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TPS62231-Q1: Power efficiency doesn't match datasheet

Bill D
Prodigy 60 points
Part Number: TPS62231-Q1
Other Parts Discussed in Thread: TPS62743

First, I'm using a "TPS62231DRY" not a "-Q1" but I couldn't enter that in the dialog box.  Not sure if that affects my results, but I wanted to mention it.

In my design I have a TPS62231DRY to regulate 5V -> 1.8V, and I'm measuring ~76% efficiency with currents in the range of 15mA - 25mA, when datasheet says to expect ~82%

and I also have a TPS62237DRY to regulate 5V -> 3.3V, and I'm measuring ~86% efficiency with current in the range of 10mA-11mA, which seems about right

My topology is different between the two in only the output capacitance.

I sized down the inductor to an LQM18PZ2R2MDHD because of size restrictions.  This is still 2.2uF and the Q factor should be >>25 based on the datasheet specifications of DCR=0.47 Ohms

5V -> 4.7uF -> TPS6331 ->LQM18P -> 9.1uF total capacitance  (76% efficiency)

5V -> 4.7uF -> TPS6337 ->LQM18P -> 11.6uF total capacitance (86% efficiency)

I'm using a Keysight N6705C to supply the 5V and measure current.

When testing the raw current draw I used the N6705C to supply the 3.3V or 1.8V current respectively.

Current was averaged over 30 seconds using the N6705c data logger.

Is an error of 6% allowed deviation from the datasheet spec, or is there something in the design that I failed to consider?

  • 0
    TI__Guru*** 142680 points
    Thanks for your detailed post. The efficiency strongly depends on the inductor selected. You can see figure 18 in the D/S for an example. Your inductor is much smaller and thinner than any of these and would thus be expected to have lower efficiency. Your results sound reasonable.

    The TPS62743 is a newer device which is smaller and has much higher efficiency in the uA load range. As well, that one device could be used for both of your output voltages. Table 5 in its D/S lists newer, small inductors.

    If you have a little bit of room, growing the inductor to an 0805 size would allow using some of Murata's DFE family which are very efficient.
  • 0 in reply to Chris Glaser
    Prodigy 60 points
    Thanks, Chris. I'll look at the TPS62743 for future designs.