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LM34936: Hiccup current limit

Naveen Kumar
Prodigy 30 points
Part Number: LM34936

Tool/software:

Hi,

Please clarify, We have an issue with the Hiccup current limit feature.

Vin Min: 10V

Vin Nom: 12V

Vin Max, 24V

Vout - 18V

Output Current Max: 10A

Fsw – 250KHz

Inductance: 2.2 uH

I have enabled the hiccup by connecting the Mode Pin to GND via a 93.1k resistor.

No issues on 24V operation, but when the converter is in boost mode (12V operation) and if I increase the load between 6 - 7A, at this point the converter enters into hiccup mode current limit.

I have not used the average current limit option; rather, I have used a 5-mohm current sense resistor on low-side MOSFETs and connected to the CS-CSG Pins. 

As per calculation, the peak inductor current threshold at boost mode is set for 24 A. The inductor saturation current is 62 A.

Can I change the sense resistance from 5 mohm to 4 mOhm? So that the peak current limit threshold will be 30A. Also, do I need to alter the slope capacitance value? Currently it is 180 pF.

Best Regards,

Naveen

  

  • 0
    TI__Genius 15545 points

    Hi Navee,

    Thanks for reaching out.

    We will look into this and be back with an answer until beginning of next week.

    Thanks for your patience.

    Best regards

    Moritz

  • 0 in reply to Moritz
    TI__Guru 58361 points

    Hi Naveen,

    as you can see from the scope plots your current in the inductor and the corresponding voltage on the Current Sense resistor at CS/CSG is reaching the current limit level. Therefore the HICCUP mode can be triggered.

    You need to decrease value of  the current sense resistor - so the 4mOhm could be a good option.

    Yes, slope compensation should be readjusted.  Please use the formula given at:

    8.2.2.8 Slope Compensation

    Best regards,

     Stefan