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參數(shù)資料
| 型號(hào)： | 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)： | 11/17頁 |
| 文件大?。?/td> | 559K |
| 代理商： | TPS68625 |
www.ti.com
TJ
TA
P
D
max x R
θ
JC
R
θ
CS
R
θ
SA
PDmax
VI(avg)
VO(avg)
IO(avg)
VI(avg)x I(Q)
A
B
C
T
J
A
R
θ
JC
T
C
B
R
θ
CS
T
A
C
R
θ
SA
(a)
(b)
DDPAK Package
SOT223 Package
CIRCUIT BOARD COPPER AREA
B
A
C
TPS78601, TPS78618
TPS78625, TPS78628
TPS78630, TPS78633
SLVS389D–SEPTEMBER 2002–REVISED OCTOBER 2004
THERMAL INFORMATION
The amount of heat that an LDO linear regulator
generates is directly proportional to the amount of
power it dissipates during operation. All integrated
circuits have a maximum allowable junction tempera-
ture (T
JMAX
) above which normal operation is not
assured.
A
system
designer
operating environment so that the operating junction
temperature (T
J
) does not exceed the maximum
junction temperature (T
). The two main environ-
mental variables that a designer can use to improve
thermal
performance
are
heatsinks. The purpose of this information is to aid
the designer in determining the proper operating
environment for a linear regulator that is operating at
a specific power level.
temperature due to the regulator's power dissipation.
The temperature rise is computed by multiplying the
maximum expected power dissipation by the sum of
the thermal resistances between the junction and the
case (R
Θ
JC
), the case to heatsink (R
Θ
CS
), and the
heatsink to ambient (R
Θ
). Thermal resistances are
measures of how effectively an object dissipates
heat. Typically, the larger the device, the more
surface area available for power dissipation and the
lower the object's thermal resistance.
must
design
the
air
flow
and
external
Figure 26 illustrates these thermal resistances for (a)
a SOT223 package mounted in a JEDEC low-K
board, and (b) a DDPAK package mounted on a
JEDEC high-K board.
Equation 5 summarizes the computation:
In general, the maximum expected power (P
D(max)
)
consumed by a linear regulator is computed as
shown in Equation 4:
(5)
The R
Θ
JC
is specific to each regulator as determined
by its package, lead frame, and die size provided in
the regulator's data sheet. The R
Θ
SA
is a function of
the type and size of heatsink. For example,
black
body radiator
type heatsinks can have R
Θ
CS
values
ranging from 5
°
C/W for very large heatsinks to
50
°
C/W for very small heatsinks. The R
Θ
CS
is a
function of how the package is attached to the
heatsink. For example, if a thermal compound is used
to attach a heatsink to a SOT223 package, R
Θ
CS
of
1
°
C/W is reasonable.
(4)
where:
For most TI LDO regulators, the quiescent current is
insignificant compared to the average output current;
therefore, the term V
I(avg)
x I
(Q)
can be neglected. The
operating junction temperature is computed by adding
the ambient temperature (T
A
) and the increase in
V
I(avg)
is the average input voltage.
V
O(avg)
is the average output voltage.
I
O(avg)
is the average output current.
I
(Q)
is the quiescent current.
Figure 26. Thermal Resistances
11
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