LT1521/LT1521-3
LT1521-3.3/LT1521-5
300mA Low Dropout
Regulators with Micropower
Quiescent Current and Shutdown
FEATURES
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DESCRIPTION
The LT
®
1521/LT1521-3/LT1521-3.3/LT1521-5 are low
dropout regulators with micropower quiescent current
and shutdown. These devices are capable of supplying
300mA of output current with a dropout voltage of 0.5V.
Designed for use in battery-powered systems, the low
quiescent current, 12µA operating and 6µA 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 LT1521/LT1521-3/LT1521-3.3/
LT1521-5 include the ability to operate with very small
output capacitors. They are stable with only 1.5µF on the
output while most older devices require between 10µF and
100µF for stability. Small ceramic capacitors can be used,
enhancing manufacturability. Also, the input may be con-
nected to voltages lower than the output voltage, including
negative voltages, without reverse current flow from out-
put to input. This makes the LT1521 series ideal for backup
power situations where the output is held high and the
input is low or reversed. Under these conditions only 5µA
will flow from the output pin to ground.
, LTC and LT are registered trademarks of Linear Technology Corporation.
Dropout Voltage: 0.5V
Output Current: 300mA
Quiescent Current: 12
µ
A
No Protection Diodes Needed
Adjustable Output from 3.8V to 20V
Fixed Output Voltages: 3V, 3.3V, 5V
Controlled Quiescent Current in Dropout
Shutdown I
Q
= 6µA
Reverse Battery Protection
No Reverse Current
Thermal Limiting
APPLICATIONS
s
s
s
Low Current Regulator
Regulator for Battery-Powered Systems
Post Regulator for Switching Supplies
TYPICAL APPLICATION
5V Battery-Powered Supply with Shutdown
8
IN
LT1521-5
5
SHDN
GND
3
SENSE
2
OUT
1
5V
300mA
0.6
0.5
DROPOUT VOLTAGE (V)
+
6V
1µF
1.5µF
0.4
0.3
0.2
0.1
V
SHDN
(PIN 5) OUTPUT
<0.25
OFF
>2.80
ON
NC
ON
LT1521 • TA01
0
0
50
U
U
U
Dropout Voltage
100
150
200
250
OUTPUT CURRENT (mA)
300
LT1521 • TA02
1
LT1521/LT1521-3
LT1521-3.3/LT1521-5
ABSOLUTE
MAXIMUM
RATINGS
Input Voltage ......................................................
±
20V*
Output Pin Reverse Current .................................. 10mA
Adjust Pin Current ................................................ 10mA
Shutdown Pin Input Voltage (Note 1) .......... 6.5V, – 0.6V
Shutdown Pin Input Current (Note 1) ..................... 5mA
Output Short-Circuit Duration .......................... Indefinite
PACKAGE/ORDER INFORMATION
TOP VIEW
TOP VIEW
OUT
SENSE/ADJ*
NC
GND
1
2
3
4
8
7
6
5
IN
NC
NC
SHDN
OUT 1
SENSE/ADJ* 2
GND 3
NC 4
MS8 PACKAGE
8-LEAD PLASTIC MSOP
*PIN 2 = SENSE FOR LT1521-3/
LT1521-3.3/LT1521-5
PIN 2 = ADJ FOR LT1521
T
JMAX
= 125°C,
θ
JA
= 125°C/ W
*PIN 2 = SENSE FOR LT1521-3/LT1521-3.3/LT1521-5
= ADJ FOR LT1521
T
JMAX
= 125°C,
θ
JA
= 70°C/ W
SEE THE APPLICATIONS INFORMATION SECTION
ORDER PART NUMBER
LT1521CMS8
LT1521CMS8-3
LT1521CMS8-3.3
LT1521CMS8-5
ORDER PART NUMBER
LT1521CS8
LT1521CS8-3
LT1521CS8-3.3
LT1521CS8-5
LT1521IS8
LT1521IS8-3
LT1521IS8-3.3
LT1521IS8-5
S8 PART MARKING
1521
15213
152133
15215
1521I
1521I3
1521I33
1521I5
MS8 PART MARKING
LTEZ
LTFB
LTDU
LTFA
Consult factory for Military grade parts.
2
U
U
W
W W
U
W
(Note 1)
Storage Temperature Range ................. – 65°C to 150°C
Operating Junction Temperature Range (Note 2)
Commercial ........................................... 0°C to 125°C
Industrial ......................................... – 40°C to 125°C
Lead Temperature (Soldering, 10 sec).................. 300°C
*For applications requiring input voltage ratings greater than 20V, contact
the factory.
FRONT VIEW
8
7
6
5
IN
GND
GND
SHDN
1
TAB IS
GND
2
3
OUT
GND
IN
S8 PACKAGE
8-LEAD PLASTIC SO
ST PACKAGE
3-LEAD PLASTIC SOT-223
T
JMAX
= 125
°C, θ
JA
= 50°C/ W
SEE THE APPLICATIONS INFORMATION SECTION
ORDER PART NUMBER
LT1521CST-3
LT1521CST-3.3
LT1521CST-5
LT1521IST-3
LT1521IST-3.3
LT1521IST-5
ST PART MARKING
15213
152133
15215
1521I3
1521I33
1521I5
LT1521/LT1521-3
LT1521-3.3/LT1521-5
ELECTRICAL CHARACTERISTICS
PARAMETER
Regulated Output Voltage
(Note 4)
CONDITIONS
LT1521-3
V
IN
= 3.5V, I
OUT
= 1mA, T
J
= 25°C
4V < V
IN
< 20V, 1mA < I
OUT
< 300mA
LT1521-3.3
V
IN
= 3.8V, I
OUT
= 1mA, T
J
= 25°C
4.3V < V
IN
< 20V, 1mA < I
OUT
< 300mA
LT1521-5
V
IN
= 5.5V, I
OUT
= 1mA, T
J
= 25°C
6V < V
IN
< 20V, 1mA < I
OUT
< 300mA
LT1521 (Note 5) V
IN
= 4.3V, I
OUT
= 1mA, T
J
= 25°C
4.8V < V
IN
< 20V, 1mA < I
OUT
< 300mA
LT1521-3
∆V
IN
= 4.5 to 20V, I
OUT
= 1mA
LT1521-3.3
∆V
IN
= 4.8 to 20V, I
OUT
= 1mA
LT1521-5
∆V
IN
= 5.5 to 20V, I
OUT
= 1mA
LT1521 (Note 5)
∆V
IN
= 4.3 to 20V, I
OUT
= 1mA
LT1521-3
∆I
LOAD
= 1mA to 300mA, T
J
≤
25°C
LT1521-3.3
∆I
LOAD
= 1mA to 300mA, T
J
≤
25°C
LT1521-5
∆I
LOAD
= 1mA to 300mA, T
J
≤
25°C
LT1521 (Note 5)
∆I
LOAD
= 1mA to 300mA, T
J
≤
25°C
LT1521-3
∆I
LOAD
= 1mA to 300mA, T
J
>25°C
LT1521-3.3
∆I
LOAD
= 1mA to 300mA, T
J
> 25°C
LT1521-5
∆I
LOAD
= 1mA to 300mA, T
J
> 25°C
LT1521 (Note 5)
∆I
LOAD
= 1mA to 300mA, T
J
> 25°C
I
LOAD
= 1mA, T
J
= 25°C
I
LOAD
= 1mA
I
LOAD
= 50mA, T
J
= 25°C
I
LOAD
= 50mA
I
LOAD
= 100mA, T
J
= 25°C
I
LOAD
= 100mA
I
LOAD
= 150mA, T
J
= 25°C
I
LOAD
= 150mA
I
LOAD
= 300mA, T
J
= 25°C
I
LOAD
= 300mA
I
LOAD
= 0mA
I
LOAD
= 1mA
I
LOAD
= 10mA
I
LOAD
= 50mA
I
LOAD
= 100mA
I
LOAD
= 150mA
I
LOAD
= 300mA
T
J
= 25°C
V
OUT
= Off to On
V
OUT
= On to Off
V
SHDN
= 0V
V
IN
= V
OUT
(NOMINAL) + 1V, V
SHDN
= 0V
V
IN
– V
OUT
= 1V(Avg), V
RIPPLE
= 0.5V
P–P
,
f
RIPPLE
= 120Hz, I
LOAD
= 150mA
V
IN
– V
OUT
= 7V, T
J
= 25°C
V
IN
= V
OUT
(NOMINAL) + 1.5V,
∆V
OUT
= – 0.1V
q
q
q
q
q
q
q
q
MIN
2.950
2.900
3.250
3.200
4.925
4.850
3.695
3.640
Line Regulation
Load Regulation
Dropout Voltage (Note 6)
TYP
3.000
3.000
3.300
3.300
5.000
5.000
3.750
3.750
1.5
1.5
1.5
1.5
– 20
– 20
– 25
– 20
– 20
– 20
– 25
– 20
130
290
q
q
350
q
400
q
500
q
q
q
q
q
q
q
q
q
q
q
q
Ground Pin Current (Note 7)
Adjust Pin Bias Current (Notes 5, 8)
Shutdown Threshold
Shutdown Pin Current (Note 9)
Quiescent Current in Shutdown (Note 10)
Ripple Rejection
Current Limit
0.25
50
12
65
300
0.8
1.4
2.2
6.5
50
1.20
0.75
2.0
6
58
400
400
MAX
3.050
3.100
3.350
3.400
5.075
5.150
3.805
3.860
20
20
20
20
– 30
– 30
– 45
– 30
– 55
– 55
– 75
– 55
170
250
350
450
420
550
470
600
600
750
20
100
450
1.5
2.5
4.0
12.0
100
2.80
5.0
12
UNITS
V
V
V
V
V
V
V
V
mV
mV
mV
mV
mV
mV
mV
mV
mV
mV
mV
mV
mV
mV
mV
mV
mV
mV
mV
mV
mV
mV
µA
µA
µA
mA
mA
mA
mA
nA
V
V
µA
µA
dB
mA
mA
800
q
320
3
LT1521/LT1521-3
LT1521-3.3/LT1521-5
ELECTRICAL CHARACTERISTICS
PARAMETER
Input Reverse Leakage Current
Reverse Output Current (Note 11)
CONDITIONS
V
IN
= – 20V, V
OUT
= 0V
LT1521-3
V
OUT
= 3V, V
IN
< 3V, T
J
= 25°C
LT1521-3.3
V
OUT
= 3.3V, V
IN
< 3.3V, T
J
= 25°C
LT1521-5
V
OUT
= 5V, V
IN
< 5V, T
J
= 25°C
LT1521 (Note 5) V
OUT
= 3.8V, V
IN
< 3.75V, T
J
= 25°C
MIN
q
TYP
5
5
5
5
MAX
1.0
10
10
10
10
UNITS
mA
µA
µA
µA
µA
The
q
denotes specifications which apply over the full operating
temperature range.
Note 1:
Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
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 5mA.
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
limited. When operating at maximum output current, the input voltage
range must be limited.
Note 5:
The LT1521 (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 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 total sum of the
shutdown pin current (2µA) and the ground pin current (4µA).
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.
TYPICAL PERFORMANCE CHARACTERISTICS
Guaranteed Dropout Voltage
0.8
= TEST POINTS
0.7
0.7
DROPOUT VOLTAGE (V)
DROPOUT VOLTAGE (V)
0.6
0.5
0.4
0.3
0.2
0.1
0
0
T
J
≤
125°C
0.6
0.5
0.4
0.3
0.2
0.1
0
–50 –25
0
I
LOAD
= 300mA
I
LOAD
= 150mA
I
LOAD
= 100mA
QUIESCENT CURRENT (µA)
T
J
≤
25°C
50
200
250
150
OUTPUT CURRENT (mA)
100
4
U W
Dropout Voltage
0.8
15.0
12.5
10.0
7.5
5.0
2.5
Quiescent Current
V
SHDN
= OPEN
V
SHDN
= 0V
V
IN
= 6V
R
L
=
∞
I
LOAD
= 0
50
25
75
0
TEMPERATURE (°C)
100
125
I
LOAD
= 50mA
I
LOAD
= 1mA
50
75
25
TEMPERATURE (°C)
100
125
300
0
–50 –25
LT1521 • TPC01
LT1521 • TPC02
LT1521 • TPC03
LT1521/LT1521-3
LT1521-3.3/LT1521-5
TYPICAL PERFORMANCE CHARACTERISTICS
LT1521-3
Output Voltage
3.08
3.06
3.38
3.36
I
OUT
= 1mA
OUTPUT VOLTAGE (V)
OUTPUT VOLTAGE (V)
OUTPUT VOLTAGE (V)
3.04
3.02
3.00
2.98
2.96
2.94
2.92
–50
–25
0
50
75
25
TEMPERATURE (°C)
100
125
LT1521
Adjust Pin Voltage
3.83
3.81
I
LOAD
= 1mA
QUIESCENT CURRENT (µA)
50
45
40
35
30
25
20
15
10
5
0
OUTPUT VOLTAGE (V)
3.79
3.77
3.75
3.73
3.71
3.69
3.67
–50
–25
0
50
75
25
TEMPERATURE (°C)
100
125
QUIESCENT CURRENT (µA)
LT1521-5
Quiescent Current
50
45
T
J
= 25°C
R
L
=
∞
QUIESCENT CURRENT (µA)
GROUND PIN CURRENT (µA)
QUIESCENT CURRENT (µA)
40
35
30
25
20
15
10
5
0
0
1
2
3 4 5 6 7
INPUT VOLTAGE (V)
8
9
10
V
SHDN
= 0V
V
SHDN
= OPEN
U W
LT1521-3.3
Output Voltage
5.08
5.06
5.04
5.02
5.00
4.98
4.96
4.94
–25
0
75
50
25
TEMPERATURE (°C)
100
125
LT1521-5
Output Voltage
3.34
3.32
3.30
3.28
3.26
3.24
3.22
–50
4.92
–50 –25
0
50
75
25
TEMPERATURE (°C)
100
125
LT1521 • TPC04
LT1521 • TPC05
LT1521 • TPC06
LT1521-3
Quiescent Current
50
T
J
= 25°C
R
L
=
∞
LT1521-3.3
Quiescent Current
45
40
35
30
25
20
15
10
5
8
9
T
J
= 25°C
R
L
=
∞
V
SHDN
= OPEN
V
SHDN
= 0V
0
1
2
3 4 5 6 7
INPUT VOLTAGE (V)
0
10
0
1
2
3 4 5 6 7
INPUT VOLTAGE (V)
8
9
10
LT1521 • TPC07
LT1521 • TPC08
LT1521 • TPC09
LT1521
Quiescent Current
50
45
40
35
30
25
20
15
10
5
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
L
=
∞
1000
900
800
700
600
500
400
300
200
100
0
LT1521-3
Ground Pin Current
T
J
= 25°C
*FOR V
OUT
= 3V
R
LOAD
= 60Ω
I
LOAD
= 50mA*
R
LOAD
= 120Ω
I
LOAD
= 25mA*
R
LOAD
= 300Ω
I
LOAD
= 10mA*
R
LOAD
= 3k
I
LOAD
= 1mA*
0
1
2
3 4 5 6 7
INPUT VOLTAGE (V)
8
9
10
LT1521 • TPC10
LT1521 • TPC11
LT1521 • TPC12
5
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