LTC3452
Synchronous Buck-Boost
MAIN/CAMERA White LED Driver
FEATURES
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DESCRIPTIO
High Efficiency:
≥
85% Over Entire Li-Ion Battery
Range
Wide V
IN
Range: 2.7V to 5.5V
Independent MAIN/CAMERA Current Control
Up to 425mA Continuous Output Current
Internal Soft-Start
Open/Shorted LED Protection
PWM Brightness Control
LED Current Matching Typically <2.5%
Constant Frequency 1MHz Operation
Low Shutdown Current: 6.5µA
Overtemperature Protection
Small Thermally Enhanced 20-Lead
(4mm
×
4mm) QFN Package
The LTC
®
3452 is a synchronous buck-boost DC/DC con-
verter optimized for driving two banks of white LEDs from
a single Li-Ion battery input. Five parallel LEDs can be
driven at up to 25mA each in the low power LED bank,
while two LEDs can be driven at up to 150mA each (or a
single LED at 300mA) in the high power LED bank. The
regulator operates in either synchronous buck, synchro-
nous boost or buck-boost mode, depending on input
voltage and LED maximum forward voltage. Optimum
efficiency is achieved by sensing which LED requires the
largest forward voltage drop at its programmed current,
and regulating the common output rail for lowest dropout.
Efficiency of 85% can be achieved over the entire usable
range of a Li-Ion battery (2.7V to 4.2V).
Maximum LED current for each LED display is program-
mable with a single external resistor. Dual enable pins
allow for PWM brightness control in the low power bank
and independent on/off control for the high current bank
(optimal for LED camera flash). In shutdown, the supply
current is only 6.5µA.
A high constant operating frequency of 1MHz allows the
use of a small external inductor. The LTC3452 is offered
in a low profile (0.75mm) thermally enhanced 20-lead
(4mm
×
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
L
4.7µH
V
IN
SINGLE
Li-Ion CELL
2.7V TO 4.2V
5
×
20mA White LED Display + 200mA Camera Light Driver
+
EN
H
I
SETH
6.19k
LED
L1
V
C
0.1µF
EN
L
I
SETL
10.2k
GND
GND
PGND
EXPOSED PAD
MAIN DISPLAY LED BACKLIGHT
D1: AOT 2015
D2 TO D6: NICHIA NSCW100
L: COILCRAFT DO3314-472
LTC3452
1MHz
BUCK/BOOST
LED
L2
LED
L3
LED
L4
LED
L5
2.2µF
V
IN
PV
IN
SW1
SW2
V
OUT
D1
CAM
LED
H1
LED
H2
D2
0mA TO
20mA
D3
0mA TO
20mA
D4
0mA TO
20mA
D5
0mA TO
20mA
D6
0mA TO
20mA
200mA
4.7µF
EFFICIENCY (%)
3452 TA01a
U
Torch and Flash Mode Efficiency
95
93
91
89
87
85
83
81
79
77
75
2.7
3.1
3.5
3.9 4.3
V
IN
(V)
4.7
5.1
5.5
FLASH MODE AT 200mA
T
A
= 25°C
(V
– V
LEDx
) • I
LEDx
EFFICIENCY =
Σ
OUT
V
IN
• I
IN
TORCH MODE AT 100mA
3452 TA01b
U
U
3452f
1
LTC3452
ABSOLUTE
(Note 1)
AXI U
RATI GS
PACKAGE/ORDER I FOR ATIO
TOP VIEW
UF PACKAGE
20-LEAD (4mm
×
4mm) PLASTIC QFN
T
JMAX
= 125°C,
θ
JA
= 40°C/W
EXPOSED PAD (PIN 21) IS GND, MUST BE SOLDERED TO PCB
ORDER PART NUMBER
LTC3452EUF
UF PART MARKING
3452
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 specifications which apply over the full operating temperature range, otherwise specifications are T
A
= 25°C.
V
IN
= PV
IN
= V
OUT
= 3.6V unless otherwise specified. (Note 2)
PARAMETER
Input Supply Voltage (V
IN
)
Input DC Supply Current
Normal Operation
Shutdown
UVLO
Undervoltage Lockout Threshold
EN
L,H
DC Threshold for Normal Operation (V
IH
)
EN
L,H
DC Threshold for Shutdown (I
LEDx
= 0)
(V
IL
)
EN
L,H
Input Current (I
IH
, I
IL
)
EN
L
PWM Frequency
I
SETL,H
Servo Voltage
LED
Hx
Output Current Ratio (I
LEDHx
/I
SETH
)
LED
Hx
Output Current Matching
LED
Hx
Pin Voltage
2.7V
≤
V
IN
≤
5.5V, R
ISETL
= R
ISETH
= 51.1k, I
LEDx
= 0 (Note 4)
2.7V
≤
V
IN
≤
5.5V, V
ENL
= V
ENH
= 0V
V
IN
< UVLO Threshold
V
IN
Rising
V
IN
Falling
2.7V
≤
V
IN
≤
5.5V, V
ENL,H
Rising
2.7V
≤
V
IN
≤
5.5V, V
ENL,H
Falling
2.7V
≤
V
IN
≤
5.5V
2.7V
≤
V
IN
≤
5.5V (Note 5)
R
ISETL
= R
ISETH
= 20k
●
●
CONDITIONS
●
MIN
2.7
LED
H1
LED
L3
LED
L4
LED
L5
GND
V
IN
, PV
IN
, SW1, SW2, V
OUT
Voltage ........... – 0.3V to 6V
LED
L1
to LED
L5
Voltage ... – 0.3V to (V
OUT
+ 0.3V) or 6V
LED
H1
, LED
H2
Voltage ..... – 0.3V to (V
OUT
+ 0.3V) or 6V
V
C
, EN
L
, EN
H
,
I
SETL
, I
SETH
Voltage ............ – 0.3V to (V
IN
+ 0.3V) or 6V
LED
L1
to LED
L5
Current ....................................... 50mA
LED
H1
, LED
H2
Current ....................................... 250mA
Operating Temperature Range (Note 2) .. – 40°C to 85°C
Junction Temperature (Note 3) ............................ 125°C
Storage Temperature Range ................ – 65°C to 125°C
PGND
20 19 18 17 16
V
IN
1
EN
L
2
I
SETL
3
LED
L1
4
LED
L2
5
6
7
8
9 10
21
15 V
C
14 EN
H
13 I
SETH
12 LED
H2
11 GND
V
OUT
SW1
SW2
PV
IN
TYP
MAX
5.5
UNITS
V
mA
µA
µA
V
V
V
V
0.6
6.5
3
1.6
●
●
●
●
1
18
5
2.3
1.2
2.0
1.87
0.54
0.52
0.2
–1
10
788
780
730
714
1
800
800
768
768
1
250
812
812
806
806
6
I
LEDHx
= 100mA, V
LEDHx
= 300mV
●
mA/mA
mA/mA
%
mV
3452f
(Max – Min)/[(Max + Min)/2] • 100%, I
LEDHx
= 100mA,
V
LEDHx
= 300mV, 2.7V
≤
V
IN
≤
5.5V
I
LEDHx
= 100mA
2
U
µA
kHz
mV
mV
W
U
U
W W
W
LTC3452
ELECTRICAL CHARACTERISTICS
The
●
denotes specifications which apply over the full operating temperature range, otherwise specifications are T
A
= 25°C.
V
IN
= PV
IN
= V
OUT
= 3.6V unless otherwise specified. (Note 2)
PARAMETER
LED
Lx
Output Current Ratio (I
LEDLx
/I
SETL
)
(Note 6)
CONDITIONS
I
LEDLx|MAX
= 20mA, V
LEDLx
= 300mV
PWM Duty Cycle = 6%
●
MIN
1.8
1.75
3.66
3.56
7.32
7.12
14.72
14.32
29.44
28.64
58.88
57.92
117.12
114.56
TYP
2
2
4
4
8
8
16
16
32
32
64
64
128
128
256
245
2.5
130
MAX
2.16
2.21
4.28
4.38
8.56
8.76
17.04
17.44
33.92
34.56
67.2
68.16
134.4
137.6
268.8
272.64
8
UNITS
mA/mA
mA/mA
mA/mA
mA/mA
mA/mA
mA/mA
mA/mA
mA/mA
mA/mA
mA/mA
mA/mA
mA/mA
mA/mA
mA/mA
mA/mA
mA/mA
%
mV
PWM Duty Cycle = 19%
●
PWM Duty Cycle = 31%
●
PWM Duty Cycle = 44%
●
PWM Duty Cycle = 56%
●
PWM Duty Cycle = 69%
●
PWM Duty Cycle = 81%
●
PWM Duty Cycle = 94%
LED
Lx
Output Current Matching
LED
Lx
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
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 LTC3452E 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.
(Max – Min)/[(Max + Min)/2] • 100%, I
LEDLx
= 20mA,
V
LEDLx
= 300mV
I
LEDLx
= 20mA
V
LEDLx
= V
LEDHy
= 0V
Switches A and D at 100mA
Switches B and C at 100mA
Switch A
Switch D
Switches A and D
Switches B and C
234.24
●
229.12
●
4.35
4.5
210
205
4.75
V
mΩ
mΩ
1000
–1
–1
0.9
1600
200
2400
1
1
mA
mA
µA
µA
MHz
µs
1
650
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.
Note 5:
Do not exceed 50kHz PWM frequency in the application.
Note 6:
This parameter is tested in a setup which forces conditions
equivalent to those programmed by the indicated duty cycle.
3452f
3
LTC3452
TYPICAL PERFOR A CE CHARACTERISTICS
Shutdown Current vs Temperature
20
18
SHUTDOWN CURRENT (µA)
SHUTDOWN CURRENT (µA)
12
10
8
6
4
2
0
2.7
16
14
12
10
8
6
4
2
V
IN
= 2.7V
V
IN
= 3.6V
V
IN
= 5.5V
V
IN
= 4.2V
UVLO THRESHOLD (V)
0
–55
–35 –15
5 25 45 65 85
105
125
TEMPERATURE (°C)
3452 G01
Enable Thresholds vs Temperature
1200
1100
V
IN
= 3.6V
900
1000
ENABLE THRESHOLDS (mV)
ENABLE THRESHOLDS (mV)
1000
900
800
700
600
500
400
300
200
–55 –35 –15
5 25 45 65 85 105 125
TEMPERATURE (°C)
3452 G04
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
V
ISETL,H
(mV)
V
IH
V
IL
I
SETL,H
Servo Voltage vs V
IN
812
808
804
T
A
= 25°C
4.60
4.58
4.56
4.54
V
ISETL,H
(mV)
VOUT (V)
800
796
792
788
784
780
2.7
3.1
3.5
3.9 4.3
V
IN
(V)
4.7
5.1
5.5
4
U W
Shutdown Current vs V
IN
T
A
= 25°C
2.5
Undervoltage Lockout Threshold
vs Temperature
2.3
2.1
V
IN
RISING
1.9
V
IN
FALLING
1.7
3.1
3.5
3.9 4.3
V
IN
(V)
4.7
5.1
5.5
1.5
–55
–35
–15
5
25 45
65 85 105
125
TEMPERATURE (°C)
3452 G03
3452 G02
Enable Thresholds vs V
IN
T
A
= 25°C
I
SETL,H
Servo Voltage
vs Temperature
812
808
804
800
796
792
788
784
780
–55 –35 –15
5 25 45 65 85 105 125
TEMPERATURE (°C)
3452 G06
V
IN
= 3.6V
R
ISETL
= 10.2k
R
ISETH
= 4.99k
800
3452 G05
Maximum Regulated V
OUT
vs Temperature
V
IN
= 3.6V
4.52
4.50
4.48
4.46
4.44
4.42
4.40
–55 –35 –15
5 25 45 65 85 105 125
TEMPERATURE (°C)
3452 G08
3452 G07
3452f
LTC3452
TYPICAL PERFOR A CE CHARACTERISTICS
PMOS R
DS(ON)
vs Temperature
325
300
V
IN
= 2.7V
275
275
250
225
200
175
150
5 25 45 65 85 105 125
TEMPERATURE (°C)
3452 G10
250
225
V
IN
= 5.5V
200
175
150
125
–55 –35 –15
V
IN
= 4.2V
FREQUENCY (kHz)
R
DS(ON)
(mΩ)
R
DS(ON)
(mΩ)
V
IN
= 3.6V
Output Voltage Ripple
(Front Page Application)
V
IN
= 3V
V
OUT
= 3.1V
I
LED
= 100mA
U W
NMOS R
DS(ON)
vs Temperature
325
300
Oscillator Frequency
vs Temperature
1050
1040
1030
V
OUT
= 3V
V
IN
= 2.7V
V
IN
= 3.6V
1020
1010
1000
990
980
970
960
V
IN
= 4.2V
V
IN
= 5.5V
V
IN
= 3.6V
V
IN
= 5.5V
V
IN
= 4.2V
V
IN
= 2.7V
125
–55 –35 –15
5 25 45 65 85 105 125
TEMPERATURE (°C)
3452 G11
950
–55 –35 –15
5 25 45 65 85 105 125
TEMPERATURE (°C)
3452 G12
Start-Up Transient
CH1, V
OUT
1V/DIV
CH2, I
LED
300mA FINAL VALUE
CH3, EN
H
1V/DIV
3452 G13
V
IN
= 3.6V
I
LEDH
= 300mA
3452 G14
3452f
5
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