I ever designed a circuit with the 8 D/A converter of Signetics company. Because I overlooked what reason already,be after all, anyway the parts of an apparatus that I use differs a bit with normal circumstance, I am suffer from one’s own actions really, let oneself be immersed in a trouble.

 

Graph 1: The D/A converter of Signetics inputs configuration.

 

Carry incidentally, this kind of converter is early with respect to stop production. If the graph is shown 1 times,its input is configured. Stem from some kind of reason, I think to there is 40kΩ resistance in chip the likelihood is very useful, because this my use “Trim” cites a base, is not “Vref” bring a foot to regard imitate as the input. Circuit job is regular, I am extremely satisfactory.

 

Happy days always is very brief, be less than a year of time, the issue came. Although my circuit still works good, but the rate that D/A changes becomes suddenly mysterious, reading ascendant Yuanchao is normal limits. The thing is such:

 

Graph 2: Signetics D/A converter revised input configuration.

 

Signetics company raised a new diode parallel connection to the resistance that cites a foot to be linked together with “Trim” . Why to want so do? Nobody tells me the answer, the staff member that is Signetics only comparatives in the phone feel embarrassed, admit to a few users must configure their circuit afresh. Knew those who have this lot to be not me one person, also be a little solace.

 

This thing gave me two lessons.

 

The first lesson is, at the beginning I should use Vref to bring a foot to regard imitate as the input. In that way word, I can notice another supplier Datel to did not increase diode in same parts of an apparatus at that time. The same job that their parts of an apparatus still assumes like me is good.

 

The 2nd lesson is, the configuration that cannot trust a supplier blindly absolutely is controlled. I also had seen a few manufacturers revise these parts of an apparatus in the lifecycle of semiconductor device, for example RCA company is in 20 centuries 80 time later period its axial transistor of even 2N6578 power turns into denotative plane.

 

Never had seen before me, later also had not encountered this to because negligence configures the circuit develop that control and causes a function to differ to attack,be planted again structural circumstance.

 

Signetics already not answer exist. But if produce such job again, I am met certainly keep one’s countenance.

The article is reprinted design from electronic technology.