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LM5021 slope compensation

David Woo
Prodigy 530 points
Other Parts Discussed in Thread: LM5021

 

We have some questions on the slope compensation design of LM5021. It seems that there is not too much design rules for this. I can only see only few description about the slope compensation. This is not enough for us to design the slope compensation.

Could you send me the calculation details on how to design the slope compensation of LM5021?

  • 0
    TI__Guru* 86266 points

    Hello David,

    I reviewed the LM5021 data sheet and there is an internal 0 to 50uA that is used to generate slope compensation. There is 1.8k ohm resistor internal from the CS pin to the PWM comparator.  This gives 90mV of slope compensation if an external resistor is not added between the CS pin and the current sense resistor.

    If more slope compensation is needed you can use an external resistor (Re) between the CS resistor and the current sense (CS) pin.

    The dv/dt = fs*50uA*(Re+1.8kohm). This needs to be set to support 0.5 the inductor’s current down slope (di). 

    The following equation should help to set the slope compensation (di/2)*Rs = 50uA*(Re+1.8kohm)

    Regards,

    Mike