TPS53667: ISUM (DROOP) function

Hi Kohei,

Yes, the droop function will drop VOUT by R_LOADLINE * IOUT if it's enabled.  For example, a 1mΩ load line will drop VOUT from its set point by 50mV at 50A.

Load lines can be used to reduce the CPU power consumption at high loads which make thermal designs easier. A 50mV reduction in VOUT at 50A saves 2.5W of power. That power isn't burned in the converter, it simply isn't drawn from the input supply.

Load lines can also save a great deal of output capacitance by making it easier to hit the transient response requirements. You can read more about that on page 14 of this app note.

The reason load lines aren't always used is because not all processors can tolerate the drop in VOUT from the converter. One main reason may be their DC tolerances are too tight to accommodate a loadline in the first place. You need to check with the processor vendor spec document to determine if you can use a load line.

Let me know if you have any other questions.

Cheers,

Carmen