TPS62140: Efficiency and Input voltage relation

Vignesh,

In general higher input voltage will increase the switching losses in the converter, therefore lowering the efficiency.

Vignesh,

The efficiency is:

Pout / Pin

or:

Pout / (Pout + Pdiss)

and

Pdiss is primarily composed of losses in the IC and losses in the inductor.  There are other losses as well, but they can generally be ignored.  The IC losses are what we are concerned with here.  At the first order they can be approximated by"

Pdiss (IC) = quiescent losses + conduction losses + switching losses + gate charge losses + dead time losses.

The switching losses are equal to (Vin * Iout * (trise + tfall) *Fsw) / 2

where:

Vin is the input voltage

Iout is the output current

trise is the rise time of the switch node voltage

tfall is the fall time of the switch node voltage

Fsw is the switching frequency

The switching loss will increase as Vin increases. Since that loss term is in the denominator of the efficiency equation, as it increases, the efficiency will decrease.