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CD40106B: Whether the threshold Voltage will impact frequency

Mirthunraju M
Prodigy 220 points
Part Number: CD40106B

Hi,

Need you confirmation, Whether the threshold Voltage will impact the output frequency of Astable Multivibrator?

also confirm the Threshold Voltage value of CD40106 according to the below mention graph,

Regards,

Mirthunraju M

  • 0
    Guru 261430 points

    Yes, the frequency depends on VN and VP. And these thresholds have large tolerances.

    If you care about an accurate frequency, use a comparator instead.

  • 0 in reply to Clemens Ladisch
    Expert 1185 points

    Hi Clemens,

    Thanks for your feedback. Could you please provide any application note explaining threshold voltage effect on Frequency?

    Regards,

    Srikanth Kacchu

  • 0 in reply to Srikanth Kacchu1
    Expert 1185 points

    Hi Clemens,

    We have tested CD41016 and attached input and output waveforms below.

    As per above captured waveform, we have considered VP = 2.9V and VN = 1.9V (This is same as datasheet specification). Applying datasheet formula, we are getting 1.35KHz whereas oscilloscope capture shows 2.09KHz. Pls let us know the reason for this difference.

    Regards,

    Srikanth Kacchu

  • 0 in reply to Srikanth Kacchu1
    Guru 261430 points

    When the CD40106B has a 5 V supply, VN can be anywhere between 0.9 V and 2.8 V, and VP can be anywhere between 2.2 V and 2.6 V. Also, the capacitor is likely to have huge tolerances.

  • 0 in reply to Srikanth Kacchu1
    TI__Genius 16430 points

    Hi Srinkanth,

    We don't have any application note (to my knowledge) that explains the effect beyond the equation you provided in your original post. Just adhere to that equation using Vt+ as Vp and Vt- as Vn and you should be fine.

    If you're trying to get a specific frequency you should probably measure the specific Vp/Vn for that device since there is a range like Clemens said. In addition I'd also measure the capacitor you're using if it is high tolerance.

    Best,

    Malcolm