TPS75301-Q1 Datasheet, PDF (24/31 Pages) Texas Instruments – FAST-TRANSIENT-RESPONSE 1.5-A LOW-DROPOUT VOLTAGE REGULATORS

TPS75101ĆQ1, '75115ĆQ1, '75118ĆQ1, '75125ĆQ1, '75133ĆQ1 WITH POWER GOOD
ą
TPS75301ĆQ1, TPS75315ĆQ1, TPS75318ĆQ1, TPS75325ĆQ1, TPS75333ĆQ1 WITH RESET
FASTĆTRANSIENTĆRESPONSE 1.5ĆA LOWĆDROPOUT VOLTAGE REGULATORS
SGLS159A − APRIL 2003 − REVISED APRIL 2008
THERMAL INFORMATION
thermally enhanced TSSOP-20 (PWP − PowerPad) (continued)
Figure 28 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 26 and Figure
27. As discussed earlier, copper has been added on the PWB to conduct heat away from the device. R_θJA for this
assembly is illustrated in Figure 26 as a function of heat-sink area. A family of curves is included to illustrate the effect
of airflow introduced into the system.
Heat-Sink Area
1 oz Copper
Board thickness
Board size
Board material
Copper trace/heat sink
Exposed pad mounting
62 mils
3.2 in. × 3.2 in.
FR4
1 oz
63/67 tin/lead solder
Figure 28. PWB Layout (Including Copper Heatsink Area) for Thermally Enhanced PWP Package
From Figure 26, R_θJA for a PWB assembly can be determined and used to calculate the maximum power-dissipation
limit for the component/PWB assembly, with the equation:
PD(max)
+
TJmax * TA
R _qJA(system)
(5)
Where:
T_Jmax is the maximum specified junction temperature (150°C absolute maximum limit, 125°C recommended
operating limit) and T_A is the ambient temperature.
P_D(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:
ǒ Ǔ _{PD(total) + VI * VO IO ) VI IQ}
(6)
Since the quiescent current of the TPS75133QPWP is very low, the second term is negligible, further simplifying
the equation to:
ǒ Ǔ _{PD(total) + VI * VO IO}
(7)
For the case where T_A = 55°C, airflow = 200 ft/min, copper heat-sink area = 4 cm², the maximum power-dissipation
limit can be calculated. First, from Figure 26, we find the system R_θJA is 50°C/W; therefore, the maximum
power-dissipation limit is:
PD(max)
+
TJmax * TA
R _qJA(system)
+
125°C * 55
50 °CńW
C°
+
1.4
W
(8)
24
• POST OFFICE BOX 655303 DALLAS, TEXAS 75265