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參數(shù)資料
| 型號： | TPS68625 |
| 廠商： | Texas Instruments, Inc. |
| 英文描述： | ULTRALOW-NOISE, HIGH PSRR, FAST RF 1.5 A LOW-DROPOUT LINEAR REGULATORS |
| 中文描述： | 超低噪聲，高PSRR，快速射頻1.5低壓差線性穩(wěn)壓器 |
| 文件頁數(shù)： | 12/17頁 |
| 文件大小： | 559K |
| 代理商： | TPS68625 |
www.ti.com
R
θ
JAmax
(125
55)
°
C 2.5 W
28
°
C W
(9)
TJ
TA
P
D
max x R
θ
JA
(6)
R
θ
JA
T
J
–T
A
P
D
max
(7)
DDPAK Power Dissipation
The DDPAK package provides an effective means of
managing power dissipation in surface mount appli-
cations. The DDPAK package dimensions are pro-
vided in the
Mechanical Data
section at the end of
the data sheet. The addition of a copper plane
directly underneath the DDPAK package enhances
the thermal performance of the package.
15
20
25
30
35
40
0.1
1
10
100
Copper Heatsink Area cm
2
θ
J
R
C
°
No Air Flow
150 LFM
250 LFM
1 oz. Copper
Power Plane
1 oz. Copper
Ground Plane
2 oz. Copper Solder Pad
with 25 Thermal Vias
Thermal Vias, 0.3 mm
Diameter, 1,5 mm Pitch
P
D
max
(5
2.5) V x 1 A
2.5 W
(8)
TPS78601, TPS78618
TPS78625, TPS78628
TPS78630, TPS78633
SLVS389D–SEPTEMBER 2002–REVISED OCTOBER 2004
Even if no external
black body radiator
type heatsink
is attached to the package, the board on which the
regulator is mounted provides some heatsinking
through the pin solder connections. Some packages,
like the DDPAK and SOT223 packages, use a copper
plane underneath the package or the circuit board's
ground plane for additional heatsinking to improve
their thermal performance. Computer-aided thermal
modeling can be used to compute very accurate
approximations of an integrated circuit's thermal per-
formance in different operating environments (e.g.,
different types of circuit boards, different types and
sizes of heatsinks, and different air flows, etc.). Using
these models, the three thermal resistances can be
combined into one thermal resistance between junc-
tion and ambient (R
Θ
JA
). This R
Θ
JA
is valid only for the
specific operating environment used in the computer
model.
From Figure 27,
DDPAK Thermal Resistance vs
Copper Heatsink Area
, the ground plane needs to be
1 cm
2
for the part to dissipate 2.5 W. The operating
environment used in the computer model to construct
Figure 27 consisted of a standard JEDEC High-K
board (2S2P) with a 1 oz. internal copper plane and
ground plane. The package is soldered to a 2 oz.
copper pad. The pad is tied through thermal vias to
the 1 oz. ground plane. Figure 28 shows the side
view of the operating environment used in the com-
puter model.
Equation 5 simplifies into Equation 6:
Rearranging Equation 6 gives Equation 7:
Using Equation 6 and the computer model generated
curves shown in Figure 27 and Figure 30, a designer
can quickly compute the required heatsink thermal
resistance/board area for a given ambient tempera-
ture, power dissipation, and operating environment.
Figure 27. DDPAK Thermal Resistance vs Copper
Heatsink Area
To illustrate, the TPS78625 in a DDPAK package
was chosen. For this example, the average input
voltage is 5 V, the output voltage is 2.5 V, the
average output current is 1 A, the ambient tempera-
ture 55
°
C, the air flow is 150 LFM, and the operating
environment is the same as documented below.
Neglecting the quiescent current, the maximum aver-
age power is shown in Equation 8:
Figure 28. DDPAK Thermal Resistance
Substituting T
J
max for T
J
into Equation 6 gives
Equation 9:
12
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