ANALOG DEVICES LT 1521 CST-3.3 Datasheet

OUTPUT CURRENT (mA)

0

0

DROPOUT VOLTAGE (V)

0.1

0.2

0.3

0.4

0.6

50

100 150 200

LT1521 • TA02

250 300

0.5

FEATURES

LT1521/LT1521-3

LT1521-3.3/LT1521-5

300mA Low Dropout

Regulators with Micropower

Quiescent Current and Shutdown

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DESCRIPTIO

■

Dropout Voltage: 0.5V

■

Output Current: 300mA

■

Quiescent Current: 12µA

■

No Protection Diodes Needed

■

Adjustable Output from 3.8V to 20V

■

Fixed Output Voltages: 3V, 3.3V, 5V

■

Controlled Quiescent Current in Dropout

■

Shutdown IQ = 6µA

■

Reverse Battery Protection

■

No Reverse Current

■

Thermal Limiting

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APPLICATIO S

■

Low Current Regulator

■

Regulator for Battery-Powered Systems

■

Post Regulator for Switching Supplies

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 con­nected to voltages lower than the output voltage, including
negative voltages, without reverse current flow from out­put 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.

TYPICAL APPLICATIO

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5V Battery-Powered Supply with Shutdown

6V 1.5µF1µF

8

IN

5

SHDN

V

SHDN

<0.25 OFF
>2.80 ON

LT1521-5

GND

3

(PIN 5) OUTPUT

NC ON

OUT

SENSE

1

2

Dropout Voltage

5V
300mA

+

LT1521 • TA01

1521335fb

1

LT1521/LT1521-3
LT1521-3.3/LT1521-5

WW

W

ABSOLUTE MAXIMUM RATINGS

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(Note 1)

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

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W

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PACKAGE/ORDER INFORMATION

TOP VIEW

OUT

SENSE/ADJ*

1
2

NC

3

GND

4

MS8 PACKAGE

8-LEAD PLASTIC MSOP

*PIN 2 = SENSE FOR LT1521-3/
LT1521-3.3/LT1521-5

PIN 2 = ADJ FOR LT1521

T

= 125°C, θJA = 125°C/W

JMAX

8
7
6
5

IN
NC
NC
SHDN

SENSE/ADJ*

*PIN 2 = SENSE FOR LT1521-3/LT1521-3.3/LT1521-5

SEE THE APPLICATIONS INFORMATION SECTION

1

OUT

2

GND

3

NC

4

8-LEAD PLASTIC SO

= ADJ FOR LT1521

T

= 125°C, θJA = 70°C/W

JMAX

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.

TOP VIEW

S8 PACKAGE

8

IN
GND

7

GND

6

SHDN

5

TAB IS

SEE THE APPLICATIONS INFORMATION SECTION

FRONT VIEW

GND

ST PACKAGE

3-LEAD PLASTIC SOT-223

T

= 125°C, θJA = 50°C/W

JMAX

3

OUT

2

GND

1

IN

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

MS8 PART MARKING

LTEZ
LTFB
LTDU
LTFA

Consult LTC Marketing for parts specified with wider operating temperature ranges.

S8 PART MARKING

1521
15213
152133
15215

1521I
1521I3
1521I33
1521I5

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

2

1521335fb

LT1521/LT1521-3

LT1521-3.3/LT1521-5

ELECTRICAL CHARACTERISTICS

The ● denotes the specifications which apply over the full operating

temperature range, otherwise specifications are at TA = 25°C.

PARAMETER CONDITIONS MIN TYP MAX UNITS

Regulated Output Voltage LT1521-3 VIN = 3.5V, I
(Note 4) 4V < VIN < 20V, 1mA < I

LT1521-3.3 VIN = 3.8V, I

4.3V < VIN < 20V, 1mA < I

LT1521-5 VIN = 5.5V, I

6V < VIN < 20V, 1mA < I

LT1521 (Note 5) VIN = 4.3V, I

4.8V < VIN < 20V, 1mA < I

Line Regulation LT1521-3 ∆VIN = 4.5 to 20V, I

LT1521-3.3 ∆VIN = 4.8 to 20V, I
LT1521-5 ∆VIN = 5.5 to 20V, I
LT1521 (Note 5) ∆VIN = 4.3 to 20V, I

Load Regulation LT1521-3 ∆I

LT1521-3.3 ∆I
LT1521-5 ∆I
LT1521 (Note 5) ∆I
LT1521-3 ∆I
LT1521-3.3 ∆I
LT1521-5 ∆I
LT1521 (Note 5) ∆I

Dropout Voltage (Note 6) I

Ground Pin Current (Note 7) I

= 1mA, TJ = 25°C 130 170 mV

LOAD

I

= 1mA ● 250 mV

LOAD

I

= 50mA, TJ = 25°C 290 350 mV

LOAD

I

= 50mA ● 450 mV

LOAD

I

= 100mA, TJ = 25°C 350 420 mV

LOAD

I

= 100mA ● 550 mV

LOAD

I

= 150mA, TJ = 25°C 400 470 mV

LOAD

I

= 150mA ● 600 mV

LOAD

I

= 300mA, TJ = 25°C 500 600 mV

LOAD

I

= 300mA ● 750 mV

LOAD

= 0mA ● 12 25 µA

LOAD

I

= 1mA ● 65 100 µA

LOAD

I

= 10mA ● 300 450 µA

LOAD

I

= 50mA ● 0.8 1.5 mA

LOAD

I

= 100mA ● 1.4 2.5 mA

LOAD

I

= 150mA ● 2.2 4.0 mA

LOAD

I

= 300mA ● 6.5 12.0 mA

LOAD

LOAD
LOAD
LOAD
LOAD
LOAD
LOAD
LOAD
LOAD

Adjust Pin Bias Current (Notes 5, 8) TJ = 25°C 50 100 nA
Shutdown Threshold V

Shutdown Pin Current (Note 9) V
Quiescent Current in Shutdown (Note 10) VIN = V
Ripple Rejection VIN – V

Current Limit VIN – V

= Off to On ● 1.20 2.80 V

OUT

V

= On to Off ● 0.25 0.75 V

OUT

= 0V ● 2.0 5.0 µA

SHDN

(NOMINAL) + 1V, V

OUT

= 1V(Avg), V

f

RIPPLE

VIN = V

OUT

= 120Hz, I

= 7V, TJ = 25°C 400 800 mA

OUT

(NOMINAL) + 1.5V, ∆V

OUT

LOAD

RIPPLE

= 150mA

= 1mA, TJ = 25°C 2.950 3.000 3.050 V

OUT

= 1mA, TJ = 25°C 3.250 3.300 3.350 V

OUT

= 1mA, TJ = 25°C 4.925 5.000 5.075 V

OUT

= 1mA, TJ = 25°C 3.695 3.750 3.805 V

OUT

< 300mA ● 2.900 3.000 3.100 V

OUT

< 300mA ● 3.200 3.300 3.400 V

OUT

< 300mA ● 4.850 5.000 5.150 V

OUT

< 300mA ● 3.640 3.750 3.860 V

OUT

= 1mA ● 1.5 20 mV

OUT

= 1mA ● 1.5 20 mV

OUT

= 1mA ● 1.5 20 mV

OUT

= 1mA ● 1.5 20 mV

OUT

= 1mA to 300mA, TJ ≤ 25°C–20–30mV
= 1mA to 300mA, TJ ≤ 25°C–20–30mV
= 1mA to 300mA, TJ ≤ 25°C–25–45mV
= 1mA to 300mA, TJ ≤ 25°C–20–30mV
= 1mA to 300mA, TJ >25°C–20–55mV
= 1mA to 300mA, TJ > 25°C–20–55mV
= 1mA to 300mA, TJ > 25°C–25–75mV
= 1mA to 300mA, TJ > 25°C–20–55mV

= 0V ● 612µA

SHDN

= 0.5V

,5058dB

P–P

= –0.1V ● 320 400 mA

OUT

1521335fb

3

LT1521/LT1521-3
LT1521-3.3/LT1521-5

ELECTRICAL CHARACTERISTICS

The ● denotes the specifications which apply over the full operating

temperature range, otherwise specifications are at TA = 25°C.

PARAMETER CONDITIONS MIN TYP MAX UNITS

Input Reverse Leakage Current VIN = –20V, V
Reverse Output Current (Note 11) LT1521-3 V

LT1521-3.3 V
LT1521-5 V
LT1521 (Note 5) V

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

> 110°C and I

J

< 1mA, output voltage

OUT

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.

= 0V ● 1.0 mA

OUT

= 3V, VIN < 3V, TJ = 25°C510µA

OUT

= 3.3V, VIN < 3.3V, TJ = 25°C510µA

OUT

= 5V, VIN < 5V, TJ = 25°C510µA

OUT

= 3.8V, VIN < 3.75V, TJ = 25°C510µA

OUT

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

Note 7: Ground pin current is tested with V

DROPOUT

)

= V

IN

(nominal) and a

OUT

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

= 0V flows out of the shutdown

SHDN

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.

W

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TYPICAL PERFORMANCE CHARACTERISTICS

Guaranteed Dropout Voltage

0.8
= TEST POINTS

0.7

0.6

0.5

0.4

0.3

DROPOUT VOLTAGE (V)

0.2

0.1

TJ ≤ 125°C

0

50 100 200

0

OUTPUT CURRENT (mA)

TJ ≤ 25°C

150

250

LT1521 • TPC01

300

Dropout Voltage

0.8

0.7

0.6

0.5

0.4

0.3

DROPOUT VOLTAGE (V)

0.2

0.1

0

–25 0 50

–50

TEMPERATURE (°C)

I

I

LOAD

LOAD

= 300mA

= 100mA

I

LOAD

I

LOAD

25

I

LOAD

= 50mA

= 1mA

75 100 125

= 150mA

4

LT1521 • TPC02

Quiescent Current

15.0

12.5

10.0

7.5

5.0

QUIESCENT CURRENT (µA)

2.5

0

–50

VIN = 6V

= ∞

R

L

I

LOAD

–25 0

= 0

25 75

TEMPERATURE (°C)

V

= OPEN

SHDN

V

= 0V

SHDN

50 100 125

LT1521 • TPC03

1521335fb

W

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TYPICAL PERFORMANCE CHARACTERISTICS

LT1521/LT1521-3

LT1521-3.3/LT1521-5

LT1521-3
Output Voltage

3.08

3.06

3.04

3.02

3.00

2.98

OUTPUT VOLTAGE (V)

2.96

2.94

2.92
–25 0 50

–50

LT1521
Adjust Pin Voltage

3.83
I

= 1mA

LOAD

3.81

3.79

3.77

3.75

3.73

OUTPUT VOLTAGE (V)

3.71

3.69

3.67

–25 0 50

–50

25

TEMPERATURE (°C)

25

TEMPERATURE (°C)

75 100 125

LT1521 • TPC04

75 100 125

LT1521 • TPC07

LT1521-3.3
Output Voltage

3.38
I

= 1mA

OUT

3.36

3.34

3.32

3.30

3.28

OUTPUT VOLTAGE (V)

3.26

3.24

3.22

–25 0 50

–50

LT1521-3
Quiescent Current

50
45
40
35
30
25
20
15

QUIESCENT CURRENT (µA)

10

5
0

213579

0

25

TEMPERATURE (°C)

V

= OPEN

SHDN

V

= 0V

SHDN

6

4

INPUT VOLTAGE (V)

75 100 125

LT1521 • TPC05

TJ = 25°C

=

∞

R

L

8

LT1521 • TPC08

OUTPUT VOLTAGE (V)

10

LT1521-5
Output Voltage

5.08

5.06

5.04

5.02

5.00

4.98

4.96

4.94

4.92
–25 0 50

–50

LT1521-3.3
Quiescent Current

50
45
40
35
30
25
20
15

QUIESCENT CURRENT (µA)

10

5
0

213579

0

25

TEMPERATURE (°C)

6

4

INPUT VOLTAGE (V)

75 100 125

LT1521 • TPC06

TJ = 25°C

=

∞

R

L

8

LT1521 • TPC09

10

LT1521-5
Quiescent Current

50
45
40
35
30
25
20
15

QUIESCENT CURRENT (µA)

10

5
0

213579

0

V

SHDN

V

= 0V

SHDN

6

4

INPUT VOLTAGE (V)

TJ = 25°C

R

=

L

= OPEN

8

LT1521 • TPC10

LT1521
Quiescent Current

50

∞

10

45
40
35
30
25
20
15

QUIESCENT CURRENT (µA)

10

5
0

0

V

SHDN

213579

4

INPUT VOLTAGE (V)

V

SHDN

= 0V

6

TJ = 25°C

= OPEN

=

R

L

8

LT1521 • TPC11

∞

10

LT1521-3
Ground Pin Current

1000

TJ = 25°C

900

*FOR V

800
700
600
500
400
300

GROUND PIN CURRENT (µA)

200
100

0

0

OUT

213579

= 3V

R
I

R

= 120Ω

LOAD

= 25mA*

I

LOAD

R

LOAD

I

LOAD

R

= 3k

LOAD

= 1mA*

I

LOAD

6

4

INPUT VOLTAGE (V)

LOAD

LOAD

= 300Ω

= 10mA*

= 60Ω

= 50mA*

8

LT1521 • TPC12

1521335fb

10

5

LT1521/LT1521-3

TEMPERATURE (°C)

–50

SHUTDOWN PIN THRESHOLD (V)

2.0

1.8

1.6

1.4

1.2

1.0

0.8

0.6

0.4

0.2
0

0

50

75

LT1521 • TPC21

–25

25

100

125

I

LOAD

= 1mA

INPUT VOLTAGE (V)

0

GROUND PIN CURRENT (mA)

8

7

6

5

4

3

2

1

0

8

LT1521 • TPC15

2

4

6

10

7

1

3

5

9

R

LOAD

= 11Ω

I

LOAD

= 300mA*

R

LOAD

= 22Ω

I

LOAD

= 150mA*

R

LOAD

= 33Ω

I

LOAD

= 100mA*

TJ = 25°C
*FOR V

OUT

= 3.3V

LT1521-3.3/LT1521-5

W

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TYPICAL PERFORMANCE CHARACTERISTICS

LT1521-3
Ground Pin Current

8

7

6

5

4

3

2

GROUND PIN CURRENT (mA)

1

0

2

1

0

4

3

INPUT VOLTAGE (V)

LT1521-5
Ground Pin Current

1000

TJ = 25°C

900

*FOR V

800
700
600
500
400
300

GROUND PIN CURRENT (µA)

200
100

0

0

= 5V

OUT

213579

4

INPUT VOLTAGE (V)

R
I

LOAD

5

LOAD

TJ = 25°C
*FOR V

R

LOAD

I

LOAD

R

LOAD

I

LOAD

R

= 30Ω

LOAD

= 100mA*

I

LOAD

6

7

R

LOAD

I

LOAD

R

LOAD

I

LOAD

= 500Ω

= 10mA*

R

LOAD

I

LOAD

6

= 3V

OUT

= 10Ω

= 300mA*

= 20Ω

= 150mA*

8

9

LT1521 • TPC13

= 100Ω

= 50mA*

= 200Ω

= 25mA*

= 5k

= 1mA*

8

LT1521 • TPC16

LT1521-3.3
Ground Pin Current

1000

900
800
700
600
500
400
300

GROUND PIN CURRENT (µA)

200
100

0

10

0

R

LOAD

I

LOAD

R
I

LOAD

213579

INPUT VOLTAGE (V)

= 66Ω

= 50mA*

= 3.3k

LOAD

= 1mA*

4

TJ = 25°C
*FOR V

R

LOAD

= 25mA*

I

LOAD

R

LOAD

= 10mA*

I

LOAD

6

= 3.3V

OUT

= 132Ω

= 330Ω

8

LT1521 • TPC14

10

LT1521-5
Ground Pin Current

8

TJ = 25°C

7

*FOR V

6

5

4

3

2

GROUND PIN CURRENT (mA)

1

10

0

0

OUT

2

1

= 5V

4

3

INPUT VOLTAGE (V)

R

LOAD

I

LOAD

= 50Ω

= 100mA*

6

5

R
I

LOAD

R
I

LOAD

LOAD

LOAD

= 16.7Ω

= 300mA*

= 33.3Ω

= 150mA*

7

8

9

LT1521 • TPC17

10

LT1521-3.3
Ground Pin Current

LT1521
Ground Pin Current

1000

TJ = 25°C

900
800
700
600
500
400
300

GROUND PIN CURRENT (µA)

200
100

0

213579

0

*FOR V

R

= 75Ω

LOAD

= 50mA*

I

LOAD

6

4

INPUT VOLTAGE (V)

R

LOAD

I

LOAD

R

LOAD

I

LOAD

R

LOAD

I

LOAD

V

OUT

OUT

= V

ADJ

= 3.75V

= 150Ω

= 25mA*

= 375Ω

= 10mA*

= 3.8k

= 1mA*

8

LT1521 • TPC18

10

LT1521
Ground Pin Current

8

TJ = 25°C

= V

V

7

OUT

*FOR V

6

5

4

3

2

GROUND PIN CURRENT (mA)

1

0

1

0

6

ADJ

= 3.75V

OUT

2

4

3

INPUT VOLTAGE (V)

R

LOAD

I

LOAD

R

LOAD

I

LOAD

R

LOAD

I

LOAD

5

= 12.5Ω

=300mA*

= 25Ω

=150mA*

= 37.5Ω

=100mA*

6

7

8

9

LT1521 • TPC19

Shutdown Pin Threshold

Ground Pin Current

10

VIN = 3V (LT1521-3)

9

= 3.3V (LT1521-3.3)

V

IN

= 5V (LT1521-5)

V

IN

8

= 3.75V (LT1521)

V

IN

7

DEVICE IS OPERATING
IN DROPOUT

6
5

TJ = 25°C

4
3

GROUND PIN CURRENT (mA)

2
1

10

0

0

50

100

OUTPUT CURRENT (mA)

150 200

TJ = 125°C

TJ = 55°C

250

LT1521 • TPC20

300

(On-to-Off)

1521335fb

W

SHUTDOWN PIN VOLTAGE (V)

0

SHUTDOWN PIN INPUT CURRENT (mA)

25

20

15

10

5

0

2

4

59

LT1521 • TPC24

13

6

7

8

U

TYPICAL PERFORMANCE CHARACTERISTICS

Shutdown Pin Threshold
(Off-to-On)

2.0

1.8

1.6

1.4

1.2

1.0

0.8

0.6

0.4

SHUTDOWN PIN THRESHOLD (V)

0.2
0

–50

I

–25

I

LOAD

= 1mA

LOAD

0

25

TEMPERATURE (°C)

= 300mA

50

75

100

LT1521 • TPC22

125

Shutdown Pin Current

3.0
V

= 0V

SHDN

2.5

2.0

1.5

1.0

SHUTDOWN PIN CURRENT (µA)

0.5

0

–50

–25 0

TEMPERATURE (°C)

50 100 125

25 75

LT1521/LT1521-3

LT1521-3.3/LT1521-5

Shutdown Pin Input Current

LT1521 • TPC23

Adjust Pin Bias Current

200

175

150

125

100

75

50

ADJUST PIN BIAS CURRENT (nA)

25

0

–25 0 50

–50

25

TEMPERATURE (°C)

75 100 125

LT1521 • TPC25

Current Limit

0.6
VIN = 7V

= 0V

V

OUT

0.5

0.4

0.3

0.2

SHORT-CIRCUIT CURRENT (A)

0.1

0

–50

–25 0

25 75

TEMPERATURE (°C)

50 100 125

LT1521 • TPC28

Reverse Output Current

50

TJ = 25°C

45

V

IN

CURRENT FLOWS

40

INTO OUTPUT PIN
V

OUT

35

(LT1521-3/LT1521-3.3

30

LT1521-5)
V

OUT

25
20
15
10

REVERSE OUTPUT CURRENT (µA)

5
0

0

= 0V

= V

SENSE

= V

(LT1521)

ADJ

LT1521-3.3

LT1521-3

3579

21

4

OUTPUT VOLTAGE (V)

LT1521

LT1521-5

6

8

LT1521 • TPC26

10

Reverse Output Current Ripple Rejection

8

VIN = 0V

7

6

5

4

3

2

OUTPUT PIN CURRENT (µA)

1

0

= 3V (LT1521-3)

V

OUT

= 3.3V (LT1521-3.3)

V

OUT

= 5V (LT1521-5)

V

OUT

= 3.75V (LT1521)

V

OUT

–25 0 50

–50

25

TEMPERATURE (°C)

75 100 125

LT1521 • TPC29

Current Limit

0.6
V

= 0V

OUT

0.5

0.4

0.3

0.2

SHORT-CIRCUIT CURRENT (A)

0.1

0

0

12

66

VIN = V
RIPPLE AT f = 120Hz

64

62

60

58

56

RIPPLE REJECITON (dB)

54

52

–50

I

LOAD

–25 0

= 150mA

35

INPUT VOLTAGE (V)

(NOMINAL) + 1V + 0.5V

OUT

25 75

TEMPERATURE (°C)

467

LT1521 • TPC27

P-P

50 100 125

LT1521 • TPC30

1521335fb

7

LT1521/LT1521-3
LT1521-3.3/LT1521-5

W

U

TYPICAL PERFORMANCE CHARACTERISTICS

Ripple Rejection

100

I

= 150mA

LOAD

90

= 6V + 50mV

V

IN

80
70
60
50
40
30

RIPPLE REJECTION (dB)

20
10

0

100 100k

10 1k 10k 1M

RIPPLE

RMS

C

OUT

SOLID TANTALUM

C

OUT

SOLID TANTALUM

FREQUENCY (Hz)

LT1521-5
Transient Response

VIN = 6V

0.2

0.1

–0.1

DEVIATION (V)

OUTPUT VOLTAGE

–0.2

= 0.1µF

C

IN

= 1.5µF

C

OUT

0

= 33µF

= 3.3µF

LT1521 • TPC31

Load Regulation

0

∆I

= 1mA TO 300mA

LOAD

–5

–10

–15

–20

–25

LOAD REGULATION (mV)

–30

–35

–40

–50

LT1521-5

LT1521*

VIN = V

OUT

*V

= V

ADJ

–25 0 50

LT1521-5
Transient Response

0.2

0.1
0

–0.1

DEVIATION (V)

OUTPUT VOLTAGE

–0.2

(NOMINAL + 1V)

OUT

25

TEMPERATURE (°C)

LT1521-3

LT1521-3.3

75 100 125

LT1521 • TPC32

VIN = 6V

= 0.1µF

C

IN

= 33µF

C

OUT

150
100

(mA)

50

LOAD CURRENT

10050 150 250 350 450

0

200

TIME (µs)

300

400

LT1521 • TPC33

500

UUU

PIN FUNCTIONS

OUT (Pin 1): The output pin supplies power to the load. A
minimum output capacitor of 1.5µF is required to prevent
oscillations, but larger values of output capacitor will be
necessary to deal with larger load transients. See the
Applications Information section for more on output
capacitance and reverse output characteristics.

SENSE (Pin 2): For fixed voltage versions of the LT1521
(LT1521-3, LT1521-3.3, LT1521-5), the sense pin is the
input to the error amplifier. Optimum regulation will be
obtained at the point where the sense pin is connected to

300
200

(mA)

100

LOAD CURRENT

1.00.5 1.5 2.5 3.5 4.5

0

2.0
TIME (ms)

3.0

4.0

LT1521 • TPC34

5.0

the output pin of the regulator. In critical applications small
voltage drops caused by the resistance (RP) of PC traces
between the regulator and the load, which would normally
degrade regulation, may be eliminated by connecting the
sense pin to the output at the load as shown in Figure 1
(Kelvin Sense Connection). Note that the voltage drop
across the external PC traces will add to the dropout
voltage of the regulator. The sense pin bias current is 5µA
at the nominal regulated output voltage. This pin is inter­nally clamped to –0.6V (one VBE).

1521335fb

8

UUU

PIN FUNCTIONS

5

IN

+

V

IN

4

SHDN

Figure 1. Kelvin Sense Connection

LT1521

GND

3

OUT

SENSE

LT1521/LT1521-3

LT1521-3.3/LT1521-5

R

P

1

+

2

R

P

LOAD

LT1521 • F01

VBE). This allows the shutdown pin to be driven directly by
5V logic or by open collector logic with a pull-up resistor.
The pull-up resistor is only required to supply the leakage
current of the open collector gate, normally several micro­amperes. Pull-up current must be limited to a maximum of
5mA. A curve of the shutdown pin input current as a
function of voltage appears in the Typical Performance
Characteristics. If the shutdown pin is not used it can be
left open circuit. The device will be active (output on) if the
shutdown pin is not connected.

ADJ (Pin 2): For adjustable LT1521, the adjust pin is the
input to the error amplifier. This pin is internally clamped
to 6V and –0.6V (one VBE). It has a bias current of 50nA
which flows into the pin. See Adjust Pin Bias Current vs
Temperature in the Typical Performance Characteristics
section. The adjust pin reference voltage is 3.75V refer­enced to ground. The output voltage range that can be
produced by this device is 3.75V to 20V.

SHDN (Pin 5): The shutdown pin is used to put the device
into shutdown. In shutdown the output of the device is
turned off. This pin is active low. The device will be shut
down if the shutdown pin is pulled low. The shutdown pin
current with the pin pulled to ground will be 1.7µA. The
shutdown pin is internally clamped to 7V and –0.6V (one

U

WUU

APPLICATIONS INFORMATION

The LT1521 is a 300mA low dropout regulator with
micropower quiescent current and shutdown. The device
is capable of supplying 300mA at a dropout of 0.5V and
operates with very low quiescent current (12µA). In shut-
down, the quiescent current drops to only 6µA. In addition
to the low quiescent current, the LT1521 incorporates
several protection features which make it ideal for use in
battery-powered systems. The device is protected against
both reverse input voltages and reverse output voltages.
In battery backup applications where the output can be
held up by a backup battery when the input is pulled to
ground, the LT1521 acts like it has a diode in series with
its output and prevents reverse current flow.

IN (Pin 8): Power is supplied to the device through the
input pin. The input pin should be bypassed to ground if
the device is more than six inches away from the main
input filter capacitor. In general, the output impedance of
battery rises with frequency, so it is advisable to include a
bypass capacitor in battery-powered circuits. A bypass
capacitor in the range of 1µF to 10µF is sufficient. The
LT1521 is designed to withstand reverse voltages on the
input pin with respect to ground and the output pin. In the
case of reversed input, which can happen if a battery is
plugged in backwards, the LT1521 will act as if there is a
diode in series with its input. There will be no reverse
current flow into the LT1521 and no reverse voltage will
appear at the load. The device will protect both itself and
the load.

Adjustable Operation

The adjustable version of the LT1521 has an output
voltage range of 3.75V to 20V. The output voltage is set by
the ratio of two external resistors as shown in Figure 2. The
device servos the output voltage to maintain the voltage at
the adjust pin at 3.75V. The current in R1 is then equal to

3.75V/R1. The current in R2 is equal to the sum of the
current in R1 and the adjust pin bias current. The adjust pin
bias current, 50nA at 25°C, flows through R2 into the
adjust pin. The output voltage can be calculated using the
formula in Figure 2. The value of R1 should be less than
400k to minimize errors in the output voltage caused by
the adjust pin bias current. Note that in shutdown the

1521335fb

9

LT1521/LT1521-3
LT1521-3.3/LT1521-5

U

WUU

APPLICATIONS INFORMATION

IN

V

IN

SHDN

V

= 3.75V 1 + + (I

OUT

= 3.75V

V

ADJ

= 50nA AT 25°C

I

ADJ

OUTPUT RANGE = 3.75V TO 20V

R2

)

R1

+ R2)

ADJ

)

LT1521

GND

OUT

R2

ADJ

R1

Figure 2. Adjustable Operation

output is turned off and the divider current will be zero.
Curves of Adjust Pin Voltage vs Temperature and Adjust
Pin Bias Current vs Temperature appear in the Typical
Performance Characteristics. The reference voltage at the
adjust pin has a positive temperature coefficient of ap­proximately 15ppm/°C. The adjust pin bias current has a
negative temperature coefficient. These effects will tend to
cancel each other.

The adjustable device is specified with the adjust pin tied
to the output pin. This sets the output voltage to 3.75V.
Specifications for output voltages greater than 3.75V will
be proportional to the ratio of the desired output voltage
to 3.75V; (V

/3.75V). For example: load regulation for

OUT

an output current change of 1mA to 300mA is –20mV
typical at V

= 3.75V. At V

OUT

= 12V, load regulation

OUT

would be:

(12V/3.75V)(–20mV) = –64mV

Thermal Considerations

The power handling capability of the device will be limited
by the maximum rated junction temperature (125°C). The
power dissipated by the device will be made up of two
components:

1. Output current multiplied by the input/output voltage
differential: I

OUT(VIN

– V

OUT

), and

2. Ground pin current multiplied by the input voltage:
(I

)(VIN)

GND

V

OUT

+

LT1521 • F01

The ground pin current can be found by examining the
Ground Pin Current curves in the Typical Performance
Characteristics. Power dissipation will be equal to the sum
of the two components listed above.

The LT1521 series regulators have internal thermal limit­ing designed to protect the device during overload condi­tions. For continuous normal load conditions the maxi­mum junction temperature rating of 125°C must not be
exceeded. It is important to give careful consideration to
all sources of thermal resistance from junction to ambient.
Additional heat sources mounted nearby must also be
considered.

For surface mount devices, heat sinking is accomplished
by using the heat spreading capabilities of the PC board
and its copper traces. Copper board stiffeners and plated
through-holes can also be used to spread the heat gener­ated by power devices.

The following tables list thermal resistance for each pack­age. Measured values of thermal resistance for several
different board sizes and copper areas are listed for each
package. All measurements were taken in still air on
3/32" FR-4 board with one ounce copper. All NC leads were
connected to the ground plane.

Table 1. MS8 Package

COPPER AREA

TOPSIDE** BACKSIDE BOARD AREA

2500mm22500mm
1000mm22500mm

225mm22500mm
100mm22500mm

* Pin 4 is ground. ** Device is mounted on topside.

2

2500mm

2

2500mm

2

2500mm

2

2500mm

Table 2. S8 Package*

COPPER AREA

TOPSIDE** BACKSIDE BOARD AREA

2500mm22500mm
1000mm22500mm

225mm22500mm
100mm22500mm

* Pins 3, 6, 7 are ground. ** Device is mounted on topside.

2

2500mm

2

2500mm

2

2500mm

2

2500mm

THERMAL RESISTANCE

(JUNCTION-TO-AMBIENT)

2

2

2

2

2

2

2

2

110°C/W
115°C/W
120°C/W
130°C/W

THERMAL RESISTANCE

(JUNCTION-TO-AMBIENT)

60°C/W
60°C/W
68°C/W
74°C/W

10

1521335fb

LT1521/LT1521-3

LT1521-3.3/LT1521-5

U

WUU

APPLICATIONS INFORMATION

Table 3. SOT-223 Package
(Thermal Resistance Junction-to-Tab 20°C/W)

COPPER AREA

TOPSIDE* BACKSIDE BOARD AREA

2500mm22500mm
1000mm22500mm

2

225mm

100mm
1000mm21000mm
1000mm

* Tab of device attached to topside copper.

2

2

2500mm
2500mm

2

2500mm

2

2500mm

2

2500mm

2

2500mm

2

1000mm

0 1000mm

Calculating Junction Temperature

Example: Given an output voltage of 3.3V, an input voltage
range of 4.5V to 7V, an output current range of 0mA to
150mA and a maximum ambient temperature of 50°C,
what will the maximum junction temperature be?

The power dissipated by the device will be equal to:

I

OUT(MAX)(VIN(MAX)

– V

OUT

) + I

Where,

I

OUT(MAX)

V

IN(MAX)

I

GND

at (I

= 150mA

= 7V

= 150mA, VIN = 7V) = 2.1mA

OUT

So,

P = 150mA(7V – 3.3V) + (2.1mA)(7V) = 0.57W

If we use a SOT-223 package, then the thermal resistance
will be in the range of 50°C/W to 65°C/W depending on the
copper area. So the junction temperature rise above
ambient will be approximately equal to:

0.57W(60°C/W) = 34.2°C

The maximum junction temperature will then be equal to the
maximum junction temperature rise above ambient plus the
maximum ambient temperature or:

T

= 50°C + 34.2°C = 84.2°C

JMAX

Output Capacitance and Transient Performance

The LT1521 is designed to be stable with a wide range of
output capacitors. A minimum output capacitor of 1.5µF

THERMAL RESISTANCE

(JUNCTION-TO-AMBIENT)

2

2

2

2

2

2

GND(VIN(MAX)

50°C/W
50°C/W
58°C/W
64°C/W
57°C/W
60°C/W

)

is required to prevent oscillations. The LT1521 is a
micropower device and output transient response will be
a function of output capacitance. See the Transient
Response curves in the Typical Performance Characteris­tics. Larger values of output capacitance will decrease the
peak deviations and provide improved output transient
response for larger load current deltas. Bypass capaci­tors, used to decouple individual components powered by
the LT1521, will increase the effective value of the output
capacitor.

Protection Features

The LT1521 incorporates several protection features which
make it ideal for use in battery-powered circuits. In
addition to the normal protection features associated with
monolithic regulators, such as current limiting and ther­mal limiting, the device is protected against reverse input
voltages, reverse output voltages and reverse voltages
from output to input.

Current limit protection and thermal overload protection
are intended to protect the device against current overload
conditions at the output of the device. For normal opera­tion, the junction temperatures should not exceed 125°C.

The input of the device will withstand reverse voltages of
20V. Current flow into the device will be limited to less
than 1mA (typically less than 100µA) and no negative
voltage will appear at the output. The device will protect
both itself and the load. This provides protection against
batteries that can be plugged in backward.

For fixed voltage versions of the device, the output can be
pulled below ground without damaging the device. If the
input is left open circuit or grounded, the output can be
pulled below ground by 20V. The output will act like an
open circuit, no current will flow out of the pin. If the input
is powered by voltage source, the output will source the
short-circuit current of the device and will protect itself by
thermal limiting. For the adjustable version of the device,
the output pin is internally clamped at one diode drop
below ground. Reverse current for the adjustable device
must be limited to 5mA.

1521335fb

11

LT1521/LT1521-3
LT1521-3.3/LT1521-5

U

WUU

APPLICATIONS INFORMATION

In circuits where a backup battery is required, several
different input/output conditions can occur. The output
voltage may be held up while the input is either pulled to
ground, pulled to some intermediate voltage or is left open
circuit. Current flow back into the output will vary depend­ing on the conditions. Many battery-powered circuits
incorporate some form of power management. The fol­lowing information will help optimize battery life. Table 4
summarizes the following information.

The reverse output current will follow the curve in Figure
3 when the input is pulled to ground. This current flows
through the output pin to ground. The state of the shut­down pin will have no effect on output current when the
input pin is pulled to ground.

In some applications it may be necessary to leave the input
on the LT1521 unconnected when the output is held high.
This can happen when the LT1521 is powered from a

rectified AC source. If the AC source is removed, then the
input of the LT1521 is effectively left floating. The reverse
output current also follows the curve in Figure 3 if the input
pin is left open. The state of the shutdown pin will have no
effect on the reverse output current when the input pin is
floating.

When the input of the LT1521 is forced to a voltage below
its nominal output voltage and its output is held high, the
output current will follow the curve shown in Figure 3. This
can happen if the input of the LT1521 is connected to a
discharged (low voltage) battery and the output is held up
by either a backup battery or by second regulator circuit.
When the input pin is forced below the output pin or the
output pin is pulled above the input pin, the input current
will typically drop to less than 2µA (see Figure 4). The state
of the shutdown pin will have no effect on the reverse
output current when the output is pulled above the input.

50

TJ = 25°C

45

V

IN

CURRENT FLOWS

40

INTO OUTPUT PIN
V

OUT

35

(LT1521-3/LT1521-3.3

30

LT1521-5)
V

OUT

25
20
15
10

REVERSE OUTPUT CURRENT (µA)

5
0

0

= 0V

= V

SENSE

= V

(LT1521)

ADJ

LT1521-3.3

LT1521-3

3579

21

4

OUTPUT VOLTAGE (V)

LT1521

LT1521-5

6

Figure 3. Reverse Output Current

8

LT1521 • F03

5

V

= 3V (LT1521-3)

OUT

= 3.3V (LT1521-3.3)

V

OUT

= 5V (LT1521-5)

V

OUT

4

3

LT1521-3.3

LT1521-5

4

LT1521 • F04

5

3

2

INPUT CURRENT (µA)

1

10

0

0

LT1521-3

1

2

INPUT VOLTAGE (V)

Figure 4. Input Current

12

1521335fb

LT1521/LT1521-3

LT1521-3.3/LT1521-5

U

WUU

APPLICATIONS INFORMATION

Table 4. Fault Conditions

INPUT PIN SHDN PIN OUTPUT/SENSE PINS RESULTING CONDITIONS

< V

(Nominal) Open (High) Forced to V

OUT

< V

(Nominal) Grounded Forced to V

OUT

Open Open (High) > 1V Reverse Output Current ≈ 5µA (See Figure 3)
Open Grounded > 1V Reverse Output Current ≈ 5µA (See Figure 3)

≤ 0.8V Open (High) ≤ 0V Output Current = 0
≤ 0.8V Grounded ≤ 0V Output Current = 0

> 1.5V Open (High) ≤ 0V Output Current = Short-Circuit Current

–20V < VIN < 20V Grounded ≤ 0V Output Current = 0

(Nominal) Reverse Output Current ≈ 5µA (See Figure 3)

OUT

Input Current ≈ 1µA (See Figure 4)

(Nominal) Reverse Output Current ≈ 5µA (See Figure 3)

OUT

Input Current ≈ 1µA (See Figure 4)

U

PACKAGE DESCRIPTION

MS8 Package

8-Lead Plastic MSOP

(Reference LTC DWG # 05-08-1660)

0.889

± 0.127

(.035 ± .005)

5.23

(.206)

MIN

0.42 ± 0.04

(.0165 ± .0015)

TYP

RECOMMENDED SOLDER PAD LAYOUT

0.254

(.010)

GAUGE PLANE

0.18

(.077)

NOTE:

1. DIMENSIONS IN MILLIMETER/(INCH)

2. DRAWING NOT TO SCALE

3. DIMENSION DOES NOT INCLUDE MOLD FLASH, PROTRUSIONS OR GATE BURRS.
MOLD FLASH, PROTRUSIONS OR GATE BURRS SHALL NOT EXCEED 0.152mm (.006") PER SIDE

4. DIMENSION DOES NOT INCLUDE INTERLEAD FLASH OR PROTRUSIONS.
INTERLEAD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.152mm (.006") PER SIDE

5. LEAD COPLANARITY (BOTTOM OF LEADS AFTER FORMING) SHALL BE 0.102mm (.004") MAX

DETAIL “A”

(.126 – .136)

(.0256)

° – 6° TYP

0

DETAIL “A”

3.2 – 3.45

0.65

BSC

0.53 ± 0.015

(.021 ± .006)

SEATING

PLANE

3.00 ± 0.102
(.118 ± .004)

(NOTE 3)

4.88

± 0.1

(.192 ± .004)

(.043)

0.22 – 0.38

(.009 – .015)

1.10

MAX

8

12

0.65

(.0256)

BCS

7

0.52

5

4

(.206)

REF

3.00 ± 0.102
(.118 ± .004)

NOTE 4

0.86

(.034)

REF

0.13 ± 0.05

(.005 ± .002)

MSOP (MS8) 1001

1521335fb

6

3

13

LT1521/LT1521-3
LT1521-3.3/LT1521-5

PACKAGE DESCRIPTION

U

S8 Package

8-Lead Plastic Small Outline (Narrow .150 Inch)

(Reference LTC DWG # 05-08-1610)

0.189 – 0.197*
(4.801 – 5.004)

7

8

6

5

0.228 – 0.244

(5.791 – 6.197)

0.010 – 0.020

(0.254 – 0.508)

0.008 – 0.010

(0.203 – 0.254)

*

DIMENSION DOES NOT INCLUDE MOLD FLASH. MOLD FLASH
SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE

**

DIMENSION DOES NOT INCLUDE INTERLEAD FLASH. INTERLEAD
FLASH SHALL NOT EXCEED 0.010" (0.254mm) PER SIDE

×

°

45

0.016 – 0.050

(0.406 – 1.270)

0°– 8° TYP

0.053 – 0.069

(1.346 – 1.752)

0.014 – 0.019

(0.355 – 0.483)

TYP

0.150 – 0.157**
(3.810 – 3.988)

1

3

2

4

0.004 – 0.010

(0.101 – 0.254)

0.050

(1.270)

BSC

SO8 1298

14

1521335fb

PACKAGE DESCRIPTION

0.248 – 0.264
(6.30 – 6.71)

0.114 – 0.124
(2.90 – 3.15)

0.264 – 0.287
(6.70 – 7.30)

0.130 – 0.146
(3.30 – 3.71)

LT1521/LT1521-3

LT1521-3.3/LT1521-5

U

ST Package

3-Lead Plastic SOT-223

(Reference LTC DWG # 05-08-1630)

0.071
(1.80)

MAX

0.0905
(2.30)

NOM

0.024 – 0.033
(0.60 – 0.84)

0.181
(4.60)

NOM

0.033 – 0.041
(0.84 – 1.04)

0.012
(0.31)

MIN

10°

MAX

10° – 16°

0.010 – 0.014
(0.25 – 0.36)

10° – 16°

0.0008 – 0.0040

(0.0203 – 0.1016)

ST3 (SOT-233) 1298

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 its circuits as described herein will not infringe on existing patent rights.

1521335fb

15

LT1521/LT1521-3
LT1521-3.3/LT1521-5

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ThinSOT is a registered trademark of Linear Technology Corporation.

, VIN = 1.8V to 20V, ThinSOT

RMS

, VIN = 1.8V to 20V, MSOP-8

RMS

, VIN = 1.8V to 20V, SO-8

RMS

, VIN = 1.8V to 20V, MSOP-8

RMS

®

16

Linear Technology Corporation

1630 McCarthy Blvd., Milpitas, CA 95035-7417

[phone] ● FAX: [phone]

●

www.linear.com

1521335fb

LT/CPI 0302 REV B 1.5K • PRINTED IN USA

 LINEAR TECHNOLOGY CORPORATION 1995