TPS62160: inverting circuit only going to -2V

Part Number: TPS62160

Hi all

My customer has built an inverting DC-DC with the TPS62160, 3.3V => -5.5V, similar to Figure 7 in the datasheet.

TPS62160 doesn't go below -2V. The IC heats up and consumes a lot of current but Vout is somehow stuck at -2V.

If Vout is set to -2V or higher (with R111,R113) the TPS62160 performs normal. VIN has been tested at 3.3V, 5.5V, 12V, no difference. In and out Capacitance has been increased without any impact.

At FB the Voltage -1.76V is measured. If Vout is set to -2V or higher the FB Voltage is -0.8V as described in the Datasheet.

Please find Figure 7 and the detailed customer schematic below.

Please review and comment.

Best regards

Ueli

---------------------------

over 3 years ago

0 Nancy Zhang over 3 years ago

TI__Mastermind 47000 points

Hi Ue,

The schematic seems ok. Here is my suggestions.

1. Could you try to remove the input caps between Vin and -Vout? They are C131/C132/C133/C134/C135/C136. Is D102 schottky diode? I am not sure if those caps provides an AC path and causes IC malfunction. Please refer to the application note in the link as below.

https://www.ti.com/lit/an/slva469c/slva469c.pdf?ts=1629141117350&ref_url=https%253A%252F%252Fwww.ti.com%252Fsitesearch%252Fdocs%252Funiversalsearch.tsp%253FlangPref%253Den-US%2526searchTerm%253DSLVA469C%2526nr%253D28

2. When you test -5.5V, did you add any load or no load? Could you try to add some load?

3. Is it possible to change the inductor value to 4.7uH or 10uH?

4. If it is possible, could you send me the layout file? I will review it. My email address: nancy_zhang@ti.com

Please let me know the test result.

Thanks,

Nancy

0 Ue over 3 years ago in reply to Nancy Zhang

TI__Genius 16495 points

Hi Nancy

Thank you for the quick reply. I will ask the customer to post the answers to your questions.

Best regards

Ueli

0 Wendelin Albrecht over 3 years ago

Prodigy 50 points

Hi Nancy

Thank you for the help.

1. Removed all of them but no impact. D102 MBR0520 is a Schottkey Diode yes, foraward Voltage 0.3V.

2. I added 30mA Load and 85mA Load. 30mA->-2V, 85mA->-1V Vout

3. tryed 2.2uH, 4.7uH, 10uH with 85mA load, same result

4. Layer1:

Layer2=GND

Layer3=3.3V

Layer4=Signal

If you need I can send you more detailed Layout data.

Best Regards

Wendelin

0 Nancy Zhang over 3 years ago

TI__Mastermind 47000 points

Hi Ueli,

Please see my comments as attached and let me know your result.

The layout is not good. We can talk about layout after you verify the suggestion.

Hope this helps.

Thanks,

Nancy

0 Nancy Zhang over 3 years ago

TI__Mastermind 47000 points

Hi Ueli,

Forgot to attach slide. See attached.

Thanks,

NancyTPS62160 Inverting issue.pptx

+1 Wendelin Albrecht over 3 years ago in reply to Nancy Zhang

Prodigy 50 points

Hi Nancy

Thanks for the answer.

I removed the ouput Caps as recommended, but no impact. To improve I_out_max I also tryed to change Vin to 12V, Inductivity to 10uH and Cout to 10uF.

Best Regards,

Wendelin

0 Nancy Zhang over 3 years ago in reply to Wendelin Albrecht

TI__Mastermind 47000 points

Hi Wendelin,

1. Could you take some waveforms during start up for -5.5V(bad) and >-2V(good)? The waveform should include Vin/Vout/FB/PG.

2. Could you try to check Vin start up slew rate? For inverting buck-boost topology, If Vin start up too fast, it may not have enough time to charge up the energy during on time. Is it possible to try to use external slow DC power supply?

3. Could you please send me the layout file? My email address: nancy_zhang@ti.com. We can work to debug offline.

Thanks,

Nancy

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TPS62160: inverting circuit only going to -2V