TPS62080 Vout Level under Low Current Load Conditions

Robert Schwanke

Other Parts Discussed in Thread: TPS62080, TPS62230

We designed this regulator to operate at +1.9V (R1 = 80.6kohm, R2 = 25kOhm) on our board following the recommended circuit and layout in the data sheet. When we initially powered up, this supply was running at +2.45V and FB was at 0.55V. When I applied ~300 mA load (5+ ohms) Vout dropped to the programmed value and FB was 0.45V.

This regulator is supposed to work at LOW output currents so we expected this to operate at FB = 0.45V and Vout = +1.9V down to 2mA or lower.

Any idea why this does not operate lower?

Thanks,

Bob

over 10 years ago

0 Michael Helmlinger over 10 years ago

TI__Expert 5055 points

Hi,
Could you post your PCB layout and schematic/BOM?
What is the application?

Thanks,
Michael

0 Robert Schwanke over 10 years ago in reply to Michael Helmlinger

Prodigy 95 points

When 1v9_VCC is loaded with 300+ mA load, then Vout = 1.9V.

0 Michael Helmlinger over 10 years ago in reply to Robert Schwanke

TI__Expert 5055 points

Thanks for schematic and layout.

Could you please disassemble the 22pF FF cap? (C206) and check if there is a difference?
Could you also send me a scope plot of the device start-up? (Vin, Vout, Inductor-current, PG)

Thanks,
Michael

0 Robert Schwanke over 10 years ago in reply to Michael Helmlinger

Prodigy 95 points

Removing the C206 pin did not seem to make any difference.

Inserted below is a scope shot of the waveforms.

Chan4 (red) is the external bench power supply

Chan2 (green) is the voltage at the VIN pin.

Chan1 (yellow) is the FB pin.

Chan3 (blue) is the VOUT pin

Same data just plotted in Excel and zoomed in.

0 Michael Helmlinger over 10 years ago in reply to Robert Schwanke

TI__Expert 5055 points

1. Could you please provide a scpoe plot of the startup with the issue you described where the VFB is at 0.55V?

2. In the scope plot above it looks like there is a high impedance in the Vin path.

3. Why is the output voltage in the scope plot above at 1.7V. Is this a different circuit?

3. There is a delay of 4ms between the bench power supply voltage and the Vin. Which curcuit is between the bench power supply and the TPS62080?

4. Could you try to connect the bench supply direct to the TPS62080 and check if the issue is still there?

5. I made some bench measurements on the TPS62080 but i cannot see anything similar.

Regards,

Michael

0 Michael Helmlinger over 10 years ago in reply to Michael Helmlinger

TI__Expert 5055 points

If you have sensitive information you can send me an email. m-helmlinger@ti.com

0 Jeyalakshmi Kanniah1 over 10 years ago in reply to Michael Helmlinger

Prodigy 170 points

Hi,

I am going to use TPS62080 device in my new design and the maximum load current is 300mA. So I am bit concern of the above mentioned issue.

Is that issue has been resolved?. If its yes, Please let me know the solution details.

Suggestions for most appericated.

Thanks inadvance.

Regards,

Jeyalakshmi

0 Michael Helmlinger over 10 years ago in reply to Jeyalakshmi Kanniah1

TI__Expert 5055 points

Hi Jeyalakshmi,

We can see if this customer has more details to assist in the debugging of this circuit, but I did not hear of it being debugged so far.

Judging from other threads, this is fairly common in a public forum like this.

For currents that low, we have the TPS62230 family.

Regards,

Michael

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TPS62080 Vout Level under Low Current Load Conditions