Hi,
We got a question from customer about LM3150.
Could you help us?
[Question]
My customer is evaluating LM3150 on EVM.
They set fsw=200kHz under the following condition.
Vin=32V
Vout=24V
fsw=200kHz
Ron=1.1MHz
But now the device is switching fsw=270kHz.
- Are there any reason that switching frequency doesn't match between Ron setting and real value?
- How much is the recommended range of Ron?
Best Regards,
tateo
Hi Tateo ,
The on Time of this COT may be expressed as
Where VIN is the voltage at the high side of the RON resistor (typically PVIN), VD is the diode voltage present at the RON pin (0.65V typical), and kON is a constant value set internally (100 µA•µs nominal=100pC). This equation can be re-arranged such that RON is a function of switching frequency:
In CCM the frequency may be determined using the relationship:
As you can see from the equations above , Ron is dependant on Kon as well as Vd which may have tolerance involved .
The above equation gives 1.18Meg for 200Khz switching operation .
With Best Regards
Ambreesh
Thank you for your replay.
I found ton data in datasheet.
I think there is much deviation between the calculated value and ton data in datasheet.
Does the variation of kon and Vd be related this deviation?
- the calculated value *Ron=32k -
Vin=10V, ton=0.32usec
Vin=18V, ton=0.18usec
Vin=42V, ton=0.077usec
Best Regards,
tateo
