Hello
The design is a 28V system power input stage that shall be compliant with MIL-STD-1275D. Therefore:
- The input can have stationary voltages from 18V to 33V.
- The input shall tolerate battery reversals with no operation behavior.
- The input shall tolerate +-250V 1000us spikes.
- The input shall tolerate 100V 1000ms surges (these are managed downstream with an active surge suppresor).
For reverse battery protection we opt for LM74610, as its floating behavior makes it ideal for withstanding 100V+ transients. To deal with the 250V transients we want to set two unidirectional TVS, back to back. Then, for positive spikes we set a 30KPA90A unidirectional TVS, which breaks at 100V and clamps at 146V. These overvoltages are chopped downstream by a 150V capable IC.
The problem arises when dimensioning for negative spikes. The 45V reverse voltage limit for the LM74610 is key here. As our system admits up to +33V stationary, the maximum clamping voltage for the negative TVS shall be 45 - 33 = 12V. But then, reverse battery connections (up to 33V) will blow up the TVS bridge.
Do you know of any solution to overcome this? Any alternative P/N?
Thank you
