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Query about OP467

Question asked by WayneQ on Dec 17, 2013
Latest reply on Dec 17, 2013 by harryh

Hi, there

 

Seeking your technical advice regarding part OP467 applied in my circuit, please see the following problem statement.

 

Refer schematic below, U38A & U38B is Analog Devices part (OP467), I facing problem where the standby voltage at line ‘X_Temp’ is as high as -1.6V, whereas voltage measured from a  good part is at the range from

-0.051V to -0.081V. With the higher voltage at ‘X_Temp’, my test will definitely failed.

The reject quantity is 8 out of 10 boards. The 2 boards that passing the test are using same OP467 with same date code (1331).

1.jpg

By the theory explanation, the Op Amp should be able to work as a buffering circuit and always ensure the voltage Vout feedback to Vin- to be always near to zero volt.

 

Please see the following table of voltage comparison in between a good board and bad board.

 

Signal

Voltage from pass and Golden board

Voltage from a few failed boards

X_Temp

‘- 0.055V to -0.081V

-0.8V to -1.6V

U38.2

0V

0V

U38.3

0V

0V

U38.1

-0.36V

-0.85V to -1.6V

U38.6

0V

0V

U38.5

0V

0V

U38.7

  1. 0.36V
  2. 0.85V to 1.6V

TP34

-0.83V

-0.37V

TP35

  1. 0.83V
  2. 0.37V

 

Performed evaluation to swap the OP467 in between a good board and failed board, the failure is follows the OP467. So I can conclude the test failure is coming from OP467 itself.

Anyway, haven’t say the part OP467 is defective but could be the reason of component matching or tolerance issue. (Seeking your advice on this)

Be noted that, the part has been run in mass production and this is the first time facing this problem.

 

And the resistance for R133 with 499Kohm is pre-designed and run for quite some time and it is in the mass production now. This problem is a recent case.

 

Could you please help give some comments on the issue?

 

thanks!

 

Br,

Wayne

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