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LM5176-Q1: Design review

Jeffrey Chung1
Genius 3300 points
Part Number: LM5176-Q1
Other Parts Discussed in Thread: LM5176

Hi,

I'd like to request the design review of LM5176-Q1. First review had already been done on previous post. Revision details are as follows. Please refer to the attached schematic.

1. Added CV(Constant Voltage) control circuit / 2. Changed inductor and value (GSTL1770P series) / 3. Changed VIN range (12V~18V) / 4. Changed MOSFET (NVMFS5C410NL)

Schematic_LM5176-Q1_05OCT2020.pdf

Additionally, my customer's questions are as follows. please kindly answer me about questions below.

1. Is there any problem on selecting inductors like below? (conditions that charge starts from 12V and max charge current is 33A)

Inductor_GSTL1770P series.pdf

2. Is this two phases possible to control CC and CV simultaneously?

3. If so, the slave also is followed if the master FB only is controlled. right?

4. When master comp pin is 0V(off), slave comp pin is 0V(off) too? Please explain in more detail.

5. Do you have a document how to calculate VOUT by PWM frequency for CV control?

6. What is the reason why RC snubber circuit(D to S of MOSFET) should be deleted on previous design review?

7. I want to delete the MOSFETs of Q6, Q42, Q10, Q45 for cost reduction. Is there any problem?

Regards,

  • 0
    TI__Guru 65200 points

    Hello Jeffrey,

    Let me try to answer your questions:

    1. Is there any problem on selecting inductors like below? (conditions that charge starts from 12V and max charge current is 33A)
    It seems that the inductors are ok. Why did you mark the 1uH inductor?

    2. Is this two phases possible to control CC and CV simultaneously?
    The 2 phases regulate the output voltage and the additional opamp for the sensing of the output current make sure that they share current. The devices then can individually limit the current, but will not regulate the voltage if the current is limited.

    3. If so, the slave also is followed if the master FB only is controlled. right?
    The slave has its own feedback and the external opamp makes sure that they share current evenly, see this app note: 

    4. When master comp pin is 0V(off), slave comp pin is 0V(off) too? Please explain in more detail.
    Why do you expect this?

    5. Do you have a document how to calculate VOUT by PWM frequency for CV control?
    The output voltage is not dependent on the PWM frequency. The output voltage is regulated.

    6. What is the reason why RC snubber circuit(D to S of MOSFET) should be deleted on previous design review?
    Which MOSFET are you referring to?

    7. I want to delete the MOSFETs of Q6, Q42, Q10, Q45 for cost reduction. Is there any problem?
    You need to check in your design if the remaining transistors get too hot.

  • 0 in reply to Brigitte
    Genius 3300 points

    Hi Brigitte,

    Thanks for your support. Please refer to my answers below on your additional questions.

    1. Is there any problem on selecting inductors like below? (conditions that charge starts from 12V and max charge current is 33A)
    It seems that the inductors are ok. Why did you mark the 1uH inductor? --> Because L2(GSTL1770P-1R0M) is 1uH inductor.

    4. When master comp pin is 0V(off), slave comp pin is 0V(off) too? Please explain in more detail.
    Why do you expect this? --> They want to make sure whether master comp pin only is controlled for two phases control or master/slave comp pins are individually controlled.

    6. What is the reason why RC snubber circuit(D to S of MOSFET) should be deleted on previous design review?
    Which MOSFET are you referring to? --> (C211, R160), (C210, R158), (C217, R171), (C218, R173) Please refer to the previous reviewed schematic below.

    5824.TI DR_0724_Reviewed.pdf

    Regards,

  • 0 in reply to Jeffrey Chung1
    TI__Guru 65200 points

    Hello Jeffrey,

    1. Ah, the 1uH inductor is used in the input filter circuit, sorry, did not check this part.

    4. The COMP pin of the devices shall be independently controlled, as the devices shall regulate independently. Please remove the CC_LIMIT connection to the COMP pin of the subordinate (slave) device. This shall never be connected to the COMP pin of the master. The subordinate with follow the same current as defined for the main (master) controller by the sharing circuit.

    6. Thank you for sharing the first reviewed file. You had 2 snubber circuits on all 4 switch nodes. There is only one snubber per switch node necessary and it should be the one on the rectifier transistor. If you place the other snubbers as well, they might ring with each other. So please remove them.

    7. BTW, I would place the MOSFETs in the design, even if you keep them unpopulated at the beginning. If they are on the board you have the possibility to populate them if the single ones are getting too hot.

    The schematic looks as recommended then. Please keep the layout recommendations in mind.

  • 0 in reply to Brigitte
    Genius 3300 points

    Hi Brigitte,

    Thanks for your kind response. Let me ask you if they have some additional questions.

    Regards,

  • 0 in reply to Brigitte
    Genius 3300 points

    Hi Brigitte,

    I'd like to ask you one more question. You said that The output voltage is not dependent on the PWM frequency and the output voltage is regulated. I think that it means CV control PWM circuit(Master #1 LM5176 section) in schematic is not needed. Is it right? If so, should be deleted that circuit?

    Regards,

  • 0 in reply to Jeffrey Chung1
    TI__Guru 65200 points

    Hello Jeffrey,

    The switching frequency is constant. The PWM is regulating the output voltage by changing the duty cycle, not the frequency.

    I am confused why do you think you can remove the main constant voltage regulation? If you remove this the device will not operate properly.

  • 0 in reply to Brigitte
    Genius 3300 points

    Hi Brigitte,

    I'm sorry that I misunderstood as you said on previous post. Thanks for your clear explanation.

    Regards,