Other Parts Discussed in Thread: CSD18534Q5A, CSD18514Q5A,
Hello, i have designed a schematich through webench tool for LM25145 regulator, my specs are:
Vin = 24V
Vout = 12V (about 6A current)
actually i have:
RT resistor = 11.2 Kohm
EN = tied to 18V.
Cin = 10uf ceramic
Cout = 4x22uF ceramic
Cbst = 100nf
Rilim = 470ohm.
Rfb1 = 1Kohm.
Rfb2 = 14Kohm.
Inductor = 4.7uH 6.25mohm 15.5A
Q1 = CSD18534Q5A
Q2 = CSD18514Q5A
The problem is that i can t get proper regulation, output voltage is swinging around 12V for some seconds, then it goes to 20-22V. During this initial period, there is a loud "frying" noise. Putting probe at SW pin, i see a wave of 1.47 MHz frequency and amplitude from 5V to 28-29V. Duty cycle is ~ 33%. Voltage at Vcc is alaways 4.8-5V not very stable.
I can t understand why i have such high switching frequency, and why i can t get 12V output. What should i check?