TS4974 datasheet(18/25 Pages) STMICROELECTRONICS

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Application information

TS4974

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and the maximum value is obtained when:

and its value is:

Equation 3

Note:

This maximum value is only dependent on the power supply voltage and load

values.

The efficiency is the ratio between the output power and the power supply:

Equation 4

The maximum theoretical value is reached when Vpeak = VCC, so:

The maximum die temperature allowable for the TS4974 is 125°C. However, in case of

overheating, a thermal shutdown set to 150° C, puts the TS4974 in standby until the

temperature of the die is reduced by about 5° C.

To calculate the maximum ambient temperature Tamb allowable, you need to know:

●

Power supply voltage value, VCC

●

Load resistor value, RL

●

The package type, RTHJA

Example: VCC=5 V, RL=8 Ω, RTHJAflip-chip=80° C/W (125 mm

2 copper heatsink).

Using the power dissipation formula given above in Equation 3 this gives a result of:

Pdissmax = 633mW

Tamb is calculated as follows:

Equation 5

Therefore, the maximum allowable value for Tamb is:

Tamb = 125-80x0.633 = 74.3°C

∂Pdiss

∂P

out

--------------------- = 0

)

(

Vcc

max

Pdiss

η=

out

supply

------------------- =

πV

peak

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

η= π

----- = 78.5%

amb

125

° CR

TJHA

dissmax

–

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