I'm using a PTB78560C in a new design and it's causing headaches. It's a fairly simple implementation with only a single load and no tracking. Layout was done following proper procedure and with minimal trace lengths and loop sizes. The design details are:
Ta: -40degrees to +70degrees Celsius
Even though the regulator produces exactly 12VDC, I have two problems:
1) At 20degrees Celsius ambient temperature, the inductor and transformer get very hot (>60degrees Celsius), even while just pushing 5W load power
2) The regulator seems to radiate noise to a profound degree, so much so that I cannot do any worthwhile measurements on the board. Just measuring ground, i.e. both the ground lead and test probe connected at the same point, I get 500mV switching noise with the same light load as before.
Any assistance would be appreciated.
PTB78560C absolute maximum output capacitance is limited to1500uF.
1. The maximum SOA thermal limits for 2 Amp load at 48V is 70°C which under the following external pcb conditions of 100mm x100mm copper planes and no air flow. The 0.5 Amp load to 2 amps load transformer temperature is 60°C or higher when operated at 50V vin.At 2 Amps, the transformer temperature is about 80-85°C.
2. The method to measure conducted emission is with a closely coupled probe on the vin bus± pins across a 1-2.2uf cermaic capacitor . The scope probe must directly contact the +/- capacitors pads,. The scope ground lead must be only 0.3 to 0.5cm long. When the measurement is a long scope prbe , the E-fields , which have no power in them, are easily detected. They do not affect the emissions data.
The best method to reduce radiated emissions is to add a series input filters to reduce EMC emission, whch ultimately reduce radiated emissions. The average radiated emissions are class A limits. A suggested conducted filter is attached.
Thanks for the tips. Would it be possible to reduce radiated & conducted emissions to class B with external filtering or would that require a different converter?
Thanks for the response. The class B is obtainable only if the filters, all of them ,common mode and differential mode ( separate ) components, are located in close proximity to the module.
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