LM76005: 100% duty cycle with an external floating voltage with respect to SW pin?

3922514

Part Number: LM76005

Hi TI

Is it possible to apply a true floating bootstrap voltage to the BOOT pin, so that the LM76005 becomes capable of maintaining 100% duty cycle?

We have an application where the dropout can become very small, and we do not want the LM76005 to enter any form of pulse skipping mode or similar, due to noise considerations.

The average current on this BOOT pin is very small, so it could be possible, perhaps.

It would be possible if the maximum on-time is determined by the UVLO of the BOOT voltage, the it would never enter UVLO, if an external voltage was supplied to this pin with respect to SW pin.

The external voltage should then be below 5.5V and above 3.3V.

BR Thomas

over 3 years ago

0 Arief Hernadi over 3 years ago

TI__Mastermind 23815 points

Hi,

I believe we still have a minimum off time requirement that needs to be met since the IC did not just look at the UVLO on the BOOT voltage in order to determine when to foldback the frequency.
Therefore adding a constant supply on BOOT will not ensure 100% duty cycle operation in your case.
We have some dropout curve for some VOUT and you can see how the VOUT and the VIN behaves at dropout (near 100%) duty cycle
https://www.ti.com/lit/ds/symlink/lm76005-q1.pdf?ts=1615424029637&ref_url=https%253A%252F%252Fwww.google.com%252F#page-29

Thanks
-Arief

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LM76005: 100% duty cycle with an external floating voltage with respect to SW pin?