TPS63001 problem

[nickagian]

I am using a TPS63001 regulator. The connection diagram is attached. Only difference is that I use an inductance of 2.2uH and that the device is not TPS63031 but as I said the TPS63001.

I face the following problem: When at start-up the input voltage of the regulator is 4.4V or above then everything seem to be ok. The output voltage is 3.3V. However, when the input voltage is below 4.4V at start-up then the regulator cannot produce 3.3V (the output is in fact around 1.9V). Only when the voltage rises above 4.4V the regulator can preserve its output voltage. However, if it has started operating then the input voltage can fall to a value around 3.2V without problem (but not lower). Can anyone please help me with this situation? I am a little bit desperate, because I have followed the connection diagram as it is in the regulator's datasheet but now the device does not seem to operate... I do not know what to do now...

I have also changed the output capacitance to a double one (two capacitors of 10uF) but the results were worse. the device could not start regulating at all.

 

[mneary]

I see a conflict between the diagram on page 1 where VIN and VINA are connected, and others where it is not. On page 4 it is called an 'input'. I would try using a 0 ohm resistor for R? in your board.

Is the PowerPAD™ connected to PGND?

 

[nickagian]

Thank you for your reply!

Yes, you have right. The two diagrams are a little bit different. But I guess there is no much difference in the end. VINA is the power supply for the internal control stage of the IC. However, I will try replacing the resistance with 0ohm. The PowerPAD is indeed connected to GND. The point is -and I do not know if this is a problem- that there is no different ground plains for GND and PGND. Does this matter? I do not know at all... Or perhaps it is a heating problem?