> The lowest of the maximum Vdd ratings on these chips is 6V. =A0There is a
> situation where some customers may need to power the board from 5V.
....

> Looking at transorbs and zeners (with a series fuse or polyswitch) gives
> me the impression that they will not save the logic chips being
> toasted. =A0Any ideas?

Many. But is that a 6V max OPERATING spec and not just abs max.
For not much money [tm] you should be able to handle the whole input
voltage range, with the ICs seeing allowable operating voltage.

What is the manufacturing budget for the power supply?

What is the MINIMUM allowed operating voltage.
What is the maximum allowed OPERATING voltage.

eg a 5V out LDO with good dropout operation and >=3D 36V Vin rating is a
total solution if it itself can be made transient proof, provided that
the circuitry will operate at V_LDO_Out when w Vin is 5V.

If you run that at 36V directly it may toast or shut down the LDO
after a whilebut it then allows you to put protection, switching etc
ahead of the LDO.

More anon.


 Russell

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