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This is a reliability doubt regarding an LDO. I was attending a conference on hi-reliability application of PMICs. During such a discussion one of the speakers said that when using an LDO ina hi rel application, the worst case is that the LDO fails and the input comes at the output as it is. Suppose Vin = 3.3V and output = 1.8V, when it fails Vout = 3.3V.

So one must make provisions to protect it. How can that be done ? Would using a TVS protection(unidirectional) diode do the trick ? So basically it will clamp the Vout to a more manageable,say 1.5V or so. is this a good approach ?

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  • \$\begingroup\$ Not really doing much if the input impedance is low enough to fry the TVS itself, better think crowbar like to disconnect \$\endgroup\$ – PlasmaHH Nov 25 '15 at 11:55
  • \$\begingroup\$ Then this holds true for any circuit that can use the TVS diode. \$\endgroup\$ – Board-Man Nov 25 '15 at 11:57
  • \$\begingroup\$ And input impedance of what ? The LDO? \$\endgroup\$ – Board-Man Nov 25 '15 at 11:58
  • \$\begingroup\$ I think @PlasmaHH is referring to the output impedance of the source feeding the input of the LDO. E.g. If the source is strong enough, it will cascade the failure into the TVS... and you're right, of course, about that always being true. \$\endgroup\$ – DrFriedParts Nov 25 '15 at 12:24
  • \$\begingroup\$ What's the "high reliability" goal? To protect whatever the LDO is powering from damage or to keep the circuit working? Two very different goals and answers. \$\endgroup\$ – John D Nov 25 '15 at 17:32
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No, this won't help, because then you're effectively shorting the power rail to ground via the TVS. Instead, you would need a Crowbar Circuit to trip a fuse or PTC.

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