LM5039EVAL: Ramp signal

Sergei Ivanov

Part Number: LM5039EVAL
Other Parts Discussed in Thread: LM5039

Hello!

In the eval. board circuit (figure 12 in snva423c.pdf) R16 = 64.9K. But according to formula (2) on page 15 of LM5039 datasheet R16 must be 98K. Am I right?

over 6 years ago

0 Sonal Singh over 6 years ago

TI__Expert 6080 points

Hello Sergei,

Can you please share your selected value of Input voltage, Cff and what is the desired duration of the ON time of the controller. Also, what is the switching frequency?

Kind Regards,
Sonal

0 Sergei Ivanov over 6 years ago in reply to Sonal Singh

Prodigy 160 points

According to evaluation circuit: Vinmax = 75V, Cff = 470p, frequency is 400kHz.

0 Sonal Singh over 6 years ago in reply to Sergei Ivanov

TI__Expert 6080 points

Hello,

Yes the for a switching frequency of 400kHz your ON time at 50% duty cycle is 1.25usec, which will give you a value of Rff= 62Kohm at 48Vin according to my calculation. Can you please check your calculations again?

Please hit Answered if your query has been resolved.
Kind Regards,
Sonal

0 Sergei Ivanov over 6 years ago in reply to Sonal Singh

Prodigy 160 points

Hello!

Why do you use 48Vin if maximum Vin is 75V?

0 Sonal Singh over 6 years ago in reply to Sergei Ivanov

TI__Expert 6080 points

You can go ahead and use 75Vin as long as the time constant calculation is met.

Please hit Answered if your query has been solved.
Kind Regards,
Sonal

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LM5039EVAL: Ramp signal