Datasheet LT1123 Datasheet (Linear Technology)

LT1123

Low Dropout

Regulator Driver

EATU

F

■

Extremely Low Dropout

■

Low Cost

■

Fixed 5V Output, Trimmed to ±1%

■

700µA Quiescent Current

■

3-Pin TO-92 Package

■

1mV Line Regulation

■

5mV Load Regulation

■

Thermal Limit

■

4A Output Current Guaranteed

RE

S

A

PPLICATITYPICAL

O

DUESCRIPTIO

The LT1123 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.

U

5V Low Dropout Regulator Dropout Voltage

SEALED

LEAD ACID

5.4 – 7.2V

* REQUIRED IF DEVICE IS
MORE THAN 6" FROM MAIN
FILTER CAPACITOR

†



REQUIRED FOR STABILITY



(LARGER VALUES INCREASE
STABILITY)

0.5

DRIVE

LT1123

GND

620Ω

20Ω

FB

MOTOROLA
MJE1123

+

OUTPUT = 5V/4A

†

10µF

LT1123 TA01

0.4

0.3

0.2

DROPOUT VOLTAGE (V)

0.1

0

1

0

OUTPUT CURRENT (A)

3

4

2

5

LT1123 TA02

+

10µF*

1

LT1123

WU

U

PACKAGE

/

O

RDER I FOR ATIO

W

O

A

LUTEXI T

S

Drive Pin Voltage (V
Feedback Pin Voltage (V
Operating Junction Temperature Range ... 0°C to 125°C

Storage Temperature Range ................ –65°C to 150°C

A

DRIVE

WUW

ARB

U
G

I

S

to Ground) ..................... 30V

to Ground) .................... 30V

FB

BOTTOM VIEW

3

DRIVE FB GND

ORDER PART

12

NUMBER

LT1123CZ

Lead Temperature (Soldering, 10 sec.)................ 300°C

Z PACKAGE

3-LEAD TO-92 PLASTIC

LECTRICAL C CHARA TERIST

E

PARAMETER CONDITIONS MIN TYP MAX UNITS

Feedback Voltage I

Feedback Pin Bias Current V
Drive Current VFB = 5.20V, 2V ≤ V

Drive Pin Saturation Voltage I

Line Regulation 5V < V
Load Regulation ∆I
Temperature Coefficient of V

OUT

ICS

= 10mA, TJ = 25°C 4.90 5.00 5.10 V

DRIVE

5mA ≤ I
3V ≤ V

= 5.00V, 2V ≤ V

FB

= 4.80V, V

V

FB

= 0.5V, V

V

FB

DRIVE

I

DRIVE

DRIVE

≤ 100mA

DRIVE

≤ 20V ● 4.80 5.00 5.20 V

DRIVE

≤ 15V ● 300 500 µA

DRIVE

≤ 15V ● 0.45 1.0 mA

DRIVE

= 3V ● 125 170

DRIVE

= 3V, ≤ TJ ≤ 100°C 25 100 150

DRIVE

= 10mA, VFB = 4.5V 1.4 V
= 125mA, VFB = 4.5V 2.0

< 20V ● 1.0 ±20 mV

DRIVE

= 10 to 100mA ● –5 –50 mV

0.2 mV/°C

The ● indicates specifications which apply over the full operating temperature range.

W

SPL

I

2

IIFED BLOCK

IDAGRA

W

DRIVE

CURRENT

LIMIT

THERMAL

LIMIT

GROUND

–

+

5V

FB

LT1123 SBD01

LPER

FEEDBACK PIN VOLTAGE (V)

0

0

DRIVE CURRENT (mA)

50

100

150

1234

LT1123 G03

56

200

TJ = 125°C

TJ = –50°C

TJ = 25°C

V

DRIVE

= 3V

F

O

R

ATYPICA

UW

CCHARA TERIST

E

C

LT1123

ICS

Feedback Pin Bias Current vs
Temperature

400

VFB = 5V

300

200

FEEDBACK PIN BIAS CURRENT (µA)

100

0

25 50 75 100

TEMPERATURE (°C)

Feedback Pin Bias Current vs
Feedback Pin Voltage

500

400

300

200

100

FEEDBACK PIN BIAS CURRENT (µA)

TJ = 125°C

TJ = 25°C

TJ = 0°C

LT1123 G01

125

Minimum Drive Pin Current vs
Temperature

600

V

= 3V

DRIVE

500

400

300

200

100

MINIMUM DRIVE PIN CURRENT (µA)

0

0

25 50 75 100

TEMPERATURE (°C)

Drive Pin Saturation Voltage vs
Drive Current

2.5
VFB = 4.5V

2.0

1.5

1.0

DRIVE PIN VOLTAGE (V)

0.5

TJ = 0°C

TJ = 125°C

TJ = 25°C

LT1123 G02

125

Drive Current vs Feedback Pin
Voltage

Output Voltage vs Temperature

5.03

5.02

5.01

5.00

4.99

OUTPUT VOLTAGE (V)

4.98

0

FU CTIO AL DESCRIPTIO 

The LT1123 is a three pin device designed to be used in
conjunction with a discrete PNP transistor to form an
inexpensive ultra-low dropout regulator. The device incor­porates a trimmed 5V bandgap reference, error amplifier,
a current-limited Darlington driver, and an internal ther­mal limit circuit. The internal circuitry connected to the
drive pin is designed to function at the saturation voltage
of the Darlington driver. This allows a resistor to be

1

0

FEEDBACK PIN VOLTAGE (V)

2

0

3

4

5

LT1123 G04

0

40

20

DRIVE CURRENT (mA)

80

60

100

120

LT1123 G05

140

4.97
–50

–25 0

50 100 125

25 75

TEMPERATURE (°C)

LT1123 G06

U UU

inserted in series with the drive pin. This resistor is used
to limit the base drive to the PNP and also to limit the power
dissipation in the LT1123. The value of this resistor will be
defined by the operating requirements of the regulator
circuit. The LT1123 is designed to sink a minimum of
125mA of base current. This is sufficient base drive to
form a regulator circuit which can supply output currents
up to 4A at a dropout voltage of less than 0.75V.

3

LT1123

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PI FU CTIO S

Drive Pin: The drive pin serves two functions. It provides
current to the LT1123 for its internal circuitry including
startup, 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 speci­fications as Drive Current with VFB = 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 VFB = 4.80V gives the range of current
available under nominal operating conditions, when the
device is regulating. Drive current with VFB = 0.5V gives the
range of drive current available with the feedback pin
pulled low as it would be during startup 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 (VFB = 5V). This can be seen
in the curve of Drive Current vs VFB Voltage in the Typical
Performance Characteristic curves. This can provide some
foldback in the current limit of the regulator circuit.

All internal circuitry connected to the drive pin is designed
to operate at the saturation voltage of the Darlington
output driver (1.4 – 2V). This allows a resistor to be
inserted between the base of the external PNP device and
the drive pin. This resistor is used to limit the base drive to
the external PNP below the value set internally by the
LT1123, and also to help limit power dissipation in the
LT1123. The operating voltage range of this pin is from
0V to 30V. Pulling this pin below ground by more than one
VBE will forward bias the substrate diode of the device.
This condition can only occur if the power supply leads are
reversed and will not damage the device if the current is
limited to less than 200mA.

Feedback Pin (VFB): The feedback pin also serves two
functions. It provides a path for the bias current of the
reference and error amplifier and contributes a portion of
the drive current for the Darlington output driver. The sum
total of these currents is the Feedback Pin Bias Current
(300µA typical). The second function of this pin is to
provide the voltage feedback to the error amplifier.

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The LT1123 is designed to be used in conjunction with an
external PNP transistor. The overall specifications of a
regulator circuit using the LT1123 and an external PNP will
be heavily dependent on the specifications of the external
PNP. While there are a wide variety of PNP transistors
available that can be used with the LT1123, the specifica­tions given in typical transistor data sheets are of little use
in determining overall circuit performance.

Linear Technology has solved this problem by cooperat­ing with Motorola to design and specify the MJE1123. This
transistor is specifically designed to work with the LT1123
as the pass element in a low dropout regulator. The
specifications of the MJE1123 reflect the capability of the
LT1123. For example, the dropout voltage of the MJE1123
is specified up to 4A collector current with base drive
currents that the LT1123 is capable of generating (20mA

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to 120mA). Output currents up to 4A with dropout volt­ages less than 0.75V can be guaranteed.

The following sections describe how specifications can be
determined for the basic regulator. The charts and graphs
are based on the combined characteristics of the LT1123
and the MJE1123. Formulas are included that will enable
the user to substitute other transistors that have been
characterized. A chart is supplied that lists suggested
resistor values for the most popular range of input volt­ages and output current.

BASIC REGULATOR CIRCUIT

The basic regulator circuit is shown in Figure 1. The
LT1123 senses the voltage at its feedback pin and drives
the base of the PNP (MJE1123) in order to maintain the

4

LT1123

PPLICATI

A

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output at 5V. The drive pin of the LT1123 can only sink
current; RB is required to provide pullup on the base of the
PNP. RB must be sized so that the voltage drop caused by
the minimum drive pin current is less than the emitter/
base voltage of the external PNP at light loads. The
recommended value for RB is 620Ω. For circuits that are
required to run at junction temperatures in excess of
100°C the recommended value of RB is 300Ω.

DRIVE

LT1123

GND

RB
620Ω

R

D

MJE1123

V

FB

+

OUT

10µF ALUM

LT1123 F01

= 5V

V

IN

Figure 1. Basic Regulator Circuit

RD is used to limit the drive current available to the PNP
and to limit the power dissipation in the LT1123. Limiting
the drive current to the PNP will limit the output current of
the regulator which will minimize the stress on the regu­lator circuit under overload conditions. RD is chosen
based on the operating requirements of the circuit, prima­rily dropout voltage and output current.

DROPOUT VOLTAGE

The dropout voltage of an LT1123 based regulator circuit
is determined by the VCE saturation voltage of the discrete
PNP when it is driven with a base current equal to the
available drive current of the LT1123. The LT1123 can sink
up to 150mA of base current (150mA typ., 125mA min.)
when output voltage is up near the regulating point (5V).
The available drive current of the LT1123 can be reduced
by adding a resistor (RD) in series with the drive pin (see
the section below on current limit). The MJE1123 is
specified for dropout voltage (VCE sat.) at several values of
output current and up to 120mA of base drive current. The
chart below lists the operating points that can be guaran-

Dropout Voltage

DROPOUT VOLTAGE

DRIVE CURRENT

20mA 1A 0.16V 0.3V
50mA 1A 0.13V 0.25V

120mA 1A 0.2V 0.35V

0.75

0.50

DROPOUT VOLTAGE (V)

0.25

OUTPUT CURRENT

1.0
BASED ON 

MJE1123 SPECS

I

DRIVE

0

0

2A 0.25V 0.4V

4A 0.45V 0.75V

I

= 120mA

DRIVE

= 20mA

I

= 50mA

DRIVE

1

2

OUTPUT CURRENT (A)

TYP MAX

3

4

LT1123 F02

Figure 2. Maximum Dropout Voltage

0.75

0.65

0.55

0.45

0.35

0.25

DROPOUT VOLTAGE(V)

0.15

0.05

IC = 4A, IB = 0.12A

IC = 2A, IB = 0.05A

IC = 1A, IB = 0.02A

20

60

40

CASE TEMPERATURE (°C)

80

100

120

LT1123 F03

Figure 3. Dropout Voltage vs Temperature

teed by the combined data sheets of the LT1123 and
MJE1123. Figure 2 illustrates the chart in graphic form.
Although these numbers are only guaranteed by the data
sheet at 25°C, Dropout Voltage vs Temperature (Figure 3)
clearly shows that the dropout voltage is nearly constant
over a wide temperature range.

5

LT1123

PPLICATI

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SELECTING R

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In order to select RD the user should first choose the value
of drive current that will give the required value of output
current. For circuits using the MJE1123 as a pass transis­tor this can be done using the graph of Dropout Voltage vs
Output Current (Figure 2). For example, 20mA of drive
current will guarantee a dropout voltage of 0.3V at 1A of
output current. For circuits using transistors other than
the MJE1123 the user must characterize the transistor to
determine the drive current requirements. In general it is
recommended that the user choose the lowest value of
drive current that will satisfy the output current require­ments. This will minimize the stress on circuit compo­nents during overload conditions.

Figure 4 can be used to select the value of RD based on the
required drive current and the minimum input voltage.
Curves are shown for 20mA, 50mA, and 120mA drive
current corresponding to the specified base drive currents
for the MJE1123. The data for the curves was generated
using the following formula:

RD = (VIN – VBE – V

DRIVE

)/(I

DRIVE

+ 1mA)

where VIN = the minimum input voltage to the circuit

VBE = the maximum emitter/base voltage of the
PNP pass transistor
V

= the maximum Drive pin voltage of the

DRIVE

LT1123
I

= the minimum drive current required

DRIVE

The current through RB is assumed to be 1mA

1k

I

= 20mA

DRIVE

I

= 50mA

D

100

R

DRIVE

I

DRIVE

= 120mA

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:

VBE = 0.95V at IC = 1A
V

= 1.75V

DRIVE

For 50mA drive current assume:

VBE = 1.2V at IC = 2A
V

= 1.9V

DRIVE

For 120mA drive current assume:

VBE = 1.4V at IC = 4A
V

= 2.1V

DRIVE

The RD Selection Chart lists the recommended values for
RD for the most useful range of input voltage and output
current. The chart includes a number for power dissipa­tion for the LT1123 and RD.

RD Selection Chart

INPUT
VOLTAGE

5.5V R

6.0V R

7.0V R

8.0V R

9.0V R

10.0V R

OUTPUT CURRENT:
DROPOUT VOLTAGE:

D

Power (LT1123) 0.05W 0.14W ––
Power (R

D

Power (LT1123) 0.05W 0.15W 0.37W
Power (R

D

Power (LT1123) 0.06W 0.14W 0.38W
Power (R

D

Power (LT1123) 0.06W 0.15W 0.38W
Power (R

D

Power (LT1123) 0.20W 0.16W 0.41W
Power (R

D

Power (LT1123) 0.22W 0.17W 0.43W
Power (R

) 0.12W 0.32W ––

D

) 0.13W 0.35W 0.76W

D

) 0.16W 0.36W 0.89W

D

) 0.17W 0.42W 0.97W

D

) 0.07W 0.47W 1.11W

D

) 0.07W 0.52W 1.25W

D

0 – 1A

0.3V

120Ω 43Ω ––

150Ω 51Ω 20Ω

180Ω 75Ω 27Ω

240Ω 91Ω 36Ω

270Ω 110Ω 43Ω

330Ω 130Ω 51Ω

0 – 2A

0.4V

0 – 4A

0.75V

6

10

715

6

5

Figure 4. RD Resistor Value

9

10

8

V

IN

131211

14

LT1123 F04

Note that in some conditions RD may be replaced with a
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.

LT1123

VIN (V)

6

R

D

(Ω)

8

1k

LT1123 F07

10

100

7 15

14

131211

10

9

5

0.4W

0.7W

0.1W

0.2W

0.3W

0.5W

PPLICATI

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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 transistors
is plotted. The spread of current limit is reasonably well
controlled.

15
14
13
12

11

10

9
8
7
6
5

NUMBER OF UNITS

4

3

2
1

0

4.00

4.25 4.50

Figure 5. Short Circuit Current for 30 Random Devices

5.00

4.75 5.25 6.00

OUTPUT CURRENT (A)

5.50 5.75

LT1123 F05

The curve in Figure 6 can be used to determine the range
of current limit of an LT1123 regulator circuit using an
MJE1123 as a pass transistor. The curve was generated
using the Beta versus IC curve of the MJE1123. The
minimum and maximum value curves are extrapolated
from the minimum and maximum Beta specifications.

THERMAL CONSIDERATIONS

The thermal characteristics of three components need to
be considered; the LT1123, the pass transistor, and RD.
Power dissipation should be calculated based on the worst
case conditions seen by each component during normal
operation.

The worst case power dissipation in the LT1123 is a
function of drive current, supply voltage, and the value of
RD. Worst case dissipation for the LT1123 occurs when
the drive current is equal to approximately one half of its
maximum value. Figure 7 plots the worst case power
dissipation in the LT1123 versus RD and VIN. The graph
was generated using the following formula:

D

2

;R 10

D

>Ω

V–V

()

P

IN BE

=

D

4R

where VBE = the emitter/base voltage of the PNP pass

transistor (assumed to be 0.6V)

For some operating conditions RD may be replaced with a
short. This is possible in applications where the operating

9

8

7

6

5

(A)

C

I

4

3

2

1

0

0

0.05 0.15
IB (A)

Figure 6. MJE1123 IC vs I

0.10

LT1123 F06

B

Figure 7. Power in LT1123

7

LT1123

PPLICATI

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requirements (input voltage and drive current) are at the
low end and the output will not be shorted. For RD = 0 the
following formula may be used to calculate the maximum
power dissipation in the LT1123.

PD = (VIN – VBE)(I

DRIVE

)

where VIN = maximum input voltage

VBE = emitter/base voltage of PNP
I

= required maximum drive current

DRIVE

The maximum junction temperature rise above ambient
for the LT1123 will be equal to the worst case power
dissipation multiplied by the thermal resistance of the
device. The thermal resistance of the device will depend
upon how the device is mounted, and whether a heat sink
is used. Measurements show that one of the most effective
ways of heat sinking the TO-92 package is by utilizing the
PC board traces attached to the leads of the package. The
table below lists several methods of mounting and the
measured value of thermal resistance for each method. All
measurements were done in still air.

THERMAL

RESISTANCE

Package alone.............................................................................. 220°C/W

Package soldered into PC board with plated through

holes only.............................................................................. 175°C/W

Package soldered into PC board with 1/4 sq. in. of copper trace

per lead .................................................................................145°C/W

Package soldered into PC board with plated through holes in

board, no extra copper trace, and a clip-on type heat sink:

Thermalloy type 2224B.............................................. 160°C/W

Aavid type 5754.......................................................... 135°C/W

The maximum operating junction temperature of the
LT1123 is 125°C. The maximum operating ambient
temperature will be equal to 125°C minus the maximum
junction temperature rise above ambient.

1k

0.25W

0.5W
1W

100

(Ω)

D

R

10

5

7 15

6

Figure 8. Power in R

9

10

8

VIN (V)

131211

D

2W

14

LT1123 F08

where VBE = emitter/base voltage of the PNP pass

transistor
V

= voltage at the drive pin of the LT1123

DRIVE

= V

of the drive pin in the worst case

SAT

The worst case power dissipation in the PNP pass transis­tor is simply equal to:

P

= (VIN – V

MAX

where VIN = Maximum V

I

= Maximum I

OUT

OUT

)(I

IN

OUT

OUT

)

The thermal resistance of the MJE1123 is equal to:

70°C/W Junction to Ambient (no heat sink)

1.67°C/W Junction to Case

The PNP will normally be attached to either a chassis or a
heat sink so the actual thermal resistance from junction to
ambient will be the sum of the PNP's junction to case
thermal resistance and the thermal resistance of the heat
sink or chassis. For non-standard heat sinks the user will
need to determine the thermal resistance by experiment.

The worst case power dissipation in RD needs to be
calculated so that the power rating of the resistor can be
determined. The worst case power in the resistor will
occur when the drive current is at a maximum. Figure 8
plots the required power rating of RD versus supply
voltage and resistor value. Power dissipation can be
calculated using the following formula:

2

P

V–V –V

()

IN BE DRIVE

=

R

D

R

8

The maximum junction temperature rise above ambient
for the PNP pass transistor will be equal to the maximum
power dissipation times the thermal resistance, junction
to ambient, of the PNP. The maximum operating junction
temperature of the MJE1123 is 150°C. The maximum
operating ambient temperature for the MJE1123 will be
equal to 150°C minus the maximum junction temperature
rise.

LT1123

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THERMAL LIMITING

The thermal limit of the LT1123 can be used to protect both
the LT1123 and the PNP pass transistor. This is accom­plished 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 tempera­ture 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 < VIN < 7V
I

OUT

MAX

Max ambient temp. = 70°C
V

= 5V

OUT

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

= 50mA

DRIVE

2. The next step is to determine the value of RD. Based
on 50mA of drive current and a minimum input voltage of

5.5V, we can select RD from the graph of Figure 4. From the
graph the value of RD is equal to 50Ω, so we should use the
next lowest 5% value which is 47Ω.

RD = 47Ω

S

= 1.5A

I FOR ATIO

WU

U

Given: V
Then: P

Assuming a thermal resistance of 150°C/W, the maximum
junction temperature rise above ambient will be equal to
(P

)(150°C/W) = 33°C. The maximum operating junc-

MAX

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 tem­perature of 125°C for the LT1123.

The power rating for RD can be found from the plot of
Figure 8 using VIN = 7V and RD = 47Ω. From the plot, R
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

IN

MAX

The maximum operating junction temperature of the
MJE1123 is 150°C. The difference between the maximum
operating junction temperature of 150°C and the maxi­mum 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 tempera­ture 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.

= 7V, VBE = 0.6V, RD = 47Ω

IN

MAX

(LT1123) = 0.22W.

MAX

– V

OUT

)(I

OUT

) = (7V – 5V)(1.5A) = 3W

MAX

D

3. We can now look at the thermal requirements of the
circuit.

Worst case power in the LT1123 will be equal to:

V–V

()

IN

MAX

4R

2

BE

D

Refer to Linear Technology’s list of Suggested Manufac­turers of Specialized Components for information on
where to find the required heat sinks, resistors and capaci­tors. This listing is available through Linear Technology’s
marketing department.

9

LT1123

U

O

PPLICATITYPICAL

SA

SWITCHING

REGULATOR

V

IN

Isolated Feedback for Switching Regulators

V

IN

1k

DRIVE

FB

LT1123

GND

5V Regulator with Anti-Sat Miminizes

Ground Pin Current in Dropout

MJE1123

620Ω

2N2907

DRIVE

LT1123

GND

1N4148

1N4148

1k

FB

5V
OUTPUT

+

10µF
ALUM

LT1123 TA04

5V Shunt Regulator or Voltage Clamp

1k

IRL510

DRIVE

FB

LT1123

GND

+

10µF
ALUM

LT1123 TA11

5V
OUTPUT

LT1123 TA03

INTERNAL

BATTERY

GEL CELL

5V/2A Regulator with Remote Sensing

600Ω

MJE1123

75Ω

7V

DRIVE

LT1123

GND

FB

100Ω

REMOTE

LOAD

100Ω

Undervoltage Indicator On for VIN < (VZ +5V)

1k

V

IN

DRIVE

LT1123

GND

2.4k

FB

Battery Backup Regulator

+

10µF

620Ω

6V

ALUM

1N4148

DRIVE

LT1123

GND

MJE1123

1N4148

20Ω

FB

620Ω

+

V

470k

LT1123 TA12

MJE1123

5V OUTPUT

10µF
ALUM

Z

+

100µF
OR LARGER

+

10µF
ALUM

LT1123 TA08

EXTERNAL
POWER

LT1123 TA07

10

U

+

5-CELL NiCAD

BATTERY PACK

(6V)

R1

1.5k

R2

820Ω

+ +

+

5V/1A
OUTPUT

MJE1123

10µF
10V

10µF
10V

LT1123 TA06

* PACKS WILL SHARE CURRENT

DRIVE

LT1123

GND

FB

O

PPLICATITYPICAL

SA

5V/1A Regulator with Shutdown 5V/1A Regulator with Shutdown

LT1123

6V

GEL CELL

HI = ON

LO = OFF

MM74C906

(OPEN COLLECTOR

OUTPUT)

V

> V

IN

OUT

1/6

50k

MPSA12

LT1123

Adjusting V

620Ω

R

D

DRIVE

FB

LT1123

DRIVE

GND

620Ω

FB

OUT

MJE1123

V

Z

MJE1123

+

10µF
ALUM

5V/1A
OUTPUT

LT1123 TA09

+

10µF
ALUM

+

10µF
ALUM

6V

GEL CELL

HI = ON

LO = OFF

*P-CHANNEL, LOGIC LEVEL

1/6

MM74C906

(OPEN COLLECTOR

OUTPUT)

1M

DRIVE

LT1123

GND

620Ω

Si9400DY*

68Ω

FB

+

10µF
ALUM

5V/1A OUTPUT

LT1123 TA10

5V Regulator Powered by Multiple Battery Packs*

V

*

OUT

GND

Adjusting V

DRIVE

LT1123

GND

620Ω

R

D

FB

> V

V

IN

OUT

*V

= (5V + VZ)

OUT

LT1123 TA13

OUT

MJE1123

V

*

OUT

X

+

10µF
ALUM

LT1123 TA14

I

FB

R

*V

= (5V + (IFB • RX))

OUT

≈ 300µA

I

FB

Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no represen­tation that the interconnection of circuits as described herein will not infringe on existing patent rights.

11

LT1123

PACKAGE DESCRIPTIO

0.060 ± 0.005

(1.524± 0.127)

DIA

0.180 ± 0.005

(4.572 ± 0.127)

0.180 ± 0.005

(4.572 ± 0.127)

U

Dimensions in inches (millimeters) unless otherwise noted.

Z Package

3-Lead TO-92

0.060 ± 0.010

(1.524 ± 0.254)

0.90

(2.286)

NOM

0.140 ± 0.010

(3.556 ± 0.127)

0.500

(12.79)

MIN

0.050 ± 0.005

(1.270 ± 0.127)

0.050

(1.270)

MAX

UNCONTROLLED
LEAD DIA

0.020 ± 0.003

(0.508 ± 0.076)

0.016 ± 0.03

(0.406 ± 0.076)

5°

NOM

0.015 ± 0.02

(0.381 ± 0.051)

10° NOM

Z3 1191

T

JMAXθJA

125°C 220°C/W

SEE DATA IN THERMAL
CONSIDERATIONS

12

Linear Technology Corporation

1630 McCarthy Blvd., Milpitas, CA 95035-7487

[phone]

●

FAX

: [phone]

●

TELEX

: 499-3977

LT/GP 0192 10K REV 0

 LINEAR TECHNOLOGY CORPORATION 1992