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I am designing a project where I'm going to use the MAX1709 step-up converter. There is a possibility to switch the converter ON/OFF with the help of ONA/ONB inputs, but according to schematic in the datasheet the input voltage will be available on the output even if the IC switched OFF because the input DC-connected to the output via a schotky diode.

Could you confirm, please, if I understand this schematic correctly ? If so, is there a way to "completely" switch the circuit so that there is no voltage on the output ?

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  • \$\begingroup\$ You do understand it correctly. You need a different topology with an active switch there instead of a diode, if you want to be able to cut power entirely. Or you could add an external, non-synchronous power switch with back-to-back FETs or something similar. \$\endgroup\$ – Hearth Feb 16 at 17:24
  • \$\begingroup\$ @Hearth Yes, I understand what you are talking about, it can be a separate MOSFET-switch. Is schottky required for this schematic ? Why did you say "instead of diode"? \$\endgroup\$ – hanni76 Feb 16 at 17:32
  • \$\begingroup\$ You could probably do this with a synchronous-switching converter. It might not work with a MOSFET because of the body diode, though. The non-synchronous switch I mentioned in the last sentence there is a different thing. \$\endgroup\$ – Hearth Feb 16 at 17:33
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For the use of this chip , you do not get a True Shutdown, which is an option on some boost IC at extra cost.

Alternatively, you can keep same performance with ripple, noise and step load regulation if you use a low RdsOn input switch before shunt bulk cap with same layout recommendations or use layout in IC kit.

Or choose a different design.

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    \$\begingroup\$ Thank you for the answer. I decided to add ON/OFF controller LTC295x series with a P-channel MOSFET to my schematics. I will put it right before the converter. \$\endgroup\$ – hanni76 Feb 17 at 19:04

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