AN4444 datasheet(55/68 Pages) STMICROELECTRONICS

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AN4444

Design guidelines

Figure 46. Simulation model of the thermal impedance ZthJA of the ST7590 mounted on the

reference design board

The actual dissipated power PD can be calculated as:

Equation 10

where

Equation 11

and

Equation 12

Note that power consumption by receiving circuitry and linear regulators is considered

negligible for thermal analysis purpose. The relationship between current absorption from

the power supply (ICC) and PA output current to the load (IOUT) is shown in Figure 2 on

page 9.

A transmission output level VOUT rms of 1.5 V, together with the current limit IOUT rms(LIMIT) of

1 A, correspond to a maximum output power POUT of 1.5 W. In these conditions, the

required dissipation results as follows:

Equation 13

Referring to the relationship between dissipated power and temperature, it can be proved

that in a continuous transmission, i.e.: with ZthJA at its steady state value of 50 °C/W, with an

ambient temperature of 25 °C the maximum dissipation can be 2 W. However, controlling

the transmission duty cycle and total duration it becomes possible to get higher dissipation.

OUT









rms

OUT

rms

OUT





LIMIT

OUT

LIMIT

MAX

)

(

)

(

)

(

)

(

)

(















AN4444 Datasheet(PDF) 55 Page - STMicroelectronics

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