TPS610985: Boot issues with inline fuse (3 ohm resistance).

HI Sergio:

What's your Vin range, Vout and load condition? And please measure the Vin, Vout, and SW waveform with us.

Hi Minqiu, 

Input 2.7V to 3.3V from a battery but the plots shown are from a power supply.   Load is approx 5-30mA (feeding two small M4 and M0 ) processors.  This is a low power sensor product.  The problem is that the inline fuse's DC 3 ohms resistance drops the input voltage to the DC-DC for a small amount of time during the DC-DC inrush period.  Once this happens the DC-DC does not recover and leaves its output at 1.8V.   The DC-DC works fine without the fuse but does not boot with the fuse.  The plots below the two cases.  First two plots are the bad boot case with the inline fuse between the supply and DC-DC, Vin (yellow), DC-DV Output(blue)  and Vin(yellow), DC-DC Input (blue).  The next two plots after that are the good boot case where the inline fuse is removed between the supply and DC-DC.   Vin (yellow), DC-DV Input (blue)  and Vin(yellow), DC-DC Output (blue).  

Thanks for your comments. 

Sergio

Hi Sergio:

Sorry that my reply is missed last week...Maybe caused by net issue.

May you introduce the signals with details? What's the "DC-DV"? And is the "Vin" same as the pin of IC? Why it rise from zero and so unstable?

Hi Sergio:

Hope everything well.

May I know if there is any update?

Minqiu, 

I provided all the plots and data you requested back on March 19.  Do you not see the plots?  Maybe they are not shown on your PC but I can see the info. 

Thanks
Sergio

Hi Sergio:

Yes, I have seen the plots. But I'm confused about the signals. To reduce the misunderstanding, I need you help to make them clearer: 

May you introduce the signals with details? What's the "DC-DV"? And is the "Vin" same as the pin of IC? Why it rise from zero and so unstable?

It's better if you could note them in schematic. 

Hi Minqiu, 

Do you have access to a development board for this DC-DC?  If you do then you can see the same problem I am having by adding a 4 ohm resistor between the battery and the regulator. 

Configure like this, 2.5V at the power supply, 4 ohms series, to DC-DC input.     The problem I have is that this TPS610985 is terrible at recovering from a series resistance, the kind you add if you have an inline fuse between the converter and the battery. 

Do you work for TI? 

Hi Serfio:

Yes, I work for TI.

I did the test before. And I can't reproduce the phenomen. 

Attached is the waveform I tested today. I use a DC supply and series 4ohom resistance. The Vin is powered from 0 to 2.5V. 

I saw you post some waveforms before. But I'm confused about the signal relationship and setup. May you clarify these points I asked before, or catch similiar waveform for me? Better with another probe for Battery output port. 

Hi Minqiu, 

Is it possible to do this privately?  I'd like to share the schematic sections for the power supply and loads so you can see the exact configuration. 

Please let me know. 

Thanks

Sergio