R5975D datasheet(31/47 Pages) STMICROELECTRONICS

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R5975D

Application information

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 [(

switching loss +quiescent loss)

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.

In applications where the current to the output is pulsed, the thermal impedance should be

considered instead of the thermal resistance.

The thermal impedance of the system could be much lower than the thermal resistance,

which is a static parameter. And so the maximum power losses can be higher than 2.5 W if

a pulsed output power is requested from the load:

Equation 30

Therefore, depending on the pulse duration and its frequency, the maximum output current

can be delivered to the load.

The characterization of the thermal impedance is strictly dependent on the layout of the

board. In Figure 17 the measurement of the thermal impedance of the demonstration board

of the R5975D is provided.

Figure 17. Measurement of the thermal impedance of the demonstration board

As can be seen, for example, for load pulses with a duration of 1 second, the actual thermal

impedance is lower than 20

C/W. This means that, for short pulses, the device can deliver

a higher output current value.

PMAX t

T

ZTH t

-----------------

TJ MAX TAMB

–

ZTH t

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R5975D データシート(PDF) 31 Page - STMicroelectronics