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This question is in regards to an example application circuit that appears in the Linear Technology / Analog datasheet for the LTC4355, and is discussed in this article. The circuit uses ideal diode controllers to provide redundant power from dual power supplies in an AdvancedTCA application. While I'm familiar with diode-or'ing redundant power supplies (either with real diodes or ideal diodes), I'm used to seeing this on the high side only with low sides just tied together. I understand that AdvancedTCA uses negative supplies, and would therefore understand low-side-only diodes... but why both?

diagram from link

The AdvancedTCA specification does not seem to address this. It mentions that fuses are needed both high side and low side, but does not seem to require both high and low side diodes.

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  • \$\begingroup\$ I noticed that TI has a reference implementation of a similar AdvancedTCA design (ti.com/lit/ug/sluu212a/sluu212a.pdf) which uses ideal diodes on the low side, and uses schottky's on the high (return) side... So I strongly believe there's an advantage being gained here by not tying the return nodes together. \$\endgroup\$
    – addaon
    Mar 27, 2020 at 3:25
  • \$\begingroup\$ One more related question on this -- I'm used to single-point connecting chassis ground to logic ground; but how would chassis ground be connected in this configuration? Connecting it to the logic ground on the device side of the fuses and diode-or's presumably bypasses the protection they provide? \$\endgroup\$
    – addaon
    Mar 28, 2020 at 3:11
  • \$\begingroup\$ Please use the edit link to update your original question with this comment. Could you meanwhile also elaborate why you would connect chassis ground to logic ground? \$\endgroup\$
    – Huisman
    Mar 30, 2020 at 12:50

1 Answer 1

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Why use both high side and low Side diode-ORs ... ?

It is to protect against all forms of misconnections (see below).
Linear Technology explains it in their Design Note 444.

It can be easily seen that removing one of both ORing diode pairs in Figure 4 will result in a short of one of the power supplies.
And in Figure 5 Battery A and Battery B would have been in series if there were only 1 ORing diode pair. (Worst case, the batteries would be shorted via the ground wiring.)

enter image description here

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