LTC3454
1A Synchronous Buck-Boost
High Current LED Driver
FEATURES
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DESCRIPTION
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
input voltage and LED forward voltage. P
LED
/P
IN
efficiency
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-
ing shutdown, with dual external resistors and dual enable
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.
L,
LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
High Efficiency: >90% Typical in Torch Mode,
>80% in Flash Mode
Wide V
IN
Range: 2.7V to 5.5V
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
APPLICATIONS
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Cell Phone Camera Flash
Cell Phone Torch Lighting
Digital Cameras
PDAs
Misc Li-Ion LED Drivers
TYPICAL APPLICATION
High Efficiency Torch/Flash LED Driver
V
IN
2.7V TO 4.2V
1-CELL Li-Ion
L1
5μH
10μF
V
IN
A
SW1
SW2
D
V
OUT
10μF
I
LED
100
95
LED
LED
EN2 EN1 I
LED
0
0
0 (SHUTDOWN)
0
1
150mA
EN1 (TORCH) 1
0
850mA
1
1
1A
EN2 (FLASH)
I
SET1
I
SET2
LTC3454
LED: LUMILEDS LXL-PWF1
L1: SUMIDA CDRH6D28-5RONC
GND (EXPOSED PAD)
R
ISET2
3.65k
1%
3454 TA01a
LED Power Efficiency vs V
IN
I
LED
= 150mA
90
EFFICIENCY (%)
85
80
75
70
R
ISET1
20.5k
1%
65 T
A
= 25°C
EFFICIENCY = (V
OUT
– V
LED
)I
LED
/V
IN
I
IN
60
2.7 3.1 3.5 3.9 4.3 4.7 5.1
V
IN
(V)
I
LED
= 1A
B
C
V
C
0.1μF
1MHz
BUCK-BOOST
5.5
3454 TA01b
3454fa
1
LTC3454
ABSOLUTE MAXIMUM RATINGS
(Note 1)
PIN CONFIGURATION
TOP VIEW
EN1
EN2
I
SET1
I
SET2
LED
1
2
3
4
5
11
10 SW1
9 V
IN
8 V
C
7 V
OUT
6 SW2
V
IN
, SW1, SW2, V
OUT
Voltage ...................... –0.3V to 6V
V
C
, EN1, EN2, I
SET1
, I
SET2
Voltage.............................–0.3V to (V
IN
+ 0.3V) or 6V
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
DD PACKAGE
10-LEAD (3mm 3mm) PLASTIC DFN
T
JMAX
= 125°C,
θ
JA
= 40°C/W
EXPOSED PAD (PIN 11) IS GND, MUST BE SOLDERED TO PCB
ORDER INFORMATION
LEAD FREE FINISH
LTC3454EDD#PBF
TAPE AND REEL
LTC3454EDD#TRPBF
PART MARKING
LBQX
PACKAGE DESCRIPTION
10-Lead (3mm
×
3mm) Plastic DFN
TEMPERATURE RANGE
–40°C to 85°C
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/
The
l
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
IN
= 3.6V, R
ISET
= 20.5k unless otherwise noted. (Note 2)
PARAMETER
Input Supply Voltage (V
IN
)
Input DC Supply Current
Normal Operation
Shutdown
UVLO
Undervoltage Lockout Threshold
V
EN1
, V
EN2
DC Threshold for Normal Operation (V
IH
)
V
EN1
, V
EN2
DC Threshold for Shutdown (V
IL
)
V
EN1
, V
EN2
Input Current
I
SET1
and I
SET2
Servo Voltage
LED Output Current to Programming Current Ratio
LED Pin Voltage
Regulated Maximum V
OUT
PMOS Switch R
ON
NMOS Switch R
ON
Forward Current Limit
Reverse Current Limit
PMOS Switch Leakage
NMOS Switch Leakage
3.08k ≤ R
ISET1
||R
ISET2
≤ 20.5k
I
LED
/(I
ISET1
+ I
ISET2
), I
LED
= 500mA (Note 5)
I
LED
= 1A
LED Pin Open, Programmed I
LED
= 1A
Switches A and D (V
OUT
= 3.6V)
Switches B and C
Switch A
Switch D (V
OUT
= 3.6V)
Switches A, D
Switches B, C
–1
–1
2.5
l
ELECTRICAL CHARACTERISTICS
CONDITIONS
l
MIN
2.7
l
TYP
MAX
5.5
UNITS
V
μA
μA
μA
V
V
V
V
μA
mV
mV
mA/mA
mA/mA
mV
V
mΩ
mΩ
A
mA
(Typicals at V
IN
= 3.6V, R
ISET1
= R
ISET2
= 20.5k)
2.7V ≤ V
IN
≤ 5.5V (Note 4)
2.7V ≤ V
IN
≤ 5.5V, V
EN1
= V
EN2
= 0V
V
IN
< UVLO Threshold, V
EN1
= V
EN2
= V
IN
V
IN
Rising
V
IN
Falling
825
0
5
l
1200
1
10
2.3
1.2
1
1.75
l
l
l
l
l
2.05
1.90
0.68
0.66
800
800
3850
3850
105
5.15
170
130
3.4
275
0.2
–1
780
788
3725
3775
4.95
812
812
3975
3925
5.35
1
1
μA
μA
3454fa
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LTC3454
The
l
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
IN
= 3.6V, R
ISET
= 20.5k unless otherwise noted. (Note 2)
PARAMETER
Oscillator Frequency
Soft-Start Time
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 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.
CONDITIONS
MIN
0.9
TYP
1.0
200
Note 3:
T
J
is calculated from the ambient temperature T
A
and power
dissipation PD according to the following formula:
T
J
= T
A
+ (PD •
θ
JA
°C/W).
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.
MAX
1.15
UNITS
MHz
μs
ELECTRICAL CHARACTERISTICS
TYPICAL PERFORMANCE CHARACTERISTICS
Undervoltage Lockout Threshold
vs Temperature
2.4
2.3
ENABLE THRESHOLDS (mV)
2.2
UVLO THRESHOLD (V)
2.1
2.0
1.9
1.8
1.7
1.6
1.5
1.4
–55 –35 –15
5 25 45 65 85 105 125
TEMPERATURE (°C)
3454 G01
Enable Thresholds
vs Temperature
1200
1100
1000
900
800
700
600
500
400
300
200
–55 –35 –15
5 25 45 65 85 105 125
TEMPERATURE (°C)
3454 G02
Enable Thresholds vs V
IN
1200
1100
ENABLE THRESHOLDS (mV)
1000
900
800
700
600
500
400
300
200
2.7
3.1
3.5
3.9 4.3
V
IN
(V)
4.7
5.1
5.5
V
IH
V
IL
T
A
= 25°C
V
IN
= 3.6V
V
IN
RISING
V
IH
V
IL
V
IN
FALLING
3454 G03
I
SET1,2
Servo Voltage
vs Temperature
812
808
804
800
796
792
788
–55 –35 –15
V
IN
= 3.6V
R
ISET1,2
= 15k
812
808
804
800
796
792
I
SET1,2
Servo Voltage vs V
IN
T
A
= 25°C
R
ISET1
= R
ISET2
= 15k
812
808
804
800
796
792
788
3.1
3.5
3.9 4.3
V
IN
(V)
4.7
5.1
5.5
I
SET1,2
Servo Voltage vs R
ISET
V
IN
= 3.6V
T
A
= 25°C
V
ISET1,2
(mV)
V
ISET1,2
(mV)
5 25 45 65 85 105 125
TEMPERATURE (°C)
3454 G04
788
2.7
V
ISET1,2
(mV)
3
7
11
19
15
R
ISET
(kΩ)
23
27
31
3454 G06
3454 G05
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LTC3454
TYPICAL PERFORMANCE CHARACTERISTICS
LED Current Programming Ratio
vs Temperature
4050
4000
3950
3900
RATIO
3850
3800
3750
3700
3650
–55 –35 –15
PROGRAMMED I
LED
= 1A
PROGRAMMED I
LED
= 500mA
PROGRAMMED I
LED
= 150mA
5 25 45 65 85 105 125
TEMPERATURE (°C)
3454 G07
LED Current Programming Ratio
vs V
IN
4050
4000
3950
V
LED
(mV)
3900
RATIO
3850
3800
3750
30
3700
3650
2.7
3.1
3.5
3.9 4.3
V
IN
(V)
4.7
5.1
5.5
PROGRAMMED I
LED
= 500mA
T
A
= 25°C
150
V
LED
vs Temperature
V
IN
= 3.6V
PROGRAMMED
I
LED
= 1A
V
IN
= 3.6V
120
90
PROGRAMMED
I
LED
= 500mA
60
PROGRAMMED
I
LED
= 100mA
5 25 45 65 85 105 125
TEMPERATURE (°C)
3454 G09
0
–55 –35 –15
3454 G08
V
LED
vs V
IN
60
PROGRAMMED I
LED
= 500mA
58 T
A
= 25°C
56
54
V
LED
(mV)
V
OUT
(V)
52
50
48
46
44
42
40
2.7
3.1
3.5
3.9 4.3
V
IN
(V)
4.7
5.1
5.5
5.40
Maximum Regulated V
OUT
vs Temperature
PROGRAMMED I
LED
= 1A
5.35 V
IN
= 3.6V
5.30
5.25
V
OUT
(V)
5.20
5.15
5.10
5.05
5.00
4.95
4.90
–55 –35 –15
5 25 45 65 85 105 125
TEMPERATURE (°C)
3454 G11
Maximum Regulated V
OUT
vs V
IN
5.40
PROGRAMMED I
LED
= 1A
5.35 T
A
= 25°C
5.30
5.25
5.20
5.15
5.10
5.05
5.00
4.95
4.90
2.7
3.1
3.5
3.9
4.3
V
IN
(V)
4.7
5.1
5.5
3454 G10
3454 G12
Maximum Regulated V
OUT
vs Programmed LED Current
5.40
300
270
240
R
DS
(mΩ)
210
180
150
120
V
IN
= 3.6V
5.35 T
A
= 25°C
5.30
5.25
V
OUT
(V)
5.20
5.15
5.10
5.05
5.00
4.95
4.90
100 200 300 400 500 600 700 800 900 1000
PROGRAMMED I
LED
(mA)
3454 G13
PMOS R
DS(ON)
vs Temperature
MEASURED AT 500mA
200
180
NMOS R
DS(ON)
vs Temperature
MEASURED AT 500mA
V
IN
= 2.7V
160
V
IN
= 2.7V
R
DS
(mΩ)
V
IN
= 3.6V
V
IN
= 5.5V
V
IN
= 4.2V
140
120
V
IN
= 3.6V
V
IN
= 5.5V
V
IN
= 4.2V
100
80
60
90
–55 –35 –15
5 25 45 65 85 105 125
TEMPERATURE (°C)
3454 G14
40
–55 –35 –15
5 25 45 65 85 105 125
TEMPERATURE (°C)
3454 G15
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LTC3454
TYPICAL PERFORMANCE CHARACTERISTICS
Oscillator Frequency vs Temperature
1100
1080
1060
FREQUENCY (kHz)
1040
1020
1000
980
960
940
920
900
–55 –35 –15
5 25 45 65 85 105 125
TEMPERATURE (°C)
3454 G16
LED Power Efficiency vs LED Current
100
95
V
OUT
= 3V
V
IN
= 5.5V
EFFICIENCY (%)
V
IN
= 4.2V
90
85
80
75
V
IN
= 3.6V
T
A
= 25°C
65 EFFICIENCY = (V
OUT
– V
LED
)I
LED
/V
IN
I
IN
FRONT PAGE APPLICATION
60
100 200 300 400 500 600 700 800 900 1000
I
LED
(mA)
3454 G17
V
IN
= 2.7V
V
IN
= 3.6V
70
Output Voltage Ripple
Back Page Application
Start-Up Transient
Back Page Application
CH1, V
OUT
1V/DIV
CH2, I
LED
500mA
FINAL VALUE
0V, 0A
CH3, V
EN1
1V/DIV
0V
20mV/DIV
V
IN
= 3.6V
I
LED
= 500mA
500ns/DIV
3454 G19
V
IN
= 3.6V
I
LED
= 500mA
5ms/DIV
3454 G19
PIN FUNCTIONS
EN1 (Pin 1):
Enable Input Pin for I
SET1
Current.
EN2 (Pin 2):
Enable Input Pin for I
SET2
Current.
I
SET1
(Pin 3):
LED Current Programming Pin. A resistor
to ground programs the current through the LED to I
LED
= 3850(0.8V/R
ISET1
). This amount of current adds to any
amount set by EN2/I
SET2
if used.
I
SET2
(Pin 4):
LED Current Programming Pin. A resistor
to ground programs the current through the LED to I
LED
= 3850(0.8V/R
ISET2
). This amount of current adds to any
amount set by EN1/I
SET1
if used.
LED (Pin 5):
Low Dropout Output for LED Current Biasing.
Connect the LED between V
OUT
and the LED pin.
SW2 (Pin 6):
Switching Node. External inductor con-
nects between SW1 and SW2. Recommended value is
4.7μH/5μH.
V
OUT
(Pin 7):
Buck-Boost Output Rail. Bypass to GND with
a ceramic capacitor. Recommended value is 10μF
.
V
C
(Pin 8):
Compensation Point for the Internal Error
Amplifier Output. Connect a ceramic capacitor from V
C
to GND. Recommended value is 0.1μF
.
V
IN
(Pin 9):
Voltage Input Supply Pin (2.7V ≤ V
IN
≤ 5.5V).
Bypass to GND with a ceramic capacitor. Recommended
value is 10μF
.
SW1 (Pin 10):
Switching Node. External inductor con-
nects between SW1 and SW2. Recommended value is
4.7μH/5μH.
Exposed Pad (Pin 11):
Ground Pin. Solder to PCB ground
for electrical contact and optimal thermal performance.
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