A5974D datasheet(27/46 Pages) STMICROELECTRONICS

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A5974D

Application information

Figure 15 represents the estimation of power losses for different output voltages at

VIN = 5 V and TAMB = 60 C. The calculations are performed considering the RDS(on) of the

power element equal to 0.4 A.

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, whilst the rest of the traces are the total internal losses for different output voltage.

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 losses is for VOUT = 3.3 V, where the

system can manage a continuous output current up to 2.35 A. The device could deliver

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

2 W is reached with an output current of 2.35 A, so the maximum output power is derated.

A5974D データシート(PDF) 27 Page - STMicroelectronics