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LM5116 compensation components

Phillip S
Prodigy 90 points
Other Parts Discussed in Thread: LM5116

Hi

I am attempting to work out what the compensation components should be for a LM5116 and I would appreciate some assistance. The datasheet is not particularly straight forward and very technical in this area.

Is there a simple set of equations for working out what the compensation components (Rcomp, Ccomp and Chf) should be?

I tried using the webench to work out what they would be, but there is an error in the webench. It will not allow switching frequencies above 298kHz even though the LM5116 is rated to 1MHz.

Below is a description of the converter.

  • Switching Frequency = 768kHz
  • Vin= 15volts to 35volts
  • Vout=12.4 volts
  • Iout=4.9 amps
  • Ripple Current = 700mA
  • Output Inductance = 15uH
  • Output Capacitance = 300uF
  • Current Sense Gain A = 4.7 (by default it is set to 10)
  • Current Sense Resistor = 0.05ohms

I have considered using a different converter, but I need the high input voltage range, high switching frequency, and high efficiency.

Any assistance would be appreciated.

Thanks

Phil

  • 0
    TI__Expert 6365 points

    Hey Phil,

    The maxim frequency is defined by the off time and on time of the controller and WEBENCH uses a conservative Toff value of 580nS. That is why WEBENCH came up with the maxium operating freq. of  298KHz.  If we were to push the envelop by using minim Toff value of 320nS as specified by the datasheet,  the calculated max freq. will be at 541KHz.  Your 760KHz design won't work at low Vins. it will have regulation issues at around 16.5V. 

    Below is an off time equation determines the maxim operating frequency using Toff (580nS) and your input & output conditions:

     Freq < ( Vin_Min - Vout ) / (Vin_Min *580nS)  

    I would suggest to use WEBENCH for the recommended design and more critically is a good layout which has to be optimized to assure good performance.

    Regards,

    Howard Chen

    WEBENCH Applications Engineer

  • 0 in reply to Howard Chen-WEBENCH Design Center
    Prodigy 90 points

    Thanks for the Info Howard. I do recall reading something about that. It was something to do with charging the boot capacitor? Thanks for the reminder.