CD14538BPW - Trigger Error with hight temperature

Arthur Deniau

Other Parts Discussed in Thread: CD14538B

Hi,

We use a CD14538BPW to have a 1s trigger.

With the formula T=CxRx, I have Cx=10uF et Rx=100K.

At 20°C the pulse is 1s, but at 70°C the pulse is near 500ms.

The Temperature operation range of CD14538B is -55 to +125 so we are in the spec.

Do you have an idea to explain our problem?

Arthur

0 C. Ryan Land over 9 years ago

Hi Arthur,

Is the temperature of your entire system 70C or just the CD14538B?

Try to apply 70C to the CD14538BPW alone, if possible. That way we can rule out temperature-dependent capacitive or resistive components.

-Ryan

0 Arthur Deniau over 9 years ago in reply to C. Ryan Land

Hi Ryan,

I tried to apply hight temperature only on CD14538B and its capa and resistor and I have the same issue.

But Apply temperature only to CD14538B is not possbile because the resistor and capacitor are closer to Cd14538B.

I think not that the resistor can lose a half of its nominal value. So I have not explaination....

Arthur

0 Chris Cockrill over 9 years ago

What voltage are you operating at?

0 Arthur Deniau over 9 years ago in reply to Chris Cockrill

I find the problem. In the datasheet it is recommended to put a diode 1N5395 or equivalent to protect IC during a rapid power down.

So the problem is the diode. If I take off the Diode, I have good result with high temperature.

I go trying to find a diode with good characteristic at high temperature.

Thanks for your help.

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