is the first line of defense. Controlling slew rate can help too.
     
  12. MrChips

    Moderator

    Oct 2, 2009
    12,449
    3,365
    Ok, I concede. Presumably the op is using the DAC to drive a connection cable to a capacitive load. So the problem is not as much board layout as proper cable termination.
     
  13. jmbdr03

    Thread Starter New Member

    Feb 22, 2012
    7
    0
    thanks for help guys!
     
Loading...