electric1
Junior Member level 2
Hi,
I built a prototype of battery charger, using LTC4020 which fits many of my requirements. I also have their demo board which proves that it can work in my application, 4S LiFePO4 battery, 14.4V CC/CV charging profile, 8A current limit.
My experience is with low power digital circuits and MCU programming, I don't have much experience with PWM power circuits, although I built a few simple buck converters before, with various success. This is my first project at ~100W power level and I need high efficiency due to small project footprint and limited airflow for cooling.
I tried to make my PCB layout similar to the demo board, followed application notes as much as I could, etc.
In the end my prototype seems to be functional without a load, i.e. it holds correct output voltage, I can see PWM forms on my scope, they seem to be similar to signals observed on the demo board, but as soon as I apply the load, even 2-3 Amps, my FETs heat up within few seconds forcing me to cut the load to prevent burning up FETs.
I tried few different FETs, same and similar to what demo board has and what is recommended in app notes. Selected FETs for low Qg and low RDSon balance, which I believe is important to minimize both switching and conduction losses. Same results every time, immediate heating up of FETs, bottom ones heat up noticeably faster than top ones.
I use the circuit as buck in my testing, input voltage is 28V, output is 14.4V
Any advise how to troubleshoot this problem? My schematic is essentially the same as the demo board.
I'm even willing to pay someone with experience to help me, but I don't know if its against the rules here or how to even approach such engagement.
I built a prototype of battery charger, using LTC4020 which fits many of my requirements. I also have their demo board which proves that it can work in my application, 4S LiFePO4 battery, 14.4V CC/CV charging profile, 8A current limit.
My experience is with low power digital circuits and MCU programming, I don't have much experience with PWM power circuits, although I built a few simple buck converters before, with various success. This is my first project at ~100W power level and I need high efficiency due to small project footprint and limited airflow for cooling.
I tried to make my PCB layout similar to the demo board, followed application notes as much as I could, etc.
In the end my prototype seems to be functional without a load, i.e. it holds correct output voltage, I can see PWM forms on my scope, they seem to be similar to signals observed on the demo board, but as soon as I apply the load, even 2-3 Amps, my FETs heat up within few seconds forcing me to cut the load to prevent burning up FETs.
I tried few different FETs, same and similar to what demo board has and what is recommended in app notes. Selected FETs for low Qg and low RDSon balance, which I believe is important to minimize both switching and conduction losses. Same results every time, immediate heating up of FETs, bottom ones heat up noticeably faster than top ones.
I use the circuit as buck in my testing, input voltage is 28V, output is 14.4V
Any advise how to troubleshoot this problem? My schematic is essentially the same as the demo board.
I'm even willing to pay someone with experience to help me, but I don't know if its against the rules here or how to even approach such engagement.