AMC1200: amc1200

Hi Ross,

Approximately how quickly are you cycling through -40 to 75C? 

How many devices out of how many tested are seeing this issue? 

hI

We ramp down down to -40 and hold it there for 40 mins(including ramp down( about 5c per min), the ramp up to 75c at a ramp rate of 10C /min and the hold it for 45mins. we have tested 12 units and 5 have failed during the cycles. the failed units seem to fail at a temp around -30c. we never go below -40c

regards

Ross

hi Alex, the unit filed again at -32 and -30. is there any reason why the device is susceptible to issues at low temps? its failed 34 times out of 11 thermal cycles, always around -30C

regards

Ross

Hi Ross,

Can you please provide the schematic/layout showing the decoupling capacitors on the power supplies?

If you cycle the power supply while the device is showing the issue, does the issue resolve? 

hi Alex, 

sorry Alex. I can not provided the details, as this is classified and need to check what I can share. The supplies are decoupled via 100nF caps, 5v vdd1 and 3.3v vdd2. If the power is recycled then it usually resolves itself unit the next thermal cycle. unfortunately this is not an issue as its in a aircraft

Hi Alex to explain basically the works of the the circuit  as follows,

the main aircraft supply is monitored, if it drops below  say 60% level it alarms. The aircraft supply is reduced by a resistor network, filtered the fed into the AMC1200. the acm1200 output is filtered and fed to a diff amp with a small gain of 2, then finally passed into an ADC in a processor, which checks the level. 

regards

Ross

Hi Ross,

Understood. 

Can you please clarify your meaning with this sentence? "unfortunately this is not an issue as its in a aircraft"

Sometimes with these issues we see that while the thermal chamber may report a certain temperature value, in reality the temperature the device see's may be slightly different. For example if the temperature chamber is in the process of cooling down from  25C to -40C, the chamber must blow air that is cooler than -40C which could come in contact with the device. If you have access to a temperature probe that can be placed next to the PCB to confirm the temperature near the IC, this may help with the investigation. 

Hi Alex,

just to say that the supply is always present on the aircraft, hence no on/off switch to the unit o reset it. 

we have temp monitoring inside the unit. It reports that the inside gets to about 1C higher than the outside whiles not active. when active about +10C

today we saw failures at between -20 to -25C. 

regards

Ross

Hi Alex,

would tin dipping cause an issue with these devices, i cant see why it would?

regards

Ross

Hi Ross,

Thank you for clarifying. 

Is this the same unit that is now failing at -20C to -25C (Indicating performance is getting worse over time)?

How many devices out of how many tested are showing this behavior? 

I do not see why tin dipping would cause an issue. 

At this point, I recommend to go forward with the customer returns process so that we can perform in depth analysis. 

https://www.ti.com/support-quality/additional-information/customer-returns.html

hi Alex

to share schematic and gerbers, I need a NDA and an open general export licence doc signed. do you have an email address that i han forward you these? please email me it

cheers

Roos

Hi Alex, we can send some of the unused devices to be checked but the device on the unit is formally coated, we can remove it, but would this be an issue for you?

regards

Ross

Hi Ross,

I'll need to connect with members of my field team for the NDA and export license documents. 

Conformal coating can sometimes be an issue, depends on if the device can be removed without mechanical damage. 

Hi Ross,

Is it OK for my team to reach out to you through the email registered with this account?

Hi Alex

just to say we have two batches of the acm1200.

first batch was date code 2232 lot cod 2655768MY2 they seem to be ok

second batch  date code 2232 lot cod 3655788MY2 fail intermittently

this may shed some light on it. also would using a automotive part help us with the lower temps? are the pre tested? 

regards

Ros

Hi Ross,

The team has asked me to confirm the date codes with you thinking there may be a typo. Can you please confirm? 

Hi Alex

these codes are correct the first was for 10 and the second was for 100 devices. these codes are from Mouser electronic UK.

regards

Ross

Thank you Ross. 

Hi Ross,

One other confirmation - have you replaced the device showing failure with a known good device to confirm there is no issue on the board and that the behavior follows the unit? 

hi Alex 

here is a picture of the batch that fails 

Thanks Ross. 

Have you been contacted by my colleague? 

It would be best to share this through the customer return channel so that it can be recorded properly. 

hi Alex yes we are working through the NDA  with TI and Mouser with the parts

cheers

Ross