Problem: On +24V power up, an LM22674MR-ADJ Step-Down Voltage Regulator internally shorts itself to ground. The fault does not happen on every printed circuit board.
Circuit Description & information: I have utilized two LM22674MR-ADJ on one printed circuit board which produce separate DC outputs - one for 5V and one for 7V. (Please see attached for schematic and board layout). The PWRIN ranges from 8V to 40V. Both regulators really only need to output upto 50 mA, although these are sized for 500mA (for future use). The typical resistances are as follows: PWRIN to ground = >222K, +5V to ground = >5Kohm, and +7V to ground > 6Kohm.
I initially used the WEBENCH tool to design these circuits and have built the circuit with the recommended BOM and layout. On the second page of the attachment, you can see an example of the damage to one of the LM22674s that is caused during the power up. It should be noted, that the circuit works at 24V steady state. Also, the problem idoes not consistently occur on one circuit or the other... sometimes the +5V regulator circuit blows, and sometimes it is the +7V regulator circuit.
Initially I tought the problem was related to the power supply providing 24V, but different supplies proved me wrong.
If anyone can help, please do! I am stuck.http://e2e.ti.com/cfs-file.ashx/__key/CommunityServer-Discussions-Components-Files/216/5543.Power-Supply.pdf