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LMR61428 application note for the SEPIC configuration

Ioannis Mourtsiadis1
Prodigy 100 points
Other Parts Discussed in Thread: LMR61428, LM2621, LM3481

Hi,

I'm looking for an application note, describing the SEPIC configuration of the LMR61428. As mentioned in the datasheet the LMR61428 could be configured as a SEPIC converter. I will need to have it working for the following parameters:

Vin MIN = 3.3V

Vin MAX = 12 V

Vout = 5V

Iout 1.5 A

Thank you for your kind support

  • 0
    Prodigy 100 points

    Hi,

    Anybody from TI technical support can help me please, I just need an App Note about SEPIC converter for the LMR61428.

    Thank you in Advance

  • 0 in reply to Ioannis Mourtsiadis1
    TI__Genius 15810 points

    Hello,

    Sorry for the late reply. There is an example of SEPIC on the datasheet of a similar part LM2621 (http://www.ti.com/lit/ds/symlink/lm2621.pdf). We do not have any other app notes for SEPIC implementation using the LMR61428.

    But as such for your load current, the switch current is going to be more than 2.85A which is the max that the LMR61428 can support. For 3V input, you should be able to use the LM3481 low side controller.

    Regards,
    Akshay

  • 0 in reply to Akshay Mehta
    Prodigy 100 points

    Dear Akshay,

    Thank you for your answer. I would then ask you in another way, how can I calculate the maximum load current I can have with  LMR61428 with the following parameters:

    Vin min = 3.2 V

    Vout = 5V

    Iout = ??

    Using it as a SEPIC or just Boost Converter. I need to know if this chip (due to excellent price) can fit-in in any way to my project (even down sized) requirements.

    Thank you in advance for your prompt reply

    Warmest Regards

  • 0 in reply to Ioannis Mourtsiadis1
    Prodigy 100 points

    Hi,

    Anybody from TI technical support can help me please, I just need some guide in order to decide if I can use the LMR61428 for my application.

    Thank you in Advance

  • 0 in reply to Ioannis Mourtsiadis1
    TI__Genius 15810 points

    Hello,

    Assuming a 40% ripple ratio on the inductor current and allowance of up to 90% of max switch current rating, you could use the following formula to figure out the max load current possible:

    Iout = 0.9*Iswrating*(1-D)/1.2

    For LMR61428, Iswrating is 2.85A and D for SEPIC and boost topologies can be calculated as follows:

    Dsepic = Vout/(Vout + Vin)

    Dboost = (Vout-Vin)/Vout.

    I hope this helps.

    Regards,
    Akshay