A5975D datasheet(30/50 Pages) STMICROELECTRONICS

30 / 50 page

Application information

A5975D

30/50

Doc ID 018760 Rev 1

Figure 15.

Power losses estimation (VIN = 5 V, fSW = 250 kHz)

The red trace represents the maximum power which can be taken away, as calculated

above, while the other traces are the total internal losses for different output voltages.

The embedded conduction losses are proportional to the duty cycle required for the

conversion. Assuming the input voltage constant, the switching losses are proportional to

the output current while the quiescent losses can be considered as constant.

As a consequence, in Figure 15 the maximum power loss is for VOUT=3.3 V, where the

system can manage a continuous output current up to 2.5 A. The device could deliver a

continuous output current up to 3 A to the load, however, the maximum power loss of 2.5 W

is reached with an output current of 2.5 A, so the maximum output power is derated.

Figure 16 plots the power losses for VIN=12 V and main output rails.

Figure 16.

Power loss estimation (VIN = 12 V, fSW = 250 kHz)

At VIN=12 V and VOUT=5 V the device can deliver 3 A continuously (see Figure 17) because

the total power loss is now lower than 2.5 W ((

Δ switching loss +Δ quiescent loss) < Δ

conduction loss).

As a consequence, the calculation of the internal power losses must be done for each

specific operating condition given by the final application.

A5975D Datasheet(PDF) 30 Page - STMicroelectronics