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LM555: Asking for the LM555 design application issues

SHH
Mastermind 32696 points

Part Number: LM555


Hi Team,

cusotmer implement LM555 on the application..
And cusotmer found the PWM waveform and Duty cycle are are as expected.

Could you please help for the issues?

(1) PWM waveform issue : the waveform doesn’t really to 0V. and it have Overshot and Undershot.
(2) Duty issue:
cusotmer's requirement is F=25K and D=15%(High:15%; Low: 85%) .
The actual waveform show F=22.45K/ 21.76K, D= about 85%(High)

Please provide your comment for the issues.
Thank you!!

here is the review post

Thanks,
SHH

  • 0
    TI__Guru**** 174826 points
    SHH,

    There appears to be an external short on the LM555 output pin. the low output level should be much closer to ground.
    Are the waveforms taken on pin 3? The output high time is 85% and low time 15%. I mentioned that at least twice in the other post.

    With a 15V VCC the LM555 can sink up to 200mA, at 5V the maximum sink current is much less. See figures 4,5,6 in data sheet.