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LT1123CST#PBF

P1-P3P4-P6P7-P9P10-P12P13-P15P16-P16
1
LT1123
1123fb
Low Dropout
Regulator Driver
The LT
®
1123 is a 3-pin bipolar device designed to be used
in conjunction with a discrete PNP power transistor to
form an inexpensive low dropout regulator. The LT1123
consists of a trimmed bandgap reference, error amplifier,
and a driver circuit capable of sinking up to 125mA from
the base of the external PNP pass transistor. The LT1123
is designed to provide a fixed output voltage of 5V.
The drive pin of the device can pull down to 2V at 125mA
(1.4V at 10mA). This allows a resistor to be used to reduce
the base drive available to the PNP and minimize the
power dissipation in the LT1123. The drive current of the
LT1123 is folded back as the feedback pin approaches
ground to further limit the available drive current under
short-circuit conditions.
Total quiescent current for the LT1123 is only 700µA. The
device is available in a low cost TO-92 package.
■
Extremely Low Dropout
■
Low Cost
■
Fixed 5V Output, Trimmed to ±1%
■
700µA Quiescent Current
■
1mV Line Regulation
■
5mV Load Regulation
■
Thermal Limit
■
4A Output Current Guaranteed
■
Available in a 3-Pin TO-92 Package
5V Low Dropout Regulator Dropout Voltage
FEATURES
DESCRIPTIO
U
TYPICAL APPLICATIO
U
620Ω
10µF*
SEALED
LEAD ACID
5.4 TO 7.2V
*REQUIRED IF DEVICE IS
MORE THAN 6" FROM MAIN
FILTER CAPACITOR
OUTPUT = 5V/4A
10µF
†
LT1123 TA01
20Ω
†
REQUIRED FOR STABILITY
(LARGER VALUES INCREASE
STABILITY)
MOTOROLA
MJE1123
DRIVE
LT1123
GND
FB
+
+
OUTPUT CURRENT (A)
0
DROPOUT VOLTAGE (V)
0.3
0.4
0.5
4
LT1123 TA02
0.2
0.1
0
1
2
3
5
, LTC and LT are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
2
LT1123
1123fb
Drive Pin Voltage (V
DRIVE
to Ground) ..................... 30V
Feedback Pin Voltage (V
FB
to Ground) .................... 30V
Operating Junction Temperature Range ... 0°C to 125°C
ORDER PART
NUMBER
LT1123CST
ABSOLUTE AXI U RATI GS
WWWU
Storage Temperature Range ................. –65°C to 150°C
Lead Temperature (Soldering, 10 sec)................. 300°C
PACKAGE/ORDER I FOR ATIO
UU
W
(Note 1)
ORDER PART
NUMBER
LT1123CZ
ST PART MARKING
3
2
1
FRONT VIEW
TAB IS
GND
FB
GND
DRIVE
ST PACKAGE
3-LEAD PLASTIC SOT-223
BOTTOM VIEW
DRIVE FB GND
Z PACKAGE
3-LEAD TO-92 PLASTIC
1123
θ
JA
AT TAB ≈ 20°C/W
T
JMAX
= 125°C, θ
JA
= 220°C/W
PARAMETER CONDITIONS MIN TYP MAX UNITS
Feedback Voltage I
DRIVE
= 10mA, T
J
= 25°C 4.90 5.00 5.10 V
5mA ≤ I
DRIVE
≤ 100mA
3V ≤ V
DRIVE
≤ 20V ● 4.80 5.00 5.20 V
Feedback Pin Bias Current V
FB
= 5.00V, 2V ≤ V
DRIVE
≤ 15V ● 300 500 µA
Drive Current V
FB
= 5.20V, 2V ≤ V
DRIVE
≤ 15V ● 0.45 1.0 mA
V
FB
= 4.80V, V
DRIVE
= 3V ● 125 170
V
FB
= 0.5V, V
DRIVE
= 3V, 0°C ≤ T
J
≤ 100°C 25 100 150
Drive Pin Saturation Voltage I
DRIVE
= 10mA, V
FB
= 4.5V 1.4 V
I
DRIVE
= 125mA, V
FB
= 4.5V 2.0
Line Regulation 5V < V
DRIVE
< 20V ● 1.0 ±20 mV
Load Regulation ∆I
DRIVE
= 10 to 100mA ● –5 –50 mV
Temperature Coefficient of V
OUT
0.2 mV/°C
Note 1: Absolute Maximum Ratings are those values beyond which the life
of the device may be impaired.
ELECTRICAL CHARACTERISTICS
The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at T
A
= 25°C.
Consult LTC Marketing for parts specified with wider operating temperature ranges.
3
LT1123
1123fb
TEMPERATURE (°C)
0
100
FEEDBACK PIN BIAS CURRENT (µA)
200
300
400
25 50 75 100
LT1123 G01
125
V
FB
= 5V
Feedback Pin Bias Current
vs Temperature
FEEDBACK PIN VOLTAGE (V)
0
FEEDBACK PIN BIAS CURRENT (µA)
300
400
500
4
LT1123 G04
200
100
0
1
2
3
5
T
J
= 125°C
T
J
= 0°C
T
J
= 25°C
TEMPERATURE (°C)
–50
OUTPUT VOLTAGE (V)
5.01
5.02
5.03
25 75
LT1123 G06
5.00
4.99
–25 0
50 100 125
4.98
4.97
Output Voltage vs Temperature
TEMPERATURE (°C)
0
0
MINIMUM DRIVE PIN CURRENT (µA)
200
400
600
25 50 75 100
LT1123 G02
125
100
300
500
V
DRIVE
= 3V
Minimum Drive Pin Current
vs Temperature
DRIVE CURRENT (mA)
0
0
DRIVE PIN VOLTAGE (V)
1.0
2.5
40
80
100
LT1123 G05
0.5
2.0
1.5
20
60
120
140
T
J
= 125°C
T
J
= 0°C
T
J
= 25°C
V
FB
= 4.5V
Drive Pin Saturation Voltage
vs Drive Current
CCHARA TERIST
ICS
UW
AT
Y
P
I
CA
LPER
F
O
R
C
E
FEEDBACK PIN VOLTAGE (V)
0
0
DRIVE CURRENT (mA)
50
100
150
1234
LT1123 G03
56
200
T
J
= 125°C
T
J
= –50°C
T
J
= 25°C
V
DRIVE
= 3V
Drive Current
vs Feedback Pin Voltage
Feedback Pin Bias Current
vs Feedback Pin Voltage
UU
U
PI FU CTIO S
Drive Pin: The drive pin serves two functions. It provides
current to the LT1123 for its internal circuitry including
start-up, bias, current limit, thermal limit and a portion of
the base drive current for the output Darlington. The sum
total of these currents (450µA typical) is equal to the
minimum drive current. This current is listed in the speci-
fications as Drive Current with V
FB
= 5.2V. This is the
minimum current required by the drive pin of the LT1123.
The second function of the drive pin is to sink the base
drive current of the external PNP pass transistor. The
available drive current is specified for two conditions.
Drive current with V
FB
= 4.80V gives the range of current
available under nominal operating conditions, when the
device is regulating. Drive current with V
FB
= 0.5V gives the
range of drive current available with the feedback pin
pulled low as it would be during start-up or during a short-
circuit fault. The drive current available when the feedback
pin is pulled low is less than the drive current available
when the device is regulating (V
FB
= 5V). This can be seen
in the curve of Drive Current vs V
FB
Voltage in the Typical
Performance Characteristics curves. This can provide
some foldback in the current limit of the regulator circuit.
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LT1123CST#PBF

Mfr. #:
Buy LT1123CST#PBF
Manufacturer:
Analog Devices / Linear Technology
Description:
Linear Voltage Regulators Low Dropout Reg Driver
Lifecycle:
New from this manufacturer.
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