I have a customer who has observed the following:
Question on TPS55340Q. I have designed a boost regulator using your TPS55340 part. The input is from 8.5 to 12.6V. The output is set to 13.5V. The regulator is capable of 3A output current. In a new version of my PCB I find that the regulator is dropping out of regulation when the output current is about 2.2Amps. I have noticed that a previous PCB version of the same schematic, which had no problem delivering the 3A output with a 9Volt input, has the SYNC pin and AGND pin connected directly together. On the new PCB (same schematic) the SYNC pin is connected to GND through a trace that is approximately 10mm long. Again this PCB has problems delivering the 3Amps output at 9V input. Now, when I put a solder-ball between the AGND and SYNC pins, this PCB will then deliver the 3A output with 9Vinput. Can you give me an explanation why this is occurring? I have verified this situation in 3 of the new PCBs and have successfully fixed it, with the solder ball between SYNC and AGND, in all 3 cases. I will note that I am running the controller at a frequency set by the external resistor (I use 78.7Kohm). The SYNC is not used so I am tying it to GND. Looking forward to your response on this strange behavior
I stressed that the data sheet states that they must be directly connected together, but he asked why the short trace could cause this issue. Do you have any explanation? Can there be any voltage differential between the pins for the part to regulate properly?
Please let me know if you have any further questions. I can supply the schematic etc. if need be off-line.
Thanks for your help with this!
Richard Elmquist
