Other Parts Discussed in Thread: LM2267X-22680DESIGN-CALC,
Hi Team,
I have a customer who has a question about the formula in the datasheet for the LM2267x. In the older datasheets (2008), the formula for Vin_Min is given below:
Now if we use this for a 12V output:
VOUT: 12V, Iout: 300 mA
VD: Diode: 0.5V
TOFFMIN: 300ns
Fmax: 600kHz (max. Value according to the datasheet)
VQ: internal Mosfet deop 0.5V
We get a VIN_Min of 15.2V
If we use the current datasheet (2014 Rev), the formula is different:
Now in this case, for the same VOut of 12V, 300mA
VOUT: 12V, Iout: 300 mA
Rdson:0.32 Ohm (max. Value according to datasheet)
TOFF: 300ns
Fsw_max: 600kHz
RL: 0,41Ohm k
We get a VIN_Min of 18.6V, which is significantly different from the result we got from the first formula.
Complicating this further, when I try to simulate in WEBENCH the two configurations with the different VIN_Mins, I get the following message (for the 18.6V VIN_Min):
It seems that WEBENCH thinks that 18.6V is too low for the 12V 300mA output.
Also the lm2267x-22680design-calc
Thanks and Regards,
Mihir Gupta
FAE - South Germany