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LM5176: Difficult to find a stable COMP network to work using dinamic Vout change and current limit

Part Number: LM5176
Other Parts Discussed in Thread: PMP10594, TLV272

Dear Sirs.,

I write to receive Help to find a method for determining the best COMPENSATING network connected to COMP pin, so the LM5176 can work fine on the entire VIN (10V-30V) and VOUT (11V-32V) ranges.

I must use the LM5176 as battery charger for 12V and 24V batteries, so my input voltage can be from 10V to 30V and the same for the output voltage, clearly the Vout is dinamically changed injecting a current on the FB network and I used the same current limit method on the Application Note SNVA846 + PMP10594 demo board. I must adapt the current limiting value and Vout based on the application field and situations but with the same hardware.

I'm using a switching frequncy of about 100kHz (82kOhm on RT pin) and what happen is that at NO LOAD I can ear an audible noise on the bulck capacitors or on power inductor, the same with some load conditions (5A, 10A etc...) and Vout values combinations. But if I set a Vout that at NO Load don't emit noise and the gate signals are stable, for example 15V in the output with 12.3V in the input, I can add load to the charger up to 750W wihout any problems, and it reamin stable and supply a very large amount of power with a very stable Vout.

I tested many combinations of Compensation Network values, but I have Always stability problems or for some Vout-Vin values and then also during curren limiting by external circuit with TLV272 opamp.

Since I can't satbilize it for a simple 12V battery charger with input range from 10V to 16V and Vout form 11V to 15V my question is could it works stable for a larger Vin and Vout and Load current ranges? Can I trust on this BUCK-BOOST Controller or I should choose another one, for my project?

Could you help me in this hard goal (for me)?

Thank you in advance!

 

  • Hi Pierannuzi,

    Thanks for reaching out with you questions and for considering the LM5176 in your design.

    The best starting point is using the LM5176 quick-start calculator to help calculate the correct loop compensation components. My advice is to start with the worst case operating condition (minimum input voltage and output voltage set to 24V). 

    snvc208 (1).zip

    Please let me know if you have any questions.

    Thanks,

    Garrett

  • Dear Mr. Garrett,

    thank you for your support, but I just tried to Mount the Capacitos and resistors values suggested inside the quick-start calculator, but the converter begin srongly unsatble! After start-up (connected the Vin at 12V) it emit a strange sound and I can't regulate the outptut voltge (simply by a trimmer and a resistor in series with the FB pin).

    The only combination of value that stabilize the converter are: Cc2 = 1uF, Cc1 = 3.3nF and Rc = 22K, and Cslope = 100pF

    You can see that these values are very different respect the suggested in my case by quick-start calculator:  Cc2 = 390pF, Cc1 = 2.2nF and Rc = 22K, and Cslope = 820pF, mainly about Cslope and principally Cc2.

    Consider that with my "almost stable" setup (Cc2 = 1uF, Cc1 = 3.3nF and Rc = 22K, and Cslope = 100pF) I can fix the output voltage at 14.4V and supply form 5A to 40A without problems, but if I change the output voltage there are some values that make the converter unstable with or without load current.

    Have you any idea how I can do to find a solution?

    Thank you in advance.

  • Pierannuzi,

    Can you please post the schematic that you are using? This will help me double check the compensation values. What is the maximum load current of the output voltages?

    Thanks,

    Garrett

  • Dear Mr. Garrett,

     Can I have your email address to send the schematic drawings? Since it is a project for my company, I don't wish share it on the forum, Is it possible?

    Thank you in davance!

    Best regards, 

  • Pierannunzi,

    I have sent you a friend request. Once you accept that you can send me a direct message with the schematic. This was the schematic will not be shared publicaly.

    Thanks,

    Garrett

  • Dear Mr. Garrett,

    I sent you the private message, I hope you cna help me to solve my situation.

    Thank you in advance.

    Best regrads,