Tool/software:
Hi,
We have SSD application need check when load at 180mA(sleep mode) this time is work in PFM mode or PWM mode.
Because when leave sleep mode, will sink a huge current. If this time not in PFM, it may caused output voltage have big drop.
Do I need also provide more information likes input/output voltage?
Thanks!
Jeff
Hello Jeff,
thanks for reaching out in E2E.
You are right, the transition point from PFM to PWM depends on input and output voltage. The transition point can be estimated for the most common Vin/Vout combinations from some of the diagrams in the datasheet. For example the Efficiency plot on the first page is showing efficiency for both, Forced-PWM and Auto-PFM/PWM devices. The curves with higher efficiency at low load belong to the Auto-PFM/PWM device variants. The curves, with lower efficiency at lower load belong to the Forced PWM device variants. At higher load both curves overlay and match, because the Auto-PFM/PWM device has transitioned to PWM and behaves same as the Forced PWM device. So the point, where the curves come together, is the point of PFM to PWM transition for the Auto-PFM/PWM device.
The switching frequency plot is also giving an indication of the transition point by the knee in this curve. At lower load (PFM) the frequency rises faster with load, but stays more or less constant for higher load (PWM). The knee is the transition point.
Could you please help me to understand your concern with the PWM transition in your application? The input current of the IC corresponds to the load, translated with the help of the efficiency curve. The efficiency usually increases with transition to PWM (see first picture). The higher input current (even at better efficiency) is required to deliver the output current. Please let me know more details on the "sink a huge current" scenario.
Best regards,
Andreas.
