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LMQ66410: Efficiency at light load mode

Fabio Leitao
Prodigy 140 points
Part Number: LMQ66410
Other Parts Discussed in Thread: LMR43610, LMR36501, LMR36500, LMR36502, LMR36506, TPS7A26, TPS62903, TPS62901

Hi TI team,

We have been using the TPS62740DSSR for a low power application. Among other great features, this device shows an efficiency up to 90% at 10µA Output Current.

However, a new requirement for voltage input is need and is this case, the application will require an input voltage from 4V to 16v, Max load current < 300mA.
Additionally, it also requires a high efficiency when operating with a light load.


The LMQ66410 seems to be suitable for this application, even though the converter's input range (up to 36V) and the max current are larger parameters than required.
 - Is there any other option that could be suggested? 
 - I.e, the LMR43610 also seems a good option, is it the main difference the integration of the Cboot and Vin capacitors?
What would be the best way to estimate /compare the performance of these alternatives in terms of efficiency, compared to the initial device TPS62740DSSR special when operating with a light load?

Thank you for your attention.

  • 0
    TI__Mastermind 21000 points

    Hi Fabio,

    I think for light-load efficiencies, you may want to look for the LMR36500, LMR36501, or LMR36502. It can run into light loads up to 200mA, which may help with your efficiency requirements.

    Usually for comparing efficiencies, I suggest checking the application portion of the DS for some initial comparisons. 

    Thanks,

    Richard 

  • 0 in reply to Richard Fu22
    Prodigy 140 points

    Hi Richard,
    Thank you for your reply.

    I had a look on your suggestion and was checking the LMR36506 ( up to 600mA from the same family).
    I was trying to get some efficiency and input current estimation using the Webench tool.
     
    Here is the link for the circuit and configuration using the LMR36503RFRPER.
    Vin = 8.5V, Vout = 2.8V, Iout = 1uA

    (webench.ti.com/.../SDP.cgi

     
    From the system information, considering that the output current is around 1uA - 10uA, the efficiency shown is very low (around 0%- 2%). That might increase the input current to some hundreds of uA or maybe in the mA range.

    On the other hand, the TPS62740DSSR (Vin=4.2V, Vout = 2.8V) shows an efficiency of around 48% considering an output current of 1uA, keeping the input current < 2uA. This is also observed in our experimental tests.

    So, the LMR36506 compared to the TPS62740DSSR, doesn't seem to be a good alternative. 

    Could you provide some recommendations considering this information?

    i.e The approach of using an LDO (maybe the TPS7A26 ) for the light load as described in the following (https://e2e.ti.com/blogs_/b/powerhouse/posts/how-to-improve-buck-converter-light-load-efficiency-with-an-ldo-part-2) could also be considered.
    But because in our application the range between the low/high load current profiles are in the hundred mA difference, (<1A) probably and alternative similar to the TPS62740DSSR but with higher input range could be suggested.

    Thank you for your attention,

    Best regards,

    Fabio



  • 0 in reply to Fabio Leitao
    TI__Mastermind 21000 points

    Hi Fabio,

    In this case, it may be better to take a look at the LMQ66410 for your application. However, if the efficiencies in that part is not enough, I've also looped in the low VIN buck converter apps team to help find a reasonable solution.

    Thanks,

    Richard

  • 0 in reply to Richard Fu22
    Prodigy 140 points

    Hi again,

    I've just used the Webench tool for the LMQ66410, the efficiency is slightly better compared to the previous but still bellow 5%, which makes it not good enough for our application (considering the results using the TPS62740DSSR).

    I'll be waiting for further feedback.


    Thank you for your support,  


    Fabio

  • 0 in reply to Fabio Leitao
    TI__Mastermind 29760 points

    Hello, 

    can you look into TPS62903?

    Thanks 

    Tahat

  • 0 in reply to Tahar Allag
    Prodigy 140 points

    Hi Tahar,

    Yes, we have just done some calculations considering the TPS62901 ( from the same family) , and ordered some parts for efficiency measurements.
     
    Thank you for your suggestion.

  • 0 in reply to Fabio Leitao
    TI__Mastermind 29760 points

    Perfect, please let me know if you need further support