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PDF LT3012 Data sheet ( Hoja de datos )
| Número de pieza | LT3012 | |
| Descripción | 4V to 80V Low Dropout Micropower Linear Regulator | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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FEATURES
n Wide Input Voltage Range: 4V to 80V
n Low Quiescent Current: 40μA
n Low Dropout Voltage: 400mV
n Output Current: 250mA
n No Protection Diodes Needed
n Adjustable Output from 1.24V to 60V
n 1μA Quiescent Current in Shutdown
n Stable with 3.3μF Output Capacitor
n Stable with Aluminum, Tantalum or Ceramic
Capacitors
n Reverse-Battery Protection
n No Reverse Current Flow from Output to Input
n Thermal Limiting
n Thermally Enhanced 16-Lead TSSOP and
12-Pin (4mm × 3mm) DFN Packages
APPLICATIONS
n Low Current High Voltage Regulators
n Regulator for Battery-Powered Systems
n Telecom Applications
n Automotive Applications
LT3012
250mA, 4V to 80V
Low Dropout
Micropower Linear Regulator
DESCRIPTION
The LT®3012 is a high voltage, micropower low dropout
linear regulator. The device is capable of supplying 250mA of
output current with a dropout voltage of 400mV. Designed
for use in battery-powered or high voltage systems, the low
quiescent current (40μA operating and 1μA in shutdown)
makes the LT3012 an ideal choice. Quiescent current is
also well controlled in dropout.
Other features of the LT3012 include the ability to operate
with very small output capacitors. The regulator is stable
with only 3.3μF on the output while most older devices
require between 10μF and 100μF for stability. Small ce-
ramic capacitors can be used without any need for series
resistance (ESR) as is common with other regulators.
Internal protection circuitry includes reverse-battery
protection, current limiting, thermal limiting and reverse
current protection.
The device is available with an adjustable output with a
1.24V reference voltage. The LT3012 regulator is available
in the 16-lead TSSOP and 12 pin low profile (0.75mm)
(4mm × 3mm) DFN packages with an exposed pad for
enhanced thermal handling capability.
L, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
TYPICAL APPLICATION
5V Supply with Shutdown
VIN
5.4V TO
80V
IN OUT
LT3012
1μF
SHDN ADJ
GND
VSHDN
<0.3V
>2.0V
OUTPUT
OFF
ON
750k
VOUT
5V
250mA
3.3μF
249k
3012 TA01
400
350
300
250
200
150
100
50
0
0
Dropout Voltage
50 100 150 200
OUTPUT CURRENT (mA)
250
3012 TA02
3012fd
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TYPICAL PERFORMANCE CHARACTERISTICS
LT3012
Typical Dropout Voltage
600
500 TJ = 125°C
400
300 TJ = 25°C
200
100
0
0 50 100 150 200 250
OUTPUT CURRENT (mA)
3012 G01
Guaranteed Dropout Voltage
600
= TEST POINTS
TJ ≤ 125°C
500
400
TJ ≤ 25°C
300
200
100
0
0 50 100 150 200 250
OUTPUT CURRENT (mA)
3012 G02
Dropout Voltage
600
500
IL = 250mA
400 IL = 100mA
300 IL = 50mA
200 IL = 10mA
100 IL = 1mA
0
–50 –25
0 25 50 75 100 125 150
TEMPERATURE (°C)
3012 G03
Quiescent Current
100
VIN = 6V
90 RL = ∞
80 IL = 0
70
60
50 VSHDN = VIN
40
30
20
10
0
–50 –25
VSHDN = GND
0 25 50 75 100 125 150
TEMPERATURE (°C)
3012 G04
ADJ Pin Voltage
1.260
IL = 1mA
1.255
1.250
1.245
1.240
1.235
1.230
1.225
1.220
–50 –25
0 25 50 75 100 125 150
TEMPERATURE (°C)
3012 G05
Quiescent Current
80
TJ = 25°C
70 RL = ∞
VOUT = 1.24V
60
50 VSHDN = VIN
40
30
20
10
VSHDN = GND
0
0 1 2 3 4 5 6 7 8 9 10
INPUT VOLTAGE (V)
3012 G06
Quiescent Current
250
TJ = 25°C
225 RL = ∞
200 VOUT = 1.24V
175
150
125 VSHDN = VIN
100
75
VSHDN = GND
50
25
0
0 10 20 30 40 50 60 70 80
INPUT VOLTAGE (V)
3012 G07
GND Pin Current
1.2
TJ = 25°C
*FOR VOUT = 1.24V
1.0
RL = 49.6Ω
0.8 IL = 25mA*
RL = 124Ω
0.6 IL = 10mA*
0.4
RL = 1.24k
0.2 IL = 1mA*
0
0 1 2 3 4 5 6 7 8 9 10
INPUT VOLTAGE (V)
3012 G08
GND Pin Current
10
TJ = 25°C, *FOR VOUT = 1.24V
9
8
RL = 4.96Ω
7 IL = 250mA*
6
5
4 RL = 12.4Ω
IL = 100mA*
3
2
1 RL = 24.8Ω, IL = 50mA*
0
0 1 2 3 4 5 6 7 8 9 10
INPUT VOLTAGE (V)
3012 G09
3012fd
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LT3012
APPLICATIONS INFORMATION
For an application with transient high power peaks, average
power dissipation can be used for junction temperature
calculations as long as the pulse period is significantly less
than the thermal time constant of the device and board.
Calculating Junction Temperature
Example 1: Given an output voltage of 5V, an input volt-
age range of 24V to 30V, an output current range of 0mA
to 50mA, 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:
IOUT(MAX) • (VIN(MAX) – VOUT) + (IGND • VIN(MAX))
where:
IOUT(MAX) = 50mA
VIN(MAX) = 30V
IGND at (IOUT = 50mA, VIN = 30V) = 1mA
So:
P = 50mA • (30V – 5V) + (1mA • 30V) = 1.28W
The thermal resistance will be in the range of 40°C/W to
62°C/W depending on the copper area. So the junction
temperature rise above ambient will be approximately
equal to:
1.31W • 50°C/W = 65.5°C
The maximum junction temperature will then be equal to
the maximum junction temperature rise above ambient
plus the maximum ambient temperature or:
TJMAX = 50°C + 65.5°C = 115.5°C
Example 2: Given an output voltage of 5V, an input voltage
of 48V that rises to 72V for 5ms(max) out of every 100ms,
and a 5mA load that steps to 50mA for 50ms out of every
250ms, what is the junction temperature rise above ambi-
ent? Using a 500ms period (well under the time constant
of the board), power dissipation is as follows:
P1(48V in, 5mA load) = 5mA • (48V – 5V)
+ (200μA • 48V) = 0.23W
P2(48V in, 50mA load) = 50mA • (48V – 5V)
+ (1mA • 48V) = 2.20W
P3(72V in, 5mA load) = 5mA • (72V – 5V)
+ (200μA • 72V) = 0.35W
P4(72V in, 50mA load) = 50mA • (72V – 5V)
+ (1mA • 72V) = 3.42W
Operation at the different power levels is as follows:
76% operation at P1, 19% for P2, 4% for P3, and
1% for P4.
PEFF = 76%(0.23W) + 19%(2.20W) + 4%(0.35W)
+ 1%(3.42W) = 0.64W
With a thermal resistance in the range of 40°C/W to
62°C/W, this translates to a junction temperature rise
above ambient of 26°C to 38°C.
High Temperature Operation
Care must be taken when designing LT3012 applications to
operate at high ambient temperatures. The LT3012 works
at elevated temperatures but erratic operation can occur
due to unforeseen variations in external components. Some
tantalum capacitors are available for high temperature
operation, but ESR is often several ohms; capacitor ESR
above 3Ω is unsuitable for use with the LT3012. Ceramic
capacitor manufacturers (Murata, AVX, TDK, and Vishay
Vitramon at this writing) now offer ceramic capacitors that
are rated to 150°C using an X8R dielectric. Device instability
will occur if output capacitor value and ESR are outside
design limits at elevated temperature and operating DC
voltage bias (see information on capacitor characteristics
under Output Capacitance and Transient Response). Check
each passive component for absolute value and voltage
ratings over the operating temperature range.
Leakages in capacitors or from solder flux left after
insuficient board cleaning adversely affects low
quiescent current operation. The output voltage resistor
divider should use a maximum bottom resistor value of
124k to compensate for high temperature leakage, setting
divider current to 10μA. Consider junction temperature
increase due to power dissipation in both the junction and
nearby components to ensure maximum specifications are
not violated for the device or external components.
3012fd
11
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| Páginas | Total 16 Páginas | |
| PDF Descargar | [ Datasheet LT3012.PDF ] | |
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