LT1123CST#PBF Linear Technology, LT1123CST#PBF Datasheet - Page 7

• Manufacturer Part Number: LT1123CST#PBF
• Description: IC LDO REGULATOR DRIVR 5V SOT223
• Manufacturer: Linear Technology
• Type: Positive Fixedr

Specifications of LT1123CST#PBF

• Number Of Outputs: 1
• Voltage - Output: 5V
• Current - Supply: 700µA
• Operating Temperature: 0°C ~ 125°C
• Package / Case: SOT-223 (3 leads + Tab), SC-73, TO-261
• Primary Input Voltage: 20V
• Output Voltage Fixed: 5V
• Dropout Voltage Vdo: 300mV
• No. Of Pins: 3
• Output Current: 4A
• Voltage Regulator Case Style: SOT-223
• Operating Temperature Range: 0°C To +125°C
• Rohs Compliant: Yes
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Voltage - Input: -

APPLICATIO S I FOR ATIO
The following assumptions were made in calculating the
data for the curves. Resistors are 5% tolerance and the
values shown on the curve are nominal.
For 20mA drive current assume:
For 50mA drive current assume:
For 120mA drive current assume:
The R
R
current. The chart includes a number for power dissipa-
tion for the LT1123 and R
Note that in some conditions R
short. This is possible in circuits where an overload is
unlikely and the input voltage and drive requirements are
low. See the section on Thermal Considerations for more
information.
R
INPUT
VOLTAGE
5.5V
6.0V
7.0V
8.0V
9.0V
10.0V
D
D
V
V
V
V
V
V
Selection Chart
for the most useful range of input voltage and output
BE
DRIVE
BE
DRIVE
BE
DRIVE
D
= 0.95V at I
= 1.2V at I
= 1.4V at I
Selection Chart lists the recommended values for
OUTPUT CURRENT:
DROPOUT VOLTAGE:
R
Power (LT1123)
Power (R
R
Power (LT1123)
Power (R
R
Power (LT1123)
Power (R
R
Power (LT1123)
Power (R
R
Power (LT1123)
Power (R
R
Power (LT1123)
Power (R
= 1.75V
= 1.9V
= 2.1V
D
D
D
D
D
D
D
D
D
D
D
D
C
C
)
)
)
)
)
)
C
= 2A
= 4A
U
= 1A
U
D
.
0A to 1A
0.05W
0.12W
0.05W
0.13W
0.06W
0.16W
0.06W
0.17W
0.20W
0.07W
0.22W
0.07W
120Ω
150Ω
180Ω
240Ω
270Ω
330Ω
D
0.3V
may be replaced with a
W
0A to 2A
0.14W
0.32W
0.15W
0.35W
0.14W
0.36W
0.15W
0.42W
0.16W
0.47W
0.17W
0.52W
110Ω
130Ω
0.4V
43Ω
51Ω
75Ω
91Ω
U
0A to 4A
0.37W
0.76W
0.38W
0.89W
0.38W
0.97W
0.41W
1.11W
0.43W
1.25W
0.75V
20Ω
27Ω
36Ω
43Ω
51Ω
––
––
––
Current Limit
For regulator circuits using the LT1123, current limiting is
achieved by limiting the base drive to the external PNP
pass transistor. This means that the actual system current
limit will be a function of both the current limit of the
LT1123 and the Beta of the external PNP. Beta-based
current limit schemes are normally not practical because
of uncertainties in the Beta of the pass transistor. Here the
drive characteristics of the LT1123 combined with the
Beta characteristics of the MJE1123 can provide reliable
Beta-based current limiting. This is shown in Figure 5
where the current limit of 30 randomly selected transis-
tors is plotted. The spread of current limit is reasonably
well controlled.
Figure 5. Short-Circuit Current for 30 Random Devices
11
10
15
14
13
12
9
8
7
6
5
4
2
2
3
1
0
9
8
7
6
5
4
3
1
0
4.00
0
4.25 4.50
Figure 6. MJE1123 I
OUTPUT CURRENT (A)
0.05
4.75
I
5.00
B
(A)
5.25
0.10
C
5.50 5.75
vs I
LT1123 F06
LT1123 F05
B
6.00
0.15
LT1123
1123fb
7