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ADM3251E Tout suffers defects

Question asked by AKKB on Mar 27, 2015
Latest reply on Mar 30, 2015 by RAnslow

Hi,

we have a bigger problem with defective AMD3251E ICs on several controller boards that were returned from one of our customers. These boards are in service in large quantities at other customers without problems and we would like to find out, what could probably have caused the found defects.

The defect situation is identical on all of the 5 boards, we already investigated (more likely defects are reported from the concerned customer):


Except the missing signal on the T_out-Pin (16) on the RS232 side, everything else appears o.k..
Especially the isolated supply with 5V_iso, V+ (+10V) and V- (-10V) is working regular (tested with oscilloscope).

The Input signal at Tin (9) is also o.k..

Then we checked whether the intrinsic diode forward voltages between the Pins on the RS232 side could be measured on the defective ICs (1x IC already removed from board, 4x IC still mounted on board):


All tested defective ADM3251-ICs show (Pin No's in brackets):
V- (12) => Tout (16):  no diode forward voltage and resistance > 20 MOhm !!!
Tout (16) => V+ (19):  no diode forward voltage and resistance > 20 MOhm !!!
Tout (16) <=> GNDiso (11): no diode forward voltages and resistance > 20 MOhm
V- (12) => GNDiso (11):  1 diode forward voltage
GNDiso (11) => V+ (19):  1 diode forward voltage
V- (12) => V+ (19):  2 diode forward voltages

 

In comparison, non-defective ADM3251-ICs show:
V- (12) => Tout (16):  1 diode forward voltage
Tout (16) => V+ (19):  1 diode forward voltage
Tout (16) <=> GNDiso:  no diode forward voltages and resistance > 20 MOhm
V- (12) => GNDiso (11):  1 diode forward voltage
GNDiso (11) => V+ (19):  1 diode forward voltage
V- (12) => V+ (19):  2 diode forward voltages


It seems, the Tout-Pins (16) of the defective ICs have lost any electrical connection to one of the related circuits inside the IC resp. the output stage "disappeared".

Since we only know that our customer tried to connect our controller boards via RS232 to his laptops but in no case was able to get connection, it might be something wrong with his laptop/s interface/s or RS232 cable/s, destructing the output of the AMD3251 ICs.

 

With this post we hope to get a clue what kind of "mistreatment" is able or likely to produce defects of the kind we found on the returned controller boards. Maybe, anyone has made a similar experience.


See also the attached excerpt of our controller board schematic, the PCB design follows the datasheet recommendations.

RS232_schematic.jpg
Thanks in advance for any advice.

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