You have hit on the key issue; I have a “standard hat”, but I also want to use the functionality of a power mode 1 hat (firmware automatically sets usb_max_current_enable=1).
I see a couple of ways to get this not sure which are legal/correct.
1)Two hats (one standard and one power mode 1)
2)Two EEPROMs (one standard address and one power mode 1 address) on the same hat
3)A standard/power hat but with a power mode 1 address
4)A standard/power hat with some method of set usb_max_current_enable=1 from EEPROM dtoverlay
The last is the best but I do not know how to make the firmware setting from dtoverlay? If I can not do that then it looks like I will build and standard/power hat with a power mode 1 address and just not be in compliance with the hat+ standard.
On the issue of a 5v/5A MOSFET I understand the need to have a MOSFET that goes to Min RDSon at a voltage 10% to 20% below the target voltage of the buck (so 4.5v to 4.0). what I am not sure I have correct is how to calculate power dissipation; if I have it right it would be P=(I*I) R since the duty cycle is 100% that can be ignored. The AO4409 is obsolete and the substitutes prices are quite high so I was looking at is https://assets.nexperia.com/documents/d ... 8-20QX.pdf and it’s max RDSon resistance is 30mOmhs so at 5A it would need to dissipate .75watts max. That looks well within the 1.7W (Ta). Let me know if I have this wrong.
I see a couple of ways to get this not sure which are legal/correct.
1)Two hats (one standard and one power mode 1)
2)Two EEPROMs (one standard address and one power mode 1 address) on the same hat
3)A standard/power hat but with a power mode 1 address
4)A standard/power hat with some method of set usb_max_current_enable=1 from EEPROM dtoverlay
The last is the best but I do not know how to make the firmware setting from dtoverlay? If I can not do that then it looks like I will build and standard/power hat with a power mode 1 address and just not be in compliance with the hat+ standard.
On the issue of a 5v/5A MOSFET I understand the need to have a MOSFET that goes to Min RDSon at a voltage 10% to 20% below the target voltage of the buck (so 4.5v to 4.0). what I am not sure I have correct is how to calculate power dissipation; if I have it right it would be P=(I*I) R since the duty cycle is 100% that can be ignored. The AO4409 is obsolete and the substitutes prices are quite high so I was looking at is https://assets.nexperia.com/documents/d ... 8-20QX.pdf and it’s max RDSon resistance is 30mOmhs so at 5A it would need to dissipate .75watts max. That looks well within the 1.7W (Ta). Let me know if I have this wrong.
Statistics: Posted by wkeeling — Wed Dec 11, 2024 5:27 pm