LTC3453EUF#PBF [Linear]
LTC3453 - Synchronous Buck-Boost High Power White LED Driver; Package: QFN; Pins: 16; Temperature Range: -40°C to 85°C;
| 型号： | LTC3453EUF#PBF |
| 厂家： | 
Linear |
| 描述： | LTC3453 - Synchronous Buck-Boost High Power White LED Driver; Package: QFN; Pins: 16; Temperature Range: -40°C to 85°C 驱动器 |
| 文件： | 总12页 (文件大小：191K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
LTC3453
Synchronous Buck-Boost
High Power White LED Driver
U
DESCRIPTIO
FEATURES
■
High Efficiency: 90% Typical Over Entire
The LTC®3453 is a synchronous buck-boost DC/DC con-
verter optimized for driving up to 4 white LEDs at a
combined current of up to 500mA from a single Li-Ion
battery input. The regulator operates in either synchro-
nous buck, synchronous boost, or buck-boost mode,
depending on input voltage and LED maximum forward
voltage. Optimum efficiency is achieved using a propri-
etary architecture that determines which LED requires the
largest forward voltage drop at its programmed current,
and regulates the common output rail for lowest dropout.
Efficiency of 90% can be achieved over the entire usable
range of a Li-Ion battery (2.7V to 4.2V).
Li-Ion Battery Range
■
Wide VIN Range: 2.7V to 5.5V
Up to 500mA Continuous Output Current
Internal Soft-Start
Open/Shorted LED Protection
LED Current Matching Typically <2%
Constant Frequency 1MHz Operation
Low Shutdown Current: 6µA
Overtemperature Protection
Small Thermally Enhanced 16-Lead (4mm x 4mm)
QFN Package
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■
■
■
■
■
■
■
■
LEDcurrentisprogrammabletooneoffourlevels(includ-
ing shutdown) with dual current setting resistors and dual
enable pins. In shutdown, the supply current is only 6µA.
APPLICATIO S
■
Cell Phones
■
Digital Cameras
A high constant operating frequency of 1MHz allows the
use of a small external inductor. The LTC3453 is offered
in a low profile (0.75mm) thermally enhanced 16-lead
(4mm x 4mm) QFN package.
■
PDAs
■
Portable Devices
, LTC and LT are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
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TYPICAL APPLICATIO
High Efficiency Torch/Flash LED Driver
L1
4.7µH
Torch Mode Efficiency vs V
IN
V
IN
100
90
80
70
60
50
180
160
140
120
100
80
1-CELL
Li-Ion
150mA/500mA
V
PV
SW1
SW2
V
OUT
2.2µF
4.7µF
IN
IN
2.7V to 4.2V
EFFICIENCY
D1
LED1
LED2
LED3
LED4
I
1MHz
BUCK-BOOST
IN
V
C
EN1
EN2
SET1
SET2
0.1µF
EN1 (TORCH)
EN2 (FLASH)
I
= 150mA
LED
= 25°C
D1: LUMILEDS LXCL-PWF1
L1: VISHAY DALE IDCS-2512
T
A
I
I
2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5
(V)
EN1 EN2
I
LED
V
8.25k
1%
IN
0
1
0
1
0
0
1
1
0 (SHUTDOWN)
150mA
3453 TA01b
LTC3453
3453 TA01a
3.48k
1%
350mA
500mA
GND
GND
PGND
3453fa
1
LTC3453
W W
U W
U
W
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ABSOLUTE AXI U RATI GS
PACKAGE/ORDER I FOR ATIO
(Note 1)
TOP VIEW
VIN, PVIN, SW1, SW2, VOUT Voltage ............ –0.3V to 6V
LED1 to LED4 Voltage ...... –0.3V to (VOUT + 0.3V) or 6V
VC, EN1, EN2,
16 15 14 13
V
1
2
3
4
12
V
C
IN
I
SET1, ISET2 Voltage .......... –0.3V to (VIN + 0.3V) or 6V
EN1
SET1
11 EN2
17
I
I
10
9
LED1 to LED4 Peak Current ................................ 250mA
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
LED1
LED4
5
6
7
8
UF PACKAGE
16-LEAD (4mm × 4mm) PLASTIC QFN
TJMAX = 125°C, θJA = 40°C/W, θJC = 2.6°C/W
EXPOSED PAD (PIN 17) IS PGND, MUST BE SOLDERED TO PCB
ORDER PART NUMBER
LTC3453EUF
UF PART MARKING
3453
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.
ELECTRICAL CHARACTERISTICS
The
●
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T = 25°C, V = V = 3.6V unless otherwise noted. (Note 2)
OUT
A
IN
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
Input Supply Voltage
●
2.7
5.5
V
Input DC Supply Current
Normal Operation
Shutdown
2.7V ≤ V ≤ 5.5V, R
||R
= 51.1k, I = 0 (Note 4)
LEDx
= 0V
0.6
6
3
1
18
5
mA
µA
µA
IN
ISET1 ISET2
2.7V ≤ V ≤ 5.5V; V
= V
IN
EN1
EN2
UVLO
V
< UVLO Threshold
IN
Undervoltage Lockout Threshold
V
V
Rising
Falling
●
2
1.9
2.3
V
V
IN
IN
1.6
EN1,2 DC Threshold for Normal Operation
2.7V ≤ V ≤ 5.5V, V
Rising
Falling
●
●
●
0.65
0.63
1
V
V
IN
EN1,2
EN1,2
EN1,2 DC Threshold for Shutdown (I
EN1,2 Input Current
= 0) 2.7V ≤ V ≤ 5.5V, V
0.2
–1
LEDx
IN
V
= 3.6V
1
µA
EN1,2
I
Servo Voltage
R
R
= 4.12k, 0°C ≤ T ≤ 85°C
788
780
800
800
812
812
mV
mV
SET1,2
ISET1,2
ISET1,2
A
= 4.12k, –40°C ≤ T ≤ 85°C
●
●
A
LED Output Current Ratio
LED Output Current Matching
LED Pin Drain Voltage
I
/(I
+ I
), I
SET2 LEDx
= 75mA, V = 300mV,
LEDx
365
357
384
384
403
403
mA/mA
mA/mA
LED SET1
2.7V ≤ V ≤ 5.5V
IN
(MAX – MIN)/[(MAX + MIN)/2] • 100%, I
= 75mA
2
6
%
LEDx
V
= 300mV
= 75mA
= 0V
LEDx
I
130
4.5
mV
V
LEDx
Regulated Maximum V
V
●
4.4
4.6
OUT
LEDx
PMOS Switch R
NMOS Switch R
Switches A and D, @ 100mA
Switches B and C, @ 100mA
Switch A
0.3
Ω
ON
ON
0.25
1612
200
Ω
Forward Current Limit
Reverse Current Limit
1125
2100
mA
mA
3453fa
Switch D
2
LTC3453
ELECTRICAL CHARACTERISTICS
The
temperature range, otherwise specifications are at T = 25°C, V = V
OUT
●
denotes the specifications which apply over the full operating
= 3.6V unless otherwise noted. (Note 2)
A
IN
PARAMETER
CONDITIONS
MIN
TYP
MAX
1
UNITS
µA
PMOS Switch Leakage
NMOS Switch Leakage
Oscillator Frequency
Soft-Start Time
Switches A and D
Switches B and C
●
●
1
µA
0.9
1
1.1
MHz
ms
0.65
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 3: T is calculated from the ambient temperature T and power
J A
dissipation P according to the following formula:
D
T = T + (P • θ °C/W).
J
A
D
JA
Note 4: Dynamic supply current is higher due to the gate charge being
delivered at the switching frequency.
Note 2: The LTC3453E 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.
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TYPICAL PERFOR A CE CHARACTERISTICS
Input DC Supply Current in
Shutdown vs Temperature
Undervoltage Lockout Threshold
vs Temperature
I
Servo Voltage vs
SET1,2
Temperature
20
18
16
14
12
10
8
2.2
2.1
2.0
1.9
1.8
1.7
812
808
804
800
796
792
788
FRONT PAGE APPLICATION
V
= 3.6V
IN
R
= 8.25k
ISET1,2
V
= 5.5V
IN
V
RISING
IN
V
= 4.2V
IN
V
= 3.6V
IN
V
FALLING
IN
V
= 2.7V
IN
6
4
2
0
–55 –35 –15
5
25 45 65 85 105 125
–55 –35 –15
5
25 45 65 85 105 125
–55 –35 –15
5
25 45 65 85 105 125
TEMPERATURE (°C)
TEMPERATURE (°C)
TEMPERATURE (°C)
3453 G01
3453 G02
3453 G04
Regulated Maximum V
Temperature
vs
Oscillator Frequency vs
Temperature
OUT
I
Servo Voltage vs V
SET1,2
IN
812
808
804
800
796
792
788
4.55
4.54
4.53
4.52
4.51
4.50
4.49
4.48
4.47
4.46
4.45
1050
1040
1030
1020
1010
1000
990
T
= 25°C
V
= 3.6V
V
OUT
= 3V
A
IN
V
IN
= 5.5V
R
= 8.25k
ALL LED PINS OPEN
ISET1,2
V
= 4.2V
IN
V
= 3.6V
IN
V
IN
= 2.7V
980
970
960
950
2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5
(V)
–55 –35 –15
5
25 45 65 85 105 125
–55 –35 –15
5
25 45 65 85 105 125
V
TEMPERATURE (°C)
TEMPERATURE (°C)
IN
3453 G05
3453 G06
3453 G07
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LTC3453
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TYPICAL PERFOR A CE CHARACTERISTICS
Efficiency vs LED Current
Output Voltage Ripple
Startup Transient
100
90
80
70
60
50
FRONT PAGE APPLICATION
/P , V = 3.6V, T = 25°C
P
LED IN IN
A
CH1, V
OUT
2V/DIV
20mV/DIV
AC COUPLED
0V
CH2, EN1
1V/DIV
0V
3453 G08
3453 G09
5µs/DIV
1ms/DIV
FRONT PAGE APPLICATION
FRONT PAGE APPLICATION
V
LED
= 3.6V
V
LED
= 3.6V
IN
IN
100 150 200 250 300 350 400 450 500
I
= 150mA
I
= 150mA
LED CURRENT (mA)
3453 G07
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PI FU CTIO S
VIN (Pin 1): Signal Voltage Input Supply Pin [2.7V ≤ VIN ≤
5.5V]. Recommended bypass capacitor to GND is 2.2µF
ceramic or larger. Connect to PVIN (Pin 16).
EN2 (Pin 11): Enable Input Pin for ISET2 Current.
VC (Pin 12): Compensation Point for the Internal Error
AmplifierOutput.Recommendedcompensationcapacitor
to GND is 0.1µF ceramic or larger.
EN1 (Pin 2): Enable Input Pin for ISET1 Current.
ISET1 (Pin 3): White Led Current Programming Pin. A
resistortogroundprogramseachcurrentsourceoutputto
ILED = 384(0.8V/RISET1). This amount of current adds to
any amount set by EN2/ISET2 if also used.
VOUT (Pin 13): Buck-Boost Output Pin. Recommended
bypass capacitor to GND is 4.7µF ceramic.
SW2 (Pin 14): Switching Node Pin. Connected to internal
power switches C and D. External inductor connects
between SW1 and SW2. Recommended value is 4.7µH.
LED1 to LED4 (Pins 4, 6, 7, 9): Individual Low Dropout
Current Source Outputs for White LED Current Biasing.
Connect each white LED between VOUT and an individual
LEDx pin. Unused LEDx outputs should be connected to
SW1 (Pin 15): Switching Node Pin. Connected to internal
power switches A and B. External inductor connects
between SW1 and SW2. Recommended value is 4.7µH.
VOUT
.
PVIN (Pin16):PowerVoltageInputSupplyPin. Connectto
VIN (Pin 1).
GND (Pins 5 and 8): Signal Ground Pin. Connect to PGND
(Exposed Pad).
Exposed Pad (Pin 17): Power Ground Pin. Connect to
GND (Pin 8) and solder to PCB ground for optimum
thermal performance.
ISET2 (Pin 10): White Led Current Programming Pin. A
resistortogroundprogramseachcurrentsourceoutputto
ILED = 384(0.8V/RISET2). This amount of current adds to
any amount set by EN1/ISET1 if also used.
3453fa
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LTC3453
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BLOCK DIAGRA
OPTIONAL
OPTIONAL
15
14
SW1
SW2
PV
IN
V
V
OUT
SWITCH A
SWITCH D
OUT
16
1
13
V
IN
2.7V TO 5.5V
V
IN
GATE
DRIVERS
AND
ANTICROSS-
CONDUCTION
SWITCH B
SWITCH C
UNDERVOLTAGE
LOCKOUT
UV
OT
LED1
4
FORWARD
CURRENT
LIMIT
REVERSE
CURRENT
LIMIT
OVERTEMP
PROTECTION
LED
DETECT
+
–
+
–
BANDGAP
REFERENCE
1.23V
1612mA
200mA
LED2
6
+
–
LOGIC
LED
+
–
DETECT
AB PWM
COMPARATOR
CD PWM
COMPARATOR
LED3
7
UV
OT
LED
DETECT
1MHz
OSCILLATOR
V
C
12
MAIN
ERROR AMP
SAFETY
ERROR AMP
V
OUT
LED4
9
V
–
+
–
+
1.23V
BIAS
327k
LED
DETECT
V
FB
OR
123k
SOFT
1.23V
START
CLAMP
4
LED CURRENT
SETTING AMP 1
800mV
+
–
∑
I
LED
384
6
7
9
I
I
SET1
3
R
R
ISET1
LED CURRENT
SETTING AMP 2
800mV
+
–
I
LED
384
SET2
10
ISET2
EN1
EN2
2
SHUTDOWN
11
GND
5
GND
EXPOSED PAD (PGND)
8
17
3453 BD
3453fa
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LTC3453
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OPERATIO
Buck-Boost DC-DC Converter
Buck Mode (VIN > VOUT
)
The LTC3453 employs an LTC proprietary buck-boost
DC/DC converter to generate the output voltage required
to drive the LEDs. This architecture permits high-effi-
ciency, low noise operation at input voltages above, below
or equal to the output voltage by properly phasing four
internal power switches. The error amp output voltage on
theVC pindeterminesthedutycycleoftheswitches. Since
the VC pin is a filtered signal, it provides rejection of
frequencies well below the factory trimmed switching
frequency of 1MHz. The low RDS(ON), low gate charge
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.
Inbuckmode,switchDisalwaysonandswitchCisalways
off. Referring to Figure 2, when the control voltage VC is
above voltage V1, switch A begins to turn on 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 voltage in-
creases, the duty cycle of switch A increases until the
maximum duty cycle of the converter in buck mode
reaches DCBUCK|max given by:
DCBUCK|max = 100% – DC4SW
where DC4SW equals the duty cycle in % of the “four
switch” range.
DC4SW = (150ns • f) • 100%
where f is the operating frequency in Hz.
Beyond this point the “four switch” or buck-boost region
is reached.
Figure 1 shows a simplified diagram of how the four
internal power switches are connected to the inductor,
VIN, VOUT and GND. Figure 2 shows the regions of opera-
tion of the buck-boost as a function of the control voltage
VC. The output switches are properly phased so transi-
tions between regions of operation are continuous, fil-
tered and transparent to the user. When VIN approaches
VOUT, thebuck-boostregionisreachedwheretheconduc-
tion time of the four switch region is typically 150ns.
Referring to Figures 1 and 2, the various regions of
operation encountered as VC increases will now be
described.
Buck-Boost or Four-Switch Mode (VIN ≈ VOUT
)
Referring to Figure 2, when the control voltage VC is above
voltage V2, switch pair AD continue to operate for duty
cycle DCBUCK|max, and the switch pair AC begins to phase
in. As switch pair AC phases in, switch pair BD phases out
accordingly. When the VC voltage reaches the edge of the
buck-boostrangeatvoltageV3, switchpairACcompletely
phases out switch pair BD and the boost region begins at
75%
D
MAX
BOOST
V4 (≈2.1V)
A ON, B OFF
PWM CD SWITCHES
BOOST REGION
PV
V
IN
OUT
D
MIN
BOOST
16
13
V3 (≈1.65V)
V2 (≈1.55V)
BUCK/BOOST REGION
FOUR SWITCH PWM
D
MAX
PMOS A
PMOS D
NMOS C
BUCK
SW1
15
SW2
14
D ON, C OFF
PWM AB SWITCHES
BUCK REGION
V1 (≈0.9V)
0%
NMOS B
DUTY
CYCLE
CONTROL
VOLTAGE, V
3453 F02
C
3453 F01
Figure 1. Simplified Diagram of Internal Power Switches
Figure 2. Switch Control vs Control Voltage, V
C
3453fa
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LTC3453
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OPERATIO
duty cycle DC4SW. The input voltage VIN where the four
switch region begins is given by:
Soft-Start
The LTC3453 includes an internally fixed soft-start which
is active when powering up or coming out of shutdown.
The soft-start works by clamping the voltage on the VC
node and gradually releasing it such that it requires
0.65ms to linearly slew from 0.9V to 2.1V. This has the
effect of limiting the rate of duty cycle change as VC
transitions 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.
VIN = VOUT/[1 – (150ns • f)]
and the input voltage VIN where the four switch region
ends is given by
VIN = VOUT • (1 – DC4SW) = VOUT • [1 – (150ns • f)]
Boost Mode (VIN < VOUT
)
In boost mode, switch A is always on and switch B is
always off. Referring to Figure 2, when the control voltage
VC is above voltage V3, switches C and D will alternate
conducting similar to a typical synchronous boost regula-
tor. The maximum duty cycle of the converter is limited to
88% typical and is reached when VC is above V4.
Main Error Amp
The main error amplifier is a transconductance amplifier
with source and sink capability. The output of the main
erroramplifierdrivesacapacitortoGNDattheVC pin. This
capacitor sets the dominant pole for the regulation loop.
(SeetheApplicationsInformationsectionforselectingthe
capacitor value.) The error amp gets its feedback signal
fromaproprietarycircuitwhichmonitorsall4LEDcurrent
sources to determine which LED to close the regulation
loop on.
Forward Current Limit
If the current delivered from VIN through PMOS switch A
exceeds 1612mA (typical), switch A is shut off immedi-
ately. 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.
Safety Error Amp
Reverse Current Limit
The safety error amplifier is a transconductance amplifier
with sink only capability. In normal operation, it has no
effect on the loop regulation. However, if any of the LED
pins open-circuits, the output voltage will keep rising, and
safety error amp will eventually take over control of the
regulationlooptopreventVOUTrunaway.TheVOUT thresh-
old at which this occurs is approximately 4.5V.
If the current delivered from VOUT backwards through
PMOS switch D exceeds 200mA (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.
Undervoltage Lockout
TopreventoperationofthepowerswitchesathighRDS(ON)
,
LED Current Setting Amplifiers and Enable Circuit
an undervoltage lockout is incorporated on the LTC3453.
Whentheinputsupplyvoltagedropsbelowapproximately
1.9V, the four power switches and all control circuitry are
turned off except for the undervoltage block, which draws
only several microamperes.
The LTC3453 includes two LED current setting amplifiers
that work in conjunction with dual external current setting
resistors and dual enable pins to program LED current to
one of four levels (including shutdown). All four LED
currentsourceoutputsareprogrammedtothesamelevel.
When both enable inputs are logic low, the LTC3453 is in
shutdown, thebuck-boostisdisabledandallLEDcurrents
are zero. In shutdown, the input supply current is typically
6µA. Ifeitherenableinputislogichigh, thebuck-boostwill
regulate the output voltage such that the LEDs are biased
Overtemperature Protection
If the junction temperature of the LTC3453 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.
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7
LTC3453
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OPERATIO
at the current programmed by resistors RISET1 and/or
etary architecture that determines which of the four LEDs
requires the largest forward voltage drop at its pro-
grammed current, and then generates a feedback voltage
based on this one for closing the buck-boost regulation
loop. This results in the lowest output voltage required for
regulating all of the LEDs and thus the highest LED power
efficiency. The voltage present at the LED pin of the
“controlling LED” will be typically 130mV at 75mA of
current.
R
ISET2. Individually enabled, each LED current setting
amplifier programs the output LED current to
ILED = 384 (0.8V/RISET1,2
)
Ifbothenableinputsarelogichigh,thesettingcurrentsare
summed internally and the output LED current will be
given by
ILED = 384 [0.8V/(RISET1 || RISET2) ]
Thus three different (nonzero) current levels are program-
mable, optimal for low current LED torch and high current
LED camera flash applications.
LED Detect Circuit
If fewer than four LED outputs are required, unused ones
shouldbeconnectedtoVOUT. EachLEDpinhasaninternal
LED detect circuit that disables the output current source
to save power if an output is not needed. A small 30µA
current is employed to detect the presence of an LED at
startup.
LED Current Sources
Each LED pin is driven by a current source specifically
designedforlowdropout. TheLTC3453employsapropri-
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APPLICATIO S I FOR ATIO
Component Selection
For high efficiency, choose an inductor with a high fre-
quencycorematerial, suchasferrite, toreducecoreloses.
The inductor should have low ESR (equivalent series
resistance) to reduce the I2R losses, and must be able to
handlethepeakinductorcurrentwithoutsaturating.Molded
chokes or chip inductors usually do not have enough core
to support peak inductor currents >1A. To minimize radi-
ated noise, use a toroid, pot core or shielded bobbin
inductor. For the white LED application, a 4.7µH inductor
valueisrecommended. SeeTable1foralistofcomponent
suppliers.
Inductor Selection
The high frequency operation of the LTC3453 allows the
use of small surface mount inductors. The inductor cur-
rent ripple is typically set to 20% to 40% of the maximum
inductor current. For a given ripple the inductance terms
are given as follows:
V
2 • VOUT – V
•100%
(
)
IN(MIN)
IN(MIN)
L >
L >
,
2
f •IOUT(MAX) •%Ripple • VOUT
Table 1. Inductor Vendor Information
SUPPLIER
Coilcraft
WEB SITE
VOUT • VIN(MAX) – VOUT •100%
(
)
www.coilcraft.com
www.cooperet.com
www.murata.com
www.japanlink.com/sumida
www.vishay.com
f •IOUT(MAX) •%Ripple • V
IN(MAX)
Cooper/Coiltronics
Murata
where f = operating frequency, Hz
Sumida
%Ripple = allowable inductor current ripple, %
VIN(MIN) = minimum input voltage, V
VIN(MAX) = maximum input voltage, V
VOUT = output voltage, V
Vishay-Dale
IOUT(MAX) = maximum output load current
3453fa
8
LTC3453
U
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APPLICATIO S I FOR ATIO
Input Capacitor Selection
Optional Schottky Diodes
Since the VIN pin is the supply voltage for the IC it is
recommended to place at least a 2.2µF, low ESR bypass
capacitor to ground. See Table 2 for a list of component
suppliers.
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
diode such as an MBRM120T3 or equivalent. Do not use
ordinary rectifier diodes, since the slow recovery times
will compromise efficiency.
Table 2. Capacitor Vendor Information
SUPPLIER
AVX
WEB SITE
www.avxcorp.com
www.sanyovideo.com
www.t-yuden.com
www.component.tdk.com
Sanyo
Closing the Feedback Loop
Taiyo Yuden
TDK
The LTC3453 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
given by:
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:
1
fFILTER_POLE
=
Hz
2 • π • L •COUT
IOUT(MAX) • VOUT – V
•100
(
)
IN(MIN)
where COUT is the output filter capacitor.
The output filter zero is given by:
%Ripple_Boost =
%Ripple_Buck =
%
COUT • VOUT2 • f
V
IN(MAX) – VOUT •100
(
)
%
1
8• VIN(MAX) • f2 •L •COUT
fFILTER_ZERO
=
Hz
2 • π •RESR •COUT
where COUT = output filter capacitor, F
where RESR is the capacitor equivalent series resistance.
The output capacitance is usually many times larger in
order to handle the transient response of the converter.
For a rule of thumb, the ratio of the operating frequency to
the unity-gain bandwidth of the converter is the amount
the output capacitance will have to increase from the
above calculations in order to maintain the desired tran-
sient response.
A troublesome feature in Boost mode is the right-half
plane zero (RHP), and is given by:
2
V
IN
fRHPZ
=
Hz
2• π •IOUT •L•VOUT
The loop gain is typically rolled off before the RHP zero
frequency.
The other component of ripple is due to the ESR (equiva-
lent series resistance) of the output capacitor. Low ESR
capacitors should be used to minimize output voltage
ripple. For surface mount applications, Taiyo Yuden, TDK,
AVX ceramic capacitors, AVX TPS series tantalum capaci-
tors or Sanyo POSCAP are recommended. For the white
LED application, a 4.7µF capacitor value is recommended.
See Table 2 for a list of component suppliers.
A simple Type I compensation network can be incorpo-
rated to stabilize the loop but at a cost of reduced band-
width and slower transient response. To ensure proper
phase margin, the loop requires to be crossed over a
decade before the LC double pole.
3453fa
9
LTC3453
U
W U U
APPLICATIO S I FOR ATIO
The unity-gain frequency of the error amplifier with the
Since the maximum continuous output current is limited
to 500mA, this sets a minimum limit on the parallel
combination of RISET1 and RISET2 equal to
Type I compensation is given by:
gm
fUG
=
RMIN = (RISET1 || RISET2)|MIN = 4(384[0.8V/500mA])
= 2458Ω
2 • π •CVC
where gm is the error amp transconductance (typically
1/5.2k) and CVC is the external capacitor to GND at the
VC pin. For the white LED application, a 0.1µF or greater
capacitor value is recommended.
Although the LTC3453 can safely provide this current
continuously, theexternalLED(s)maynotberatedforthis
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
a high current with one of the RISET resistors and pulsing
the appropriate enable pin.
Paralleling LED Outputs for Higher Current
Two or more LED output pins can be connected together
in parallel to achieve higher output current in fewer than 4
LEDs. For a very high power LED such as a LumiLED, all
four outputs can be connected in parallel for maximum
total output current, as shown in the cover page applica-
tion of this datasheet.
Varying LED Brightness
Continuously variable LED brightness control can be
achieved by interfacing directly to one or both of the ISET
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
LTC3453 in and out of shutdown and result in erratic
operation.
Maximum LED Current
As described in the Operation section, the output LED
current with both enable pins logic high is equal to
ILED = 384 [0.8V/(RISET1 || RISET2)]
V
IN
V
OUT
V
V
OUT
IN
ENx
LED1
LTC3453
ENx
LED1
LTC3453
I
SETx
LED4
I
SETx
LED4
0.8V – V
DAC
I
LED
= 384
I
= 384 • IDAC
LED
0.8V
R
≥ R
R
SET
SET
MIN
IDAC ≤
R
MIN
VOLTAGE
DAC
CURRENT
DAC
V
DAC
(a)
(b)
V
IN
V
OUT
V
V
OUT
IN
ENx
LED1
ENx
LED1
LTC3453
SETx
LED4
LTC3453
I
I
SETx
LED4
0.8V
+ R
0.8V – V
PWM
R
100
R
SET
MIN
POT
I
LED
= 384
I
LED
= 384
= 384
R
≥ R
MIN
SET
R
R
MIN
POT
SET
V
PWM
0.8V – (DC% • V
)
R
DVCC
1µF
R
SET
DV
CC
f
≥ 5kHz
PWM
(c)
(d)
3453 F03
Figure 3. Brightness Control Methods: (a) Using Voltage DAC, (b) Using Current DAC, (c) Using Potentiometer, (d) Using PWM Input
3453fa
10
LTC3453
U
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APPLICATIO S I FOR ATIO
Unused Outputs
operation as described previously (if the output were
initially designated unused at power-up by connecting its
LEDx pin to VOUT). Efficiency is not materially affected.
If fewer than 4 LED pins are to be used, unused LEDx pins
should be connected to VOUT. The LTC3453 senses which
current source outputs are not being used and shuts off
the corresponding output currents to save power. A small
tricklecurrent(~30µA)isstillappliedtounusedoutputsto
detect if a white LED is later switched in and also to
distinguish unused outputs from used outputs during
startup.
IfanindividualLEDfailsasanopencircuit,thecontrolloop
will initially attempt to regulate off of its current source
feedback signal, since it will appear to be the one requiring
the largest forward voltage drop to run at its programmed
current. This will drive VOUT higher. As the open circuited
LED will never accept its programmed current, VOUT must
be voltage-limited by means of a secondary control loop.
The LTC3453 limits VOUT to 4.5V in this failure mode. The
other LEDs will still remain biased at the correct pro-
grammed current but the overall circuit efficiency will
decrease.
LED Failure Modes
If an individual LED fails as a short circuit, the current
sourcebiasingitisshutofftosavepower. Thisisthesame
U
PACKAGE DESCRIPTIO
UF Package
16-Lead Plastic QFN (4mm × 4mm)
(Reference LTC DWG # 05-08-1692)
0.72 ±0.05
4.35 ± 0.05
2.90 ± 0.05
2.15 ± 0.05
(4 SIDES)
PACKAGE OUTLINE
0.30 ±0.05
0.65 BSC
RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS
BOTTOM VIEW—EXPOSED PAD
PIN 1 NOTCH R = 0.20 TYP
OR 0.35 × 45° CHAMFER
0.75 ± 0.05
R = 0.115
TYP
4.00 ± 0.10
(4 SIDES)
15
16
0.55 ± 0.20
PIN 1
TOP MARK
(NOTE 6)
1
2
2.15 ± 0.10
(4-SIDES)
(UF16) QFN 1004
0.200 REF
0.30 ± 0.05
0.65 BSC
0.00 – 0.05
NOTE:
1. DRAWING CONFORMS TO JEDEC PACKAGE OUTLINE MO-220 VARIATION (WGGC)
2. DRAWING NOT TO SCALE
3. ALL DIMENSIONS ARE IN MILLIMETERS
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
5. EXPOSED PAD SHALL BE SOLDER PLATED
6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION
ON THE TOP AND BOTTOM OF PACKAGE
3453fa
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no represen-
tationthattheinterconnectionofitscircuitsasdescribedhereinwillnotinfringeonexistingpatentrights.
11
LTC3453
U
TYPICAL APPLICATIO
High Efficiency 4 White LED Driver
4.7µH
V
IN
1-CELL
Li-Ion
V
IN
PV
IN
SW1
SW2
V
OUT
2.2µF
4.7µF
30mA
D1
30mA
D2
30mA
D3
30mA
D4
LED1
LED2
LED3
LED4
1MHz
BUCK-BOOST
V
C
EN1
EN2
0.1µF
EN
D1 TO D4: NICHIA NSCW100
L1: VISHAY DALE IDCS-2512
I
I
SET1
SET2
10.2k
LTC3453
3453 TA02
GND
GND
PGND
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
LT1937
LTC3205
LTC3216
Constant Current, 1.2MHz, High Efficiency White LED
Boost Regulator
V : 1V to 10V, V
ThinSOT Package
= 34V, I = 1.2mA, I = <1µA,
IN
OUT(MAX) Q SD
Constant Current, 1.2MHz, High Efficiency White LED
Boost Regulator
V : 2.5V to 10V, V
= 34V, I = 1.9mA, I = <1µA,
Q SD
IN
OUT(MAX)
ThinSOT Package/SC70 Package
High Efficiency, Multi-Display LED Controller
V : 2.8V to 4.5V, V
= 6V, I = 50µA, I = <1µA,
Q SD
IN
OUT(MAX)
OUT(MAX)
OUT(MAX)
QFN-24 Package
1A Low Noise High Current LED Charge Pump 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
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
LTC3454
1A Synchronous Buck-Boost High Power LED Driver
V : 2.7V to 5.5V, 1MHz, I < 6µA, DFN Package
IN SD
LT3465/LT3465A Constant Current, 1.2MHz/2.7MHz, High Efficiency White LED V : 2.7V to 16V, V
= 34V, I = 1.9mA, I = <1µA,
Q SD
IN
OUT(MAX)
Boost Regulator with Integrated Schottky Diode
ThinSOT Package
LT3466
LT3479
Dual Constant Current, 2MHz, High Efficiency White LED
Boost Regulator with Integrated Schottky Diode
V : 2.7V to 24V, V
DFN Package
= 40V, I = 5mA, I = <16µA,
Q SD
IN
OUT(MAX)
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
OUT(MAX)
DFN Package/TSOPP Package
3453fa
LT 0206 REV A • PRINTED IN USA
12 LinearTechnology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
●
●
(408) 432-1900 FAX: (408) 434-0507 www.linear.com
© LINEAR TECHNOLOGY CORPORATION 2005
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