LP2952 National Semiconductor, LP2952 Datasheet - Page 10

• Manufacturer Part Number: LP2952
• Description: Adjustable Micropower Low-Dropout Voltage Regulators
• Manufacturer: National Semiconductor

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Application Hints
The next parameter which must be calculated is the maxi-
mum allowable temperature rise, T
by using the formula:
where: T
Using the calculated values for T
quired value for junction-to-ambient thermal resistance,
The heatsink is made using the PC board copper. The heat
is conducted from the die, through the lead frame (inside the
part), and out the pins which are soldered to the PC board.
The pins used for heat conduction are given in Table 1 .
Figure 2 shows copper patterns which may be used to dissi-
pate heat from the LP2952 and LP2953. Table 2 shows
some values of junction-to-ambient thermal resistance (
for values of L and W for 1 oz. copper.
LP2952IN, LP2952AIN,
LP2952IN-3.3,
LP2952AIN-3.3
LP2953IN, LP2953AIN,
LP2953IN-3.3,
LP2953AIN-3.3
LP2952IM, LP2952AIM,
LP2952IM-3.3,
LP2952AIM-3.3,
LP2953IM, LP2953AIM,
LP2953IM-3.3,
LP2953AIM-3.3
(J–A)
T
R
(max) = T
, can now be found:
FIGURE 1. P
perature
T
J
A
(max) is the maximum allowable junction tem-
(max) is the maximum ambient temperature
Part
TABLE 1. Heat Conducting Pins
J
(max) − T
Current/Voltage Diagram
TOTAL
A
= (V
(max)
(Continued)
IN
14-Pin DIP
16-Pin DIP
Package
R
− V
Surface
16-Pin
Mount
(J–A)
(max) and P(max), the re-
R
(max). This is calculated
OUT
= T
) I
DS011127-7
L
R
(max)/P(max)
+ (V
4, 5, 12, 13
10, 11, 12
1, 8, 9, 16
IN
3, 4, 5,
) I
Pins
G
J–A
)
10
* For best results, use L = 2H
*
HEATSINK REQUIREMENTS (Military Temperature
Range Devices)
The
LP2953AMJ is limited by the maximum junction temperature
(+150˚C) and the two parameters that determine how quickly
heat flows away from the die: the ambient temperature and
the junction-to-ambient thermal resistance of the part .
The military temperature range (−55˚C
are manufactured in ceramic DIP packages which contain a
* 14-Pin DIP is similar, refer to Table 1 for pins designated for heatsinking.
16-Pin DIP
14-Pin DIP
Surface Mount
TABLE 2. Thermal Resistance for Various Copper
Package
maximum
FIGURE 2. Copper Heatsink Patterns
allowable
Heatsink Patterns
L (in.)
1
2
3
4
6
1
2
3
1
2
3
6
4
2
power
H (in.)
0.19
0.19
0.19
0.19
0.19
0.5
1.5
0.5
1.5
0.5
1.5
1
1
1
dissipation
T
J
DS011127-8
+150˚C) parts
J–A
70
60
58
66
66
65
51
49
83
70
67
69
71
73
(˚C/W)
for
the