Tool/software: WEBENCH® Design Tools
dear
my design is VIN=18~72v, VOUT=12v, ILOAD=3A.
the LM5088-2 :
The RES pin is normally connected to an external capacitor that sets the timing for hiccup mode current limiting. I connected 22nf to GND, the LM5088-2 start up by 0 load ok, and then keep power on , slowly full load ok, but power off after, then power on , start up by 0.1A or full load not work. I changed the res pin capacitor 22nf to 10uf, the start up by full load ok.
and also I checked the Application Note 1913 LM5088 Evaluation Board, the res pin capacitor is 22nf.
1. I want to know why my demo board not work , by the res pin capacitor 22nf ? and how to calculated the res capacitor?
2. the SW RC Snubber Networks such as the Application Note 1913 LM5088 Evaluation Board R6(5.1ohm) and C20(1000pf), I deleted the R6, VIN=30V , alternating wide and narrow pulses at the SW pin, above 30V or below , the SW is normally square waveform. why?
3.my design demo board , the RC Snubber Networks R6(5.1ohm) work so hot , the temperature up to 80°C ( 25°C ambient temperature test). why ? I just test the rms of R6 is 1.03V, then calculate the power consumption is 1.03*1.03/5.1=0.208W, the R6 ( Nominal power value is 2W),why so hot?
