Hi,
I want to use the MAX20078 for various configuartions. I want also use the OUT pin (3V comparison) as a safety feature
I'm a bit confused about the calculation of the fsw. If I see the block diagramm, ton and fsw depends on the ton-pin input and the OUT-pin.
If I keep R1 and C1 fixed achtually the should be only a change depending on the voltage at the OUT pin.
At the same time the OUT input is internal compared with 3V for an over voltage protection. Means I shall not exceed this 3V.
So in the following I set the 3V as a fixed voltage at the OUT_pin for calculating Vout_max.
And I set R3, R1 and C1 (see datasheet Figure 4) to fixed values.
Uin: 48V
R1=39k
C1=1nF
R3=30k
Two cases
- R2=330k for Vout_max=36V -> OUT=3V at 36V Vout
Calculated frequency is 308kHz - R2=10k for Vout_max=4V -> OUT=3V at 4V Vout
Calculated frequency is 34kHz
I don't understand why the frequency shall be different. Yes from the formula, but from my Understanding it should not.
Where is my mistake?
Or is the formula just to calculate some first values for one configuration?