• State Resolved
  • Locked Locked
  • Replies 3 replies
  • Subscribers 62 subscribers
  • Views 278 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

TLVM13640: Buck Converter

Kishan Suchet Palani
Prodigy 10 points
Part Number: TLVM13640
Other Parts Discussed in Thread: TLVM13620

Tool/software:

Hi,

I am designing in a new buck converter targetting an output voltage of 5V @ 2A with an input of 32VDC. This 5V is the main supply line for many buck converters and LDOs. I have the following questions:

1. I had found the following reply on a similar question posted on your forum and I am unable to simulate the system and have the following query: 

The webench model does not allow me to use the number of capacitors we currently have. We plan to have 2x47uF(suggested by the tool), 3x100uF(electrolytic), 6x100nF and a few more smaller decoupling caps. Could you please tell me if this would affect the integrated loop compensation or cause issues with the output? 

2. It is stated that the Pk-Pk inductor ripple currnet is to be 30-50% of the maximum rated current(max 2A for a 4A module). However, the Webench module provides a ripple current of about 2.59A, which amounts to about 0.6475A @1MHz switching frequency. Would this be a recommended operation condition for the chip?

3. The webench model does not allow for simulations to be performed(it says simulation is not enabled for this model), is there any other way I could do a simulation of my intended circuit? I am also getting different answers for the Pk-Pk Inductor ripple current on the web bench model and the Quickstart calculator for the buck converter. Is there one I should consider to be more accurate, as I usually rely on the Webench model for simulations/power calculations. 

Thank you for your time, 

Kishan

  • 0
    TI__Mastermind 22300 points

    Hi Kishan,

    I have numbered my answers to match the questions:

    1) The amount of capacitance you have on the output should be OK, but it is true that too much output capacitance can have a negative impact. Your effective total cap is also likely lower than the rated values. Often our recommended BOMs in the datasheet represent the minimum amount of capacitance for stability so you can use the lowest component configuration. 

    2) Refer to Section 8.3.5 of the datasheet. Even for the 2-A configuration, you are targeting the current ripple for the maximum possible output of the device. When designing for converters and modules, you need to size the components for the maximum possible output, even if you plan to operate nominally below that value. The recommendation for current ripple is always at the maximum rated current. For your application targeting 2A, you should use the 2A device: https://www.ti.com/product/TLVM13620

    Table 8-4 shows the recommended Fsw for various input and output configurations. If you follow these recommendations in the datasheet you will have a stable design.

    3) If you scroll down below the schematic on Webench, you will see estimated phase margin along with other parameters. We do not have simulation models available for this device outside of the Webench estimations. 

    Best regards,

    Ridge

  • 0 in reply to Ridge Lahti
    Prodigy 10 points

    Hi Ridge,

    Thank you so much for your reply.

    1) Thank you for your input. We like to have as much decoupling as possible to prevent noise/ringing. Good to know that the output capcitance would not affect the output.

    2) The maximum possible current that we expect from the power supply is 2A(not all the time, but maybe a few spikes ~1.9A). We have chosen this device to have enough derating for our application. A correction on my post: I had posted that the ripple current is 0.6475A @ 1MHz, it was supposed to mean 2.59A ripple current which amounts to 64.75% of 4A(Maximum current) at 1MHz. Would you advice against using a 4A maximum output device, even though our application would never cross 2A output current? 

    3) Great, thank you for letting me know. I was looking for simulations like on other devices for scenarios such as start up, full load etc. I will take a look at these graphs.

    4) Thank you for pointing to TLVM13620. It appears to be a very similar device(inductor size, switching frequency etc.) to TLVM13640. However, I am still worried that the ripple currnet would be far greater than the recommended limit, a 2.59A ripple current would mean ~130% of maximum output current. Would this be recommended?

    5) This brings me to another question, Are these devices meant to be operated with standard input 12,24 upto 28V? Meaning that 32V getting converted to 5V is not a typical application scenario and might not be suitable ?

    Thank you for your time

    Kishan

  • 0 in reply to Kishan Suchet Palani
    TI__Mastermind 22300 points

    Hello,

    The TLVM13620 is better suited to your application. If you follow the recommendations in the datasheet for configuring a 5V output application, your design will be OK. 

    These modules are optimized for specific conditions since the inductor is included inside the package. If you follow the recommendations in Section 8.3.2 of the datasheet and use the recommended 1MHz switching frequency, the design will be stable. The ripple should not exceed a the current limit rating of the device.

    The 4A and 2A devices are optimized for their respective maximum currents. The ripple estimation on the 4A device does not apply to the 2A device,.

    Your 32V input should be OK. What we show in the datasheet are often the most common application rails. Just make sure to have appropriate clamping on the input if you expect line transients to go beyond the absolute maximum rating of the device.

    Best regards,

    Ridge