LT3094 input diode

[cape zoloh]

I'm currently constructing a bipolar power supply based of the LT3045 and LT3094.

I don't want to use the "Power Good" function, but I still need reverse input protection. This is lost if not using the function, but "if reverse input protection is additionally required, tie the anode of a 1N4148 diode to IN and its cathode to PGFB" - Page 12, LT3045 datasheet. The schematic for this to go with the text is located on page 28, the last figure, I've also attached it as an image.

I'm trying to find the equivalent solution for the LT3094, but it is not mentioned in the datasheet. This is where I need your help.

LT3045 datasheet: https://www.analog.com/media/en/technical-documentation/data-sheets/LT3045.pdf
LT3045 datasheet: https://www.analog.com/media/en/technical-documentation/data-sheets/LT3094.pdf

[exe]

What do you mean by reverse input protection? Do you expect input wires to be swapped?

Anyway, you can add a diode at the input for protection (this will increase dropout by 0.7-0.8V).

[cape zoloh]

Yes, I need reverse input protection without the voltage drop of putting one in series, which is possible with the LT3045. I wonder how to do the same thing with the LT3094.

[exe]

Yes, I need reverse input protection without the voltage drop of putting one in series, which is possible with the LT3045.

No, lt3045 doesn't have a diode in series with the input. The diode there does something else.

[David Hess]

The LT3045 has built in reverse input protection because the PNP output transistor has a high base-emitter breakdown voltage and its collector is isolated from the substrate.  The LT3094 does not because the NPN output transistor has a low base-emitter breakdown voltage and its collector is not isolated from the substrate.

The only reason to have reverse input protection is if the input can be shorted, like with a crowbar circuit.  Usually it is sufficient to put a power diode across the input-to-output to limit the reverse voltage across the regulator to a low value and this is commonly seen on 3-terminal linear regulators for exactly this purpose.  For the LT3094, a big schottky diode should be used because of the substrate diode but may be this will not be enough.