
TPS75201-EP TPS75215-EP TPS75218-EP TPS75225-EP TPS75233-EP WITH RESET
TPS75401-EP
’
75415-EP
’
75418-EP
’
75425-EP
’
75433-EP WITH POWER GOOD
FAST-TRANSIENT-RESPONSE 2-A LOW-DROPOUT VOLTAGE REGULATORS
SGLS165
–
APRIL 2003
24
POST OFFICE BOX 655303
DALLAS, TEXAS 75265
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
θ
JA
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.
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
Heat-Sink Area
1 oz Copper
Figure 28. PWB Layout (Including Copper Heatsink Area) for Thermally Enhanced PWP Package
From Figure 26, R
θ
JA
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
RJA(system)
TA
Where:
(5)
T
J
max 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 TPS75233QPWPEP regulator. The equation
for calculating total internal power dissipation of the TPS75233QPWPEP is:
PD(total)
VI
VO
IO
VI
IQ
(6)
Since the quiescent current of the TPS75233QPWPEP is very low, the second term is negligible, further simplifying
the equation to:
PD(total)
VI
VO
IO
(7)
For the case where T
A
= 55
°
C, airflow = 200 ft/min, copper heat-sink area = 4 cm
2
, the maximum power-dissipation
limit can be calculated. First, from Figure 26, we find the system R
θ
JA
is 50
°
C/W; therefore, the maximum
power-dissipation limit is:
PD(max)
TJmax
RJA(system)
TA
125 C
50 C W
55 C
1.4 W
(8)