TPS22992: Unpowered behavior

Hello Chris,

There is no internal pull-down at ON pin.

Device will work during this state but it may not follow the switching timings mentioned in data sheet.

I don't think my question was understood.  What I am asking is if the part is not powered but the input pin ON, has a voltage level present of 3V from a back-up battery, will this cause any latch-up conditions, current path through the part, or any other undesired behavior in the part or is it tolerant to this pin being powered when the part is not powered?  The second part of the question was about the "Smart Pull Down" resistor on this input and if it would be in place in this unpowered condition.

Hello Chris,

Sorry for the confusion earlier.

This device has smart pull down resistor at ON pin which will pull down the ON pin to avoid floating.

In your case ON will be high but VIN is not present. Device will start when VIN reaches to min operating voltage.

How ever timing mentioned in datasheet may vary. 

Thank you for the response but my question still was not addressed.  Will the smart pull-down resistor be in place when power is not applied?  In the situation I described power will not be applied to the part and the only signal that will see a voltage level above ground reference will be the ON pin.  In this situation, will the smart pull down be connected to the ON pin resulting in a current path to ground through the smart resistor or will it be seen as a high impedance path. 

My first question also was not addressed: ...if the part is not powered but the input pin ON, has a voltage level present of 3V from a back-up battery, will this cause any latch-up conditions, current path through the part, or any other undesired behavior in the part or is it tolerant to this pin being powered when the part is not powered? 

Hello Chris,

1. Device needs VBIAS for charge pump and control logic to work. With out VBIAS smart pull-down may not effectively work. ON pin will be in floating state when no voltage at VIN and VBIAS. 

2. In this condition device will work but it may not follow the slew rate set by CT pin. Correct sequence is VBIAS>>VIN>>VON. 

You can consider TPS22953 which doesn't have this smart pull-up and other thing similar like CT and PG.

Amrit - What I prefer is the smart pull-down to have no effect on the applied voltage to the ON pin when power is not applied to VIN or VBIAS.  You mentioned that without VIN and VBIAS that the smart pull-down may not effectively work, is there a way to definitively confirm that the smart pull-down will not affect the current path on this input - that is, will it truly be floating so no current flows through this pin?

You also mentioned that the device will work without being powered, are you saying that w/o power the internal MOSFET will be closed allowing current to flow between VIN and VOUT?  Please explain further what you mean.  My original question was not if the part will work, but if the part is ok to have a voltage applied at the ON pin but have no voltage applied to VIN and VBIAS.  Is there going to be any leakage path through the ON pin in this state or any harm to the part?

I could also consider the TPS22953 but would need you to answer the same question as I asked for the TPS22992.  If no voltage is applied to VIN and VBIAS but I have a voltage of around 3V on the EN pin, is there going to be any leakage path through the EN pin in this state or any harm to the part?

Hello Chris,

This test condition has not been tested as part of characterization.

I will ask design team to simulate this to get the exact device behaviors. I will get back once I have these results.

Tentative time will be end of next week.

Thanks 

Amrit