Our customer is using LMR14050-Q1 at following condition.
VIN:7V
Vout:5V
IOUTMAX:4.5A
SW frequency:2MHz
In light load condition(a few hundereds mA),this part can be switching 2Mhz.
But heavy load conditon(4.5A) switching frequency goes down to 200kHz.
(I attached SW waveform)
Please let us know why switching frequency goes down to 200kHz at heavy load condition.
Hello Kura,
Looking at this switch node scope shot you sent:
It looks like the input voltage at the IC droops at the heavy load.
This may be due to your input supply limiting the current or higher impedance between your supply and the LMR circuit.
I think what is happening is the IC is getting into dropout condition, because of the lowering input voltage. It looks like the frequency is reduced in order to maximize the duty cycle (there is minimum off time each cycle) and to still maintain regulation.
I will forward this to the applications engineer for this part for additional comments.
Cheers,
Denislav
Hi Kura,
I aggre with Denislav's suggestion. You can check the VIN voltage at heavy load. Aslo for 5V/4.5A output at 2.2MHz, the device will be very hot. Even hit shermal shutdown if your layout is not that good for heat dissipation. For so large power out put, a lower frequency is suggested, 400kHz for an instance.
Also I saw the VFB(#5pin) waveform shown as below, it is not supposed to be like this. Can you double check which pin waveform is this?
BR
Luke
