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TPS43061: Output voltage decreases with load: TPS43061

Part Number: TPS43061
Other Parts Discussed in Thread: CSD17556Q5B

Hello,

i'm having a little design issue with the output voltage regulation of the TPS43061 boost converter. The design was done using the Webench tool as seen on the file and the only thing i changed were the sensing resistor to the nearest value on the market (the original design gave a resistor value of about 4.2 mOhm and i changed them to 5 mOhm) and the transistor M2 for a CSD17556Q5B. I also added the resistor Ruvlo_H = 13.3 KOhm and Ruvlo_L = 1.96 KOhm for the enable pin to the design. When i tested the circuit board i designed it was giving, as expected, the 12V output (i'm trying to step up from a 3 cell LiFePO4 Battery from 9.9v to 12v to drive two DC Motors), but as soon i added some load at about 0.5 Amps the output voltage dropped to 11.51V. What could be the reason of this voltage drop? What should i change on the design in order to get the fixed 12v regardless of the load current? 

Note: The maximun load peak current i'm expecting to have is about 7.5 Amps.

If it helps here's the pcb board i'm using. Thanks in advance for your help!

Regards,

Emmanuel Santiago Iglesias

webench_design_Boost.pdf