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參數(shù)資料
| 型號： | LT1123CZ |
| 廠商： | LINEAR TECHNOLOGY CORP |
| 元件分類： | 基準電壓源/電流源 |
| 英文描述： | Cap-Free, NMOS, 150mA Low Dropout Regulator with Reverse Current Protection |
| 中文描述： | 5 V FIXED POSITIVE LDO REGULATOR, 0.75 V DROPOUT, PBCY3 |
| 封裝： | PLASTIC, TO-92, 3 PIN |
| 文件頁數(shù)： | 9/12頁 |
| 文件大小： | 241K |
| 代理商： | LT1123CZ |
9
LT1123
U
S
A
O
PPLICATI
U
U
THERMAL LIMITING
The thermal limit of the LT1123 can be used to protect both
the LT1123 and the PNP pass transistor. This is accom-
plished by thermally coupling the LT1123 to the power
transistor. There are clip type heat sinks available for the
TO-92 package that will allow the LT1123 to be mounted
to the same heat sink as the PNP pass transistor. One
example is manufactured by IERC (part #RUR67B1CB).
The LT1123 should be mounted as close as possible to the
PNP. If the output of the regulator circuit can be shorted,
heat sinking must be adequate to limit the rate of tempera-
ture rise of the power device to approximately 50
°
C/
minute. This can be accomplished with a fairly small heat
sink, on the order of 3 – 4 square inches of surface area.
DESIGN EXAMPLE
Given the following operating requirements:
5.5V < V
IN
< 7V
I
OUTMAX
= 1.5A
Max ambient temp. = 70
°
C
V
OUT
= 5V
1. The first step is to determine the required drive
current. This can be found from the Maximum Dropout
Voltage curve. 50mA of drive current will guarantee 0.4V
dropout at an output current of 2A. This satisfies our
requirements.
I
DRIVE
= 50mA
2. The next step is to determine the value of R
D
. Based
on 50mA of drive current and a minimum input voltage of
5.5V, we can select R
D
from the graph of Figure 4. From the
graph the value of R
D
is equal to 50
, so we should use the
next lowest 5% value which is 47
.
R
D
= 47
3. We can now look at the thermal requirements of the
circuit.
Worst case power in the LT1123 will be equal to:
(
Given: V
INMAX
= 7V, V
BE
= 0.6V, R
D
= 47
Then:
P
MAX
(LT1123) = 0.22W.
Assuming a thermal resistance of 150
°
C/W, the maximum
junction temperature rise above ambient will be equal to
(P
MAX
)(150
°
C/W) = 33
°
C. The maximum operating junc-
tion temperature will be equal to the maximum ambient
temperature plus the junction temperature rise above
ambient. In this case we have (maximum ambient = 70
°
C)
plus (junction temperature rise = 33
°
C) is equal to 103
°
C.
This is well below the maximum operating junction tem-
perature of 125
°
C for the LT1123.
The power rating for R
D
can be found from the plot of
Figure 8 using V
IN
= 7V and R
D
= 47
. From the plot, R
D
should be sized to dissipate a minimum of 1/2W.
The worst case power dissipation, for normal operation, in
the MJE1123 will be equal to:
(V
INMAX
– V
OUT
)(I
OUTMAX
) = (7V – 5V)(1.5A) = 3W
The maximum operating junction temperature of the
MJE1123 is 150
°
C. The difference between the maximum
operating junction temperature of 150
°
C and the maxi-
mum ambient temperature of 70
°
C is 80
°
C. The device
must be mounted to a heat sink which is sized such that
the thermal resistance from the junction of the MJE1123
to ambient is less than 80
°
C/3W = 26.7
°
C/W.
It is recommended that the LT1123 be thermally coupled
to the MJE1123 so that the thermal limit circuit of the
LT1123 can protect both devices. In this case the ambient
temperature for the LT1123 will be equal to the tempera-
ture of the heat sink. The heat sink temperature, under
normal operating conditions, will have to be limited such
that the maximum operating junction temperature of the
LT1123 is not exceeded.
Refer to Linear Technology’s list of Suggested Manufac-
turers of Specialized Components for information on
where to find the required heat sinks, resistors and capaci-
tors. This listing is available through Linear Technology’s
marketing department.
V
– V
4R
INMAX
BE
2
D
)
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| LT1123CZ#PBF | 功能描述:IC REG CTRLR SGL 5V TO-92-3 RoHS:是 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - 線性晶體管驅(qū)動器 系列:- 產(chǎn)品培訓模塊:More Information on LDOs 標準包裝:2,500 系列:- 類型:正，固定式 輸出數(shù):2 輸出電壓:2.8V，3.3V 電流 - 電源:12mA 輸入電壓:5 V ~ 22 V 工作溫度:0°C ~ 70°C 封裝/外殼:16-SOIC（0.154"，3.90mm 寬） 供應(yīng)商設(shè)備封裝:16-SOIC 包裝:帶卷 (TR) |
| LT1123CZ#TR | 功能描述:IC REG CTRLR SGL 5V TO-92-3 RoHS:否 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - 線性晶體管驅(qū)動器 系列:- 產(chǎn)品培訓模塊:More Information on LDOs 標準包裝:2,500 系列:- 類型:正，固定式 輸出數(shù):2 輸出電壓:2.8V，3.3V 電流 - 電源:12mA 輸入電壓:5 V ~ 22 V 工作溫度:0°C ~ 70°C 封裝/外殼:16-SOIC（0.154"，3.90mm 寬） 供應(yīng)商設(shè)備封裝:16-SOIC 包裝:帶卷 (TR) |
| LT1123CZ#TRPBF | 功能描述:IC REG CTRLR SGL 5V TO-92-3 RoHS:是 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - 線性晶體管驅(qū)動器 系列:- 產(chǎn)品培訓模塊:More Information on LDOs 標準包裝:2,500 系列:- 類型:正，固定式 輸出數(shù):2 輸出電壓:2.8V，3.3V 電流 - 電源:12mA 輸入電壓:5 V ~ 22 V 工作溫度:0°C ~ 70°C 封裝/外殼:16-SOIC（0.154"，3.90mm 寬） 供應(yīng)商設(shè)備封裝:16-SOIC 包裝:帶卷 (TR) |
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