LT1121/LT1121-3.3/LT1121-5
Micropower Low Dropout
Regulators with Shutdown
FEATURES
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DESCRIPTION
The LT
®
1121/LT1121-3.3/LT1121-5 are micropower low
dropout regulators with shutdown. These devices are ca-
pable of supplying 150mA of output current with a dropout
voltage of 0.4V. Designed for use in battery-powered sys-
tems, the low quiescent current, 30μA operating and 16μA
in shutdown, makes them an ideal choice. The quiescent
current is well-controlled; it does not rise in dropout as it
does with many other low dropout PNP regulators.
Other features of the LT1121/LT1121-3.3/LT1121-5 include
the ability to operate with very small output capacitors. They
are stable with only 0.33μF on the output while most older
devices require between 1μF and 100μF for stability. Small
ceramic capacitors can be used, enhancing manufactur-
ability. Also the input may be connected to ground or a
reverse voltage without reverse current flow from output
to input. This makes the LT1121 series ideal for backup
power situations where the output is held high and the
input is at ground or reversed. Under these conditions only
16μA will flow from the output pin to ground.
L,
LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
0.4V Dropout Voltage
150mA Output Current
30μA Quiescent Current
No Protection Diodes Needed
Adjustable Output from 3.75V to 30V
3.3V and 5V Fixed Output Voltages
Controlled Quiescent Current in Dropout
Shutdown
16μA Quiescent Current in Shutdown
Stable with 0.33μF Output Capacitor
Reverse Battery Protection
No Reverse Current with Input Low
Thermal Limiting
Available in the 8-Lead SO, 8-Lead PDIP 3-Lead
,
SOT-23 and 3-Lead TO-92 Packages
APPLICATIONS
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Low Current Regulator
Regulator for Battery-Powered Systems
Post Regulator for Switching Supplies
TYPICAL APPLICATION
5V Battery-Powered Supply with Shutdown
0.5
8
IN
OUT
LT1121-3.3
5
SHDN
GND
3
1
3.3V
OUT
150mA
1μF
SOLID TANTALUM
DROPOUT VOLTAGE (V)
Dropout Voltage
5V
+
0.4
0.3
0.2
V
SHDN
(PIN 5) OUTPUT
<0.25
OFF
>2.8
ON
NC
ON
0.1
0
LT1121 • TA01
0
20
40 60 80 100 120 140 160
OUTPUT CURRENT (mA)
LT1121 • TA02
1121ff
1
LT1121/LT1121-3.3/LT1121-5
ABSOLUTE MAXIMUM RATINGS
(Note 1)
Input Voltage
LT1121 .............................................................. ± 30V
LT1121HV ............................................... +36V, – 30V
Output Pin Reverse Current ................................. 10mA
Adjust Pin Current ................................................ 10mA
Shutdown Pin Input Voltage (Note 2) .......... 6.5V, – 0.6V
Shutdown Pin Input Current (Note 2) .................. 20mA
Output Short-Circuit Duration ....................... Indefinite
Operating Junction Temperature Range (Note 3)
LT1121C-X ............................................ 0°C to 125°C
LT1121I-X ........................................ – 40°C to 125°C
Storage Temperature Range...................– 65°C to 150°C
Lead Temperature (Soldering, 10 sec) .................. 300°C
PACKAGE/ORDER INFORMATION
TOP VIEW
OUT 1
NC/ADJ* 2
GND 3
NC 4
N8 PACKAGE
8-LEAD PDIP
S8 PACKAGE
8-LEAD PLASTIC SO
T
JMAX
= 150°C,
θ
JA
= 120°C/W (N8, S8)
T
JMAX
= 150°C,
θ
JA
= 70°C/W (AS8)
8 IN
7 NC**
6 NC**
5
SHDN
* PIN 2 = NC FOR LT1121-3.3/LT1121-5
= ADJ FOR LT1121
** PINS 6 AND 7 ARE FLOATING (NO
INTERNAL CONNECTION) ON THE
STANDARD S8 PACKAGE.
PINS 6 AND 7 CONNECTED TO GROUND
ON THE A VERSION OF THE LT1121 (S8 ONLY).
CONNECTING PINS 6 AND 7 TO THE
GROUND PLANE WILL REDUCE THERMAL
RESISTANCE. SEE THERMAL RESISTANCE
TABLES IN THE APPLICATIONS INFORMATION
SECTION.
FRONT VIEW
3
TAB IS
GND
2
1
OUTPUT
IN
GND
V
IN
Z PACKAGE
3-LEAD PLASTIC TO-92
T
JMAX
= 150°C,
θ
JA
= 150°C/W
GND
OUT
BOTTOM VIEW
ST PACKAGE
3-LEAD PLASTIC SOT-223
T
JMAX
= 150°C,
θ
JA
= 50°C/W
ORDER PART NUMBER
LT1121CN8
LT1121CN8-3.3
LT1121CN8-5
LT1121IN8
LT1121IN8-3.3
LT1121IN8-5
LT1121CS8
LT1121CS8-3.3
LT1121CS8-5
LT1121HVCS8
LT1121IS8
LT1121IS8-3.3
LT1121IS8-5
LT1121HVIS8
LT1121ACS8
LT1121ACS8-3.3
LT1121ACS8-5
LT1121AHVCS8
LT1121AIS8
LT1121AIS8-3.3
LT1121AIS8-5
LT1121AHVIS8
S8 PART MARKING
121I3
121I5
121HVI
1121A
121A3
121A5
121AHV
121AI
121AI3
121AI5
21AHVI
ORDER PART
NUMBER
LT1121CST-3.3
LT1121IST-3.3
LT1121CST-5
LT1121IST-5
ST PART
MARKING
11213
121I3
11215
1121I5
ORDER PART
NUMBER
LT1121CZ-3.3
LT121IZ-3.3
LT1121CZ-5
LT1121IZ-5
1121
11213
11215
1121HV
1121I
Order Options
Tape and Reel: Add #TR
Lead Free: Add #PBF Lead Free Tape and Reel: Add #TRPBF
Lead Free Part Marking: http://www.linear.com/leadfree/
Consult LTC Marketing for parts specified with wider operating temperature ranges.
1121ff
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LT1121/LT1121-3.3/LT1121-5
ELECTRICAL CHARACTERISTICS
PARAMETER
Regulated Output Voltage (Note 4)
CONDITIONS
LT1121-3.3
LT1121-5
LT1121 (Note 5)
Line Regulation
V
IN
= 3.8V, I
OUT
= 1mA, T
J
= 25ºC
4.3V < V
IN
< 20V, 1mA < I
OUT
< 150mA
V
IN
= 5.5V, I
OUT
= 1mA, T
J
= 25ºC
6V < V
IN
< 20V, 1mA < I
OUT
< 150mA
V
IN
= 4.3V, I
OUT
= 1mA, T
J
= 25ºC
4.8V < V
IN
< 20V, 1mA < I
OUT
< 150mA
l
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l
The
l
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C.
MIN
3.25
3.2
4.925
4.85
3.695
3.64
TYP
3.3
3.3
5
5
3.75
3.75
1.5
1.5
1.5
–12
–20
–17
–28
–12
–18
0.13
0.3
0.37
0.42
30
90
350
1.5
4
7
150
0.25
1.2
0.75
6
16
50
58
200
l
MAX
3.35
3.4
5.075
5.15
3.805
3.86
10
10
10
–25
–40
–35
–50
–25
–40
0.16
0.25
0.35
0.5
0.45
0.6
0.55
0.7
50
120
500
2.5
7
14
300
2.8
10
22
UNITS
V
V
V
V
V
V
mV
mV
mV
mV
mV
mV
mV
mV
mV
V
V
V
V
V
V
V
V
μA
μA
μA
mA
mA
mA
nA
V
V
μA
μA
dB
LT1121-3.3
ΔV
IN
= 4.8V TO 20V, I
OUT
= 1mA
LT1121-5
ΔV
IN
= 5.5V TO 20V, I
OUT
= 1mA
LT1121 (Note 5)
ΔV
IN
= 4.3V TO 20V, I
OUT
= 1mA
ΔI
LOAD
= 1mA to 150mA, T
J
= 25ºC
ΔI
LOAD
= 1mA to 150mA
LT1121-5
ΔI
LOAD
= 1mA to 150mA, T
J
= 25ºC
ΔI
LOAD
= 1mA to 150mA
LT1121 (Note 5)
ΔI
LOAD
= 1mA to 150mA, T
J
= 25ºC
ΔI
LOAD
= 1mA to 150mA
LT1121-3.3
I
LOAD
= 1mA, T
J
= 25ºC
I
LOAD
= 1mA
I
LOAD
= 50mA, T
J
= 25ºC
I
LOAD
= 50mA
I
LOAD
= 100mA, T
J
= 25ºC
I
LOAD
= 100mA
I
LOAD
= 150mA, T
J
= 25ºC
I
LOAD
= 150mA
Load Regulation
Dropout Voltage (Note 6)
Ground Pin Current (Note 7)
I
LOAD
= 0mA
I
LOAD
= 1mA
I
LOAD
= 10mA
I
LOAD
= 50mA
I
LOAD
= 100mA
I
LOAD
= 150mA
T
J
= 25ºC
V
OUT
= Off to On
V
OUT
= On to Off
V
SHDN
= 0V
V
IN
– V
OUT
= 1V (Avg), V
RIPPLE
= 0.5V
P-P
, f
RIPPLE
= 120Hz,
I
LOAD
= 0.1A
V
IN
– V
OUT
= 7V, T
J
= 25ºC
V
IN
= –20V, V
OUT
= 0V
LT1121-3.3
V
OUT
= 3.3V, V
IN
= 0V
LT1121-5
V
OUT
= 5V, V
IN
= 0V
LT1121 (Note 5) V
OUT
= 3.8V, V
IN
= 0V
Adjust Pin Bias Current (Notes 5, 8)
Shutdown Threshold
Shutdown Pin Current (Note 9)
Ripple Rejection
Current Limit
Input Reverse Leakage Current
Reverse Output Current (Note 11)
Quiescent Current in Shutdown (Note 10) V
IN
= 6V, V
SHDN
= 0V
500
1
25
25
25
mA
mA
μA
μA
μA
16
16
16
1121ff
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LT1121/LT1121-3.3/LT1121-5
ELECTRICAL CHARACTERISTICS
The
l
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C.
limited. When operating at maximum output current the input voltage
range must be limited.
Note 5:
The LT1121 (adjustable version) is tested and specified with the
adjust pin connected to the output pin.
Note 6:
Dropout voltage is the minimum input/output voltage required to
maintain regulation at the specified output current. In dropout the output
voltage will be equal to: (V
IN
– V
DROPOUT
).
Note 7:
Ground pin current is tested with V
IN
= V
OUT
(nominal) and a
current source load. This means that the device is tested while operating in
its dropout region. This is the worst case ground pin current. The ground
pin current will decrease slightly at higher input voltages.
Note 8:
Adjust pin bias current flows into the adjust pin.
Note 9:
Shutdown pin current at V
SHDN
= 0V flows out of the shutdown pin.
Note 10:
Quiescent current in shutdown is equal to the sum total of the
shutdown pin current (6μA) and the ground pin current (9μA).
Note 11:
Reverse output current is tested with the input pin grounded and
the output pin forced to the rated output voltage. This current flows into
the output pin and out of the ground pin.
Note 1:
Stresses beyond those listed under Absolute Maximum Ratings
may cause permanent damage to the device. Exposure to any Absolute
Maximum Rating condition for extended periods may affect device
reliability and lifetime.
Note 2:
The shutdown pin input voltage rating is required for a low
impedance source. Internal protection devices connected to the shutdown
pin will turn on and clamp the pin to approximately 7V or – 0.6V. This
range allows the use of 5V logic devices to drive the pin directly. For high
impedance sources or logic running on supply voltages greater than 5.5V,
the maximum current driven into the shutdown pin must be limited to less
than 20mA.
Note 3:
For junction temperatures greater than 110°C, a minimum load
of 1mA is recommended. For T
J
> 110°C and I
OUT
< 1mA, output voltage
may increase by 1%.
Note 4:
Operating conditions are limited by maximum junction
temperature. The regulated output voltage specification will not apply
for all possible combinations of input voltage and output current. When
operating at maximum input voltage, the output current range must be
TYPICAL PERFORMANCE CHARACTERISTICS
Guaranteed Dropout Voltage
0.7
0.6
DROPOUT VOLTAGE (V)
0.5
0.4
T
J
≤ 25°C
0.3
0.2
0.1
= TEST POINTS
0
0
20
40 60 80 100 120 140 160
OUTPUT CURRENT (mA)
1121 G01
Dropout Voltage
0.7
0.6
DROPOUT VOLTAGE (V)
0.5
0.4
0.3
0.2
0.1
0
–50
I
LOAD
= 50mA
I
LOAD
= 1mA
I
LOAD
= 100mA
I
LOAD
= 150mA
QUIESCENT CURRENT (μA)
50
Quiescent Current
V
IN
= 6V
R
LOAD
=
∞
V
SHDN
= OPEN
30
T
J
≤ 125°C
40
20
V
SHDN
= 0V
10
–25
50
25
0
75
TEMPERATURE (°C)
100
125
0
–50
–25
50
25
0
75
TEMPERATURE (°C)
100
125
1121 G02
1121 G03
1121ff
4
LT1121/LT1121-3.3/LT1121-5
TYPICAL PERFORMANCE CHARACTERISTICS
LT1121-3.3
Quiescent Current
120
100
QUIESCENT CURRENT (μA)
QUIESCENT CURRENT (μA)
80
60
40
20
0
0
1
2
3 4 5 6 7
INPUT VOLTAGE (V)
8
9
10
V
SHDN
= 0V
V
SHDN
= OPEN
T
J
= 25°C
R
LOAD
=
∞
120
100
QUIESCENT CURRENT (μA)
80
V
SHDN
= OPEN
60
40
20
0
0
1
2
3 4 5 6 7
INPUT VOLTAGE (V)
8
9
10
V
SHDN
= 0V
LT1121-5
Quiescent Current
T
J
= 25°C
R
LOAD
=
∞
120
100
80
LT1121
Quiescent Current
T
J
= 25°C
R
LOAD
=
∞
V
OUT
= V
ADJ
V
SHDN
= OPEN
60
40
20
0
0
1
2
3 4 5 6 7
INPUT VOLTAGE (V)
8
9
10
V
SHDN
= 0V
1121 G04
1121 G05
1121 G06
LT1121-3.3
Output Voltage
3.38
I
OUT
= 1mA
3.36
OUTPUT VOLTAGE (V)
OUTPUT VOLTAGE (V)
3.34
3.32
3.30
3.28
3.26
3.24
3.22
–50
–25
50
25
0
75
TEMPERATURE (°C)
100
125
5.06
5.04
5.02
5.00
4.98
4.96
4.94
5.08
LT1121-5
Output Voltage
3.83
I
OUT
= 1mA
3.81
ADJ PIN VOLTAGE (V)
3.79
3.77
3.75
3.73
3.71
3.69
–25
50
25
0
75
TEMPERATURE (°C)
100
125
LT1121
Adjust Pin Voltage
I
OUT
= 1mA
4.92
–50
3.67
–50
–25
50
25
0
75
TEMPERATURE (°C)
100
125
1121 G07
1121 G08
1121 G09
LT1121-3.3
Ground Pin Current
800
700
GROUND PIN CURRENT (μA)
600
500
400
300
*FOR V
OUT
= 3.3V
200
100
0
0
1
2
3 4 5 6 7
INPUT VOLTAGE (V)
8
9
10
R
LOAD
= 3.3k
I
LOAD
= 1mA*
R
LOAD
= 330Ω
I
LOAD
= 10mA*
GROUND PIN CURRENT (μA)
R
LOAD
= 130Ω
I
LOAD
= 25mA*
T
J
= 25°C
800
700
600
500
400
300
LT1121-5
Ground Pin Current
T
J
= 25°C
GROUND PIN CURRENT (μA)
R
LOAD
= 200Ω
I
LOAD
= 25mA*
800
LT1121
Ground Pin Current
T
J
= 25°C
700 V
OUT
= V
ADJ
600
500
400
300
*FOR V
OUT
= 3.75V
200
100
0
10
0
1
2
R
LOAD
= 3.8k
I
LOAD
= 1mA*
R
LOAD
= 380Ω
I
LOAD
= 10mA*
R
LOAD
= 150Ω
I
LOAD
= 25mA*
R
LOAD
= 500Ω
I
LOAD
= 10mA*
*FOR V
OUT
= 5V
200
100
0
0
1
2
R
LOAD
= 5k
I
LOAD
= 1mA*
3 4 5 6 7
INPUT VOLTAGE (V)
8
9
3 4 5 6 7
INPUT VOLTAGE (V)
8
9
10
1121 G10
1121 G11
1121 G12
1121ff
5
