LM25037: crossover frequency

Viktorija Cecil

Part Number: LM25037

Team,

My customer is looking into using the LM25037:

I’ve been using SLVA636 to help me calculate the loop compensation network. Under section 5 in the example circuit given, it is written that the RHP Zero Frequency is 3.6kHz. However, equation 9 states that:

, which can be re-written as frhp=Rload/2 Pi Le

In the example, R_LOAD = 6Ω, and L_e = 20uH, which then means that the RHP Zero should be 471kHz.

Clearly I’ve missed something. What inductance is L_e meant to represent?

Further, the example states: “The selected crossover frequency is 0.6 kHz, or one-fifth the RHP zero frequency (3.6 kHz).” Now, one-fifth of 3.6kHz is 0.72kHz, so I’m guessing there is a rule of thumb at work here. Are there some better guidelines on selecting the crossover frequency?

Thanks!

Viktorija

over 6 years ago

0 Teng Feng over 6 years ago

TI__Genius 13660 points

Hi Viktorija,

Sorry I also can't find out where is Le from, it looks not like main inductance L. And I am confused about that The crossover frequency is limited to about 0.6 kHz, what limits the crossover frequency? For the confusion, I suggest you can directly contact to SW Lee.
In practical current mode boost converter, the crossover frequency generally can achieve several thousands Hz, which exactly is less than about one-tenth the switching frequency as this paper says. The optimum crossover frequency should be gotten from practical debug, which should consider the phase margin and converter performance such as THD.

Regards,

Teng