• State
  • Locked Locked
  • Replies 5 replies
  • Subscribers 31 subscribers
  • Views 1040 views
  • Users 0 members are here
Support feedback
Options
Options
Related

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.

DRV104 application in DC mode and PWM mode

Jian Chen44
Prodigy 30 points
Other Parts Discussed in Thread: DRV104

Hi,

By using DRV104 to drive,  my question is how long the OFF time needed in order to get designed delay time from DC mode to PWM mode.

 

This is our circuit design.

 

A 1uF capacitor connected to Delay Adju pin, so the DC to PWM delay will be  1/1.24 = 800mSec.

 

It is correct in single ON run, 780msec is near 800msec designed timing.

 

 

But if the off duration is shorter, It will not get 800msec delay; For example in below oscilloscope wave form, the time of DC is only 392msec.

 

 

  • 0
    TI__Guru** 114905 points
    Hi Jian,

    Our experts have been notified and should reply soon.
  • 0
    TI__Guru* 93105 points

    Hello Jian,

    I would not expect the DRV104 delay time to vary that much between one activation to the next. Most timings associated with the DRV104 are in the microseconds, or a little longer. You should be able to drive the input low ending the current delay or PWM output, and after a short time restart the next delay period in the cycle. A change from 800 ms to about 400 ms sounds rather extreme and I've never heard of such behavior with the DRV104.

    Can you provide your circuit, supply and load conditions? Also, how is the device being heat-sinked?

    Regards, Thomas

    PA - Linear Applications Engineering

  • 0 in reply to Thomas Kuehl
    Prodigy 30 points
    Hi Thomas,

    This is my 2nd time to send infor to you.

    Normally when on the driver, it will output DC, then after a delay (in this case is 800msec.) it goes into PWM mode. We do not have problem in below 2 conditions:
    1. in DC mode, no matter off how long, once on again, it will output in DC mode;
    2. in PWM mode, if off time is long enough, say longer than 30msec, it will output DC once on again.

    The problem is it is in PWM mode and the off time is too short, say less than 10msec, it will directly go into PWM mode once on again.
    We use it to drive pneumatic valve, the working current is about 30mA; the output in DC mode is 24Vdc. There is not heat-sink for the chip, but it is not hot. And this issue is repeatable any time even at 2nd on cycle.

    I attached circuit design in below. Let me know you are not able to see it. I have attached circuit and oscilloscope wave form in my question. Did you see them?

    Thank you very much!

    Best Regards,
    Jian
  • 0 in reply to Jian Chen44
    Prodigy 30 points

    here is the circuit

  • 0 in reply to Jian Chen44
    TI__Guru* 93105 points

    Jian,

    I was on business travel last week and unable to address the forum. Your schematic and DSO images did not appear, please repost them. Have you observed this behavior on one, or all, DRV104 devices that you have evaluated? You mention that you did not use a heat-sink with the DRV104; did you electrically connect the underside PowerPad to GND? Please provide information about the pneumatic valve used as the load.

    Regards, Thomas

    PA - Linear Applicaitons Engineering