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Question for LTC3309A application

I have used LTC3309A from 5Vin to 3.3Vout, Frequency:2MHz(With RT connecting to Vin for Default value), and Vout  setting for 3.3V; Sync/Mode is tied to Vin for Burst mode.

Question/Problem: I find the output voltage is dropped with the load is rised, ez: output current 0A, vout:3.3V; ouput current 1A, vout:3.25V; output current 3A, vout: 3.18V; output current 6A,

vout:3.1V.  This problem will cause my FPGA core voltage not steady and may make my FPGA broken down. Would someone help me to handle this case. Thanks.

  • Hello,

    There could be a few reasons why the load regulation might not be as good. Small 0402 or 0201 (better) VIN to AGND and a VIN to PGND should be placed as close to the pins as posible. Please see the Low EMI PCB Layout section and pin discriptions in the LTC3309A datasheet for more information on this. Is the FB sensed close to the load? Where is the output measured? Is there a kelvin connection to the ouput?

  • Thanks for your answer.

    Below is my layout. I use one line to connect the IC's AGND with peripheral devices. The small 0402 capcitor is a little far from my Vin pin. Would this cause my load regulation be worse than ideal design?

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