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參數(shù)資料
| 型號(hào)： | LM1085ISX-3.3 |
| 廠商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分類： | 基準(zhǔn)電壓源/電流源 |
| 英文描述： | Rheostat; Series:RNS; Power Rating:300W; Resistance Max:5ohm; Terminal Type:Lugs; Leaded Process Compatible:No; Peak Reflow Compatible (260 C):No; Number of Turns:1; Resistance:5ohm |
| 中文描述： | 3.3 V FIXED POSITIVE LDO REGULATOR, 1.5 V DROPOUT, PSSO3 |
| 封裝： | TO-263, 3 PIN |
| 文件頁(yè)數(shù)： | 9/13頁(yè) |
| 文件大?。?/td> | 744K |
| 代理商： | LM1085ISX-3.3 |
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Application Note
(Continued)
must be added, one for case to heat-sink (
θ
CH
) and one for
heatsink to ambient (
θ
HA
). The junction temperature can be
predicted as follows:
T
J
= T
A
+ P
D
(
θ
JC
+
θ
CH
+
θ
HA
) = T
A
+ P
D
θ
JA
T
J
is junction temperature, T
A
is ambient temperature, and
P
is the power consumption of the device. Device power
consumption is calculated as follows:
I
IN
= I
L
+ I
G
P
D
= (V
IN
V
OUT
) I
L
+ V
IN
I
G
Figure 6
shows the voltages and currents which are present
in the circuit.
Once the devices power is determined, the maximum allow-
able (
θ
JA(max)
) is calculated as:
θ
JA(max)
= T
R(max)
/P
D
= T
J(max
T
A(max)
)/P
D
The LM1085 has different temperature specifications for two
different sections of the IC: the control section and the output
section. The Electrical Characteristics table shows the junc-
tion to case thermal resistances for each of these sections,
while the maximum junction temperatures (T
) for each
section is listed in the Absolute Maximum section of the
datasheet. T
is 125C for the control section, while
T
J(max)
is 150C for the output section.
θ
should be calculated separately for each section as
follows:
θ
JA
(max, CONTROL SECTION) = (125C - T
A(max)
)/P
D
θ
JA
(max, OUTPUT SECTION) = (150C - T
A(max)
)/P
D
The required heat sink is determined by calculating its re-
quired thermal resistance (
θ
HA(max)
).
θ
HA(max)
=
θ
JA(max)
(
θ
JC
+
θ
CH
)
θ
HA(max)
should also be calculated twice as follows:
θ
=
θ
(max, CONTROL SECTION) - (
θ
JC
(CON-
TROL SECTION) +
θ
CH
)
θ
=
θ
(max, OUTPUT SECTION) - (
θ
JC
(OUTPUT
SECTION) +
θ
CH
)
If thermal compound is used,
θ
can be estimated at 0.2
C/W. If the case is soldered to the heat sink, then a
θ
CH
can
be estimated as 0 C/W.
After,
θ
is calculated for each section, choose the
lower of the two
θ
HA(max)
values to determine the appropriate
heat sink.
If PC board copper is going to be used as a heat sink, then
Figure 7
can be used to determine the appropriate area
(size) of copper foil required.
10094716
FIGURE 6. Power Dissipation Diagram
10094764
FIGURE 7. Heat sink thermal Resistance vs Area
L
www.national.com
9
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| LM1085ISX-5.0 | 功能描述:低壓差穩(wěn)壓器 - LDO RoHS:否 制造商:Texas Instruments 最大輸入電壓:36 V 輸出電壓:1.4 V to 20.5 V 回動(dòng)電壓（最大值）:307 mV 輸出電流:1 A 負(fù)載調(diào)節(jié):0.3 % 輸出端數(shù)量: 輸出類型:Fixed 最大工作溫度:+ 125 C 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:VQFN-20 |
| LM1085ISX-5.0/NOPB | 功能描述:低壓差穩(wěn)壓器 - LDO RoHS:否 制造商:Texas Instruments 最大輸入電壓:36 V 輸出電壓:1.4 V to 20.5 V 回動(dòng)電壓（最大值）:307 mV 輸出電流:1 A 負(fù)載調(diào)節(jié):0.3 % 輸出端數(shù)量: 輸出類型:Fixed 最大工作溫度:+ 125 C 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:VQFN-20 |
| LM1085ISX-ADJ | 功能描述:低壓差穩(wěn)壓器 - LDO RoHS:否 制造商:Texas Instruments 最大輸入電壓:36 V 輸出電壓:1.4 V to 20.5 V 回動(dòng)電壓（最大值）:307 mV 輸出電流:1 A 負(fù)載調(diào)節(jié):0.3 % 輸出端數(shù)量: 輸出類型:Fixed 最大工作溫度:+ 125 C 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:VQFN-20 |
| LM1085ISX-ADJ/NOPB | 功能描述:低壓差穩(wěn)壓器 - LDO RoHS:否 制造商:Texas Instruments 最大輸入電壓:36 V 輸出電壓:1.4 V to 20.5 V 回動(dòng)電壓（最大值）:307 mV 輸出電流:1 A 負(fù)載調(diào)節(jié):0.3 % 輸出端數(shù)量: 輸出類型:Fixed 最大工作溫度:+ 125 C 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:VQFN-20 |
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