Running LM25011 below 1 MHz

Gary Lynch

Other Parts Discussed in Thread: LM25011

I am trying to apply the LM25011 to a project and can
simplify testing by clocking it either below 150 kHz or
between 300 and 500 kHz. The data sheet gives examples that
run it at 1 MHz and specifies minimum on- and off-times,
thereby implying a maximum frequency, but I can find nothing
there or on any forum for running at a lower frequency.

Is there a fundamental lower limit on switching frequency
(other than the value of RT, which comes out to 1.2M with
5 V output)?

over 8 years ago

0 JohnTucker over 8 years ago

TI__Guru**** 191445 points

For COT devices, F = Vout/(Vin*ton). For example if Vin =12V and Vout = 5 V and Rt = 3011k, then F = 5/(12*1020E-9) = 408kHz. Does this help explain it?

0 Gary Lynch over 8 years ago in reply to JohnTucker

Expert 1310 points

Not exactly. I know how to calculate the frequency. It is obvious you can't take it much lower than 100 kHz because resistors above 5 M are expensive and change impedance if you leave fingerprints on them.

I want to know if I stumble against some other basic limit (e.g.: leakage currents into the PCB start to mess up my calculations) at 100 kHz. Why are there no examples other than 1 MHz?

0 JohnTucker over 8 years ago in reply to Gary Lynch

TI__Guru**** 191445 points

Someone from that product line would have to answer that. I was not personally involved with the development of that part.

0 Gary Lynch over 8 years ago in reply to JohnTucker

Expert 1310 points

Any chance one of them (some one from the product line) will hang out here in the foreseeable future?

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Running LM25011 below 1 MHz