I am making a 5A LED driver using MP24830. The switching FET is getting quite hot. On checking the gate with a scope I am seeing Vgs maximum just over 5V. This is enough to turn on but Rds remains higher than desired and I suspect this is causing the heat. I have tried increasing the bootstrap capacitor (even up to 1uF) - no difference. I’ve tried a few FETs too - FDD86367 (original), TK65G10N1, even IRFS3607PbF with a higher Rds but lower Qc to see if it makes a difference to the gate voltage - but it doesn’t.
Can someone advise the Vdr (pin1) - Vsw (pin 14) expected? Or any other advice here?
Hello Kaykay,
A quick look at the data sheet shows that the BST voltage is regulated at 5V or so, with a max of 6V, so it will require MOSFETs with a rated Vgs of 5V for the application. The eval boards for the device have those but are for lower LED current of 1A. What you can do is find a 5V Vgs MOSFET and plug the specs into the design spreadsheet to estimate the losses and then the thermals. The spreadsheet is on the device page as you scroll down:
Keep in mind 5A is very high for a single MOSFET LED driver, so likely will be thermally challenged.
Regards,
Keep in mind 5A is very high for a single MOSFET LED driver, so likely will be thermally challenged.
Would you recommend multiple FETs? Currently I have a switch on time around 500ns, switch off looks better - see picture. At 100khz this is considerable. I fear more FETs will only make this worse.
