LTC3453
Synchronous Buck-Boost
High Power White LED Driver
FEATURES
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DESCRIPTIO
High Efficiency: 90% Typical Over Entire
Li-Ion Battery Range
Wide V
IN
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
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).
LED current is programmable to one of four levels (includ-
ing shutdown) with dual current setting resistors and dual
enable pins. In shutdown, the supply current is only 6µA.
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.
APPLICATIO S
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Cell Phones
Digital Cameras
PDAs
Portable Devices
, LTC and LT are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
TYPICAL APPLICATIO
High Efficiency Torch/Flash LED Driver
L1
4.7µH
V
IN
1-CELL
Li-Ion
2.7V to 4.2V
LED POWER EFFICIENCY P
LED
/P
IN
(%)
2.2µF
V
IN
PV
IN
SW1
SW2
V
OUT
150mA/500mA
4.7µF
D1
LED1
LED2
V
C
0.1µF
EN1 (TORCH)
EN2 (FLASH)
8.25k
1%
EN1
EN2
I
SET1
I
SET2
3.48k
1%
LTC3453
GND
GND
PGND
3453 TA01a
1MHz
BUCK-BOOST
LED3
LED4
D1: LUMILEDS LXCL-PWF1
L1: VISHAY DALE IDCS-2512
EN1
0
1
0
1
EN2
0
0
1
1
I
LED
0 (SHUTDOWN)
150mA
350mA
500mA
U
Torch Mode Efficiency vs V
IN
100
180
90
EFFICIENCY
80
140
160
INPUT CURRENT (mA)
U
U
70
I
IN
60
I
LED
= 150mA
T
A
= 25°C
3.1
3.5
3.9 4.3
V
IN
(V)
4.7
5.1
5.5
120
100
50
2.7
80
3453 TA01b
3453fa
1
LTC3453
ABSOLUTE
(Note 1)
AXI U RATI GS
PACKAGE/ORDER I FOR ATIO
TOP VIEW
V
OUT
SW1
SW2
PV
IN
V
IN
, PV
IN
, SW1, SW2, V
OUT
Voltage ............ –0.3V to 6V
LED1 to LED4 Voltage ...... –0.3V to (V
OUT
+ 0.3V) or 6V
V
C
, EN1, EN2,
I
SET1
, I
SET2
Voltage .......... –0.3V to (V
IN
+ 0.3V) or 6V
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
16 15 14 13
V
IN
1
EN1 2
I
SET1
3
LED1 4
5
GND
12 V
C
17
11 EN2
10 I
SET2
9 LED4
6
LED2
7
LED3
8
GND
UF PACKAGE
16-LEAD (4mm
×
4mm) PLASTIC QFN
T
JMAX
= 125°C,
θ
JA
= 40°C/W,
θ
JC
= 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.
The
●
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C, V
IN
= V
OUT
= 3.6V unless otherwise noted. (Note 2)
PARAMETER
Input Supply Voltage
Input DC Supply Current
Normal Operation
Shutdown
UVLO
Undervoltage Lockout Threshold
EN1,2 DC Threshold for Normal Operation
EN1,2 Input Current
I
SET1,2
Servo Voltage
LED Output Current Ratio
LED Output Current Matching
LED Pin Drain Voltage
Regulated Maximum V
OUT
PMOS Switch R
ON
NMOS Switch R
ON
Forward Current Limit
Reverse Current Limit
2.7V
≤
V
IN
≤
5.5V, R
ISET1
||R
ISET2
= 51.1k, I
LEDx
= 0 (Note 4)
2.7V
≤
V
IN
≤
5.5V; V
EN1
= V
EN2
= 0V
V
IN
< UVLO Threshold
V
IN
Rising
V
IN
Falling
2.7V
≤
V
IN
≤
5.5V, V
EN1,2
Rising
V
EN1,2
= 3.6V
R
ISET1,2
= 4.12k, 0°C
≤
T
A
≤
85°C
R
ISET1,2
= 4.12k, –40°C
≤
T
A
≤
85°C
I
LED
/(I
SET1
+ I
SET2
), I
LEDx
= 75mA, V
LEDx
= 300mV,
2.7V
≤
V
IN
≤
5.5V
(MAX – MIN)/[(MAX + MIN)/2] • 100%, I
LEDx
= 75mA
V
LEDx
= 300mV
I
LEDx
= 75mA
V
LEDx
= 0V
Switches A and D, @ 100mA
Switches B and C, @ 100mA
Switch A
Switch D
1125
●
●
ELECTRICAL CHARACTERISTICS
CONDITIONS
MIN
●
TYP
MAX
5.5
UNITS
V
mA
µA
µA
V
V
V
V
µA
mV
mV
mA/mA
mA/mA
%
mV
2.7
0.6
6
3
1.6
2
1.9
0.65
0.2
–1
788
780
365
357
800
800
384
384
2
130
4.4
4.5
0.3
0.25
1612
200
0.63
1
18
5
2.3
1
1
812
812
403
403
6
●
●
●
●
●
EN1,2 DC Threshold for Shutdown (I
LEDx
= 0) 2.7V
≤
V
IN
≤
5.5V, V
EN1,2
Falling
4.6
2100
3453fa
2
U
V
Ω
Ω
mA
mA
W
U
U
W W
W
LTC3453
The
●
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C, V
IN
= V
OUT
= 3.6V unless otherwise noted. (Note 2)
PARAMETER
PMOS Switch Leakage
NMOS Switch Leakage
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 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.
CONDITIONS
Switches A and D
Switches B and C
●
●
ELECTRICAL CHARACTERISTICS
MIN
TYP
MAX
1
1
UNITS
µA
µA
MHz
ms
0.9
1
0.65
1.1
Note 3:
T
J
is calculated from the ambient temperature T
A
and power
dissipation P
D
according to the following formula:
T
J
= T
A
+ (P
D
•
θ
JA
°C/W).
Note 4:
Dynamic supply current is higher due to the gate charge being
delivered at the switching frequency.
TYPICAL PERFOR A CE CHARACTERISTICS
Input DC Supply Current in
Shutdown vs Temperature
20
18
16
14
V
IN
= 5.5V
2.1
808
V
IN
RISING
2.0
804
800
796
1.8
792
788
–55 –35 –15
FRONT PAGE APPLICATION
2.2
I
IN
(µA)
12
10
8
6
4
2
0
–55 –35 –15
5 25 45 65 85 105 125
TEMPERATURE (°C)
3453 G01
V
IN
= 3.6V
V
IN
= 2.7V
1.9
V
IN
FALLING
1.7
–55 –35 –15
5 25 45 65 85 105 125
TEMPERATURE (°C)
3453 G02
V
ISET1,2
(mV)
V
IN
= 4.2V
UVLO THRESHOLD (V)
I
SET1,2
Servo Voltage vs V
IN
812
808
804
T
A
= 25°C
R
ISET1,2
= 8.25k
4.55
FREQUENCY (kHz)
V
ISET1,2
(mV)
V
OUT
(V)
800
796
792
788
2.7
3.1
3.5
3.9 4.3
V
IN
(V)
4.7
U W
5.1
3453 G05
Undervoltage Lockout Threshold
vs Temperature
812
I
SET1,2
Servo Voltage vs
Temperature
V
IN
= 3.6V
R
ISET1,2
= 8.25k
5 25 45 65 85 105 125
TEMPERATURE (°C)
3453 G04
Regulated Maximum V
OUT
vs
Temperature
V
IN
= 3.6V
4.54 ALL LED PINS OPEN
4.53
4.52
4.51
4.50
4.49
4.48
4.47
4.46
5.5
4.45
–55 –35 –15
5 25 45 65 85 105 125
TEMPERATURE (°C)
3453 G06
Oscillator Frequency vs
Temperature
1050
1040
1030
1020
1010
1000
990
980
970
960
950
–55 –35 –15
5 25 45 65 85 105 125
TEMPERATURE (°C)
3453 G07
V
OUT
= 3V
V
IN
= 5.5V
V
IN
= 4.2V
V
IN
= 3.6V
V
IN
= 2.7V
3453fa
3
LTC3453
TYPICAL PERFOR A CE CHARACTERISTICS
Efficiency vs LED Current
100
FRONT PAGE APPLICATION
P
LED
/P
IN
, V
IN
= 3.6V, T
A
= 25°C
CH1, V
OUT
2V/DIV
20mV/DIV
AC COUPLED
0V
CH2, EN1
1V/DIV
0V
90
EFFICIENCY (%)
80
70
60
5µs/DIV
FRONT PAGE APPLICATION
V
IN
= 3.6V
I
LED
= 150mA
50
100 150 200 250 300 350 400 450 500
LED CURRENT (mA)
3453 G07
PI FU CTIO S
V
IN
(Pin 1):
Signal Voltage Input Supply Pin [2.7V
≤
V
IN
≤
5.5V]. Recommended bypass capacitor to GND is 2.2µF
ceramic or larger. Connect to PV
IN
(Pin 16).
EN1 (Pin 2):
Enable Input Pin for I
SET1
Current.
I
SET1
(Pin 3):
White Led Current Programming Pin. A
resistor to ground programs each current source output to
I
LED
= 384(0.8V/R
ISET1
). This amount of current adds to
any amount set by EN2/I
SET2
if also used.
LED1 to LED4 (Pins 4, 6, 7, 9):
Individual Low Dropout
Current Source Outputs for White LED Current Biasing.
Connect each white LED between V
OUT
and an individual
LEDx pin. Unused LEDx outputs should be connected to
V
OUT
.
GND (Pins 5 and 8):
Signal Ground Pin. Connect to PGND
(Exposed Pad).
I
SET2
(Pin 10):
White Led Current Programming Pin. A
resistor to ground programs each current source output to
I
LED
= 384(0.8V/R
ISET2
). This amount of current adds to
any amount set by EN1/I
SET1
if also used.
EN2 (Pin 11):
Enable Input Pin for I
SET2
Current.
V
C
(Pin 12):
Compensation Point for the Internal Error
Amplifier Output. Recommended compensation capacitor
to GND is 0.1µF ceramic or larger.
V
OUT
(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.
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.
PV
IN
(Pin 16):
Power Voltage Input Supply Pin. Connect to
V
IN
(Pin 1).
Exposed Pad (Pin 17):
Power Ground Pin. Connect to
GND (Pin 8) and solder to PCB ground for optimum
thermal performance.
4
U W
Output Voltage Ripple
Startup Transient
3453 G08
1ms/DIV
FRONT PAGE APPLICATION
V
IN
= 3.6V
I
LED
= 150mA
3453 G09
U
U
U
3453fa
LTC3453
BLOCK DIAGRA
V
IN
2.7V TO 5.5V
16
1
PV
IN
V
IN
UNDERVOLTAGE
LOCKOUT
OVERTEMP
PROTECTION
+
BANDGAP
REFERENCE
1.23V
1612mA
–
+
–
AB PWM
COMPARATOR
UV
1MHz
OSCILLATOR
MAIN
ERROR AMP
SAFETY
ERROR AMP
CD PWM
COMPARATOR
OT
LOGIC
12
V
C
V
BIAS
V
FB
–
+
–
+
1.23V
LED CURRENT
SETTING AMP 1
800mV
SOFT
START
CLAMP
+
–
I
LED
384
∑
6
3
R
ISET1
I
SET1
LED CURRENT
SETTING AMP 2
I
LED
384
9
7
800mV
+
–
10
R
ISET2
2
I
SET2
EN1
EN2
11
SHUTDOWN
5
GND
8
GND
17
EXPOSED PAD (PGND)
3453 BD
+
–
+
–
W
OPTIONAL
OPTIONAL
15
SWITCH A
SW1
SW2
14
SWITCH D
V
OUT
13
V
OUT
SWITCH B
UV
GATE
DRIVERS
AND
ANTICROSS-
CONDUCTION
SWITCH C
LED1
4
OT
FORWARD
CURRENT
LIMIT
REVERSE
CURRENT
LIMIT
LED
DETECT
200mA
LED2
6
LED
DETECT
LED3
7
LED
DETECT
V
OUT
1.23V
327k
LED
DETECT
123k
OR
4
LED4
9
3453fa
5
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