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TPS62840: start up current of TPS62840

Betty Guo
Expert 7300 points
Part Number: TPS62840

Hi,

could you help on below items:

1. In the page 8 of datasheet, the Negative current limit is 533mA. how to understand the negative current?

2. The figure 53, I find the starup current have a large spike, the current is about 800mAm. why there have a large spike?

in customer application, they found the simalar problem of current spike.Since they use battery supply, the battery voltage will be drop when current spike, which result to the output voltage drop.

3. Any suggestion to decrease the current spike and hold VIN. I suggest customer add more input capacitors.

below are customer scheamic and test waveform, please help review:

  • 0
    TI__Mastermind 19230 points

    Hi,

    -In forced PWM mode, a negative current limit (ILIMN) is enabled in order to prevent excessive current flowing backwards to the input. When the inductor current reaches ILIMN, the low-side MOSFET turns off and the highside MOSFET turns on and kept on until TON time expires. Please go through section 8.3.6 in the datasheet for a detailed explanation. 

    -During startup, the converter needs to charge the output capacitance and supply the load. So there will be an inrush current. The spikes observed are nothing but Inrush current.

    -So, one simple way to reduce inrush current would be to reduce output capacitance. You could use 10uF output capacitor as the datasheet suggests. Also, by disabling the load/ reducing the load during startup, you will see a reduction in inrush current. 

    Please let me know if this helps.

    Regards,

    Febin

  • 0 in reply to Febin
    TI__Mastermind 19230 points

    Hi,

    I hope you could solve your issue. 

    I will close this post for now. Please feel free to contact us for any further technical support.

    Regards,

    Febin