Hello! I am putting together a design which uses the MPQ4228-Q (automotive QC3.0 DFP) and in its typical application circuits (Figure 17 and 18) there is this one resistor of 10 Ohms (R11), which is placed between SW and OUT, which I guess has the role of an RC filter, along C9. However, I am not sure what its power rating should be. Given the fact that this IC does not have a dev board, I could only look at the footprints of the resistors in the PCB Layout Guidelines and I can only assume it is not rated for over 0.5W. I could not locate it, but I have neither seen resistors which have a big footprint, so I assume they are all rated for under 0.5W, which I find kind of weird given the fact that it is placed between two power output pins (which have high currents passing through them). Please let me know what its power rating should be! Thanks in advance!
Hello,
You are right to assume the role of R11 and C9 in the Typical application as shown in Figures 17 and 18. This is corroborated in the datasheet pin functions as shown:
As for the power rating of these parts, that would really depend on the power level that you plan on using for your load. What is your expected peak load current and output voltage here?
Well by looking at its TYPICAL CHARACTERISTICS (page 10/33) I can see that its output voltages are 5V@3A / 9V@2A / 12V@1.5A, which correspond to QC 3.0 Mode A…ish. (Follow-up Question: Can it output more than this? For example 12V@3A?)
So the max current is 3A. If the 10 Ohm resistor were to dissipate all the 3Amps, it would need to be rated for R*I^2=90W. By looking at various such resistors on Mouser, i could only find such resistors which have a really big package (such as the PF2272-10RJ1), which is also really expensive. So I guess, again, by looking at the PCB Layout Guidelines that the power rating of it should only absorb the voltage spike of the output. (which, in worst case scenario, should be around 10%-ish?) so I could, theoretically, put a 10 Ohm resistor which should be able to dissipate 1W. Correct me if I am wrong, please!
Hello again,
Correct, the max capable current is going to be 3A. However at 12Vout at the bus, the max current caps at 1.5A where 3A maxes out at a 5Vout bus voltage.
However I can understand the question given the maximum limits on the recommended settings:
I believe 12V @ 3A should be possible here but I will double check with the PLs here and get back to you here. I have a feeling there is also a dependency on the higher input voltage.
As for that resistor in accordance to the PCB Layout Guidelines, you should be ok.
Best,
Krishan
Hello! Thanks for your reply. For the reference, I do not want it to go above 12V 1.5A (~20W) because the input of the MPQ4228-Q will be a stable 12.92V source capable of only up to 2A (~25W), until thermal throttling, so I will stick to the default 5V3A, 9V2A and 12V1.5A. Thanks!
Understood, these currents and voltages are well corroborated in the datasheet, so this would be good to stick to. Let me know if there are any questions outside of what we just discussed for the MPQ4228.