TPS61221 efficiency too low

Christine

Other Parts Discussed in Thread: TPS61221

Dear,

I am using TPS61221 in the typical application. The circuit is shown below.

Vin=1.5V and Vout=3.3V. In my application, Iin=8.4mA, Iout=2.8mA. So the efficiency is 73%, which is much lower than that shown in Fig3. of the datasheet (about 85%).

I want to know what the possible reasons of it and how I can improve the efficiency of the chip.

Can any one help me? Thank you!

over 12 years ago

0 JohnTucker over 12 years ago

TI__Guru**** 191445 points

There are a couple possibilities. What inductor are you using? That will be about the only external component that can affect efficiency. Also, measuring technique is important. Make sure you measure Vin and Vout directly at C1 and C2. Also care must be taken in measuring the input and output current, especially the input current.

See this application note:

http://focus.ti.com/general/docs/litabsmultiplefilelist.tsp?literatureNumber=slva236

0 Christine over 12 years ago in reply to JohnTucker

Prodigy 100 points

I am using the wound inductor (value 4.7uH). What kind of inductor should be used here?

And according to the application note, the measuring technique I employed is OK.

0 JohnTucker over 12 years ago in reply to Christine

TI__Guru**** 191445 points

What is the DCR of the inductor?

0 Christine over 12 years ago in reply to JohnTucker

Prodigy 100 points

1Ω. (I use a multimeter to measure the DCR.)

0 Michael Green over 12 years ago in reply to Christine

TI__Genius 16870 points

This DCR seems a bit higher than the inductors recommended in the datasheet on page 14. Either way the switching losses should dominate at low inductor currents. At this low of current make sure you are using the highest possible resistors on your input and output rails is you have any.

0 JohnTucker over 12 years ago in reply to Michael Green

TI__Guru**** 191445 points

Yes that DCR seems high.

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TPS61221 efficiency too low