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TPS61093: Wrong output from DC-DC boost converter

Part Number: TPS61093

I have weird issue I would like help in resolving please.

I am using the TPS61093 as a boost converter.

Input voltage is a regulated 3.1V. Output voltage should be between 14.0 and 15.0V, to drive an OLED display per the OLD display spec.

The feedback resistors, with designators per the datasheet are R1 = 287K and R2 = 10.2K. This should give an output voltage of 14.57V. However the voltage output is around 13.3V with or without a load.

If I change R1 to 307K (using 680 ohm in parallel with 560 ohms), the output voltage is 14.07V without a load. If I put a 1K resistor load on the output, the output voltage is 14.06V. The voltage at FB (pin 7) is 0.456V.

I tried this on three PCBA's with repeatable results. The output is stable in all cases, and the oscilloscope trace shows no noticeable ripple or noise.

Due to tight height restrictions in the enclosure, I used a low profille Bourns SRU5018-100Y inductor, which is 10uH, rated to 1A, and has only 65 milliohms DC resistance.

So, the question is, WHY does the output voltage not meet the equation per the datasheet?

Schematic is here. 

The layout is very tight on a 4 layer PCB, without any long tracks etc.

Any help would be much appreciated.

  • Hi David,

    1. please remove the Cff.

    2. change the R7=200Kohm,

    3. add one more 0603 output capacitor.

    4. measure the VIN/VOUT waveform if you still seeing issue.

  • Hi Jasper.

    It fixed the problem! An added output capacitor made no difference. Cff didn't make any difference either. But R7 going to 200K did the trick. In fact, the output is clean and 14.46V - as per the equation. Why did this fix the problem?

    If you ever visit Australia, Iowe you a beer. Your fast response and the fix is very much appreciated, sir.