This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

TPS61240: TPS61240 consuming lots of current when switching 1 khz load

Part Number: TPS61240

Dear forum,

We are testing the TPS61240 using EV board for our product. Our product contains a load of 150mA, which is switched on every 1ms for only 50uS. According to the datasheet, the TPS61240 should handle this well. Unfortunately when we use it, the device draws continuously around 290 mA. We have added 22 uF both on the input and output lines and the TPS61240 and the voltages look stable on the oscilloscope. Any idea what could be causing this excessive current? When the TPS61240 is bypassed, the current draw is normal.

Best regards,

Tijn Kooijmans

  • Hi Tijn Kooijmans,

    What is input voltage? could measure the VIN, SW and VOUT waveform when the issue happens.
    could you try 10mA continue loading and check if the device operates well?
  • Hi Jasper,

    My input voltage is 3.7V. Please find the scope images attached. I noticed the SW is continuously showing a 3.75 Mhz signal without breaks.

    On 10mA continuous load it works well and the power consumption of the TPS61240 is very low.

    Best regards,

    Tijn

    Images: 6404.images.zip

  • Hi Tijn,

    i don't see issue from the waveform. Please slowly increase the loading the 150mA, and check what happen during the increment. if there is any big current jump.
  • Hi Jasper,

    Since it is an NFC antenna that draws 150 mA it is not very easy to lower the load. What I notice though is that if I increase the interval between the bursts, the current becomes more reasonable but still quite high. For example, if I space the 150 mA bursts with 20 ms, the average current draw becomes around 50 mA. Note that without DC/DC converter this is only 8 mA.

    Best regards,
    Tijn
  • Hi Tijin,

    it is very strange behavior. do you have the electronic load or resistor load? check what happen if the loading is 100mA or higher.
  • Hi Jasper,

    The load is an NFC antenna, which is an inductive load. Another thing I tried today is to not switch the antenna on and off at all, so that the current draw is 120 mA continuously. When using the DC/DC converter the current draw is 400 mA and the ceramic capacitors start to sing. I used a Vin of 4V this time.

    When trying the EV board with a resistive load of 35Ohm, the current draw is 225mA, Vin = 4V, which seems quite reasonable (83% efficiency if I'm right)

    Best regards,

    Tijn

  • Hi Tijn,

    Could you measure the current waveform of the antenna? if you don't have a current probe, add the 0.5ohm in series with the loading, and measure the voltage drop of the resistor.
  • Hi Jasper,

    While measuring the current waveform I did get a step closer. It turns out that there is a continuous draw, even though there should be an interval of 1 ms between the 50 us pulses. This turned out to be the NFC card detection being triggered all the time when using the DC/DC converter. Normally this only when there is an NFC tag.

    The current draw is a 13.56 Mhz sine, so I suppose we should add a bigger bulk capacitance after the DC/DC converter.

    I'm working on a way to try to get the output of the DC/DC more stable so that it doesn't trigger the card detection of the NFC reader.

    Best regards,

    Tijn

  • Hi Tijin,

    what is the condition to triggering the NFC card detection? if it is the voltage level, please also pay attention to the possible voltage drop between the EVM and the NFC device if the cable between the DCDC and the loading is long.
  • Hi Jasper,

    Thanks for your advice! I have just found the root cause of the issue, which turned out to be a resistor in the NFC circuit that needed to be increased since the antenna voltage is higher with the DC/DC converter. After changing this resistor the converter works nice and expected. 

    Best regards,

    Tijn