TPS751 datasheet(21/31 Pages) TI1

21 / 31 page

www.ti.com

Board thickness

62 mils(0.15748cm)

Boardsize

3.2in.x3.2in.

Boardmaterial

FR4

Coppertrace/heatsink

1 oz

Exposedpadmounting

63/67tin/lead(Sn/Pb)solder

Heatsink Area

1ozCopper

D(Max)

J(Max)

JA (System)

(5)

=(V

)

D(total)

OUT

(6)

=(V

)

D(total)

OUT

(7)

D(Max)

J(Max)

JA (System)

=1.4W

125

C/W

(8)

=(V

)

D(total)

OUT

=(5

3.3)

0.8=1.36W

(9)

TPS751xxQ

TPS753xxQ

SLVS241C – MARCH 2000 – REVISED OCTOBER 2007

Figure 29 is an example of a thermally-enhanced PWB layout for use with the new PWP package. This board

configuration was used in the thermal experiments that generated the power ratings shown in Figure 27 and

Figure 28. As discussed earlier, copper has been added on the PWB to conduct heat away from the device. RθJA

for this assembly is illustrated in Figure 27 as a function of heatsink area. A family of curves is included to

illustrate the effect of airflow introduced into the system.

Figure 29. PWB Layout (Including Copper Heatsink Area) for Thermally-Enhanced PWP Package

From Figure 27, RθJA for a PWB assembly can be determined and used to calculate the maximum

power-dissipation limit for the component/PWB assembly, with the equation:

Where TJmax is the maximum specified junction temperature (+150°C absolute maximum limit, +125°C

recommended operating limit) and TA is the ambient temperature.

PD(max) should then be applied to the internal power dissipated by the TPS75133QPWP regulator. The equation

for calculating total internal power dissipation of the TPS75133QPWP is:

Because the quiescent current of the TPS75133QPWP is very low, the second term is negligible, further

simplifying the equation to:

For the case where TA = +55°C, airflow = 200 ft/min, copper heat-sink area = 4 cm

2, the maximum

power-dissipation limit can be calculated. First, from Figure 27, we find the system RθJA is 50°C/W; therefore, the

maximum power-dissipation limit is:

If the system implements a TPS75133QPWP regulator, where VIN = 5 V and IOUT = 800 mA, the internal power

dissipation is:

Comparing PD(total) with PD(max) reveals that the power dissipation in this example does not exceed the calculated

limit. When it does, one of two corrective actions should be made: either raise the power-dissipation limit by

increasing the airflow or the heat-sink area, or loweri the internal power dissipation of the regulator by reducing

the input voltage or the load current. In either case, the above calculations should be repeated with the new

system parameters.

Submit Documentation Feedback

TPS751 Datasheet(PDF) 21 Page - Texas Instruments

TPS751 Datasheet(HTML) 21 Page - Texas Instruments

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31

Datasheet Download

Link URL