We have been using the LM2677 for long with no problems. Now we changed over to LM22677 and have plenty of fails at high temperatures.
We are using a standard application circuit from the webbench designer. PCB layout is more or less the same as with the LM2677 The operation parameters are:
Input voltage 24..32V
Output voltage 18V
Output current 2A.
At 85°C ambient the chips fail suddenly after a while of operation. Output voltage then is zero, input current is infinite (up to the current limit of our source). It is not the regular thermal shut down as the chip has definitely blown up.
The temperature at the TO-263 surface never exceeds 100°C
What could be the reason? Any idea how to isolate the problem?