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TPS61200 in energy-efficient designs

Max Zhegulin
Intellectual 420 points
Other Parts Discussed in Thread: TPS61201, TPS61260, TPS61070
Dear community members.

We use tps61200 DC/DC switch in battery powered application. 
With full charged batteries Vin is about 2.5V, Vout is 3.3V. 
Our application have two operational mode run and sleep.
In run mode theoretically current consumption is about 33mA. In sleep mode less 1mA (msp430 sleep, all peripheral circuitry off).
Duty cycle is two seconds in run mode, two seconds in sleep mode. 
We have made two experiments. 
The first one with switch in power save mode and the second switch without power save mode and measure real current consumton.  
In the first experiment we get the following results run in mode current consumption is 36mA, in sleep mode is 2mA. 
The second - run mode 36mA, sleep mode 10mA.
Also we noted in both experiments what sometimes switching between run and sleep mode had "stepping" character. I mean that, for example, if step is 10mA, then on mesuarment equipment I see 
36mA, 26mA, 2ma, 12mA 36mA and so on.  
Step isn't determinate each new experiment get new value. 

We have two question.
Is this "stepping" switching normal switch operation mode?
And why we get such a great difference in current consumption in sleep mode? 

P.S. layout is attached.

All comments are appreciated. 
Thanks!

max

  • 0
    TI__Guru**** 150900 points

    I am having trouble reading your post since the sentences didn't wrap around.  If you are copying and pasting from microsoft word, please use the 'paste from word' button when you post.

    Please also attach a schematic.

    The lines/traces on your layout look very small/thin.  For a switching power supply, large peak currents flow in most of the traces (to the IC, to the inductor, etc.)  Thin traces can cause excessive voltage drops and losses that may affect operation.

  • 0 in reply to Chris Glaser
    Intellectual 420 points

    Hi Chris,

    Sorry, it's my fault.

    We use tps61200 DC/DC switch in battery powered application. 
    With full charged batteries Vin is about 2.5V, Vout is 3.3V. 
    Our application have two operational mode run and sleep.
    In run mode theoretically current consumption is about 33mA. 
    In sleep mode less 1mA (msp430 sleep, all peripheral circuitry off).
    Duty cycle is two seconds in run mode, two seconds in sleep mode. 
    We have made two experiments. 
    The first one with switch in power save mode and the second switch without power save mode 
    and measure real current consumton.  
    In the first experiment we get the following results
    in run mode current consumption is 36mA, in sleep mode is 2mA. 
    The second - run mode 36mA, sleep mode 10mA.
    Also we noted in both experiments what sometimes 
    switching between run and sleep mode had "stepping" character. 
    I mean that, for example, if step is 10mA, then on mesuarment equipment I see 
    36mA, 26mA, 2ma, 12mA 36mA and so on.  
    Step isn't determinate each new experiment get new value. 

    We have two question.
    Is this "stepping" switching normal switch operation mode?
    And why we get such a great difference in current consumption in sleep mode?

    Also our switch IC is tps62001 not 62000.

    And traces width is 0.3mm

    max 

  • 0 in reply to Max Zhegulin
    TI__Guru**** 150900 points

    I assume you are aksing about the TPS61201.

    0.3 mm is 12 mils, which is smaller than desired for power traces.  They need to be as wide as possible.  Look at the EVM and/or datasheet for examples.

    The difference in input current consumption is because you are in power save mode or PWM mode.  Look at the efficieny graphs in the datasheet.  At the light load currents, the efficiency is dramatically different between the modes.  Lower efficiency means higher input current.  This is expected.

    I am not sure what you mean by 'stepping'.  Is this the current on the meter?  The typical handheld meter cannot accurately measure the RMS of a 0.25Hz waveform.  You will need to add lots of input capacitance to make the input current waveform DC, so that the meter can accurately measure it.

    At such low output currents, I would recommend a lower current IC such as the TPS61070 or TPS61260.

  • 0 in reply to Chris Glaser
    Intellectual 420 points 
    Yes, you are right, "stepping" I mean current value on meter.
    It changing not strictly from maximum (36mA) to minimum (2mA), but with intermediate points.

    So, you guess it's a result of measuring unaccuracy? 
    Not tps behavior.
  • 0 in reply to Max Zhegulin
    TI__Guru**** 150900 points

    Yes, this is simply a result of your measurement setup.  The DMM is not able to gather an accurate RMS measurement from your input current waveform. 

    You can look at the input current with a scope to see what I mean.  Adding more input capacitance (at 0.25 Hz, you will need a lot--maybe over 1 mF) after the DMM and before the PCB should allow it to measure properly.

  • 0 in reply to Chris Glaser
    Intellectual 420 points 
    Chris, 
    thanks for an advices. It's big deal that you on this forum.
    TI support is one of the best.