LM5022: What can cause the frequency higher than 2.2MHz

Johnson Pi

Part Number: LM5022
Other Parts Discussed in Thread: LM5122, LM5112

Hi!

I changed Rt to 20KOhm and from the equation, the LM5022 will posted to be about 830KHz operating frequency. But I measured the Vout and the waveform is about 11.1MHz, what can it cause the frequency higher than 2.2 MHz? Under this condition, the output is still stable for my set output voltage (2.5V).

over 7 years ago

0 Youhao Xi over 7 years ago

TI__Guru 73570 points

Can you show you waveform?

0 Johnson Pi over 7 years ago in reply to Youhao Xi

Intellectual 470 points

Hi! Please see attached the waveform of Pin Vout of LM5022

0 Youhao Xi over 7 years ago in reply to Johnson Pi

TI__Guru 73570 points

Amazing! I just learnt that the LM5022 can run so fast and you still have the output regulation. Okay, back to your question, can you double check if your RT resistor is 20kOhm? Looks like a 200 ohm is installed instead. Either a wrong resistor, or solder debris that reduces the effective resistor value.

0 Johnson Pi over 7 years ago in reply to Youhao Xi

Intellectual 470 points

Yes, it is some short between the trace.

Thank you very much!

0 Youhao Xi over 7 years ago in reply to Johnson Pi

TI__Guru 73570 points

Really appreciate your feedback and confirmation. Let us know if we can be of further assistance. Thanks!!!

0 Johnson Pi over 7 years ago in reply to Youhao Xi

Intellectual 470 points

Dear Youbao Xi,

Do you have any idea of insulated gate drive which I will used it for driver a mosfet which replaces the Boost forword diode?

Thank you advance!

0 Youhao Xi over 7 years ago in reply to Johnson Pi

TI__Guru 73570 points

If this is the case, you should consider the LM5122. You can use a discrete driver and the boot-strap technic but dead time may not be easily manageable. Use the sync Boost controller instead will avoid such issue.

0 Johnson Pi over 7 years ago in reply to Youhao Xi

Intellectual 470 points

Dear Youhao Xi,

Appreciate your quick respond.

Due to my application of high output current (higher than 8A), the main MODEFT has LM5112 for gate drive and then come to original question that I still need a gate drive for MOSFET of Syn. rectifing. Do you think the LM5122 can directly drive the MOSFET without a gate driver for 8A load?