LT3474EFE-1-PBF [Linear]
Step-Down 1A LED Driver; 降压型1A LED驱动器型号: | LT3474EFE-1-PBF |
厂家: | Linear |
描述: | Step-Down 1A LED Driver |
文件: | 总20页 (文件大小:215K) |
中文: | 中文翻译 | 下载: | 下载PDF数据表文档文件 |
LT3474/LT3474-1
Step-Down
1A LED Driver
FEATURES
DESCRIPTION
The LT®3474/LT3474-1 are fixed frequency step-down
DC/DCconvertersdesignedtooperateasconstant-current
sources. An internal sense resistor monitors the output
current allowing accurate current regulation, ideal for
driving high current LEDs. High output current accuracy
is maintained over a wide current range, from 35mA to
1A, allowing a wide dimming range.
n
True Color PWM™ Delivers Constant Color with
400:1 Dimming Range
n
Wide Input Range: 4V to 36V
n
Up to 1A LED Current
Adjustable 200kHz–2MHz Switching Frequency
n
n
Adjustable Control of LED Current
Integrated Boost Diode
n
n
High Output Current Accuracy is Maintained
Unique PWM circuitry allows a dimming range of 400:1,
avoiding the color shift normally associated with LED
current dimming.
Over a Wide Range from 35mA to 1A
n
Open LED (LT3474) and Short-Circuit Protection
n
High Side Sense Allows Grounded
Cathode Connection
The high switching frequency offers several advantages,
permitting the use of small inductors and ceramic capaci-
tors. Small inductors combined with the 16-lead TSSOP
surface mount package save space and cost versus
alternative solutions. The constant switching frequency
combined with low-impedance ceramic capacitors result
in low, predictable output ripple.
n
Uses Small Inductors and Ceramic Capacitors
n
LT3474-1 Drives LED Strings Up to 26V
n
Compact 16-Lead TSSOP Thermally Enhanced
Surface Mount Package
APPLICATIONS
With their wide input range of 4V to 36V, the LT3474/
LT3474-1 regulate a broad array of power sources, from
5V logic rails to unregulated wall transformers, lead acid
batteries and distributed power supplies. A current mode
PWM architecture provides fast transient response and
cycle-by-cycle current limiting. Frequency foldback and
thermal shutdown provide additional protection.
■
Automotive and Avionic Lighting
■
Architectural Detail Lighting
■
Display Backlighting
Constant Current Sources
■
L, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
True Color PWM is a trademark of Linear Technology Corporation. All other trademarks are
the property of their respective owners. Patent Pending
TYPICAL APPLICATION
Step-Down 1A LED Driver
Efficiency
95
V
IN
V
= 12V
IN
5V TO 36V
TWO SERIES CONNECTED
WHITE 1A LEDS
90
85
80
0.22μF
10μH
V
BOOST
SW
LT3474
IN
2.2μF
SHDN
ONE WHITE 1A LED
R
BIAS
OUT
T
75
70
REF
V
DIMMING*
CONTROL
PWM
ADJ
80.6k
0.1μF
2.2μF
65
60
55
V
LED
C
GND
LED1
*SEE APPLICATIONS SECTION FOR DETAILS
200
400
LED CURRENT (mA)
800
0
1000
600
3474 TA01a
3474 G02
3474fd
1
LT3474/LT3474-1
ABSOLUTE MAXIMUM RATINGS
PIN CONFIGURATION
(Note 1)
V Pin ........................................................(–0.3V), 36V
IN
BIAS Pin....................................................................25V
BOOST Pin Voltage ...................................................51V
BOOST above SW Pin ...............................................25V
OUT, LED Pins (LT3474)............................................15V
OUT, LED Pins (LT3474-1).........................................26V
PWM Pin...................................................................10V
TOP VIEW
DNC*
OUT
LED
1
2
3
4
5
6
7
8
16
15
14
13
12
11
10
9
DNC*
GND
PWM
V
17
V
ADJ
IN
SW
BOOST
BIAS
V
C
V
Pin .....................................................................6V
ADJ
REF
V , REF, R Pins ..........................................................3V
SHDN
C
T
SHDN Pin...................................................................V
GND
R
T
IN
BIAS Pin Current.........................................................1A
Maximum Junction Temperature (Note 2)............. 125°C
Operating Temperature Range (Note 3)
FE PACKAGE
16-LEAD PLASTIC TSSOP
θ
= 8°C/W, θ = 40°C/W
JA
EXPOSED PAD (PIN 17) IS GND, MUST BE SOLDERED TO PCB
JC
LT3474E, LT3474E-1............................ –40°C to 85°C
LT3474I, LT3474I-1............................ –40°C to 125°C
Storage Temperature Range................... –65°C to 150°C
Lead Temperature (Soldering, 10 sec) .................. 300°C
*DO NOT CONNECT EXTERNAL CIRCUITRY TO THESE PINS.
ORDER INFORMATION
LEAD FREE FINISH
LT3474EFE#PBF
LT3474IFE#PBF
TAPE AND REEL
PART MARKING
3474EFE
PACKAGE DESCRIPTION
TEMPERATURE RANGE
LT3474EFE#TRPBF
LT3474IFE#TRPBF
LT3474EFE-1#TRPBF
LT3474IFE-1#TRPBF
16-Lead TSSOP
16-Lead TSSOP
16-Lead TSSOP
16-Lead TSSOP
–40°C to 85°C
–40°C to 125°C
–40°C to 85°C
–40°C to 125°C
3474IFE
LT3474EFE-1#PBF
LT3474IFE-1#PBF
3474EFE-1
3474IFE-1
Consult LTC Marketing for parts specified with wider operating temperature ranges.
Consult LTC Marketing for information on non-standard lead based finish parts.
For more information on lead free part marking, go to: http://www.linear.com/leadfree/
For more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/
ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VIN = 12V, VBOOST = 16V, VOUT = 4V unless otherwise noted (Note 3).
PARAMETER
CONDITIONS
MIN
TYP
3.5
2.6
0.01
1
MAX
UNITS
V
l
Minimum Input Voltage
Input Quiescent Current
Shutdown Current
LED Pin Current
4
4
2
Not Switching
mA
μA
SHDN = 0.3V, V
= 0V, V
= 0V
OUT
BOOST
V
ADJ
Tied to V
0.98
0.968
0.193
0.186
1.02
1.025
0.207
0.210
A
A
A
A
REF
l
V
ADJ
Tied to V /5
0.2
REF
l
l
REF Voltage
1.23
1.25
1.265
V
3474fd
2
LT3474/LT3474-1
ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VIN = 12V, VBOOST = 16V, VOUT = 4V unless otherwise noted (Note 3).
PARAMETER
CONDITIONS
5V < V < 36V
MIN
TYP
0.01
0.0002
20
MAX
UNITS
%/V
Reference Voltage Line Regulation
Reference Voltage Load Regulation
IN
0 < I
< 250μA
%/μA
nA
REF
l
V
ADJ
Pin Bias Current (Note 4)
400
Switching Frequency
R = 80.6k
470
450
500
530
540
kHz
kHz
T
l
l
Maximum Duty Cycle
R = 80.6k
90
95
76
98
%
%
%
T
R = 10k
T
R = 232k
T
Foldback Frequency
R = 80.6k, V
= 0V
OUT
70
2.65
10.3
0.9
0.8
100
100
1.5
1
kHz
V
T
SHDN Threshold (to Switch)
SHDN Pin Current (Note 5)
PWM Threshold
2.6
8.3
0.4
2.7
12.3
1.2
V
= SHDN Threshold
μA
SHDN
V
V Switching Threshold
C
V
V Source Current
C
V = 1V
C
μA
V Sink Current
C
V = 1V
C
μA
LED to V Current Gain
μA/mA
V/mA
A/V
V
C
LED to V Transresistance
C
V to Switch Current Gain
C
2
V Clamp Voltage
C
1.9
0.01
13.8
0.1
l
V Pin Current in PWM Mode
C
V = 1V, V = 0.3V
C PWM
1
μA
OUT Pin Clamp Voltage (LT3474)
OUT Pin Current in PWM Mode
Switch Current Limit (Note 6)
13.2
14.5
10
V
l
l
V
= 4V, V
= 0.3V
PWM
μA
OUT
–40°C to 85°C
LT3474I, LT3474I-1 at 125°C
1.6
1.5
2.1
3.2
3.2
A
A
Switch V
I
I
= 1A
= 1A
380
30
500
50
1
mV
mA
μA
V
CESAT
SW
SW
Boost Pin Current
Switch Leakage Current
Minimum Boost Voltage (Note 7)
Boost Diode Forward Voltage
0.01
1.9
2.5
I
= 100mA
600
mV
DIO
operating temperature range are assured by design, characterization and
correlation with statistical process controls. The LT3474I and LT3474I-1
are guaranteed to meet performance specifications over the –40°C to
125°C operating temperature range.
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 4: Current flows out of pin.
Note 5: Current flows into pin.
Note 6: Current limit is guaranteed by design and/or correlation to static
test. Slope compensation reduces current limit at higher duty cycles.
Note 7: This is the minimum voltage across the boost capacitor needed to
Note 2: This IC includes overtemperature protection that is intended
to protect the device during momentary overload conditions. Junction
temperature will exceed 125°C when overtemperature protection is active.
Continuous operation above the specified maximum operating junction
temperature may impair device reliability.
Note 3: The LT3474E and LT3474E-1 are guaranteed to meet performance
specifications from 0°C to 70°C. Specifications over the –40°C to 85°C
guarantee full saturation of the internal power switch.
3474fd
3
LT3474/LT3474-1
TYPICAL PERFORMANCE CHARACTERISTICS
LED Current vs VADJ
LED Current vs Temperature
Switch Voltage Drop
1200
1000
800
1000
800
600
400
200
0
700
600
500
400
300
200
100
0
T
= 25°C
T
= 25°C
A
A
V
ADJ
= V
REF
600
400
200
0
V
ADJ
= V /5
REF
50
100 125
–50 –25
0
25
75
0
0.25
0.5
V
0.75
(V)
1
1.25
1000
500
SWITCH CURRENT (mA)
1500
0
TEMPERATURE (°C)
ADJ
3474 GO3
3474 G05
3474 G04
Switch Current Limit vs
Temperature
Current Limit vs Duty Cycle
Current Limit vs Output Voltage
2.5
2
2.5
2
2.5
2
T
= 25°C
A
TYPICAL
MINIMUM (85°C)
1.5
1
1.5
1
1.5
1
MINIMUM (125°C)
0.5
0.5
0
0.5
0
0
0
4
6
8
10
12
2
–50 –25
0
25
50
75 100 125
0
20
40
60
80
100
V
(V)
TEMPERATURE (°C)
OUT
DUTY CYCLE (%)
3474 G08
3474 G07
3474 G06
Oscillator Frequency vs
Temperature
Oscillator Frequency vs RT
Oscillator Frequency Foldback
600
550
500
450
600
500
R
T
= 80.6k
T
= 25°C
= 80.6k
T
= 25°C
A
T
A
R
1000
400
300
200
100
0
100
400
10
100
–50 –25
0
25
50
75 100 125
0
0.5
1
1.5
(V)
2
2.5
R
T
(kΩ)
TEMPERATURE (°C)
V
OUT
3474 G09
3474 G10
3474 G11
3474fd
4
LT3474/LT3474-1
TYPICAL PERFORMANCE CHARACTERISTICS
Boost Pin Current
Quiescent Current
Reference Voltage
1.260
1.255
1.250
1.245
1.240
1.235
3.0
2.5
2.0
1.5
1.0
0.5
0
60
50
40
30
20
10
0
T
= 25°C
T
= 25°C
A
A
0
12
18
(V)
24
30
36
–50 –25
0
25
50
75
125
0
500
750 1000 1250 1500
6
100
250
V
SWITCH CURRENT (mA)
TEMPERATURE (°C)
IN
3474 G13
3474 G14
3473 G12
Open-Circuit Output Voltage and
Input Current
Schottky Reverse Leakage
Schottky Forward Voltage Drop
500
400
300
200
100
0
20
15
10
5
60
50
8
V
= 5V
T
A
= 25°C
T
= 25°C
R
A
INPUT CURRENT
LT3474-1
7
6
5
4
3
2
1
40
30
20
10
LT3474
LT3474-1
LT3474
OUTPUT VOLTAGE
0
0
0
–50 –25
0
25
50
75 100 125
0
200
400
600
800
1000
0
10
20
(V)
30
40
TEMPERATURE (°C)
V
FORWARD VOLTAGE (mV)
IN
3474 G15
3474 G19
3474 G16
Minimum Input Voltage,
Minimum Input Voltage,
One White Luxeon III Star
Two Series Connected White
Luxeon III Stars
6
5
10
9
T
A
= 25°C
T = 25°C
A
TO START
TO RUN
4
3
8
LED VOLTAGE
TO START
TO RUN
7
LED VOLTAGE
2
1
0
6
5
0
200
400
600
800
1000
0
200
400
600
800
1000
LED CURRENT (mA)
LED CURRENT (mA)
3474 G17
3474 G18
3474fd
5
LT3474/LT3474-1
PIN FUNCTIONS
DNC(Pins1,16):Donotconnectexternalcircuitrytothese
pins, or tie them to GND. Leave the DNC pins floating.
SHDN (Pin 10): The SHDN pin is used to shut down the
switching regulator and the internal bias circuits. The
2.6V switching threshold can function as an accurate
under-voltage lockout. Pull below 0.3V to shut down the
LT3474/LT3474-1. Pull above 2.65V to enable the LT3474/
OUT (Pin 2): The OUT pin is the input to the current sense
resistor. Connect this pin to the inductor and the output
capacitor.
LT3474-1. Tie to V if the SHDN function is unused.
IN
LED (Pin 3): The LED pin is the output of the current sense
resistor. Connect the anode of the LED here.
REF (Pin 11): The REF pin is the buffered output of the
internal reference. Either tie the REF pin to the V pin for
ADJ
V (Pin 4): The V pin supplies current to the internal
a 1A output current, or use a resistor divider to generate a
IN
IN
circuitry and to the internal power switch and must be
lower voltage at the V pin. Leave this pin unconnected
ADJ
locally bypassed.
if unused.
SW (Pin 5): The SW pin is the output of the internal power
switch. Connect this pin to the inductor and switching
diode.
V (Pin 12): The V pin is the output of the internal error
C
c
amp. The voltage on this pin controls the peak switch
current. Use this pin to compensate the control loop.
BOOST (Pin 6): The BOOST pin is used to provide a drive
voltage,higherthantheinputvoltage,totheinternalbipolar
NPN power switch.
V
(Pin 13): The V
pin is the input to the internal
ADJ
ADJ
voltage to current amplifier. Connect the V
pin to the
ADJ
REF pin for a 1A output current. For lower output cur-
rents, program the V pin using the following formula:
ADJ
BIAS (Pin 7): The BIAS pin connects through a Schottky
diode to BOOST. Tie to OUT.
I
= 1A • V /1.25V.
LED
ADJ
PWM (Pin 14): The PWM pin controls the connection of
GND (Pins 8, 15, Exposed Pad Pin 17): Ground. Tie both
GND pins and the Exposed Pad directly to the ground
plane.TheExposedPadmetalofthepackageprovidesboth
electrical contact to ground and good thermal contact to
the printed circuit board. It must be soldered to the circuit
board for proper operation.
the V pin to the internal circuitry. When the PWM pin is
C
low, the V pin is disconnected from the internal circuitry
C
and draws minimal current. If the PWM feature is unused,
leave this pin unconnected.
R (Pin 9): The R pin is used to set the internal oscilla-
T
T
tor frequency. Tie an 80.6k resistor from R to GND for a
T
500kHz switching frequency.
3474fd
6
LT3474/LT3474-1
BLOCK DIAGRAM
V
IN
V
4
IN
C
IN
BIAS
7
INT REG
AND
UVLO
SHDN
10
BOOST
∑
6
5
SLOPE
COMP
R
S
Q
C1
D1
C1
Q
Q1
DRIVER
L1
R
T
SW
OSC
9
R
T
FREQUENCY
FOLDBACK
OUT
LED
2
3
C2
–
100Ω
0.1Ω
+
2V
D
LED1
1.25V
g
m
REF
11
PWM
PWM
14
13
USE WITH
PWM DIMMING
V
V
C
ADJ
12
Q2
C
C
C2
C1
R
C
1.25k
GND
8
3474 BD
Figure 1. Block Diagram
3474fd
7
LT3474/LT3474-1
APPLICATIONS INFORMATION
Operation
acrossthe0.1Ωresistorisequaltothevoltagedropacross
the 100Ω resistor, the servo loop is balanced.
The LT3474 is a constant frequency, current mode regula-
tor with an internal power switch capable of generating
a constant 1A output. Operation can be best understood
by referring to the Block Diagram.
Tying the REF pin to the V pin sets the LED pin current
ADJ
to 1A. Tying a resistor divider to the REF pin allows the
programming of LED pin currents of less than 1A. LED
pin current can also be programmed by tying the V pin
ADJ
If the SHDN pin is tied to ground, the LT3474 is shut
down and draws minimal current from the input source
directly to a voltage source up to 1.25V.
An LED can be dimmed with pulse width modulation us-
ing the PWM pin and an external NFET. If the PWM pin is
unconnected or pulled high, the part operates nominally.
tied to V . If the SHDN pin exceeds 1.5V, the internal bias
IN
circuitsturnon, includingtheinternalregulator, reference,
and oscillator. The switching regulator will only begin to
operate when the SHDN pin exceeds 2.65V.
If the PWM pin is pulled low, the V pin is disconnected
C
from the internal circuitry and draws minimal current from
Theswitcherisacurrentmoderegulator.Insteadofdirectly
modulatingthedutycycleofthepowerswitch,thefeedback
loop controls the peak current in the switch during each
cycle. Compared to voltage mode control, current mode
control improves loop dynamics and provides cycle-by-
cycle current limit.
thecompensationcapacitor.Circuitrydrawingcurrentfrom
the OUT pin is also disabled. This way, the V pin and the
C
output capacitor store the state of the LED pin current
until PWM is pulled high again. This leads to a highly
linear relationship between pulse width and output light,
allowing for a large and accurate dimming range.
A pulse from the oscillator sets the RS flip-flop and turns
on the internal NPN bipolar power switch. Current in the
switch and the external inductor begins to increase. When
this current exceeds a level determined by the voltage at
TheR pinallowsprogrammingoftheswitchingfrequency.
T
Forapplicationsrequiringthesmallestexternalcomponents
possible, a fast switching frequency can be used. If very
low or very high input voltages are required, a slower
switching frequency can be programmed.
V , current comparator C1 resets the flip-flop, turning
C
off the switch. The current in the inductor flows through
the external Schottky diode and begins to decrease. The
cycle begins again at the next pulse from the oscillator.
During startup V
will be at a low voltage. The NPN Q2
OUT
can only operate correctly with sufficient voltage at V
,
OUT
around 1.7V. A comparator senses V
and forces the V
In this way, the voltage on the V pin controls the current
OUT
C
C
pin high until V
correctly.
rises above 2V, and Q2 is operating
through the inductor to the output. The internal error
OUT
amplifier regulates the output current by continually
adjusting the V pin voltage. The threshold for switching
C
The switching regulator performs frequency foldback dur-
ing overload conditions. An amplifier senses when V is
on the V pin is 0.8V, and an active clamp of 1.9V limits
C
OUT
the output current.
lessthan2Vandbeginsdecreasingtheoscillatorfrequency
down from full frequency to 20% of the nominal frequency
The voltage on the V
pin sets the current through the
ADJ
whenV
=0V.TheOUTpinislessthan2Vduringstartup,
LED pin. The NPN Q2 pulls a current proportional to the
voltage on the V pin through the 100Ω resistor. The
OUT
shortcircuit, andoverloadconditions. Frequencyfoldback
ADJ
helps limit switch current under these conditions.
g amplifier servos the V pin to set the current through
m
C
the 0.1Ω resistor and the LED pin. When the voltage drop
3474fd
8
LT3474/LT3474-1
APPLICATIONS INFORMATION
An internal comparator will force the part into shutdown
The switch driver operates either from V or from the
IN
when V falls below 3.5V. If an adjustable UVLO threshold
BOOST pin. An external capacitor and internal Schottky
diode are used to generate a voltage at the BOOST pin
that is higher than the input supply. This allows the driver
to saturate the internal bipolar NPN power switch for ef-
ficient operation.
IN
is required, the SHDN pin can be used. The threshold
voltage of the SHDN pin comparator is 2.65V. A internal
resistor pulls 10.3μA to ground from the SHDN pin at the
UVLO threshold.
Choose resistors according to the following formula:
Open Circuit Protection
2.65V
R2=
TheLT3474hasinternalopencircuitprotection.IftheLEDis
absent or fails open, the LT3474 clamps the voltage on the
LED pin at 14V. The switching regulator then skips cycles
to limit the input current. The LT3474-1 has no internal
open circuit protection. With the LT3474-1, be careful not
VTH – 2.65V
–10.3μA
R1
V
= UVLO Threshold
TH
Example: Switching should not start until the input is
above 8V.
to violate the ABSMAX voltage of the BOOST pin; if V >
IN
25V, external open circuit protection circuitry (as shown in
Figure 2) may be necessary. The output voltage during an
open LED condition is shown in the Typical Performance
Characteristics section.
V
TH
= 8V
R1 = 100k
2.65V
8V – 2.65V
R2=
=61.9k
Undervoltage Lockout
–10.3μA
Undervoltagelockout(UVLO)istypicallyusedinsituations
wheretheinputsupplyiscurrentlimited,orhashighsource
resistance. A switching regulator draws constant power
from the source, so the source current increases as the
source voltage drops. This looks like a negative resistance
loadtothesourceandcancausethesourcetocurrentlimit
or latch low under low source voltage conditions. UVLO
prevents the regulator from operating at source voltages
where these problems might occur.
100k
Keep the connections from the resistors to the SHDN pin
short and make sure the coupling to the SW and BOOST
pins is minimized. If high resistance values are used, the
SHDN pin should be bypassed with a 1nF capacitor to
prevent coupling problems from switching nodes.
LT3474
V
IN
V
IN
OUT
10k
2.65V
R1
R2
V
C
SHDN
27V
V
C
10.3μA
C1
GND
100k
3474 F03
3474 F02
Figure 3. Undervoltage Lockout
Figure 2. External Overvoltage Protection
Circuitry for the LT3474-1.
3474fd
9
LT3474/LT3474-1
APPLICATIONS INFORMATION
Setting the Switching Frequency
V
+ V
F
(
)
OUT
DC =
The LT3474 uses a constant frequency architecture that
can be programmed over a 200kHz to 2MHz range with a
V – V + V
F
(
)
IN
SW
single external timing resistor from the R pin to ground.
T
where V is the forward voltage drop of the catch diode
The current that flows into the timing resistor is used
F
(~0.4V) and V is the voltage drop of the internal switch
to charge an internal oscillator capacitor. A graph for
SW
(~0.4V at maximum load). This leads to a minimum input
selecting the value of R for a given operating frequency
T
voltage of:
is shown in the Typical Performance Characteristics
section. Table 1 shows suggested R selections for a
T
V
OUT + V
F
V
=
– V + VSW
F
variety of switching frequencies.
IN MIN
(
)
DCMAX
= 1–t
Table 1. Switching Frequencies
SWITCHING FREQUENCY (MHz)
with DC
where t
frequency.
• f
OFF(MIN)
MAX
R (kΩ)
T
is equal to 200ns and f is the switching
2
10
0FF(MIN)
1.5
1
18.7
33.2
52.3
80.6
147
232
Example: f = 500kHz, V
= 4V
OUT
0.7
0.5
0.3
0.2
DCMAX =1− 200ns •500kHz = 0.90
4V + 0.4V
V
=
– 0.4V + 0.4V = 4.9V
IN MIN
(
)
0.9
The maximum operating voltage is determined by the
Operating Frequency Selection
absolute maximum ratings of the V and BOOST pins,
IN
The choice of operating frequency is determined by sev-
eral factors. There is a tradeoff between efficiency and
component size. Higher switching frequency allows the
useofsmallerinductorsatthecostofincreasedswitching
losses and decreased efficiency.
and by the minimum duty cycle.
V
OUT + V
DCMIN
F
V
=
– V + VSW
F
IN MAX
(
)
with DC
where t
= t
• f
MIN
ON(MIN)
Another consideration is the maximum duty cycle. In
certain applications, the converter needs to operate at a
high duty cycle in order to work at the lowest input voltage
possible. The LT3474 has a fixed oscillator off-time and
a variable on-time. As a result, the maximum duty cycle
increases as the switching frequency is decreased.
is equal to 160ns and f is the switching
ON(MIN)
frequency.
Example: f = 500kHz, V
= 2.5V
OUT
DCMIN =160ns •500kHz = 0.08
2.5V + 0.4V
V
=
– 0.4V + 0.4V = 36V
IN MAX
(
)
Input Voltage Range
0.08
Theminimumoperatingvoltageisdeterminedeitherbythe
LT3474’s undervoltage lockout of 4V, or by its maximum
duty cycle. The duty cycle is the fraction of time that the
internal switch is on and is determined by the input and
output voltages:
The minimum duty cycle depends on the switching fre-
quency. Running at a lower switching frequency might
allow a higher maximum operating voltage. Note that this
is a restriction on the operating input voltage; the circuit
will tolerate transient inputs up to the Absolute Maximum
Rating.
3474fd
10
LT3474/LT3474-1
APPLICATIONS INFORMATION
Inductor Selection and Maximum Output Current
The optimum inductor for a given application may differ
from the one indicated by this simple design guide. A
larger value inductor provides a higher maximum load
current, and reduces the output voltage ripple. If your
load is lower than the maximum load current, then you
can relax the value of the inductor and operate with higher
ripple current. This allows you to use a physically smaller
inductor, or one with a lower DCR resulting in higher
efficiency. Be aware that if the inductance differs from
the simple rule above, then the maximum load current
will depend on input voltage. In addition, low inductance
mayresultindiscontinuousmodeoperation,whichfurther
reduces maximum load current. For details of maximum
output current and discontinuous mode operation, see
Linear Technology’s Application Note 44. Finally, for duty
A good first choice for the inductor value is
900kHz
L = (VOUT + V )•
F
f
where V is the voltage drop of the catch diode (~0.4V), f
F
is the switching frequency and L is in μH. With this value
the maximum load current will be 1.1A, independent of
input voltage. The inductor’s RMS current rating must be
greater than the maximum load current and its saturation
currentshouldbeatleast30%higher.Forhighestefficiency,
the series resistance (DCR) should be less than 0.2Ω.
Table 2 lists several vendors and types that are suitable.
For robust operation at full load and high input voltages
(V > 30V), use an inductor with a saturation current
IN
cycles greater than 50% (V /V > 0.5), a minimum
OUT IN
higher than 2.5A.
inductanceisrequiredtoavoidsub-harmonicoscillations.
See Application Note 19.
Table 2. Inductors
VALUE
(μH)
I
DCR
(Ω)
HEIGHT
(mm)
Thecurrentintheinductorisatrianglewavewithanaverage
value equal to the load current. The peak switch current
is equal to the output current plus half the peak-to-peak
inductor ripple current. The LT3474 limits its switch cur-
rentinordertoprotectitselfandthesystemfromoverload
faults. Therefore, the maximum output current that the
LT3474 will deliver depends on the switch current limit,
the inductor value, and the input and output voltages.
RMS
PART NUMBER
Sumida
(A)
CR43-3R3
3.3
4.7
3.3
3.3
4.7
10
1.44
1.15
1.1
0.086
0.109
0.063
0.049
0.072
0.048
0.076
0.072
0.13
3.5
3.5
1.8
3
CR43-4R7
CDRH4D16-3R3
CDRH4D28-3R3
CDRH4D28-4R7
CDRH5D28-100
CDRH5D28-150
CDRH73-100
CDRH73-150
Coilcraft
1.57
1.32
1.3
3
3
When the switch is off, the potential across the inductor
is the output voltage plus the catch diode drop. This gives
the peak-to-peak ripple current in the inductor
15
1.1
3
10
1.68
1.33
3.4
3.4
15
1–DC V + V
(
)(
)
OUT
F
ΔIL =
DO1606T-332
DO1606T-472
DO1608C-332
DO1608C-472
MOS6020-332
MOS6020-472
3.3
4.7
3.3
4.7
3.3
10
1.3
1.1
2
0.1
0.12
0.08
0.09
0.046
0.05
2
2
L • f
(
)
2.9
2.9
2
where f is the switching frequency of the LT3474 and L
is the value of the inductor. The peak inductor and switch
current is
1.5
1.8
1.5
2
ΔIL
2
ISW PK =IL PK =IOUT
+
(
)
(
)
3474fd
11
LT3474/LT3474-1
APPLICATIONS INFORMATION
at the LT3474 input and to force this switching current into
a tight local loop, minnimizing EMI. The input capacitor
must have low impedance at the switching frequency to
do this effectively, and it must have an adequate ripple
current rating. The RMS input is:
To maintain output regulation, this peak current must be
less than the LT3474’s switch current limit I . For SW1,
LIM
I
is at least 1.6A (1.5A at 125°C) at low duty cycles and
LIM
decreases linearly to 1.15A (1.08A at 125°C) at DC = 0.8.
The maximum output current is a function of the chosen
inductor value:
VOUT V – V
(
)
<
IN
OUT
IOUT
2
ΔIL
2
CINRMS = IOUT
•
IOUT MAX = ILIM
–
V
(
)
IN
ΔIL
2
and is largest when V = 2V
sidering that the maximum load current is 1A, RMS ripple
current will always be less than 0.5A
(50% duty cycle). Con-
=1.6A • 1– 0.35•DC –
IN
OUT
(
)
Choosing an inductor value so that the ripple current is
small will allow a maximum output current near the switch
current limit.
The high switching frequency of the LT3474 reduces the
energystoragerequirementsoftheinputcapacitor, sothat
thecapacitancerequiredislessthan10μF.Thecombination
of small size and low impedance (low equivalent series
resistance or ESR) of ceramic capacitors makes them the
preferred choice. The low ESR results in very low voltage
ripple. Ceramic capacitors can handle larger magnitudes
of ripple current than other capacitor types of the same
value. Use X5R and X7R types.
One approach to choosing the inductor is to start with the
simple rule given above, look at the available inductors,
and choose one to meet cost or space goals. Then use
these equations to check that the LT3474 will be able to
deliver the required output current. Note again that these
equations assume that the inductor current is continuous.
Discontinuous operation occurs when I
is less than
OUT
An alternative to a high value ceramic capacitor is a lower
value ceramic along with a larger electrolytic capaci-
tor. The electrolytic capacitor likely needs to be greater
than 10μF in order to meet the ESR and ripple current
requirements. The input capacitor is likely to see high
surge currents when the input source is applied. Tanta-
lum capacitors can fail due to an over-surge of current.
Only use tantalum capacitors with the appropriate surge
current rating. The manufacturer may also recommend
operation below the rated voltage of the capacitor.
ΔI /2.
L
Input Capacitor Selection
Bypass the input of the LT3474 circuit with a 2.2μF or
higher ceramic capacitor of X7R or X5R type. A lower
value or a less expensive Y5V type will work if there is
additional bypassing provided by bulk electrolytic capaci-
tors or if the input source impedance is low. The following
paragraphs describe the input capacitor considerations in
more detail.
Step-down regulators draw current from the input sup-
ply in pulses with very fast rise and fall times. The input
capacitor is required to reduce the resulting voltage ripple
3474fd
12
LT3474/LT3474-1
APPLICATIONS INFORMATION
A final caution is in order regarding the use of ceramic
capacitors at the input. A ceramic input capacitor can
combine with stray inductance to form a resonant tank
circuit.Ifpowerisappliedquickly(forexamplebyplugging
the circuit into a live power source), this tank can ring,
doubling the input voltage and damaging the LT3474. The
solution is to either clamp the input voltage or dampen the
tank circuit by adding a lossy capacitor in parallel with the
ceramic capacitor. For details, see Application Note 88.
You can estimate output ripple with the following
equation:
ΔIL
8•f•C
VRIPPLE
=
for ceramic capacitors
OUT
whereΔI isthepeak-to-peakripplecurrentintheinductor.
L
The RMS content of this ripple is very low so the RMS
current rating of the output capacitor is usually not of
concern. It can be estimated with the formula:
Output Capacitor Selection
ΔIL
IC RMS
=
(
)
12
For most LEDs, a 2.2μF 6.3V ceramic capacitor (X5R or
X7R)attheoutputresultsinverylowoutputvoltageripple
and good transient response. Other types and values will
also work; the following discusses tradeoffs in output
ripple and transient performance.
The low ESR and small size of ceramic capacitors make
them the preferred type for LT3474 applications. Not all
ceramic capacitors are the same, however. Many of the
higher value capacitors use poor dielectrics with high
temperature and voltage coefficients. In particular, Y5V
and Z5U types lose a large fraction of their capacitance
with applied voltage and at temperature extremes.
Theoutputcapacitorfilterstheinductorcurrenttogenerate
an output with low voltage ripple. It also stores energy in
order to satisfy transient loads and stabilizes the LT3474’s
control loop. Because the LT3474 operates at a high
frequency, minimal output capacitance is necessary. In
addition, the control loop operates well with or without
the presence of output capacitor series resistance (ESR).
Ceramic capacitors, which achieve very low output ripple
and small circuit size, are therefore an option.
Because loop stability and transient response depend on
the value of C , this loss may be unacceptable. Use X7R
OUT
and X5R types. Table 3 lists several capacitor vendors.
Table 3. Low-ESR Surface Mount Capacitors
VENDOR
Taiyo-Yuden
AVX
TYPE
SERIES
X5R, X7R
X5R, X7R
X5R, X7R
Ceramic
Ceramic
Ceramic
TDK
3474fd
13
LT3474/LT3474-1
APPLICATIONS INFORMATION
Diode Selection
Table 4 lists several Schottky diodes and their
manufacturers.
The catch diode (D1 from Figure 1) conducts current only
during switch off time. Average forward current in normal
operation can be calculated from:
Table 4. Schottky Diodes
V
I
V at 0.5A
V at 1A
R
AVE
F
F
PART NUMBER
On Semiconductor
MBR0520L
MBR0540
(V)
(A)
(mV)
(mV)
IOUT V – V
(
)
IN
OUT
ID AVG
=
(
)
V
20
40
20
40
0.5
0.5
1
385
510
IN
620
530
550
The only reason to consider a diode with a larger current
rating than necessary for nominal operation is for the
worst-case condition of shorted output. The diode cur-
rent will then increase to one half the typical peak switch
current.
MBRM120E
MBRM140
Diodes Inc.
B0530W
1
30
20
30
40
0.5
1
430
B120
500
500
530
Peakreversevoltageisequaltotheregulatorinputvoltage.
Use a diode with a reverse voltage rating greater than the
input voltage.
B130
1
B140 HB
1
International Rectifier
10BQ030
30
1
420
If using the PWM mode of the LT3474, select a diode with
low reverse leakage.
3474fd
14
LT3474/LT3474-1
APPLICATIONS INFORMATION
BOOST and BIAS Pin Considerations
can be tied to the input (Figure 4b). The circuit in Figure
4a is more efficient because the BOOST pin current comes
from a lower voltage source. The BIAS pin can be tied to
another source that is at least 3V (Figure 4c). For example,
if a 3.3V source is on whenever the LED is on, the BIAS
pin can be connected to the 3.3V output. For LT3474-1
applications with higher output voltages, an additional
Zener diode may be necessary (Figure 4d) to maintain the
BOOST pin voltage below the absolute maximum. In any
case, be sure that the maximum voltage at the BOOST pin
is both less than 51V and the voltage difference between
the BOOST and SW pins is less than 25V.
The capacitor and internal diode tied to the BOOST pin
generate a voltage that is higher than the input voltage.
In most cases, a 0.22μF capacitor will work well. Figure 4
shows three ways to arrange the boost circuit. The BOOST
pin must be more than 2.5V above the SW pin for full ef-
ficiency. For outputs of 2.8V or higher, the standard circuit
(Figure 4a) is best. For lower output voltages, the BIAS pin
C3
BIAS
BOOST
SW
LT3474
V
V
V
OUT
IN
IN
Programming LED Current
GND
– V ≈ V
OUT
3474 F04a
The LED current can be set by adjusting the voltage on
the V pin. For a 1A LED current, either tie V to REF
V
BOOST
SW
MAX V
≈ V + V
IN OUT
ADJ
ADJ
BOOST
or to a 1.25V source. For lower output currents, program
(4a)
the V
using the following formula:
ADJ
1A •VADJ
1.25V
C3
BIAS
BOOST
ILED
=
LT3474
V
V
SW
V
OUT
IN
IN
Voltages less than 1.25V can be generated with a voltage
divider from the REF pin, as shown in Figure 5.
GND
3474 F04b
V
– V ≈ V
SW
BOOST
IN
IN
MAX V
≈ 2V
BOOST
REF
(4b)
R1
R2
LT3474
GND
V
> 3V
IN2
IN
V
ADJ
C3
BIAS
BOOST
SW
LT3474
V
V
V
OUT
IN
3474 F04
GND
Figure 5. Setting VADJ with a Resistor Divider
3474 F04c
V
– V ≈ V
SW IN2
BOOST
BOOST
MAX V
≈ V + V
IN2 IN
MINIMUM VALUE FOR V = 3V
IN2
In order to have accurate LED current, precision resistors
are preferred (1% or better is recommended). Note that
(4c)
the V
pin sources a small amount of bias current, so
ADJ
use the following formula to choose resistors:
C3
BIAS
BOOST
SW
LT3474
VADJ
1.25V – VADJ
V
IN
V
IN
V
OUT
R2 =
GND
– V ≈ V
+ 50nA
3474 F04d
R1
V
– V
Z
BOOST
MAX V
SW
OUT
≈ V + V
IN
– V
OUT Z
BOOST
(4d)
Figure 4. Generating the Boost Voltage
3474fd
15
LT3474/LT3474-1
APPLICATIONS INFORMATION
the C-RC string (tied to the V pin) shown in Figure 7 for
To minimize the error from variations in V pin current,
C
ADJ
properoperationduringstart-up. WhenthePWMpingoes
high again, the LED current returns rapidly to its previous
onstatesincethecompensationandoutputcapacitorsare
at the correct voltage. This fast settling time allows The
LT3474 to maintain diode current regulation with PWM
pulse widths as short as 40μs. If the NFET is omitted and
the cathode of the LED is instead tied to GND, use PWM
pulse widths of 1ms or greater. The maximmum PWM
use resistors with a parallel resistance of less than 4k. Use
resistors with a series resistance of 5.11k or greater so as
not to exceed the 250μA current limit on the REF pin.
Dimming Control
There are several different types of dimming control cir-
cuits. One dimming control circuit (Figure 6) changes the
voltage on the V pin by tying a low on-resistance FET to
ADJ
dimming ratio (PWM
) can be calculated from the
RATIO
the resistor divider string. This allows the selection of two
different LED currents. For reliable operation, program an
LED current of no less than 35mA. The maximum current
maximum PWM period (t
) and minimum PWM pulse
MAX
width (t ) as follows:
MIN
dimming ratio (I
) can be calculated from the maxi-
MAX
RATIO
mum LED current (I
tMAX
tMIN
= PWMRATIO
) and the minimum LED current
(I ) as follows:
MIN
Total dimming ratio (DIM
dimming ratio and the current dimming ratio.
) is the product of the PWM
RATIO
IMAX
IMIN
= IRATIO
Example: I
= 1A, I = 0.1A, t
= 12ms, t = 40μs
MAX
MIN
MAX
MIN
Another dimming control circuit (Figure 7) uses the PWM
pin and an external NFET tied to the cathode of the LED.
When the PWM signal goes low, the NFET turns off, turn-
ing off the LED and leaving the output capacitor charged.
The PWM pin is pulled low as well, which disconnects the
1A
0.1A
IRATIO
=
=10:1
12ms
PWMRATIO
=
=300:1
40μs
V pin, storing the voltage in the capacitor tied there. Use
C
DIMRATIO =10•300=3000:1
REF
R1
R2
LT3474
GND
PWM
60Hz TO
10kHz
PWM
LED
V
ADJ
LT3474
GND
3474 F05
DIM
3.3nF 10k
0.1μF
3474 F06
Figure 6. Dimming with an NFET and Resistor Divider
Figure 7. Dimming Using PWM Signal
3474fd
16
LT3474/LT3474-1
APPLICATIONS INFORMATION
LED Voltage Range
as short as possible. To prevent electromagnetic interfer-
ence (EMI) problems, proper layout of the high frequency
switching path is essential. The voltage signal of the SW
and BOOST pins have sharp rise and fall edges. Minimize
the area of all traces connected to the BOOST and SW
pins and always use a ground plane under the switching
regulator to minimize interplane coupling. In addition, the
The LT3474 can drive LED voltages from 2.4V to 12V. The
LT3474-1 can drive LED voltages from 2.4V to 30V. Be
careful not to exceed the ABSMAX rating of the OUT, LED,
or BOOST pins of the LT3474-1 since the internal output
clamp is disabled. See the Typical Application section for
an example of adding an external output clamp. If the
LED voltage can drift below 2.4V due to temperature or
component variation, add extra series resistance to bring
the overall voltage above 2.4V.
ground connection for frequency setting resistor R (refer
T
to Figure 1) should be tied directly to the GND pin and
not shared with any other component, ensuring a clean,
noise-free connection.
Layout Hints
As with all switching regulators, careful attention must
be paid to the PCB layout and component placement. To
maximize efficiency, switch rise and fall times are made
PWM
SHDN
V
IN
GND
VIA TO LOCAL GND PLANE
VIA TO OUT
Figure 8. Recommended Component Placement
3474fd
17
LT3474/LT3474-1
TYPICAL APPLICATIONS
Step-Down 1A LED Driver with PWM Dimming
LED Current in PWM Mode
V
IN
I
LED1
500mA/DIV
6V TO 36V
C3
0.22μF
6.3V
C1
2.2μF
50V
L1
10μH
V
BOOST
SW
IN
SHDN
V(PWM)
5V/DIV
D1
LT3474
R
BIAS
OUT
T
REF
V
1ms/DIV
PWM
C2
2.2μF
6.3V
ADJ
R1
80.6k
V
LED
C
C4
GND
3.3nF
LED1
M1
R2
10k
PWM
C5
0.1μF
3474 TA01
D1: B140HB
C1 TO C3: X5R OR X7R
M1: Si2302ADS
Step-Down 1A LED Driver with
Two Series Connected LED Output
Efficiency, Two LED Output
95
V
IN
90
85
80
12V TO
36V
V
= 12V
= 24V
IN
C3
C1
2.2μF
50V
L1
10μH
0.22μF
V
BOOST
SW
IN
V
IN
10V
SHDN
D1
LT3474
75
70
R
T
BIAS
OUT
REF
V
R1
ADJ
C2
2.2μF
10V
PWM
LED
65
60
55
33.2k
V
C
C4
0.1μF
GND
LED1
LED2
1A
LED
CURRENT
200
400
LED CURRENT (mA)
800
0
1000
600
3474 G01
3474 TA02
D1: MBRM 140
C1 TO C3: X5R OR X7R
3474fd
18
LT3474/LT3474-1
PACKAGE DESCRIPTION
FE Package
16-Lead Plastic TSSOP (4.4mm)
(Reference LTC DWG # 05-08-1663)
Exposed Pad Variation BA
4.90 – 5.10*
(.193 – .201)
2.74
(.108)
2.74
(.108)
16 1514 13 12 1110
9
6.60 ±0.10
2.74
(.108)
4.50 ±0.10
6.40
2.74
SEE NOTE 4
(.252)
(.108)
0.45 ±0.05
BSC
1.05 ±0.10
0.65 BSC
5
7
8
1
2
3
4
6
RECOMMENDED SOLDER PAD LAYOUT
1.10
(.0433)
MAX
4.30 – 4.50*
(.169 – .177)
0.25
REF
0° – 8°
0.65
(.0256)
BSC
0.09 – 0.20
(.0035 – .0079)
0.50 – 0.75
(.020 – .030)
0.05 – 0.15
(.002 – .006)
FE16 (BA) TSSOP 0204
0.195 – 0.30
(.0077 – .0118)
TYP
NOTE:
1. CONTROLLING DIMENSION: MILLIMETERS 4. RECOMMENDED MINIMUM PCB METAL SIZE
FOR EXPOSED PAD ATTACHMENT
*DIMENSIONS DO NOT INCLUDE MOLD FLASH. MOLD FLASH
SHALL NOT EXCEED 0.150mm (.006") PER SIDE
MILLIMETERS
(INCHES)
2. DIMENSIONS ARE IN
3. DRAWING NOT TO SCALE
3474fd
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.
19
LT3474/LT3474-1
TYPICAL APPLICATION
Step-Down 1A LED Driver with Four Series Connected LED Output
V
IN
21V TO
36V
C3
0.22μF
16V
C1
2.2μF
50V
L1
47μH
V
BOOST
SW
IN
SHDN
LT3474-1
D1
D2
BIAS
R
T
REF
V
OUT
R1
C2
2.2μF
25V
ADJ
PWM
LED
80.6k
R2
10k
V
C
C4
0.1μF
GND
D3
Q1
12V TO 18V
LED VOLTAGE
R3
100k
1A LED
CURRENT
f
= 500kHz
SW
3474 TA02a
D1: MBRM 140
D2: 7.5V Zener Diode
D3: 22V Zener Diode
Q1: MMBT3904
C1 TO C3: X5R OR X7R
RELATED PARTS
PART NUMBER DESCRIPTION
COMMENTS
: 1.6V to 18V, V
LT1618
LT1766
LT1956
LT1961
Constant Current, 1.4MHz, 1.5A Boost Converter
V
= 36V, I = 1.8mA, I = <1μA,
Q SD
IN
OUT(MAX)
OUT(MAX)
MS10 Package
60V, 1.2A (I ), 200kHz, High Efficiency Step-Down DC/DC Converter V : 5.5V to 60V, V
= 1.20V, I = 2.5mA, I = 25μA,
OUT
IN
Q
SD
TSSOP16/E Packages
60V, 1.2A (I ), 500kHz, High Efficiency Step-Down DC/DC Converter V : 5.5V to 60V, V
= 1.20V, I = 2.5mA, I = 25μA,
OUT
IN
OUT(MAX)
Q
SD
TSSOP16/E Packages
1.5A (I ), 1.25MHz, High Efficiency Step-Up DC/DC Converter
V
: 3V to 25V, V
= 35V, I = 0.9mA, I = 6μA,
OUT(MAX) Q SD
SW
IN
MS8E Package
LT1976/LT1977 60V, 1.2A (I ), 200kHz/500kHz, High Efficiency Step-Down
V : 3.3V to 60V, V
= 1.20V, I = 100μA, I = <1μA,
Q SD
OUT
IN
OUT(MAX)
DC/DC Converters with BurstMode® Operation
TSSOP16E Package
LT3430/LT3431 60V, 2.5A (I ), 200kHz, High Efficiency Step-Down DC/DC Converters
V
SD
: 5.5V to 60V, V
= 1.20V, I = 2.5μA,
OUT(MAX) Q
OUT
IN
I
= <25μA, TSSOP16/E Packages
LT3433
60V, 400mA (I ), 200kHz, High Efficiency Step-Up/Step-Down
V : 4V to 60V, V : 3.3V to 20V, I = 100μA,
SD
OUT
IN
OUT
Q
DC/DC Converters with Burst Mode Operation
I
= <1μA, TSSOP16E Package
LT3434/LT3435 60V, 2.5A (I ), 200kHz/500kHz, High Efficiency Step-Down
V : 3.3V to 60V, V
= 1.20V, I = 100μA, I = <1μA,
OUT(MAX) Q SD
OUT
IN
DC/DC Converters with Burst Mode Operation
TSSOP16E Package
LTC3453
1MHz, 800mA Synchronous Buck-Boost High Power LED Driver
V : 2.7V to 5.5V, V
= 5.5V, I = 2.5mA, I = <6μA,
Q SD
IN
OUT(MAX)
QFN Package
LT3467/LT3467A 1.1A (I ), 1.3MHz/2.1MHz, High Efficiency Step-Up DC/DC Converters V : 2.4V to 16V, V
= 40V, I = 1.2mA, I = <1μA,
Q SD
SW
IN
OUT(MAX)
with Integrated Soft-Start
ThinSOT™ Package
LT3477
LT3479
3A, 42V, 3MHz Step-Up Regulator with Dual Rail to Rail Current Sense
V
: 2.5V to 2.5V, V
= 40V, I = 5mA, I = <1μA,
OUT(MAX) Q SD
IN
QFN, TSSOP16E Packages
3A, Full Featured DC/DC Converter with Soft-Start and Inrush
Current Protection
V : 2.5V to 24V, V
DFN and TSSOP Packages
= 40V, I = 6.5mA, I = <1μA,
Q SD
IN
OUT(MAX)
Burst Mode is a registered trademark of Linear Technology Corporation.
ThinSOT is a trademark of Linear Technology Corporation.
3474fd
LT 1008 REV D • PRINTED IN USA
LinearTechnology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
20
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© LINEAR TECHNOLOGY CORPORATION 2005
(408) 432-1900 FAX: (408) 434-0507 www.linear.com
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