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TPS63051: Input current limit - Buck operation

Carlos Silva85
Expert 4915 points
Part Number: TPS63051


I’m having trouble with my device reaching the target value of 3V3 when starting up – I think this is caused by the adjustable current limit. I have ILIM0 set high and ILIM1 set low, limiting the current at start-up to 0.5*IIN_MAX. However, I am using the part purely as a buck converter (regulating 5V down to 3V3) and IIN_MAX is only specified for the when the device is in boost mode.

Can a value / range for I­IN_MAX  be provided for the part when operating in buck mode? I'm expecting Imax =<500mA

  • 0
    TI__Expert 8420 points
    Hi Carlos,

    the current limit for your operating conditions is expected to be in the range of 225mA (=550/2) to 700mA (=1400/2).
    the In_max can only be tested in boost mode therefor specified only in boost mode. A buck-boost converter consumes more current in boost mode than in buck mode for the same load. However during start up, eventhough Vin>Vout, the inrush current could reach 700mA.

    could you test it again test it again increasing the available power at the input?
  • 0 in reply to Sabrina
    TI__Expert 4915 points

    Hi Sabrina,

    Thank you for your reply.

    What makes the maximum input current only measurable in boost mode? What changes when the device operates in buck?

    I understand there will be a difference in currents based on Vin and Vout for a given power level, but I don't understand how the current limit works internally. Does it measure average input current? Inductor current (if so where?) or output current? A block diagram of the device internally that would allow me to understand its workings would be fantastic!

  • 0 in reply to Carlos Silva85
    TI__Expert 8420 points
    Hi Carlos,

    the current is measured at the high side switch at the input. this switch is "always closed" only during boost mode, which makes it possible to measure it with our automated test equipment. the block diagram is shown on Fig.4 of the datasheet.

    What is your available power budget at the input of the converter?