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PDF LTC3452 Data sheet ( Hoja de datos )
| Número de pieza | LTC3452 | |
| Descripción | Synchronous Buck-Boost MAIN/CAMERA White LED Driver | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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LTC3452www.DataSheet4U.com
Synchronous Buck-Boost
MAIN/CAMERA White LED Driver
FEATURES
■ High Efficiency: ≥85% Over Entire Li-Ion Battery
Range
■ Wide VIN 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
U
APPLICATIO S
■ 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.
DESCRIPTIO
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.
TYPICAL APPLICATIO
VIN
SINGLE
+
Li-Ion CELL
2.7V TO 4.2V
5 × 20mA White LED Display + 200mA Camera Light Driver
L
4.7µH
2.2µF
VIN PVIN SW1
ENH
SW2 VOUT
D1
CAM
LEDH1
200mA
ISETH
LEDH2
6.19k
0.1µF
VC
ENL
ISETL
1MHz
BUCK/BOOST
LTC3452
LEDL1
LEDL2
LEDL3
LEDL4
LEDL5
D2
0mA TO
20mA
D3
0mA TO D4
20mA
0mA TO D5
20mA
0mA TO D6
20mA
0mA TO
20mA
4.7µF
10.2k
GND GND PGND EXPOSED PAD
MAIN DISPLAY LED BACKLIGHT
D1: AOT 2015
D2 TO D6: NICHIA NSCW100
L: COILCRAFT DO3314-472
3452 TA01a
Torch and Flash Mode Efficiency
95
93
91
TA = 25°C
EFFICIENCY
=
Σ
(VOUT
– VLEDx) •
VIN • IIN
ILEDx
89 TORCH MODE AT 100mA
87
85
83
81 FLASH MODE AT 200mA
79
77
75
2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5
VIN (V)
3452 TA01b
3452f
1
1 page  
TYPICAL PERFOR A CE CHARACTERISTICS
LTC3452www.DataSheet4U.com
PMOS RDS(ON) vs Temperature
325
300
VIN = 2.7V
275
VIN = 3.6V
250
225
VIN = 5.5V
200 VIN = 4.2V
175
150
125
–55 –35 –15 5 25 45 65 85 105 125
TEMPERATURE (°C)
3452 G10
NMOS RDS(ON) vs Temperature
325
300
275
VIN = 2.7V
250
VIN = 3.6V
225
200 VIN = 5.5V
175 VIN = 4.2V
150
125
–55 –35 –15 5 25 45 65 85 105 125
TEMPERATURE (°C)
3452 G11
Oscillator Frequency
vs Temperature
1050
VOUT = 3V
1040
1030
1020
1010
VIN = 5.5V
VIN = 4.2V
1000
990
VIN = 3.6V
980
VIN = 2.7V
970
960
950
–55 –35 –15 5 25 45 65 85 105 125
TEMPERATURE (°C)
3452 G12
Output Voltage Ripple
(Front Page Application)
Start-Up Transient
CH1, VOUT
1V/DIV
CH2, ILED
300mA FINAL VALUE
CH3, ENH
1V/DIV
VIN = 3V
VOUT = 3.1V
ILED = 100mA
3452 G13
VIN = 3.6V
ILEDH = 300mA
3452 G14
3452f
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5 Page 
LTC3452www.DataSheet4U.com
APPLICATIO S I FOR ATIO
COMPONENT SELECTION
Inductor Selection
The high frequency operation of the LTC3452 allows the
use of small surface mount inductors. The inductor cur-
rent ripple is typically set to 20% to 40% of the maximum
average inductor current. For a given ripple the inductance
term in boost mode is:
( )L
>
VIN(MIN)2 • VOUT – VIN(MIN) • 100%
f •IOUT(MAX) • %Ripple • VOUT2
and in buck mode is:
( )L
>
VOUT • VIN(MAX) – VOUT
f •IOUT(MAX) • %Ripple •
• 100%
VIN(MAX)
where:
f = operating frequency, Hz
%Ripple = allowable inductor current ripple, %
VIN(MIN) = minimum input voltage, V
VIN(MAX) = maximum input voltage, V
VOUT = output voltage, V
IOUT(MAX) = maximum output load current
For high efficiency, choose an inductor with a high fre-
quency core material, such as ferrite, to reduce core loses.
The inductor should have low ESR (equivalent series
resistance) to reduce the I2R 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 radi-
ated noise, use a toroid, pot core or shielded bobbin
inductor. For the white LED application, a 4.7µH inductor
value is recommended. See Table 2 for a list of component
suppliers.
Table 2. Inductor Vendor Information
SUPPLIER
WEB SITE
Coilcraft
www.coilcraft.com
Cooper/Coiltronics
www.cooperet.com
Murata
www.murata.com
Sumida
www.japanlink.com/sumida
Vishay-Dale
www.vishay.com
Input Capacitor Selection
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 3 for a list of component
suppliers.
Table 3. Capacitor Vendor Information
SUPPLIER
WEB SITE
AVX www.avxcorp.com
Sanyo
www.sanyovideo.com
Taiyo Yuden
www.t-yuden.com
TDK www.component.tdk.com
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:
( )%Ripple
_
Boost
=
IOUT(MAX) • VOUT – VIN(MIN)
COUT • VOUT2 • f
• 100
%
( )%Ripple
_ Buck
=
8
VIN(MAX) – VOUT
• VIN(MAX) • f2 •L
• 100
• COUT
%
where COUT = output filter capacitor, F
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.
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 3 for a list of component suppliers.
3452f
11
11 Page | ||
| Páginas | Total 16 Páginas | |
| PDF Descargar | [ Datasheet LTC3452.PDF ] | |
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