LT1121IZ-3.3#TR [Linear]
LT1121 - Micropower Low Dropout Regulators with Shutdown; Package: TO-92; Pins: 3; Temperature Range: -40°C to 85°C;型号: | LT1121IZ-3.3#TR |
厂家: | Linear |
描述: | LT1121 - Micropower Low Dropout Regulators with Shutdown; Package: TO-92; Pins: 3; Temperature Range: -40°C to 85°C 输出元件 调节器 |
文件: | 总16页 (文件大小:158K) |
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
FEATURES
DESCRIPTION
The LT®1121/LT1121-3.3/LT1121-5 are micropower low
dropout regulators with shutdown. These devices are ca-
pableofsupplying150mAofoutputcurrentwithadropout
voltage of 0.4V. Designed for use in battery-powered sys-
tems, thelowquiescentcurrent, 30μAoperatingand16μA
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.
n
0.4V Dropout Voltage
n
150mA Output Current
n
30μA Quiescent Current
No Protection Diodes Needed
n
n
Adjustable Output from 3.75V to 30V
n
3.3V and 5V Fixed Output Voltages
n
Controlled Quiescent Current in Dropout
n
Shutdown
n
16μA Quiescent Current in Shutdown
OtherfeaturesoftheLT1121/LT1121-3.3/LT1121-5include
theabilitytooperatewithverysmalloutputcapacitors.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
inputisatgroundorreversed.Undertheseconditionsonly
16μA will flow from the output pin to ground.
n
Stable with 0.33μF Output Capacitor
n
Reverse Battery Protection
n
No Reverse Current with Input Low
n
Thermal Limiting
n
Available in the 8-Lead SO, 8-Lead PDIP, 3-Lead
SOT-23 and 3-Lead TO-92 Packages
APPLICATIONS
n
Low Current Regulator
n
Regulator for Battery-Powered Systems
L, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
n
Post Regulator for Switching Supplies
TYPICAL APPLICATION
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
1121ff
1
LT1121/LT1121-3.3/LT1121-5
ABSOLUTE MAXIMUM RATINGS
(Note 1)
Input Voltage
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
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
PACKAGE/ORDER INFORMATION
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.
*
FRONT VIEW
BOTTOM 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
T = 150°C, θ = 150°C/W
JMAX
ST PACKAGE
3-LEAD PLASTIC SOT-223
S8 PACKAGE
8-LEAD PLASTIC SO
T
= 150°C, θ = 50°C/W
JMAX
JA
JA
T
T
= 150°C, θ = 120°C/W (N8, S8)
JA
JMAX
JMAX
= 150°C, θ = 70°C/W (AS8)
JA
ORDER PART
NUMBER
ST PART
MARKING
ORDER PART
NUMBER
ORDER PART NUMBER
S8 PART MARKING
LT1121CN8
LT1121IS8-3.3
121I3
LT1121CST-3.3 11213
LT1121IST-3.3 121I3
LT1121CST-5 11215
LT1121CZ-3.3
LT121IZ-3.3
LT1121CZ-5
LT1121IZ-5
LT1121CN8-3.3 LT1121IS8-5
121I5
LT1121CN8-5
LT1121IN8
LT1121IN8-3.3 LT1121ACS8-3.3
LT1121IN8-5
LT1121CS8
LT1121CS8-3.3 LT1121AIS8
LT1121CS8-5
LT1121HVCS8
LT1121IS8
LT1121HVIS8
LT1121ACS8
121HVI
1121A
121A3
121A5
121AHV
121AI
LT1121IST-5
1121I5
LT1121ACS8-5
LT1121AHVCS8 1121
11213
LT1121AIS8-3.3 11215
LT1121AIS8-5
LT1121AHVIS8 1121I
121AI3
1121HV 121AI5
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.
1121ff
2
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 TA = 25°C.
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
Regulated Output Voltage (Note 4)
LT1121-3.3
V
= 3.8V, I
= 1mA, T = 25ºC
3.25
3.2
3.3
3.3
3.35
3.4
V
V
IN
OUT
J
l
l
l
4.3V < V < 20V, 1mA < I
< 150mA
IN
OUT
LT1121-5
V
IN
= 5.5V, I
IN
= 1mA, T = 25ºC
4.925
4.85
5
5
5.075
5.15
V
V
OUT
J
OUT
6V < V < 20V, 1mA < I
< 150mA
LT1121 (Note 5)
V
= 4.3V, I
= 1mA, T = 25ºC
3.695
3.64
3.75
3.75
3.805
3.86
V
V
IN
OUT
J
OUT
4.8V < V < 20V, 1mA < I
< 150mA
IN
l
l
l
Line Regulation
Load Regulation
1.5
1.5
1.5
10
10
10
mV
mV
mV
LT1121-3.3
LT1121-5
ΔV = 4.8V TO 20V, I
IN
= 1mA
= 1mA
= 1mA
IN
OUT
OUT
OUT
ΔV = 5.5V TO 20V, I
LT1121 (Note 5) ΔV = 4.3V TO 20V, I
IN
–12
–20
–17
–28
–12
–18
–25
–40
–35
–50
–25
–40
mV
mV
mV
mV
mV
mV
LT1121-3.3
ΔI
ΔI
ΔI
ΔI
= 1mA to 150mA, T = 25ºC
LOAD
LOAD
LOAD
LOAD
LOAD
J
l
l
l
= 1mA to 150mA
LT1121-5
= 1mA to 150mA, T = 25ºC
J
= 1mA to 150mA
LT1121 (Note 5) ΔI
ΔI
= 1mA to 150mA, T = 25ºC
J
= 1mA to 150mA
LOAD
Dropout Voltage (Note 6)
I
I
= 1mA, T = 25ºC
0.13
0.16
0.25
V
V
LOAD
LOAD
J
l
l
l
l
= 1mA
I
I
= 50mA, T = 25ºC
0.3
0.35
0.5
V
V
LOAD
LOAD
J
= 50mA
I
I
= 100mA, T = 25ºC
0.37
0.42
0.45
0.6
V
V
LOAD
LOAD
J
= 100mA
I
I
= 150mA, T = 25ºC
0.55
0.7
V
V
LOAD
LOAD
J
= 150mA
l
l
l
l
l
l
Ground Pin Current (Note 7)
I
I
I
I
I
I
= 0mA
30
90
350
1.5
4
50
120
500
2.5
7
μA
μA
LOAD
LOAD
LOAD
LOAD
LOAD
LOAD
= 1mA
= 10mA
= 50mA
= 100mA
= 150mA
μA
mA
mA
mA
7
14
Adjust Pin Bias Current (Notes 5, 8)
Shutdown Threshold
T = 25ºC
150
300
2.8
nA
J
l
l
V
V
= Off to On
= On to Off
1.2
0.75
V
V
OUT
OUT
0.25
50
l
l
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
– V
= 1V (Avg), V
= 0.5V , f
= 120Hz,
IN
OUT
RIPPLE
P-P RIPPLE
I
= 0.1A
LOAD
Current Limit
V
– V
= 7V, T = 25ºC
200
500
1
mA
mA
IN
IN
OUT
J
l
Input Reverse Leakage Current
Reverse Output Current (Note 11)
V
= –20V, V
= 0V
OUT
LT1121-3.3
LT1121-5
LT1121 (Note 5)
V
V
= 3.3V, V = 0V
16
16
16
25
25
25
μA
μA
μA
OUT
OUT
OUT
IN
= 5V, V = 0V
IN
V
= 3.8V, V = 0V
IN
1121ff
3
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 TA = 25°C.
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.
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 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 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 7: Ground pin current is tested with V = V
(nominal) and a
OUT
IN
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 3: For junction temperatures greater than 110°C, a minimum load
Note 8: Adjust pin bias current flows into the adjust pin.
of 1mA is recommended. For T > 110°C and I
< 1mA, output voltage
J
OUT
Note 9: Shutdown pin current at V
= 0V flows out of the shutdown pin.
SHDN
may increase by 1%.
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 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
Dropout Voltage
Quiescent Current
50
40
30
20
10
0
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
V
= 6V
LOAD
IN
R
= ∞
I
= 150mA
LOAD
T
≤ 125°C
J
V
= OPEN
SHDN
I
= 100mA
LOAD
T
≤ 25°C
J
I
= 50mA
LOAD
V
= 0V
SHDN
I
= 1mA
LOAD
= TEST POINTS
–50
0
25
50
75 100 125
–25
0
40 60 80 100 120 140 160
OUTPUT CURRENT (mA)
–50
0
25
50
75 100 125
20
–25
TEMPERATURE (°C)
TEMPERATURE (°C)
1121 G03
1121 G01
1121 G02
1121ff
4
LT1121/LT1121-3.3/LT1121-5
TYPICAL PERFORMANCE CHARACTERISTICS
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
R
V
= 25°C
T
= 25°C
LOAD
T = 25°C
J
LOAD
J
J
R
= ∞
= ∞
R
= ∞
LOAD
= V
OUT
ADJ
V
= OPEN
V
= OPEN
SHDN
SHDN
V
= OPEN
SHDN
V
= 0V
7
V
= 0V
7
V
= 0V
8
SHDN
SHDN
SHDN
0
1
2
3
4
5
6
8
9
10
0
1
2
3
4
5
6
8
9
10
0
1
2
3
4
5
6
7
9
10
INPUT VOLTAGE (V)
INPUT VOLTAGE (V)
INPUT VOLTAGE (V)
1121 G06
1121 G04
1121 G05
LT1121-3.3
Output Voltage
LT1121-5
Output Voltage
LT1121
Adjust Pin Voltage
3.83
3.81
3.79
3.77
3.75
3.73
3.71
3.69
3.67
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
0
25
TEMPERATURE (°C)
50
75 100 125
–50
0
25
50
75 100 125
–50
0
25
TEMPERATURE (°C)
50
75 100
125
–50
–25
–25
–25
TEMPERATURE (°C)
1121 G09
1121 G07
1121 G08
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
T
= 25°C
T
= 25°C
J
J
J
R
I
= 150Ω
LOAD
LOAD
V
= V
OUT
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
R
I
= 3.8k
LOAD
= 1mA*
= 5k
= 1mA*
R
= 3.3k
= 1mA*
LOAD
LOAD
LOAD
I
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 G12
1121 G11
1121ff
5
LT1121/LT1121-3.3/LT1121-5
TYPICAL PERFORMANCE CHARACTERISTICS
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
V
= 25°C
J
J
J
= V
OUT
ADJ
R
I
= 22Ω
LOAD
LOAD
R
= 33Ω
LOAD
LOAD
R
= 25Ω
= 150mA*
LOAD
LOAD
I
= 150mA*
I
= 150mA*
R
I
= 33Ω
LOAD
LOAD
R
= 50Ω
= 100mA*
LOAD
LOAD
= 100mA*
R
= 38Ω
= 100mA*
LOAD
I
I
LOAD
R
I
= 66Ω
= 50mA*
R
I
= 100Ω
LOAD
LOAD
LOAD
R
I
= 75Ω
LOAD
= 50mA*
LOAD
= 50mA*
LOAD
*FOR V
= 3.3V
*FOR V
= 5V
*FOR V
= 3.75V
OUT
5
OUT
OUT
0
2
4
6
8
10
1
3
7
9
0
2
6
8
10
4
1
3
5
7
9
2
6
8
9
0
4
10
1
3
5
7
INPUT VOLTAGE (V)
INPUT VOLTAGE (V)
INPUT VOLTAGE (V)
1121 G13
1121 G14
1121 G15
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
50
75 100 125
20
–25
–50
0
25
50
75 100 125
–25
TEMPERATURE (°C)
TEMPERATURE (°C)
1121 G16
1121 G18
1121 G17
LT1121
Adjust Pin Bias Current
Shutdown Pin Current
Shutdown Pin Input Current
10
9
8
7
6
5
4
3
2
1
0
400
350
300
250
200
150
100
50
25
20
V
= 0V
SHDN
15
10
5
0
0
–50
0
25
50
75 100 125
1
2
3
5
7
8
9
–50
0
25
50
75 100 125
–25
0
4
6
–25
TEMPERATURE (°C)
TEMPERATURE (°C)
SHUTDOWN PIN VOLTAGE (V)
1121 G19
1121 G21
1121 G20
1121ff
6
LT1121/LT1121-3.3/LT1121-5
TYPICAL PERFORMANCE CHARACTERISTICS
Reverse Output Current
Current Limit
Current Limit
400
350
300
250
200
150
100
50
400
350
300
250
200
150
100
50
30
25
20
15
10
5
V
= 0V
V
V
= 7V
V
V
V
V
= 0V
OUT
IN
OUT
IN
= 0V
= 5V (LT1121-5)
= 3.3V (LT1121-3.3)
= 3.8V (LT1121)
OUT
OUT
OUT
0
0
0
0
2
3
4
5
6
7
–50
0
25
50
75 100 125
1
–25
–50
0
25
50
75 100 125
–25
INPUT VOLTAGE (V)
TEMPERATURE (°C)
TEMPERATURE (°C)
1121 G23
1121 G24
1121 G22
Reverse Output Current
Ripple Rejection
Ripple Rejection
100
90
80
70
60
50
40
30
20
10
0
64
62
60
58
56
54
52
50
100
90
80
70
60
50
40
30
20
10
0
I
= 100mA
T
= 25°C
IN
V
IN
= V
OUT
(NOMINAL) + 1V
OUT
IN
J
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
0
2
4
6
8
10
1
3
5
7
9
–50
0
25
50
75
125
–25
100
FREQUENCY (Hz)
TEMPERATURE (°C)
OUTPUT VOLTAGE (V)
1121 G27
1121 G25
1121 G26
LT1121-5
Load Transient Response
LT1121-5
Load Transient Response
Load Regulation
0
–5
V
C
C
= 6V
ΔI
= 1mA TO 150mA
V
C
C
= 6V
IN
IN
LOAD
IN
IN
0.2
0.1
= 0.1μF
= 1μF
0.2
0.1
= 0.1μF
= 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
150
100
50
LT1121-5
150
100
* ADJ PIN TIED TO
OUTPUT PIN
0
0.1
0.3 0.4 0.5 0.6 0.7
TIME (ms)
0.9
0.8
1.0
0.2
0.4 0.5
0.7
0.9
0.8
1.0
50
75 100 125
0
0.1 0.3
0.2
0.6
–50
0
25
–25
TEMPERATURE (°C)
TIME (ms)
1121 G29
1121 G30
1121 G28
1121ff
7
LT1121/LT1121-3.3/LT1121-5
PIN FUNCTIONS
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 volt-
age 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 V ). This
BE
allowstheshutdownpintobedrivendirectlyby5Vlogicor
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 20mA.
A curve of shutdown pin input current as a function of
voltageappearsintheTypicalPerformanceCharacteristics.
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.
Adjust Pin: For the adjustable LT1121, the adjust pin
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.
is the input to the error amplifier. This pin is internally
clamped to 6V and –0.6V (one V ). It has a bias current
BE
of 150nA which flows into the pin. See Bias Current curve
in the Typical Performance Characteristics. 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 30V.
Shutdown Pin: This pin is used to put the device into
shutdown. In shutdown the output of the device is turned
1121ff
8
LT1121/LT1121-3.3/LT1121-5
APPLICATIONS INFORMATION
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 bat-
tery-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.
Specifications for output voltage 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 150mA is –12mV
typical at V
would be:
= 3.75V. At V
= 12V, load regulation
OUT
OUT
12V
3.75V
ꢀ
ꢁ
ꢃ
ꢄ
• –12mV = –38mV
( ) (
)
ꢂ
ꢅ
Adjustable Operation
Thermal Considerations
TheadjustableversionoftheLT1121hasanoutputvoltage
range of 3.75V to 30V. The output voltage is set by the
ratio of two external resistors as shown in Figure 1. 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, 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: I
• (V – V ), and
OUT
IN OUT
2. Ground pin current multiplied by the input voltage:
• V .
I
GND
IN
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.
TheLT1121seriesregulatorshaveinternalthermallimiting
designedtoprotectthedeviceduringoverloadconditions.
Forcontinuousnormalloadconditionsthemaximumjunc-
tion 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.
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
areas are listed for each package. All measurements were
1121ff
GND
1121 • F01
R2
V
V
I
= 3.75V 1 +
+ I
(
• R2
ADJ
)
OUT
ADJ
(
)
R1
= 3.75V
= 150nA AT 25°C
ADJ
OUTPUT RANGE = 3.75V TO 30V
Figure 1. Adjustable Operation
9
LT1121/LT1121-3.3/LT1121-5
APPLICATIONS INFORMATION
taken in still air, on 3/32" FR-4 board with 1oz copper. All
NC leads were connected to the ground plane.
Table 5. TO-92 Package THERMAL RESISTANCE
Package alone
220ºC/W
175ºC/W
Package soldered into PC board with plated through
holes only
Table 1. N8 Package*
COPPER AREA
Package soldered into PC board with 1/4 sq. inch of
copper trace per lead
145ºC/W
160ºC/W
THERMAL RESISTANCE
TOPSIDE
BACKSIDE BOARD AREA JUNCTION TO AMBIENT
Package soldered into PC board with plated through
holes in board, no extra copper trace, and a clip-on type
heat sink: Thermalloy type 2224B
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
1000 sq mm 1000 sq mm 1000 sq mm
80ºC/W
80ºC/W
85ºC/W
91ºC/W
Aavid type 5754
135ºC/W
* Device is mounted on topside. Leads are through hole and are
soldered to both sides of board.
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
100mA, and a maximum ambient temperature of 50°C,
what will the maximum junction temperature be?
Table 2. S8 Package
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.
120ºC/W
120ºC/W
125ºC/W
131ºC/W
Power dissipated by the device will be equal to:
I
• (V
– V ) + (I
• V )
GND IN
OUT MAX
IN MAX
OUT
where, I
= 100mA
= 7V
OUT IN
OUT MAX
V
IN MAX
I
at (I
= 100mA, V = 7V) = 5mA
GND
Table 3. AS8 Package*
so,
P =100mA • (7V – 3.3V) + (5mA • 7V)
= 0.405W
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 2500 sq mm 2500 sq mm
IfweuseanSOT-223package, thenthethermalresistance
will be in the range of 50°C/W to 65°C/W depending on
copperarea. Sothejunctiontemperatureriseaboveambi-
ent will be less than or equal to:
60ºC/W
60ºC/W
68ºC/W
74ºC/W
0.405W • 60°C/W = 24°C
*
Pins 3, 6 and 7 are ground.
** Device is mounted on topside.
The maximum junction temperature will then be equal to
the maximum junction temperature rise above ambient
plus the maximum ambient temperature or:
Table 4. SOT-223 Package
(Thermal Resistance Junction-to-Tab 20ºC/W)
COPPER AREA
T
= 50°C + 24°C = 74°C
JMAX
THERMAL RESISTANCE
JUNCTION TO AMBIENT
TOPSIDE*
BACKSIDE BOARD AREA
Output Capacitance and Transient Performance
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 2500 sq mm 1000 sq mm
50ºC/W
50ºC/W
58ºC/W
64ºC/W
57ºC/W
60ºC/W
The LT1121 is designed to be stable with a wide range of
outputcapacitors.Theminimumrecommendedvalueis1μF
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 that the
ESR of the capacitor is low (ceramic) the suggested series
1000 sq mm
0
1000 sq mm
* Tab of device attached to topside copper.
1121ff
10
LT1121/LT1121-3.3/LT1121-5
APPLICATIONS INFORMATION
resistor is shown in Table 6. The LT1121 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. 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
OUTPUT CAPACITANCE
SUGGESTED SERIES RESISTOR
0.33μF
0.47μF
0.68μF
>1μF
2Ω
1Ω
1Ω
The reverse output current will follow the curve in Figure
2 when the input pin 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.
None Needed
Protection Features
The LT1121 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 volt-
ages from output to input.
In some applications it may be necessary to leave the
input 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 output current also follows the curve in Figure 2
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.
Current limit protection and thermal overload protection
areintendedtoprotectthedeviceagainstcurrentoverload
conditionsattheoutputofthedevice.Fornormaloperation,
the junction temperature should not exceed 125°C.
100
The input of the device will withstand reverse voltages
of 30V. 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 backwards.
T
= 25°C
J
V
90
80
70
60
50
40
30
20
10
0
< V
IN
OUT
CURRENT FLOWS
INTO OUTPUT PIN
TO GROUND
LT1121
= V
(V
)
ADJ
OUT
LT1121-3.3
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
LT1121-5
0
2
4
6
8
10
1
3
5
7
9
OUTPUT VOLTAGE (V)
1121• F02
Figure 2. Reverse Output Current
1121ff
11
LT1121/LT1121-3.3/LT1121-5
APPLICATIONS INFORMATION
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
(Nominal)
Open (Hi)
Forced to V
(Nominal)
(Nominal)
Reverse Output Current ≈ 15μA (See Figure 2)
Input Current ≈ 1μA (See Figure 3)
OUT
OUT
<V
OUT
(Nominal)
Grounded
Forced to V
Reverse Output Current ≈ 15μA (See Figure 2)
Input Current ≈ 1μA (See Figure 3)
OUT
Open
Open
≤0.8V
≤0.8V
>1.5V
Open (Hi)
Grounded
Open (Hi)
Grounded
Open (Hi)
Grounded
Forced to V
Forced to V
≤0V
(Nominal)
(Nominal)
Reverse Output Current ≈ 15μA (See Figure 2)
Reverse Output Current ≈ 15μA (See Figure 2)
Output Current = 0
OUT
OUT
≤0V
Output Current = 0
≤0V
Output Current = Short-Circuit Current
Output Current = 0
–30V < V < 30V
≤0V
IN
1121ff
12
LT1121/LT1121-3.3/LT1121-5
PACKAGE DESCRIPTION
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
NOTE 3
.050 BSC
7
5
8
6
.245
MIN
.160 .005
.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
1121ff
13
LT1121/LT1121-3.3/LT1121-5
PACKAGE DESCRIPTION
ST Package
8-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
1121ff
14
LT1121/LT1121-3.3/LT1121-5
PACKAGE DESCRIPTION
Z Package
8-Lead Plastic TO-92 (Similar to TO-226)
(LTC DWG # 05-08-1510)
.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
1121ff
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 representa-
tion that the interconnection of its circuits as described herein will not infringe on existing patent rights.
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
Inverting 1.4MHz Switching Regulator
500mV Dropout Voltage
Q
LT1611
5V to –5V at 150mA, Low Output Noise, SOT-23 Package
SOT-23 Package, Internally Compensated
Burst Mode™ 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
LT1627
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.
1121ff
LT 0907 REV F • PRINTED IN USA
LinearTechnology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
16
●
●
© LINEAR TECHNOLOGY CORPORATION 1994
(408) 432-1900 FAX: (408) 434-0507 www.linear.com
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