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LM5176: Input Current varries while Vin is approximately around Vout

Robert Crawford
Prodigy 40 points
Part Number: LM5176

I'm seeing my input current vary around 10mA when Vin is in the range of 27.8 - 28.2 V.  The design is for a Vin of 18-36 Volts , with  Vout  set at 27.2Volts. The input current is around 1.35 Amps.

I'm switching at 400KHz. When I'm in full buck or boost mode the input current appears to vary around (1 to 2)mA. The output Voltage and current  are steady. I'm wondering what would be the cause and best way to go about trying to mitigate this current jumping around. 

  • 0
    TI__Guru* 78190 points
    Hi Robert,

    Thank you for using the LM5176. The input current variation may be caused by the buck-boost transition mode, in which the circuit operates in the buck for one cycle, then boost for one cycle. The equivalent ripple current frequency now include 1/2 switching frequency content, which can be seen as increased ripple. This is related to the transition mode and it should not be a concern. Please understand that it is the cost to get higher efficiency in the transition mode, which is desired for Vin = ~Vout.

    Thanks,
    Youhao Xi, Applications Engineering