LTC3454EDD#TRPBF [Linear]
LTC3454 - 1A Synchronous Buck-Boost High Current LED Driver; Package: DFN; Pins: 10; Temperature Range: -40°C to 85°C;型号: | LTC3454EDD#TRPBF |
厂家: | Linear |
描述: | LTC3454 - 1A Synchronous Buck-Boost High Current LED Driver; Package: DFN; Pins: 10; Temperature Range: -40°C to 85°C 驱动器 |
文件: | 总12页 (文件大小:206K) |
中文: | 中文翻译 | 下载: | 下载PDF数据表文档文件 |
LTC3454
1A Synchronous Buck-Boost
High Current LED Driver
U
DESCRIPTIO
FEATURES
■
High Efficiency: >90% Typical in Torch Mode,
The LTC®3454 is a synchronous buck-boost DC/DC
converter optimized for driving a single high power LED
at currents up to 1A from a single cell Li-Ion battery in-
put. The regulator operates in either synchronous buck,
synchronous boost, or buck-boost mode depending on
>80% in Flash Mode
■
Wide V Range: 2.7V to 5.5V
IN
■
■
■
■
■
■
■
■
Up to 1A Continuous Output Current
3.5% LED Current Programming Accuracy
Internal Soft-Start
Open/Shorted LED Protection
Constant Frequency 1MHz Operation
Zero Shutdown Current
Overtemperature Protection
Small Thermally Enhanced 10-Lead (3mm × 3mm)
DFN Package
inputvoltageandLEDforwardvoltage.P /P efficiency
LED IN
greater than 90% can be achieved over the entire usable
range of a Li-Ion battery (2.7V to 4.2V).
LED current is programmable to one of four levels, includ-
ingshutdown, withdualexternalresistorsanddualenable
inputs. In shutdown no supply current is drawn.
A high constant operating frequency of 1MHz allows the
use of small external components. The LTC3454 is offered
in a low profile (0.75mm) thermally enhanced 10-lead
(3mm × 3mm) DFN package.
U
APPLICATIO S
■
Cell Phone Camera Flash
■
Cell Phone Torch Lighting
, LTC and LT are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
■
Digital Cameras
PDAs
Misc Li-Ion LED Drivers
■
■
U
TYPICAL APPLICATIO
High Efficiency Torch/Flash LED Driver
L1
5 H
V
IN
1-CELL
Li-Ion
LED Power Efficiency vs V
IN
10 F
10 F
I
2.7V-4.2V
V
SW1
SW2
V
OUT
IN
LED
100
95
A
D
C
I
= 150mA
LED
LED
90
EN2 EN1
I
LED
0 (SHUTDOWN)
150mA
850mA
1A
LED
B
0
0
1
1
0
1
0
1
85
I
= 1A
LED
EN1 (TORCH)
EN2 (FLASH)
80
75
1MHz
BUCK-BOOST
V
I
C
SET1
70
65
60
R
20.5k
1%
I
ISET1
0.1 F
SET2
T
= 25°C
A
LTC3454
EFFICIENCY = (V
– V )I /V I
LED LED IN IN
R
3.65k
1%
OUT
ISET2
GND (EXPOSED PAD)
LED: LUMILEDS LXL-PWF1
L1: SUMIDA CDRH6D28-5RONC
3453 TA01a
3.1 3.5 3.9
4.7
2.7
5.1 5.5
4.3
(V)
V
IN
3454 TA01b
3454f
1
LTC3454
W W U W
U
W
U
ABSOLUTE AXI U RATI GS
PACKAGE/ORDER I FOR ATIO
(Note 1)
TOP VIEW
V , SW1, SW2, V
Voltage......................–0.3V to 6V
IN
OUT
, I
EN1
EN2
1
2
3
4
5
10 SW1
V , EN1, EN2, I
C
SET1 SET2
9
8
7
6
V
V
V
IN
Voltage.............................–0.3V to (V + 0.3V) or 6V
IN
I
I
11
SET1
C
LED Peak Current...................................................1.25A
Storage Temperature Range...................–65°C to 125°C
Operating Temperature Range (Note 2) ...–40°C to 85°C
Junction Temperature (Note 3) ............................. 125°C
SET2
LED
OUT
SW2
DD PACKAGE
10-LEAD (3mm × 3mm) PLASTIC DFN
T
= 125°C, θ = 40°C/W
EXPOSED PAD (PIN 11) IS GND, MUST BE SOLDERED TO PCB
JMAX
JA
ORDER PART NUMBER
LTC3454EDD
DD PART MARKING
LBQX
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.
The
●
denotes the specifications which apply over the full operating
ELECTRICAL CHARACTERISTICS
temperature range, otherwise specifications are at T = 25°C, V = 3.6V, R
= 20.5k unless otherwise noted. (Note 2)
A
IN
ISET
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
Input Supply Voltage (V )
●
2.7
5.5
V
IN
Input DC Supply Current
Normal Operation
Shutdown
(Typicals at V = 3.6V, R
= R = 20.5k)
ISET2
IN
ISET1
2.7V ≤ V ≤ 5.5V (Note 4)
825
0
5
1200
1
10
µA
µA
µA
IN
IN
2.7V ≤ V ≤ 5.5V; V
= V
= 0V
EN2
EN1
UVLO
V
< UVLO Threshold; V = V = V
IN
EN1
EN2
IN
Undervoltage Lockout Threshold
V
V
Rising
Falling
●
2.05
1.90
0.68
0.66
2.3
1.2
V
V
V
V
µA
mV
mV
IN
IN
1.75
V
V
V
, V
DC Threshold for Normal Operation (V )
DC Threshold for Shutdown (V )
Input Current
●
●
●
●
EN1 EN2
IH
, V
0.2
–1
780
788
EN1 EN2
IL
, V
EN1 EN2
1
812
812
I
and I
Servo Voltage
3.08k ≤ R ||R ≤ 20.5k
ISET1 ISET2
800
800
SET1
SET2
LED Output Current to Programming Current Ratio
LED Pin Voltage
I
I
/(I
+ I
), I = 500mA (Note 5)
●
●
3725
3775
3850
3850
3975
3925
mA/mA
mA/mA
LED ISET1
ISET2 LED
= 1A
105
5.15
170
130
3.4
mV
V
mΩ
mΩ
A
mA
µA
µA
LED
Regulated Maximum V
LED Pin Open, Programmed I
= 1A
LED
4.95
2.5
5.35
OUT
PMOS Switch R
Switches A and D (V
Switches B and C
Switch A
Switch D (V
Switches A, D
Switches B, C
= 3.6V)
ON
OUT
NMOS Switch R
ON
Forward Current Limit
Reverse Current Limit
PMOS Switch Leakage
NMOS Switch Leakage
Oscillator Frequency
Soft-Start Time
= 3.6V)
275
OUT
–1
–1
0.9
1
1
1.15
1.0
200
MHz
µs
Note 1: Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 3: T is calculated from the ambient temperature T and power
dissipation PD according to the following formula:
J
A
Note 2: The LTC3454 is guaranteed to meet specifications from 0°C to
70°C. Specifications over the –40°C to 85°C operating temperature range
are assured by design, characterization and correlation with statistical
process controls.
T = T + (PD • θ °C/W).
J A JA
Note 4: Dynamic supply current is higher due to the gate charge being
delivered at the switching frequency.
Note 5: This parameter is tested using a feedback loop which servos V
C
to 1.8V.
3454f
2
LTC3454
U W
TYPICAL PERFOR A CE CHARACTERISTICS
Undervoltage Lockout Threshold
vs Temperature
Enable Thresholds
vs Temperature
Enable Thresholds vs V
IN
2.4
2.3
2.2
2.1
2.0
1.9
1.8
1.7
1.6
1.5
1.4
1200
1100
1000
900
800
700
600
500
400
300
200
1200
1100
1000
900
800
700
600
500
400
300
200
T
= 25°C
V
= 3.6V
A
IN
V
RISING
IN
V
IH
V
IH
V
IL
V
IL
V
FALLING
IN
–55 –35 –15
5
25 45 65 85 105 125
–55 –35 –15
5
25 45 65 85 105 125
2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5
(V)
TEMPERATURE (°C)
TEMPERATURE (°C)
V
IN
3454 G01
3454 G02
3454 G03
I
Servo Voltage
SET1,2
vs Temperature
I
Servo Voltage vs V
I
Servo Voltage vs R
SET1,2 ISET
SET1,2
IN
812
808
812
808
804
800
812
808
804
800
V
= 3.6V
ISET1,2
T
= 25°C
ISET1
IN
V
T
= 3.6V
IN
A
A
R
= 15k
R
= R
= 15k
ISET2
= 25°C
804
800
796
796
792
788
796
792
788
792
788
4.3
(V)
5.1
5.5
2.7 3.1
3.5 3.9
V
4.7
–55 –35 –15
5
25 45 65 85 105 125
19
27
31
3
7
11
15
23
TEMPERATURE (°C)
R
(kΩ)
IN
ISET
3454 G05
3454 G04
3454 G06
LED Current Programming Ratio
vs Temperature
LED Current Programming Ratio
vs V
V
vs Temperature
IN
LED
4050
4000
3950
3900
3850
3800
3750
3700
3650
150
120
90
4050
4000
3950
3900
3850
3800
3750
3700
3650
V
= 3.6V
PROGRAMMED I
A
= 500mA
V
= 3.6V
IN
IN
LED
T
= 25°C
PROGRAMMED
I
= 1A
LED
PROGRAMMED
= 500mA
I
LED
60
30
0
PROGRAMMED
= 100mA
PROGRAMMED I
PROGRAMMED I
PROGRAMMED I
= 1A
= 500mA
= 150mA
LED
LED
LED
I
LED
25 45
TEMPERATURE (°C)
–55 –35 –15
5
65 85 105 125
4.3
(V)
25
5
TEMPERATURE (°C)
2.7 3.1 3.5 3.9
4.7 5.1 5.5
–55 –35 –15
45 65 85 105 125
V
IN
3454 G07
3454 G08
3454 G09
3454f
3
LTC3454
U W
TYPICAL PERFOR A CE CHARACTERISTICS
Maximum Regulated V
vs Temperature
Maximum Regulated V
OUT
OUT
V
vs V
IN
vs V
LED
IN
60
58
56
54
52
50
48
46
44
42
40
5.40
5.35
5.30
5.25
5.20
5.15
5.10
5.05
5.00
4.95
4.90
5.40
5.35
5.30
5.25
5.20
5.15
5.10
5.05
5.00
4.95
4.90
PROGRAMMED I
T
= 500mA
LED
PROGRAMMED I
A
= 1A
PROGRAMMED I
IN
= 1A
LED
LED
= 25°C
A
T
= 25°C
V
= 3.6V
2.7
3.5 3.9 4.3
(V)
4.7 5.1 5.5
3.1
3.5 3.9
V
2.7 3.1
4.3 4.7 5.1 5.5
(V)
25 45
–55 –35 –15
5
65 85 105 125
V
IN
TEMPERATURE (°C)
IN
3454 G10
3454 G12
3454 G11
Maximum Regulated V
OUT
PMOS R
vs Temperature
NMOS R
vs Temperature
DS(ON)
vs Programmed LED Current
DS(ON)
300
270
240
210
180
150
120
90
200
180
160
140
120
100
80
5.40
5.35
5.30
5.25
5.20
5.15
5.10
5.05
5.00
4.95
4.90
MEASURED AT 500mA
MEASURED AT 500mA
V
A
= 3.6V
IN
= 25°C
T
V
= 2.7V
IN
V
= 3.6V
IN
V
= 2.7V
V
IN
V
= 5.5V
IN
V
= 3.6V
IN
V
= 4.2V
IN
= 5.5V
IN
V
= 4.2V
IN
60
40
500 600
100 200 300 400
700 800 900 1000
(mA)
–55 –35 –15
5
25 45
125
–55 –35 –15
5
25 45
125
65 85 105
65 85 105
TEMPERATURE (°C)
TEMPERATURE (°C)
PROGRAMMED I
LED
3454 G13
3454 G14
3454 G15
Oscillator Frequency
vs Temperature
LED Power Efficiency
vs LED Current
1100
1080
1060
1040
1020
1000
980
100
V
= 3V
OUT
95
90
85
80
75
70
65
60
V
V
= 5.5V
= 2.7V
IN
IN
V
= 4.2V
= 3.6V
IN
V
IN
5
960
V
A
= 3.6V
IN
940
T
= 25°C
EFFICIENCY = (V
– V )I /V I
LED LED IN IN
920
OUT
FRONT PAGE APPLICATION
900
500 600
100 200 300 400
700 800 900 1000
–55 –35 –15
25 45 65 85 105 125
TEMPERATURE (°C)
I
(mA)
LED
3454 G17
3454 G16
3454f
4
LTC3454
U W
TYPICAL PERFOR A CE CHARACTERISTICS
Output Voltage Ripple
Back Page Application
Start-Up Transient
Back Page Application
CH1, V
1V/DIV
OUT
CH2, I
LED
500mA
FINAL VALUE
20mV/DIV
0V, 0A
0V
CH3, V
1V/DIV
EN1
3454 G19
3454 G19
V
I
= 3.6V
LED
5ms/DIV
V
I
= 3.6V
LED
500ns/DIV
IN
IN
= 500mA
= 500mA
U
U
U
PI FU CTIO S
V
(Pin7):Buck-BoostOutputRail. BypasstoGNDwith
EN1 (Pin 1): Enable Input Pin for I
Current.
OUT
SET1
SET2
a ceramic capacitor. Recommended value is 10µF.
EN2 (Pin 2): Enable Input Pin for I
Current.
V (Pin 8): Compensation Point for the Internal Error
C
I
(Pin 3): LED Current Programming Pin. A resistor
SET1
Amplifier Output. Connect a ceramic capacitor from V
C
to ground programs the current through the LED to I
LED
to GND. Recommended value is 0.1µF.
= 3850(0.8V/R
amount set by EN2/I
). This amount of current adds to any
ISET1
V (Pin 9): Voltage Input Supply Pin (2.7V ≤ V ≤ 5.5V).
if used.
IN
IN
SET2
Bypass to GND with a ceramic capacitor. Recommended
I
(Pin 4): LED Current Programming Pin. A resistor
SET2
value is 10µF.
to ground programs the current through the LED to I
LED
SW1 (Pin 10): Switching Node. External inductor con-
nects between SW1 and SW2. Recommended value is
4.7µH/5µH.
= 3850(0.8V/R
amount set by EN1/I
). This amount of current adds to any
ISET2
if used.
SET1
LED (Pin 5): Low Dropout Output for LED Current Biasing.
Connect the LED between V and the LED pin.
Exposed Pad (Pin 11): Ground Pin. Solder to PCB ground
for electrical contact and optimal thermal performance.
OUT
SW2 (Pin 6): Switching Node. External inductor con-
nects between SW1 and SW2. Recommended value is
4.7µH/5µH.
3454f
5
LTC3454
W
BLOCK DIAGRA
OPTIONAL
OPTIONAL
10
6
V
7
SW1
SW2
OUT
V
SWITCH A
SWITCH D
IN
9
V
IN
2.7V TO 5.5V
GATE
DRIVERS
AND
ANTICROSS-
CONDUCTION
SWITCH B
SWITCH C
UNDERVOLTAGE
LOCKOUT
UV
FORWARD
CURRENT
LIMIT
REVERSE
CURRENT
LIMIT
+
–
+
–
OVERTEMP
PROTECTION
OT
3.4A
275mA
BANDGAP
REFERENCE
1.23V
+
–
LOGIC
+
–
AB PWM
COMPARATOR
CD PWM
COMPARATOR
UV
OT
1MHz
OSCILLATOR
V
C
8
SAFETY
ERROR AMP
AUTOZEROING
ERROR AMP
V
LED
OUT
1.23V
–
+
–
+
5
377k
123k
R
SOFT
1.23V
START
CLAMP
LED CURRENT
SETTING AMP 1
800mV
800mV
+
–
CURRENT
MIRROR
I
I
ISET1
I
I
SET1
∑
3
I
3850 I
R
R
R
ISET1
LED CURRENT
SETTING AMP 2
+
–
ISET2
SET2
4
1
EN1
EN2
ISET2
SHUTDOWN
2
EXPOSED PAD (GND)
11
3454 BD
3454f
6
LTC3454
U
OPERATIO
Buck-Boost DC-DC Converter
each cycle. During the off time of switch A, synchronous
rectifier switch B turns on for the remainder of the cycle.
Switches A and B will alternate conducting similar to a
typical synchronous buck regulator. As the control volt-
age increases, the duty cycle of switch A increases until
the maximum duty cycle of the converter in buck mode
The LTC3454 employs an LTC proprietary buck-boost
DC/DCconvertertogeneratetheoutputvoltagerequiredto
drive a high current LED. This architecture permits high-
efficiency, low noise operation at input voltages above,
below or equal to the output voltage by properly phasing
fourinternalpowerswitches.Theerrorampoutputvoltage
reaches DC
|max given by:
BUCK
on the V pin determines the duty cycle of the switches.
DC
|max = 100% – DC
BUCK 4SW
C
Since the V pin is a filtered signal, it provides rejection
C
where DC
equals the duty cycle in % of the “four
4SW
switch” range.
of frequencies well below the factory trimmed switching
frequency of 1MHz. The low R
, low gate charge
DS(ON)
DC = (150ns • f) • 100%
synchronousswitchesprovidehighfrequencypulsewidth
modulation control at high efficiency. Schottky diodes
across synchronous rectifier switch B and synchronous
rectifier switch D are not required, but if used do provide
a lower voltage drop during the break-before-make time
(typically 20ns), which improves peak efficiency by typi-
cally 1% to 2% at higher loads.
4SW
where f is the operating frequency in Hz.
Beyond this point the “four switch” or buck-boost region
is reached.
Buck-Boost or Four-Switch Mode (V ≈ V
)
IN
OUT
Referring to Figure 2, when the control voltage V is above
C
Figure1showsasimplifieddiagramofhowthefourinternal
voltage V2, switch pair AD continue to operate for duty
power switches are connected to the inductor, V , V
IN OUT
cycle DC
|max, and the switch pair AC begins to phase
BUCK
and GND. Figure 2 shows the regions of operation of the
in. As switch pair AC phases in, switch pair BD phases out
buck-boost as a function of the control voltage V . The
C
accordingly. When the V voltage reaches the edge of the
C
outputswitchesareproperlyphasedsotransitionsbetween
regionsofoperationarecontinuous, filteredandtranspar-
buck-boostrangeatvoltageV3, switchpairACcompletely
phases out switch pair BD and the boost region begins at
enttotheuser.WhenV approachesV ,thebuck-boost
IN
OUT
duty cycle DC . The input voltage V where the four
4SW
IN
region is reached where the conduction time of the four
switch region is typically 150ns. Referring to Figures 1
switch region begins is given by:
and 2, the various regions of operation encountered as V
V = V /[1 – (150ns • f)]
C
IN
OUT
increaseswillnowbedescribed.
and the input voltage V where the four switch region
IN
ends is given by
Buck Mode (V > V
)
OUT
IN
V = V
• (1 – DC
) = V • [1 – (150ns • f)]
OUT
IN
OUT
4SW
In buck mode, switch D is always on and switch C is
always off. Referring to Figure 2, when the control
75%
voltage V is above voltage V1, switch A begins to turn on
C
D
MAX
V4 (2.1V)
BOOST
A ON, B OFF
BOOST REGION
BUCK REGION
V
V
IN
OUT
7
PWM CD SWITCHES
D
9
MIN
V3 (1.65V)
BOOST
BUCK/BOOST REGION
FOUR SWITCH PWM
D
MAX
PMOS A
PMOS D
NMOS C
V2 (1.55V)
BUCK
0%
SW1
10
SW2
6
D ON, C OFF
PWM AB SWITCHES
V1 (0.9V)
NMOS B
DUTY
CYCLE
CONTROL
VOLTAGE, V
3454 F02
3454 F01
C
Figure 2. Switch Control vs Control Voltage, V
Figure 1. Simplified Diagram of Internal Power Switches
C
3454f
7
LTC3454
U
W U U
APPLICATIO S I FOR ATIO
Boost Mode (V < V
)
limiting the rate of duty cycle change as V transitions
IN
OUT
C
from the buck region through the buck-boost region into
the boost region. Once the soft-start times out, it can only
be reset by entering shutdown, or by an undervoltage or
overtemperature condition.
Inboostmode,switchAisalwaysonandswitchBisalways
off. Referring to Figure 2, when the control voltage V is
C
above voltage V3, switches C and D will alternate conduct-
ing similar to a typical synchronous boost regulator. The
maximum duty cycle of the converter is limited to 88%
Autozero Error Amp
typical and is reached when V is above V4.
C
The error amplifier is an autozeroing transconductance
amp with source and sink capability. The output of this
Forward Current Limit
amplifier drives a capacitor to GND at the V pin. This
C
If the current delivered from V through PMOS switch A
IN
capacitor sets the dominant pole for the regulation loop.
(See the Applications Information section for selecting
the capacitor value). The feedback signal to the error
amp is developed across a resistor through which LED
current flows.
exceeds 3.4A (typical), switch A is shut off immediately.
Switches B and D are turned on for the remainder of the
cycle in order to safely discharge the forward inductor
current at the maximum rate possible.
Reverse Current Limit
Safety Error Amp
If the current delivered from V
backwards through
OUT
The safety error amplifier is a transconductance amplifier
with sink only capability. In normal operation, it has no
effectontheloopregulation.However,iftheLEDpinopen-
circuits, the output voltage will keep rising, and the safety
errorampwilleventuallytakeovercontroloftheregulation
PMOS switch D exceeds 275mA (typical), switch D is
shut off immediately. Switches A and C are turned on for
the remainder of the cycle in order to safely discharge the
reverse inductor current at the maximum rate possible.
looptopreventV runaway.TheV thresholdatwhich
OUT
OUT
Undervoltage Lockout
this occurs is approximately 5.15V.
TopreventoperationofthepowerswitchesathighR
,
DS(ON)
an undervoltage lockout is incorporated on the LTC3454.
Whentheinputsupplyvoltagedropsbelowapproximately
1.90V, the four power switches and all control circuitry
are turned off except for the undervoltage block, which
draws a few microamperes.
LED Current Programming and Enable Circuit
Two enable pins work in conjunction with dual external
resistors to program LED current to one of three nonzero
settings. The table below explains how the current can
be set.
Overtemperature Protection
EN1
EN2
GND
GND
I
(A)
LOAD
GND
0 (SHUTDOWN)
If the junction temperature of the LTC3454 exceeds 130°C
for any reason, all four switches are shut off immediately.
The overtemperature protection circuit has a typical hys-
teresis of 11°C.
V
3850 • 0.8V/R
3850 • 0.8V/R
IN
ISET1
ISET2
GND
V
IN
V
V
3850 • (0.8V/R
+ 0.8V/R
)
IN
IN
ISET1
ISET2
Soft-Start
With either enable pin pulled high, the buck-boost will
regulate the output voltage at the current programmed
The LTC3454 includes an internally fixed soft-start which
is active when powering up or coming out of shutdown.
by R
and/or R
.
ISET1
ISET2
The soft-start works by clamping the voltage on the V
C
With both enable pins pulled to GND, the LTC3454 is in
shutdown and draws zero current. The enable pins are
high impedance inputs and should not be floated.
node and gradually releasing it such that it requires 200µs
to linearly slew from 0.9V to 2.1V. This has the effect of
3454f
8
LTC3454
U
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APPLICATIO S I FOR ATIO
Input Capacitor Selection
COMPONENT SELECTION
SincetheV pinisthesupplyvoltagefortheICitisrecom-
IN
mendedtoplaceatleasta2.2µF,lowESRbypasscapacitor
Inductor Selection
toground.SeeTable2foralistofcomponentsuppliers.
The high frequency operation of the LTC3454 allows the
use of small surface mount inductors. The inductor cur-
rent ripple is typically set to 20% to 40% of the maximum
averageinductorcurrent. Foragivenrippletheinductance
term in Boost mode is:
Table 2. Capacitor Vendor Information
SUPPLIER
AVX
Sanyo
Taiyo Yuden
TDK
WEB SITE
www.avxcorp.com
www.sanyovideo.com
www.t-yuden.com
www.component.tdk.com
V
2 • VOUT – V
•100%
(
)
IN(MIN)
IN(MIN)
L >
2
f •IOUT(MAX) •%Ripple• VOUT
Output Capacitor Selection
The bulk value of the capacitor is set to reduce the ripple
due to charge into the capacitor each cycle. The steady
state ripple due to charge is given by:
and in Buck mode is:
V
IN(MAX) – VOUT • VOUT •100%
(
)
L >
f • VIN(MAX) •%Ripple •I OUT
IOUT(MAX) • VOUT – V
•100%
(
)
IN(MIN)
COUT • VOUT2 • f
%Ripple_Boost =
where f = operating frequency, Hz
%Ripple = allowable inductor current ripple, %
V
IN(MAX) – VOUT •100%
(
)
V
V
V
= minimum input voltage, V
= maximum input voltage, V
IN(MIN)
IN(MAX)
%Ripple_Buck =
8• VIN(MAX) • f2 •L •COUT
where C
= output filter capacitor, F
= output voltage, V
OUT
OUT
The output capacitance is usually many times larger in
ordertohandlethetransientresponseoftheconverter.For
a rule of thumb, the ratio of operating frequency to unity-
gain bandwidth of the converter is the amount the output
capacitance will have to increase from the above calcula-
tions in order to maintain desired transient response.
I
= maximum output load current
OUT(MAX)
For high efficiency, choose an inductor with a high fre-
quencycorematerial, suchasferrite, toreducecoreloses.
The inductor should have low ESR (equivalent series
2
resistance) to reduce the I R losses, and must be able
to handle the peak inductor current without saturating.
Molded chokes or chip inductors usually do not have
enough core to support peak inductor currents >1A. To
minimize radiated noise, use a toroid, pot core or shielded
bobbin inductor. For white LED application, a 4.7µH/5µH
inductor value is recommended. See Table 1 for a list of
component suppliers.
The other component of ripple is due to ESR (equivalent
series resistance) of the output capacitor. Low ESR ca-
pacitors should be used to minimize output voltage ripple.
For surface mount applications, Taiyo Yuden, TDK, AVX
ceramic capacitors, AVX TPS series tantalum capacitors
or Sanyo POSCAP are recommended. For the white LED
application, a 10µF capacitor value is recommended. See
Table 2 for a list of component suppliers.
Table 1. Inductor Vendor Information
SUPPLIER
WEB SITE
Coilcraft
www.coilcraft.com
Optional Schottky Diodes
Cooper/Coiltronics www.cooperet.com
Murata
Sumida
Toko
www.murata.com
www.japanlink.com/sumida
www.toko.com
Schottky diodes across the synchronous switches B and
D are not required, but provide a lower drop during the
break-before-make time (typically 20ns) of the NMOS to
PMOS transition, improving efficiency. Use a Schottky
Vishay-Dale
www.vishay.com
diode such as an MBRM120T3 or equivalent. Do not use
3454f
9
LTC3454
U
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APPLICATIO S I FOR ATIO
ordinary rectifier diodes, since the slow recovery times where g is the error amp transconductance (typically
m
will compromise efficiency.
1/5.2k) and C is the external capacitor to GND at the
VC
V pin. For the white LED application, a 0.1µF or greater
C
In applications in which V is greater than 4V and V
to
OUT
IN
capacitor value is recommended.
GND short-circuit protection is needed, a Schottky diode
such as MBRM12OT3 or equivalent may be used from
SW1 to GND and/or a 2Ω/1nF series snubber from SW1
to GND. The Schottky diode should be added as close
to the pins as possible. Neither of these is required for
shorted LED protection.
Maximum LED Current
As described in the Operation section, the output LED
current with both enable pins logic high is equal to
I
= 3850 [0.8V/(R
|| R )]
ISET2
LED
ISET1
Sincethemaximumcontinuousoutputcurrentislimitedto
1A, this sets a minimum limit on the parallel combination
Closing the Feedback Loop
The LTC3454 incorporates voltage mode PWM control.
The control to output gain varies with operation region
(Buck, Boost, Buck/Boost), but is usually no greater
than 15. The output filter exhibits a double pole response
givenby:
of R
and R
equal to
ISET1
ISET2
R
MIN
= (R
|| R
)|
= 3850(0.8V/1A)
ISET1
= 3080Ω
ISET2 MIN
Although the LTC3454 can safely provide this current
continuously, the external LED may not be rated for this
high a level of continuous current. Higher current levels
are generally reserved for pulsed applications, such as
LED camera flash. This is accomplished by programming
1
fFILTER_POLE
=
Hz
2 • π • L •COUT
where C
is the output filter capacitor.
OUT
a high current with one of the R
the appropriate enable pin.
resistors and pulsing
ISET
The output filter zero is given by:
1
fFILTER_ZERO
=
Hz
Varying LED Brightness
2 • π •RESR •COUT
Continuously variable LED brightness control can be
achieved by interfacing directly to one or both of the I
whereR isthecapacitorequivalentseriesresistance.
ESR
SET
A troublesome feature in Boost mode is the right-half
plane zero (RHP), and is given by:
pins. Figure 3 shows four such methods employing a
voltage DAC, a current DAC, a simple potentiometer or a
PWM input. It is not recommended to control brightness
by PWMing the enable pins directly as this will toggle
the LTC3454 in and out of shutdown and result in erratic
operation.
2
V
IN
fRHPZ
=
Hz
2• π •IOUT •L•VOUT
The loop gain is typically rolled off before the RHP zero
frequency.
LED Failure Modes
AsimpleTypeIcompensationnetworkcanbeincorporated
to stabilize the loop but at a cost of reduced bandwidth
and slower transient response. To ensure proper phase
margin, the loop is required to be crossed over a decade
before the LC double pole.
IftheLEDfailsasanopencircuit, thesafetyamplifiertakes
control of the regulation loop to prevent V
runaway.
OUT
The V
threshold at which this occurs is about 5.15V.
OUT
The safety amplifier has no effect on loop regulation at
less than 5.15V.
V
OUT
The unity-gain frequency of the error amplifier with the
Type I compensation is given by:
If the LED fails as a short-circuit, the current limiting
circuitry detects this condition and limits the peak input
current to a safe level.
gm
2 • π •CVC
fUG
=
3454f
10
LTC3454
U
W U U
APPLICATIO S I FOR ATIO
V
IN
V
V
V
OUT
OUT
IN
ENx
ENx
LTC3454
LTC3454
I
I
SETx
LED
SETx
LED
0.8V – V
DAC
I
= 3850
I
= 3850 • IDAC
LED
LED
0.8V
R
≥ R
R
SET
MIN
SET
IDAC ≤
R
MIN
VOLTAGE
DAC
CURRENT
DAC
V
DAC
(3a)
(3b)
V
IN
V
V
V
OUT
OUT
IN
ENx
ENx
LTC3454
LTC3454
I
I
SETx
LED
SETx
LED
0.8V
+ R
0.8V – V
PWM
R
SET
R
100
R
SET
MIN
POT
I
= 3850
I
= 3850
= 3850
R
≥ R
MIN
LED
LED
SET
R
MIN
POT
V
PWM
0.8V – (DC% • V
)
R
DVCC
R
SET
DV
CC
f
≥ 10kHz
PWM
(3c)
(3d)
3454 F03
Figure 3. Brightness control Methods: (a) Using Voltage DAC, (b) Using Current DAC, (c) Using Potentiometer, (d) Using PWM Input
U
PACKAGE DESCRIPTIO
DD Package
10-Lead Plastic DFN (3mm × 3mm)
(Reference LTC DWG # 05-08-1699)
R = 0.115
0.38 0.10
TYP
6
10
0.675 0.05
3.50 0.05
2.15 0.05 (2 SIDES)
1.65 0.05
3.00 0.10
(4 SIDES)
1.65 0.10
(2 SIDES)
PIN 1
TOP MARK
(SEE NOTE 6)
PACKAGE
OUTLINE
(DD10) DFN 1103
5
1
0.25 0.05
0.50 BSC
0.75 0.05
0.200 REF
0.25 0.05
0.50
BSC
2.38 0.10
(2 SIDES)
2.38 0.05
(2 SIDES)
0.00 – 0.05
BOTTOM VIEW—EXPOSED PAD
RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS
NOTE:
1. DRAWING TO BE MADE A JEDEC PACKAGE OUTLINE M0-229 VARIATION OF (WEED-2).
4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE
MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.15mm ON ANY SIDE
CHECK THE LTC WEBSITE DATA SHEET FOR CURRENT STATUS OF VARIATION ASSIGNMENT 5. EXPOSED PAD SHALL BE SOLDER PLATED
2. DRAWING NOT TO SCALE
3. ALL DIMENSIONS ARE IN MILLIMETERS
6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION ON THE
TOP AND BOTTOM OF PACKAGE
3454f
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-
tation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
11
LTC3454
U
TYPICAL APPLICATIO
500mA LED Flashlight Driver
L1
4.7 H
LED Power Efficiency vs V
IN
100
95
90
85
80
75
70
65
60
I
= 500mA
LED
V
SW1
SW2
SWD
V
OUT
2.2 F
4.7 F
LED
IN
3-CELL
ALKALINE
4.5V
SWA
SWB
EN1
LED
EN2
SWC
1MHz
BUCK-BOOST
I
= 500mA
V
C
I
LED
A
SET1
T
= 25°C
R
6.19k
1%
I
ISET1
0.1 F
EFFICIENCY = (V
– V )I /V
I
SET2
OUT
LED LED IN IN
LTC3454
4.3 4.7
(V)
2.7 3.1 3.5 3.9
5.1 5.5
GND (EXPOSED PAD)
3453 TA02
V
IN
3454 TA02b
LED: LUMILEDS, LXCL LW3C
L1: TOKO A997AS-4R7M
RELATED PARTS
PART NUMBER
DESCRIPTION
COMMENTS
V : 1.6V to 18V, V
MS10 Package/EDD Package
LT1618
Constant Current, Constant Voltage 1.4MHz, High Efficiency
Boost Regulator
= 34V, I = 1.8mA, I = <1µA,
OUT(MAX) Q SD
IN
LT1930/LT1930A 1A (I ), 1.2MHz/2.2MHz, High Efficiency Step-Up
V : 2.6V to 16V, V
ThinSOT Package
= 34V, I = 4.2mA/5.5mA, I = <1µA,
OUT(MAX) Q SD
SW
IN
DC/DC Converter
LT1932
Constant Current, 1.2MHz, High Efficiency White LED
Boost Regulator
V : 1V to 10V, V
ThinSOT Package
= 34V, I = 1.2mA, I = <1µA,
OUT(MAX) Q SD
IN
LT1937
Constant Current, 1.2MHz, High Efficiency White LED
Boost Regulator
V : 2.5V to 10V, V
ThinSOT Package/SC70 Package
= 34V, I = 1.9mA, I = <1µA,
OUT(MAX) Q SD
IN
LTC3205
LTC3215
LTC3216
High Efficiency, Multi-Display LED Controller
V : 2.8V to 4.5V, V
QFN-24 Package
= 6V, I = 50µA, I = <1µA,
Q SD
IN
OUT(MAX)
OUT(MAX)
OUT(MAX)
OUT(MAX)
700mA Low Noise Charge Pump LED Driver
V : 2.9V to 4.4V, V
= 5.5V, I = 300µA, I = <2.5µA,
Q SD
IN
DFN Package
1A Low Noise High Current Charge Pump LED
Driver with Independent Flash/Torch Current
V : 2.9V to 4.4V, V
= 5.5V, I = 300µA, I = <2.5µA,
Q SD
IN
DFN Package
LTC3440/
LTC3441
600mA/1.2A I , 2MHz/1MHz, Synchronous Buck-Boost
V : 2.4V to 5.5V, V
= 5.25V, I = 25µA/50µA, I = <1µA,
Q SD
OUT
IN
DC/DC Converter
MS-10 Package/DFN Package
LTC3443
LTC3490
LTC3453
600mA/1.2A I , 600kHz, Synchronous Buck-Boost
DC/DC Converter
V : 2.4V to 5.5V, V
DFN Package
= 5.25V, I = 28µA, I = <1µA,
OUT(MAX) Q SD
OUT
IN
Single Cell 350mA LED Driver
V : 1V to 3.2V, V
IN
= 4V, I = 20µA, I = 20µA,
OUT(MAX) Q SD
DFN Package
Synchronous Buck-Boost High Power White LED Driver
V : 2.7V to 5.5V, Up to 500mA Continuous Output Current,
IN
QFN-16 Package
LT3465/LT3465A Constant Current, 1.2MHz/2.7MHz, High Efficiency White LED
Boost Regulator with Integrated Schottky Diode
V : 2.7V to 16V, V
ThinSOT Package
= 34V, I = 1.9mA, I = <1µA,
Q SD
IN
OUT(MAX)
OUT(MAX)
OUT(MAX)
LT3466
Dual Constant Current, 2MHz, High Efficiency White LED
Boost Regulator with Integrated Schottky Diode
V : 2.7V to 24V, V
= 40V, I = 5mA, I = <16µA,
Q SD
IN
DFN Package
LT3479
3A, Full Featured DC/DC Converter with Soft-Start and
Inrush Current Protection
V : 2.5V to 24V, V
= 40V, I = 6.5mA, I = <1µA,
Q SD
IN
DFN Package/TSOPP Package
3454f
LT 1105 • PRINTED IN USA
LinearTechnology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
12
●
●
(408) 432-1900 FAX: (408) 434-0507 www.linear.com
© LINEAR TECHNOLOGY CORPORATION 2005
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