LT1121CS8-3.3#PBF [Linear]
LT1121 - Micropower Low Dropout Regulators with Shutdown; Package: SO; Pins: 8; Temperature Range: 0°C to 70°C;型号: | LT1121CS8-3.3#PBF |
厂家: | Linear |
描述: | LT1121 - Micropower Low Dropout Regulators with Shutdown; Package: SO; Pins: 8; Temperature Range: 0°C to 70°C 稳压器 |
文件: | 总16页 (文件大小:173K) |
中文: | 中文翻译 | 下载: | 下载PDF数据表文档文件 |
LT1121/LT1121-3.3/LT1121-5
Micropower Low Dropout
Regulators with Shutdown
U
FEATURES
DESCRIPTIO
The LT®1121/LT1121-3.3/LT1121-5 are micropower low
dropout regulators with shutdown. These devices are
capable of supplying 150mA of output current with a
dropout voltage of 0.4V. Designed for use in battery-
powered systems, the low quiescent current, 30μA oper-
ating 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.
■
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
Other features of the LT1121/LT1121-3.3/LT1121-5 in-
clude the ability to operate with very small output capaci-
tors. They are stable with only 0.33μF on the output while
most older devices require between 1μF and 100μF for
stability.Smallceramiccapacitorscanbeused,enhancing
manufacturability. 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.
■
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
U
APPLICATIO S
■
Low Current Regulator
■
Regulator for Battery-Powered Systems
■
Post Regulator for Switching Supplies
, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
U
TYPICAL APPLICATIO
5V Battery-Powered Supply with Shutdown
Dropout Voltage
0.5
8
1
3.3V
OUT
IN
OUT
LT1121-3.3
150mA
0.4
0.3
0.2
0.1
0
+
1μF
5V
SOLID TANTALUM
5
SHDN
GND
3
V
(PIN 5) OUTPUT
SHDN
<0.25
>2.8
NC
OFF
ON
ON
LT1121 • TA01
80
OUTPUT CURRENT (mA)
0
20 40 60
100 120 140 160
LT1121 • TA02
1121fe
1
LT1121/LT1121-3.3/LT1121-5
W W U W
ABSOLUTE AXI U RATI GS (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
W U
/O
PACKAGE RDER I FOR ATIO
TOP VIEW
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.
*
BOTTOM VIEW
FRONT VIEW
OUT
NC/ADJ*
GND
1
2
3
4
IN
8
7
6
5
**
NC**
NC**
SHDN
3
2
1
OUTPUT
GND
IN
GND OUT
TAB IS
GND
NC
V
IN
N8 PACKAGE
8-LEAD PDIP
Z PACKAGE
3-LEAD PLASTIC TO-92
ST PACKAGE
3-LEAD PLASTIC SOT-223
S8 PACKAGE
8-LEAD PLASTIC SO
T
JMAX = 150°C, θJA ≈ 50°C/W
TJMAX = 150°C, θJA ≈ 150°C/W
TJMAX = 150°C, θJA ≈ 120°C/W (N8, S8)
TJMAX = 150°C, θJA ≈ 70°C/W (AS8)
S8 PART
MARKING
ORDER PART
NUMBER
ST PART
MARKING
ORDER PART
NUMBER
ORDER PART NUMBER
LT1121CN8
LT1121IS8-3.3
121I3
121I5
LT1121CST-3.3
LT1121IST-3.3
11213
121IS3
11215
1121I5
LT1121CZ-3.3
LT121IZ-3.3
LT1121CZ-5
LT1121IZ-5
LT1121CN8-3.3 LT1121IS8-5
LT1121CN8-5
LT1121IN8
LT1121IN8-3.3 LT1121ACS8-3.3
LT1121IN8-5
LT1121CS8
LT1121HVIS8
LT1121ACS8
121HVI LT1121CST-5
1121A
121A3
121A5
121AHV
LT1121IST-5
LT1121ACS8-5
LT1121AHVCS8
1121
LT1121CS8-3.3 LT1121AIS8
LT1121CS8-5 LT1121AIS8-3.3
LT1121HVCS8 LT1121AIS8-5
LT1121IS8 LT1121AHVIS8
11213 121AI
11215 121AI3
1121HV 121AI5
1121I
21AHVI
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.
1121fe
2
LT1121/LT1121-3.3/LT1121-5
ELECTRICAL CHARACTERISTICS
The ● denotes specifications which apply over the operating temperature
range, otherwise specifications are at TA = 25°C.
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
Regulated Output Voltage
(Note 4)
LT1121-3.3
V
= 3.8V, I
= 1mA, T = 25°C
3.250
3.200
3.300
3.300
3.350
3.400
V
V
IN
OUT
J
4.3V < V < 20V, 1mA < I
< 150mA
●
●
IN
OUT
LT1121-5
V
= 5.5V, I
IN
= 1mA, T = 25°C
4.925
4.850
5.000
5.000
5.075
5.150
V
V
IN
OUT
J
6V < V < 20V, 1mA < I
< 150mA
OUT
LT1121 (Note 5)
V
= 4.3V, I
= 1mA, T = 25°C
3.695
3.640
3.750
3.750
3.805
3.860
V
V
IN
OUT
J
4.8V < V < 20V, 1mA < I
< 150mA
●
●
●
●
IN
OUT
Line Regulation
Load Regulation
LT1121-3.3
LT1121-5
ΔV = 4.8V to 20V, I
= 1mA
= 1mA
= 1mA
1.5
1.5
1.5
10
10
10
mV
mV
mV
IN
OUT
OUT
OUT
ΔV = 5.5V to 20V, I
IN
LT1121 (Note 5)
LT1121-3.3
ΔV = 4.3V to 20V, I
IN
ΔI
ΔI
= 1mA to 150mA, T = 25°C
= 1mA to 150mA
–12
–20
–25
–40
mV
mV
LOAD
LOAD
J
●
●
●
●
●
●
LT1121-5
ΔI
ΔI
= 1mA to 150mA, T = 25°C
= 1mA to 150mA
–17
–28
–35
–50
mV
mV
LOAD
LOAD
J
LT1121 (Note 5)
ΔI
ΔI
= 1mA to 150mA, T = 25°C
= 1mA to 150mA
–12
–18
–25
–40
mV
mV
LOAD
LOAD
J
Dropout Voltage
(Note 6)
I
I
= 1mA, T = 25°C
0.13
0.30
0.37
0.42
0.16
0.25
V
V
LOAD
LOAD
J
= 1mA
I
I
= 50mA, T = 25°C
0.35
0.50
V
V
LOAD
LOAD
J
= 50mA
I
I
= 100mA, T = 25°C
= 100mA
0.45
0.60
V
V
LOAD
LOAD
J
I
I
= 150mA, T = 25°C
= 150mA
0.55
0.70
V
V
LOAD
LOAD
J
●
●
●
●
●
●
●
Ground Pin Current
(Note 7)
I
I
I
I
I
I
= 0mA
30
90
50
120
500
2.5
μA
μA
LOAD
LOAD
LOAD
LOAD
LOAD
LOAD
= 1mA
= 10mA
= 50mA
= 100mA
= 150mA
350
1.5
4.0
7.0
150
μA
mA
mA
mA
nA
7.0
14.0
300
2.8
Adjust Pin Bias Current (Notes 5, 8)
Shutdown Threshold
T = 25°C
J
V
V
= Off to On
= On to Off
●
●
1.2
0.75
V
V
OUT
OUT
0.25
50
Shutdown Pin Current (Note 9)
Quiescent Current in Shutdown (Note 10)
Ripple Rejection
V
V
V
= 0V
●
●
6
10
22
μA
μA
dB
SHDN
= 6V, V
= 0V
SHDN
16
58
IN
IN
– V
= 1V (Avg), V
= 0.5V
,
OUT
RIPPLE
P-P
f
= 120Hz, I
= 0.1A
RIPPLE
LOAD
Current Limit
V
V
– V
= 7V, T = 25°C
200
500
1.0
mA
mA
IN
IN
OUT
J
Input Reverse Leakage Current
Reverse Output Current (Note 11)
= –20V, V
= 0V
●
OUT
LT1121-3.3
LT1121-5
LT1121 (Note 5)
V
V
V
= 3.3V, V = 0V
16
16
16
25
25
25
μA
μA
μA
OUT
OUT
OUT
IN
= 5V, V = 0V
IN
= 3.8V, V = 0V
IN
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
1121fe
3
LT1121/LT1121-3.3/LT1121-5
ELECTRICAL CHARACTERISTICS
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 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 – V
).
IN
DROPOUT
Note 3: For junction temperatures greater than 110°C, a minimum load of
Note 7: Ground pin current is tested with V = V
(nominal) and a
OUT
IN
1mA is recommended. For T > 110°C and I
< 1mA, output voltage
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.
J
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.
Note 8: Adjust pin bias current flows into the adjust pin.
Note 9: Shutdown pin current at V
= 0V flows out of the shutdown pin.
SHDN
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 5: The LT1121 (adjustable version) is tested and specified with the
adjust pin connected to the output pin.
U W
TYPICAL PERFOR A CE CHARACTERISTICS
Quiescent Current
Guaranteed Dropout Voltage
Dropout Voltage
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
50
40
30
20
10
0
V
= 6V
=
IN
LOAD
R
∞
I
= 150mA
LOAD
T
J
≤ 125°C
V
SHDN
= OPEN
I
= 100mA
LLOAD
T
J
≤ 25°C
I
= 50mA
LOAD
V
= 0V
SHDN
I
= 1mA
LOAD
= TEST POINTS
0
40 60 80 100 120 140 160
OUTPUT CURRENT (mA)
–50
0
25
50
75 100 125
–50
–25
0
25
50
75 100 125
20
–25
TEMPERATURE (°C)
TEMPERATURE (°C)
1121 G27
1121 G14
1121 G11
LT1121-3.3
Quiescent Current
LT1121-5
Quiescent Current
LT1121
Quiescent Current
120
100
80
60
40
20
0
120
100
80
60
40
20
0
120
100
80
60
40
20
0
T
= 25°C
LOAD
T
= 25°C
LOAD
T
R
V
= 25°C
J
R
J
R
J
=
∞
=
∞
=
∞
LOAD
= V
OUT
ADJ
V
= OPEN
V
= OPEN
SHDN
SHDN
V
= OPEN
SHDN
V
= 0V
7
V
= 0V
8
V
= 0V
7
SHDN
6
SHDN
7
SHDN
6
0
1
2
3
4
5
8
9
10
0
1
2
3
4
5
6
9
10
0
1
2
3
4
5
8
9
10
INPUT VOLTAGE (V)
INPUT VOLTAGE (V)
INPUT VOLTAGE (V)
1121 G04
1121 G02
1121 G03
1121fe
4
LT1121/LT1121-3.3/LT1121-5
U W
TYPICAL PERFOR A CE CHARACTERISTICS
LT1121-3.3
LT1121-5
LT1121
Adjust Pin Voltage
3.83
Output Voltage
Output Voltage
3.38
3.36
3.34
3.32
3.30
3.28
3.26
3.24
3.22
5.08
5.06
5.04
5.02
5.00
4.98
4.96
4.94
4.92
I
= 1mA
I
= 1mA
OUT
OUT
I
= 1mA
OUT
3.81
3.79
3.77
3.75
3.73
3.71
3.69
3.67
–50
0
25
50
75 100 125
–25
–50
0
25
50
75 100 125
–50
0
25
50
75 100 125
–25
–25
TEMPERATURE (°C)
TEMPERATURE (°C)
TEMPERATURE (°C)
1121 G24
1121 G22
1121 G23
LT1121-3.3
Ground Pin Current
LT1121-5
Ground Pin Current
LT1121
Ground Pin Current
800
700
600
500
400
300
200
100
0
800
700
600
500
400
300
200
100
0
800
700
600
500
400
300
200
100
0
T
= 25°C
OUT
T
= 25°C
T
= 25°C
J
J
J
R
I
= 150Ω
LOAD
LOAD
V
= V
ADJ
= 25mA*
R
= 200Ω
LOAD
LOAD
R
I
= 130Ω
LOAD
LOAD
I
= 25mA*
= 25mA*
R
I
= 500Ω
= 10mA*
R
= 330Ω
= 10mA*
LOAD
LOAD
LOAD
R
= 380Ω
= 10mA*
LOAD
LOAD
I
LOAD
I
*FOR V
= 3.75V
*FOR V
= 3.3V
*FOR V
= 5V
R
OUT
OUT
OUT
= 5k
= 1mA*
R
I
= 3.8k
LOAD
R
= 3.3k
= 1mA*
LOAD
LOAD
LOAD
I
= 1mA*
I
LOAD
LOAD
0
1
2
3
4
5
6
7
8
9
10
0
1
2
3
4
5
6
7
8
9
10
0
1
2
3
4
5
6
7
8
9
10
INPUT VOLTAGE (V)
INPUT VOLTAGE (V)
INPUT VOLTAGE (V)
1121 G10
1121 G06
1121 G08
LT1121-3.3
Ground Pin Current
LT1121-5
Ground Pin Current
LT1121
Ground Pin Current
10
9
8
7
6
5
4
3
2
1
0
10
9
8
7
6
5
4
3
2
1
0
10
9
8
7
6
5
4
3
2
1
0
T = 25°C
T = 25°C
T = 25°C
J
OUT
J
J
V
= V
ADJ
R
I
= 22Ω
LOAD
LOAD
R
= 33Ω
LOAD
LOAD
R
= 25Ω
= 150mA*
LOAD
LOAD
I
= 150mA*
I
= 150mA*
R
= 33Ω
LOAD
LOAD
R
= 50Ω
= 100mA*
LOAD
LOAD
I
= 100mA*
R
= 38Ω
= 100mA*
LOAD
LOAD
I
I
R
I
= 100Ω
= 50mA*
R
= 66Ω
= 50mA*
LOAD
LOAD
LOAD
R
I
= 75Ω
LOAD
= 50mA*
LOAD
I
LOAD
*FOR V
= 3.3V
6
*FOR V
= 5V
7
*FOR V
OUT
= 3.75V
OUT
5
OUT
6
0
2
4
8
10
0
2
4
8
10
1
3
7
9
1
3
5
9
0
2
6
8
9
10
4
1
3
5
7
INPUT VOLTAGE (V)
INPUT VOLTAGE (V)
INPUT VOLTAGE (V)
1121 G09
1121 G05
1121 G07
1121fe
5
LT1121/LT1121-3.3/LT1121-5
U W
TYPICAL PERFOR A CE CHARACTERISTICS
Shutdown Pin Threshold
(On-to-Off)
Shutdown Pin Threshold
(Off-to-On)
Ground Pin Current
14
12
2.0
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0
2.0
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0
V
V
V
= 3.3V (LT1121-3.3)
= 5V (LT1121-5)
= 3.75V (LT1121)
I
= 1mA
IN
IN
IN
LOAD
DEVICE IS OPERATING
I
= 150mA
LOAD
10 IN DROPOUT
T
= 125°C
J
8
6
4
2
0
I
= 1mA
LOAD
T
= 25°C
J
T
= –55°C
J
0
40 60 80 100 120 140 160
OUTPUT CURRENT (mA)
–50
0
25
TEMPERATURE (°C)
50
75 100 125
–50 –25
0
25
50
75 100 125
20
–25
TEMPERATURE (°C)
1121 G29
1121 G16
1121 G17
LT1121
Adjust Pin Bias Current
Shutdown Pin Current
Shutdown Pin Input Current
400
350
300
250
200
150
100
50
10
9
8
7
6
5
4
3
2
1
0
25
20
V
SHDN
= 0V
15
10
5
0
0
–50
0
25
50
75 100 125
–50
0
25
50
75 100 125
–25
–25
0
1
2
3
4
5
6
7
8
9
TEMPERATURE (°C)
TEMPERATURE (°C)
SHUTDOWN PIN VOLTAGE (V)
1121 G25
1121 G15
1121 G28
Reverse Output Current
Current Limit
Current Limit
30
25
20
15
10
5
400
350
300
250
200
150
100
50
400
350
300
250
200
150
100
50
V
= 0V
V
V
= 7V
V
V
V
V
= 0V
OUT
IN
OUT
IN
= 5V (LT1121-5)
= 3.3V (LT1121-3.3)
= 3.8V (LT1121)
= 0V
OUT
OUT
OUT
0
0
0
–50
0
25
50
75 100 125
0
2
3
4
5
6
7
–50
0
25
50
75
125
–25
1
–25
100
TEMPERATURE (°C)
INPUT VOLTAGE (V)
TEMPERATURE (°C)
1121 G13
1121 G20
1121 G19
1121fe
6
LT1121/LT1121-3.3/LT1121-5
U W
TYPICAL PERFOR A CE CHARACTERISTICS
Reverse Output Current
Ripple Rejection
Ripple Rejection
64
62
60
58
56
54
52
50
100
100
90
80
70
60
50
40
30
20
10
0
I
= 100mA
T = 25°C
V
IN
= V
OUT
(NOMINAL) + 1V
OUT
IN
J
IN
90
80
70
60
50
40
30
20
10
0
V
= 6V + 50mV
RIPPLE
V
= 0V
RMS
+ 0.5V RIPPLE AT f = 120Hz
P-P
= 100mA
CURRENT FLOWS
INTO OUTPUT PIN
I
OUT
C
= 47μF
OUT
SOLID TANTALUM
LT1121
= V
(V
)
ADJ
OUT
LT1121-3.3
C
= 1μF
OUT
SOLID TANTALUM
LT1121-5
10
100
1k
10k
100k
1M
–50
0
25
50
75 100 125
0
2
4
6
8
10
–25
1
3
5
7
9
FREQUENCY (Hz)
TEMPERATURE (°C)
OUTPUT VOLTAGE (V)
1121 G26
1121 G18
1121 G01
LT1121-5
Load Transient Response
LT1121-5
Load Transient Response
Load Regulation
0
–5
ΔI
= 1mA TO 150mA
V
C
C
= 6V
V
C
C
= 6V
LOAD
IN
IN
IN
IN
0.2
0.1
0.2
0.1
= 0.1μF
= 0.1μF
= 1μF
= 3.3μF
OUT
OUT
LT1121*
LT1121-3.3
–10
–15
–20
–25
–30
–35
–40
0
0
–0.1
–0.2
–0.1
–0.2
LT1121-5
150
100
50
150
100
* ADJ PIN TIED TO
OUTPUT PIN
–50
0
25
50
75 100 125
–25
0
0.1
0.3 0.4 0.5 0.6 0.7
TIME (ms)
0.8
0.9
1.0
0
0.1
0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
0.2
0.2
TEMPERATURE (°C)
TIME (ms)
1121 G21
1121 G30
1121 G31
1121fe
7
LT1121/LT1121-3.3/LT1121-5
U
U
U
PI FU CTIO S
Input Pin: 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 a
battery rises with frequency so it is usually adviseable to
include a bypass capacitor in battery-powered circuits. A
bypass capacitor in the range of 0.1μF to 1μF is sufficient.
The LT1121 is designed to withstand reverse voltages on
the input pin with respect to both ground and the output
pin. In the case of a reversed input, which can happen if a
battery is plugged in backwards, the LT1121 will act as if
there is a diode in series with its input. There will be no
reverse current flow into the LT1121 and no reverse
voltage will appear at the load. The device will protect both
itself and the load.
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 6μA. The shutdown
pin is internally clamped to 7V and –0.6V (one 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 microam-
peres. Pull-up current must be limited to a maximum of
20mA. A curve of shutdown pin input current as a function
of voltage appears in the Typical Performance Character-
istics. If the shutdown pin is not used it can be left open
circuit.Thedevicewillbeactive,outputon,iftheshutdown
pin is not connected.
AdjustPin:FortheadjustableLT1121, theadjustpinisthe
input to the error amplifier. This pin is internally clamped
to 6V and –0.6V (one VBE). It has a bias current of 150nA
which flows into the pin. See Bias Current curve in the
Typical Performance Characteristics. The adjust pin refer-
ence voltage is 3.75V referenced to ground. The output
voltage range that can be produced by this device is 3.75V
to 30V.
Output Pin: The output pin supplies power to the load. An
output capacitor is required to prevent oscillations. See
the Applications Information section for recommended
value of output capacitance and information on reverse
output characteristics.
Shutdown Pin: This pin is used to put the device into
shutdown. In shutdown the output of the device is turned
1121fe
8
LT1121/LT1121-3.3/LT1121-5
W U U
APPLICATIO S I FOR ATIO
U
The LT1121 is a micropower low dropout regulator with
shutdown, capable of supplying up to 150mA of output
current at a dropout voltage of 0.4V. The device operates
with very low quiescent current (30μA). In shutdown the
quiescent current drops to only 16μA. In addition to the
low quiescent current the LT1121 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 LT1121 acts like it has a diode in series with its output
and prevents reverse current flow.
approximately 15ppm/°C. The adjust pin bias current has
anegativetemperaturecoefficient. Theseeffectsaresmall
and 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.
Specificationsforoutputvoltagegreaterthan3.75Vwillbe
proportional to the ratio of the desired output voltage to
3.75V (VOUT/3.75V). For example: load regulation for an
output current change of 1mA to 150mA is –12mV typical
at VOUT = 3.75V. At VOUT = 12V, load regulation would be:
⎛
⎞
12V
3.75V
• –12mV = –38mV
(
) (
)
⎜
⎟
⎝
⎠
Adjustable Operation
Thermal Considerations
The adjustable version of the LT1121 has an output
voltage range of 3.75V to 30V. The output voltage is set by
theratiooftwoexternalresistorsasshowninFigure1.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
currentinR1andtheadjustpinbiascurrent.Theadjustpin
bias current, 150nA at 25°C, flows through R2 into the
adjust pin. The output voltage can be calculated according
to the formula in Figure 1. 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
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 slight positive temperature coefficient of
Power handling capability will be limited by maximum
rated junction temperature (125°C). Power dissipated by
the device will be made up of two components:
1. Output current multiplied by the input/output voltage
differential: IOUT • (VIN – VOUT), and
2. Ground pin current multiplied by the input voltage:
IGND • VIN.
The ground pin current can be found by examining the
Ground Pin Current curves in the Typical Performance
Characteristics. Powerdissipationwillbeequaltothesum
of the two components listed above.
The LT1121 series regulators have internal thermal limit-
ing designed to protect the device during overload condi-
tions. For continuous normal load conditions the maxi-
mum junction temperature rating of 125°C must not be
exceeded. It is important to give careful consideration to
allsourcesofthermalresistancefromjunctiontoambient.
Additional heat sources mounted nearby must also be
considered.
V
IN
OUT
ADJ
OUT
LT1121
R2
R1
+
SHDN
Heat sinking, for surface mount devices, 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 gener-
ated by power devices. Tables 1 through 5 list thermal
resistances for each package. Measured values of thermal
resistance for several different board sizes and copper
GND
1121 • F01
R2
V
V
= 3.75V 1 +
+ I
(
• R2
)
OUT
ADJ
(
)
R1
= 3.75V
ADJ
I
= 150nA AT 25°C
ADJ
OUTPUT RANGE = 3.75V TO 30V
Figure 1. Adjustable Operation
areas are listed for each package. All measurements were
1121fe
9
LT1121/LT1121-3.3/LT1121-5
W U U
U
APPLICATIO S I FOR ATIO
Table 5. TO-92 Package
taken in still air, on 3/32" FR-4 board with 1oz copper. All
NC leads were connected to the ground plane.
THERMAL
RESISTANCE
Package alone
220°C/W
175°C/W
Table 1. N8 Package*
Package soldered into PC board with plated
through holes only
COPPER AREA
THERMAL RESISTANCE
(JUNCTION-TO-AMBIENT)
TOPSIDE
BACKSIDE
BOARD AREA
Package soldered into PC board with 1/4 sq. inch of
copper trace per lead
145°C/W
2500 sq mm 2500 sq. mm 2500 sq. mm
1000 sq mm 2500 sq. mm 2500 sq. mm
80°C/W
80°C/W
Package soldered into PC board with plated through holes
in board, no extra copper trace, and a clip-on type
225 sq mm
2500 sq. mm 2500 sq. mm
85°C/W
heat sink:
Thermalloy type 2224B
Aavid type 5754
160°C/W
135°C/W
1000 sq mm 1000 sq. mm 1000 sq. mm
91°C/W
* Device is mounted on topside. Leads are through hole and are soldered
to both sides of board.
Calculating Junction Temperature
Table 2. S8 Package
Example: given an output voltage of 3.3V, an input voltage
range of 4.5V to 7V, an output current range of 0mA to
100mA, and a maximum ambient temperature of 50°C,
what will the maximum junction temperature be?
COPPER AREA
THERMAL RESISTANCE
(JUNCTION-TO-AMBIENT)
TOPSIDE*
BACKSIDE
BOARD AREA
2500 sq. mm 2500 sq. mm 2500 sq. mm
1000 sq. mm 2500 sq. mm 2500 sq. mm
225 sq. mm 2500 sq. mm 2500 sq. mm
100 sq. mm 1000 sq. mm 1000 sq. mm
* Device is mounted on topside.
120°C/W
120°C/W
Power dissipated by the device will be equal to:
IOUT MAX • (VIN MAX – VOUT) + (IGND • VIN)
125°C/W
131°C/W
where, IOUT MAX = 100mA
VIN MAX = 7V
Table 3. AS8 Package*
COPPER AREA
IGND at (IOUT = 100mA, VIN = 7V) = 5mA
TOPSIDE**
BACKSIDE
BOARD AREA
so,
P =100mA • (7V – 3.3V) + (5mA • 7V)
= 0.405W
2500 sq. mm 2500 sq. mm 2500 sq. mm
1000 sq. mm 2500 sq. mm 2500 sq. mm
225 sq. mm 2500 sq. mm 2500 sq. mm
100 sq. mm 2500 sq. mm 2500 sq. mm
60°C/W
60°C/W
68°C/W
74°C/W
IfweuseanSOT-223package,thenthethermalresistance
will be in the range of 50°C/W to 65°C/W depending on
copper area. So the junction temperature rise above
ambient will be less than or equal to:
*
Pins 3, 6, and 7 are ground.
** Device is mounted on topside.
0.405W • 60°C/W = 24°C
Table 4. SOT-223 Package
(Thermal Resistance Junction-to-Tab 20°C/W)
The maximum junction temperature will then be equal to
the maximum junction temperature rise above ambient
plus the maximum ambient temperature or:
COPPER AREA
THERMAL RESISTANCE
BOARD AREA
(JUNCTION-TO-AMBIENT)
TOPSIDE*
BACKSIDE
2500 sq. mm 2500 sq. mm 2500 sq. mm
1000 sq. mm 2500 sq. mm 2500 sq. mm
225 sq. mm 2500 sq. mm 2500 sq. mm
100 sq. mm 2500 sq. mm 2500 sq. mm
1000 sq. mm 1000 sq. mm 1000 sq. mm
50°C/W
50°C/W
58°C/W
64°C/W
57°C/W
60°C/W
TJMAX = 50°C + 24°C = 74°C
Output Capacitance and Transient Performance
The LT1121 is designed to be stable with a wide range of
output capacitors. The minimum recommended value is
1μF with an ESR of 3Ω or less. For applications where
space is very limited, capacitors as low as 0.33μF can be
used if combined with a small series resistor. Assuming
1000 sq. mm
0
1000 sq. mm
* Tab of device attached to topside copper
1121fe
10
LT1121/LT1121-3.3/LT1121-5
W U U
APPLICATIO S I FOR ATIO
U
that the ESR of the capacitor is low (ceramic) the sug-
gested series resistor is shown in Table 6. The LT1121 is
amicropowerdeviceandoutputtransientresponsewillbe
a function of output capacitance. See the Transient Re-
sponsecurvesintheTypicalPerformanceCharacteristics.
Larger values of output capacitance will decrease the peak
deviations and provide improved output transient re-
sponse. Bypass capacitors, used to decouple individual
components powered by the LT1121, will increase the
effective value of the output capacitor.
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.
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 cir-
cuits incorporate some form of power management. The
following information will help optimize battery life. Table
7 summarizes the following information.
Table 6. Suggested Series Resistor Values
SUGGESTED SERIES
OUTPUT CAPACITANCE
RESISTOR
0.33μF
0.47μF
0.68μF
>1μF
2Ω
1Ω
1Ω
The reverse output current will follow the curve in Figure
2whentheinputpinispulledtoground. Thiscurrentflows
through the output pin to ground. The state of the shut-
down pin will have no effect on output current when the
input pin is pulled to ground.
None Needed
Protection Features
TheLT1121incorporatesseveralprotectionfeatureswhich
make it ideal for use in battery-powered circuits. In addi-
tion to the normal protection features associated with
monolithic regulators, such as current limiting and ther-
mal limiting, the device is protected against reverse input
voltages, reverse output voltages, and reverse voltages
from output to input.
Insomeapplicationsitmaybenecessarytoleavetheinput
to the LT1121 unconnected when the output is held high.
This can happen when the LT1121 is powered from a
rectified AC source. If the AC source is removed, then the
input of the LT1121 is effectively left floating. The reverse
outputcurrentalsofollowsthecurveinFigure2iftheinput
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.
Current limit protection and thermal overload protection
areintendedtoprotectthedeviceagainstcurrentoverload
conditions at the output of the device. For normal opera-
tion, the junction temperature should not exceed 125°C.
100
T = 25°C
IN
CURRENT FLOWS
INTO OUTPUT PIN
TO GROUND
J
V
90
80
70
60
50
40
30
20
10
0
< V
OUT
The input of the device will withstand reverse voltages of
30V.Currentflowintothedevicewillbelimitedtolessthan
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 backwards.
LT1121
= V
(V
OUT
)
ADJ
LT1121-3.3
LT1121-5
For fixed voltage versions of the device, the output can be
pulled below ground without damaging the device. If the
input is 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 a voltage source, the output will source the
0
2
4
6
8
10
1
3
5
7
9
OUTPUT VOLTAGE (V)
1121• F02
Figure 2. Reverse Output Current
1121fe
11
LT1121/LT1121-3.3/LT1121-5
W U U
U
APPLICATIO S I FOR ATIO
5
4
3
2
1
0
When the input of the LT1121 is forced to a voltage below
its nominal output voltage and its output is held high, the
reverse output current will still follow the curve in Figure
2. This condition can occur if the input of the LT1121 is
connected to a discharged (low voltage) battery and the
output is held up by either a backup battery or by a 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 3). The state of the shutdown pin will have no effect
on the reverse output current when the output is pulled
above the input.
V
V
= 3.3V (LT1121-3.3)
= 5V (LT1121-5)
OUT
OUT
0
1
2
3
4
5
INPUT VOLTAGE (V)
1121 F03
Figure 3. Input Current
Table 7. Fault Conditions
INPUT PIN
SHDN PIN
OUTPUT PIN
<V
<V
(Nominal)
Open (Hi)
Forced to V
(Nominal)
Reverse Output Current ≈ 15μA (See Figure 2)
Input Current ≈ 1μA (See Figure 3)
OUT
OUT
(Nominal)
Grounded
Forced to V
(Nominal)
Reverse Output Current ≈ 15μA (See Figure 2)
Input Current ≈ 1μA (See Figure 3)
OUT
OUT
Open
Open
Open (Hi)
Grounded
Open (Hi)
Grounded
Open (Hi)
Grounded
Forced to V
Forced to V
(Nominal)
(Nominal)
Reverse Output Current ≈ 15μA (See Figure 2)
Reverse Output Current ≈ 15μA (See Figure 2)
Output Current = 0
OUT
OUT
≤0.8V
≤0.8V
>1.5V
≤0V
≤0V
≤0V
≤0V
Output Current = 0
Output Current = Short-Circuit Current
Output Current = 0
–30V < V < 30V
IN
1121fe
12
LT1121/LT1121-3.3/LT1121-5
U
PACKAGE DESCRIPTIO
N8 Package
8-Lead PDIP (Narrow 0.300)
(LTC DWG # 05-08-1510)
.400*
(10.160)
MAX
8
7
6
5
4
.255 ± .015*
(6.477 ± 0.381)
1
2
3
.130 ± .005
.300 – .325
.045 – .065
(3.302 ± 0.127)
(1.143 – 1.651)
(7.620 – 8.255)
.065
(1.651)
TYP
.008 – .015
(0.203 – 0.381)
.120
.020
(0.508)
MIN
(3.048)
MIN
+.035
.325
–.015
.018 ± .003
(0.457 ± 0.076)
.100
(2.54)
BSC
+0.889
8.255
(
)
N8 1002
–0.381
NOTE:
INCHES
1. DIMENSIONS ARE
MILLIMETERS
*THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS.
MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED .010 INCH (0.254mm)
S8 Package
8-Lead Plastic Small Outline (Narrow 0.150)
(LTC DWG # 05-08-1610)
.189 – .197
(4.801 – 5.004)
.045 ±.005
.160 ±.005
NOTE 3
.050 BSC
7
5
8
6
.245
MIN
.150 – .157
(3.810 – 3.988)
NOTE 3
.228 – .244
(5.791 – 6.197)
.030 ±.005
TYP
1
3
4
2
RECOMMENDED SOLDER PAD LAYOUT
.010 – .020
(0.254 – 0.508)
× 45°
.053 – .069
(1.346 – 1.752)
.004 – .010
(0.101 – 0.254)
.008 – .010
(0.203 – 0.254)
0°– 8° TYP
.016 – .050
(0.406 – 1.270)
.050
(1.270)
BSC
.014 – .019
(0.355 – 0.483)
TYP
NOTE:
INCHES
1. DIMENSIONS IN
(MILLIMETERS)
2. DRAWING NOT TO SCALE
3. THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS.
MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED .006" (0.15mm)
SO8 0303
1121fe
13
LT1121/LT1121-3.3/LT1121-5
U
PACKAGE DESCRIPTIO
ST Package
3-Lead Plastic SOT-223
(LTC DWG # 05-08-1630)
.248 – .264
(6.30 – 6.71)
.129 MAX
.114 – .124
(2.90 – 3.15)
.059 MAX
.264 – .287
(6.70 – 7.30)
.248 BSC
.130 – .146
(3.30 – 3.71)
.039 MAX
.059 MAX
.090
BSC
.181 MAX
RECOMMENDED SOLDER PAD LAYOUT
.033 – .041
(0.84 – 1.04)
.0905
(2.30)
BSC
10° – 16°
.010 – .014
10°
MAX
.071
(1.80)
MAX
(0.25 – 0.36)
10° – 16°
.0008 – .0040
(0.0203 – 0.1016)
.024 – .033
(0.60 – 0.84)
.012
(0.31)
MIN
.181
(4.60)
BSC
ST3 (SOT-233) 0502
1121fe
14
LT1121/LT1121-3.3/LT1121-5
U
PACKAGE DESCRIPTIO
Z Package
3-Lead Plastic TO-92 (Similar to TO-226)
(LTC DWG # 05-08-1410)
.180 ± .005
(4.572 ± 0.127)
.060 ± .005
(1.524± 0.127)
DIA
.90
(2.286)
NOM
.180 ± .005
(4.572 ± 0.127)
5°
NOM
.500
(12.70)
MIN
.050
(1.270)
MAX
UNCONTROLLED
LEAD DIMENSION
.016 ± .003
.015 ± .002
(0.406 ± 0.076)
(0.381 ± 0.051)
.050
(1.27)
BSC
.098 +.016/–.04
(2.5 +0.4/–0.1)
2 PLCS
Z3 (TO-92) 0801
.060 ± .010
TO-92 TAPE AND REEL
(1.524 ± 0.254)
REFER TO TAPE AND REEL SECTION OF
LTC DATA BOOK FOR ADDITIONAL INFORMATION
.140 ± .010
(3.556 ± 0.127)
3
2
1
10° NOM
1121fe
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 represen-
tationthattheinterconnectionofitscircuitsasdescribedhereinwillnotinfringeonexistingpatentrights.
15
LT1121/LT1121-3.3/LT1121-5
RELATED PARTS
PART NUMBER
DESCRIPTION
COMMENTS
LT1120
125mA Low Dropout Regulator with 20μA I
Includes 2.5V Reference and Comparator
50μA Quiescent Current
Q
LT1129
700mA Micropower Low Dropout Regulator
LT1175
500mA Negative Low Dropout Micropower Regulator
300mA Low Dropout Micropower Regulator with Shutdown
45μA I , 0.26V Dropout Voltage, SOT-223 Package
Q
LT1521
15μA I , Reverse Battery Protection
Q
LT1529
3A Low Dropout Regulator with 50μA I
500mV Dropout Voltage
Q
LT1611
Inverting 1.4MHz Switching Regulator
5V to –5V at 150mA, Low Output Noise, SOT-23 Package
SOT-23 Package, Internally Compensated
Burst ModeTM Operation, Monolithic, 100% Duty Cycle
LT1613
1.4MHz Single-Cell Micropower DC/DC Converter
High Efficiency Synchronous Step-Down Switching Regulator
Doubler Charge Pump with Low Noise Linear Regulator
150mA, Low Noise, LDO Micropower Regulator
500mA, Low Noise, LDO Micropower Regulator
3A Fast Transient Response LDO
LTC1627
LT1682
Low Output Noise: 60μV
(100kHz BW)
RMS
LT1762 Series
LT1763 Series
LT1764 Series
LT1962 Series
LT1963 Series
25μA Quiescent Current, 20μV
30μA Quiescent Current, 20μV
Noise
Noise
RMS
RMS
300mV Dropout, 40μV
Noise
RMS
300mA, Low Noise, LDO Micropower Regulator
1.5A Fast Transient Response LDO
30μA Quiescent Current, 20μV
Noise
RMS
300mV Dropout, 40μV
Noise
RMS
Burst Mode is a trademark of Linear Technology Corporation.
1121fe
LT 0407 REV E • PRINTED IN USA
LinearTechnology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
16
●
●
(408)432-1900 FAX:(408)434-0507 www.linear-tech.com
© LINEAR TECHNOLOGY CORPORATION 1994
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