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LM2621 - Boost Regulator -5V, 1A

Atul Bhakay
Genius 3205 points
Other Parts Discussed in Thread: LM2621

Hi, this is Atul Bhakay

I have tried using LM2621 in a boost regulator application. All the part values are as per the datasheet except the 6.8uH coil (i got a 10uH inductor). I have several problems as under:

1.  At the FB pin, i get 1.36V instead of 1.24V

2.  When the Feedback voltage divider resistors are 150K and 50K, i get 3.7V instead of 5V.

3.  I readjusted the 50K value with a lower value to get 5V

4.  I have connected a rheostat as load and current meter. The voltage starts dropping after 70mA.

There are indeed some issues with the layout (the inductor is not placed very near to the device). At this stage even if we get something close or even half of the target ratings, it would be enough. We shall rectify all the issues in second iteration.

But in the meantime, we request you to guide us through this development stage                             .     

 

  • 0
    TI__Genius 10115 points

    Ok.

    To try to get more current try a couple of things.

    1)  You can increase the size of the Rt (AKA RFQ) resistor.  It is 200K on the front page of the datasheet.  A webench design came up with 909K.

    2)  Look at your grounding between Pins 1 and 7 and your output capacitor.  You want this capacitor to be as close as possible to these pins to reduce output voltage noise.  If there is too much noise here it could cause the switchto be turning of early.

     

    Regards,

    Marc