Tool/software:
Hi Team,
We would like to check LM61440-Q1 auto mode, what is the threshold for FPWM and PFM mode switching? Is there an output current limit would consider as the switching point? And will our ATE test have this spec confirmed?
Thanks
Best,
Frank
Hi Frank,
The FPWM to PFM mode switch varies depending on its loading condition and application as it is dependent on when the output current is low enough such that reverse current through the inductor is inhibited. You can read more about this mode of operation in section 9.4.3.2 of the datasheet.
Because this "boundary" is dependent on many considerations, it is difficult to say what "threshold" there is for FPWM to PFM mode switching. You can actually observe the approximate boundaries by taking a look at the efficiency curves in the datasheet. Please see figure 10-5 below:
You can see around that the green box region is where the device is beginning to switch from PFM to FPWM operation. It varies by input voltage, but if you take a look at some of the curves in section 10.2.3 of the datasheet you will see that it will actually depend on output voltage too. You can also see in some of the EVM efficiency curves, that there is also a dependency on the set switching frequency, and from experience I can tell you that inductance also has an effect on this boundary.
Hope this helps,
Joshua Austria
