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Unexpectedly large standby current on LM2735 DC-DC boost converter

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Leo Bodnar:
Hello gentlemen,

I have used LM2735X DC-DC boost converter in a battery powered design that has no power-off switch.  The LM2735 is used in its bog standard configuration as on the front page of the datasheet.  Vin supply is 5V.  Load does not consume any current below 6V.

After going through prototype verification I have found that LM2735 consumes 2.2mA of current in shutdown mode (Ven grounded) instead of 1uA as planned.  In standby mode this drains battery in a matter of hours instead of weeks.

After going through possible leakage paths around the design I have found that the 2.2mA is flowing from the Vin, through the inductor, and into the LM2735 switch pin.  Datasheet states that switch leakage current is 1uA @ 24V. 

This does not look like a latch-up and is repeatable at each power-on and across LM2735 samples.

Can anybody suggest what might be going on there?

Thanks
Leo

cybergibbons:
Sounds very strange.

When you say:
"After going through possible leakage paths around the design I have found that the 2.2mA is flowing from the Vin, through the inductor, and into the LM2735 switch pin"


Is this measured experimentally?

The NMOS switch transistor shouldn't be letting that much current flow in that situation.

Leo Bodnar:

--- Quote from: cybergibbons on April 21, 2012, 06:44:19 pm ---Sounds very strange.

When you say:
"After going through possible leakage paths around the design I have found that the 2.2mA is flowing from the Vin, through the inductor, and into the LM2735 switch pin"


Is this measured experimentally?

The NMOS switch transistor shouldn't be letting that much current flow in that situation.

--- End quote ---

Yes, measured in situ. 

Just tried another batch of ICs and they behave as expected.
Not sure what happened there originally.  IC still worked fine, so I am a bit confused.

Anyway, new batch of ICs works fine.

Leo

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