Document
U U
FEATURES
■ Drives Up to 20 White LEDs (10 in Series per Converter) from a 3.6V Supply
■ Two Independent Step-Up Converters Capable of Driving Asymmetric LED Strings
■ Independent Dimming and Shutdown Control of the Two LED Strings
■ Internal Schottky Diodes ■ Internal Soft-Start Eliminates Inrush Current ■ Open LED Protection (39.5V Max VOUT) ■ Fixed Frequency Operation Up to 2MHz ■ 81% Efficiency Driving 16 White LEDs at 15mA
(Eight per Driver) from a 3.6V Supply ■ Wide Input Voltage Range: 2.7V to 24V ■ Available in 10-Pin DFN and 16-Pin Thermally
Enhanced TSSOP Packages
U APPLICATIO S
■ Main/Sub Displays ■ Digital Cameras, Sub-Notebook PCs ■ PDAs, Handheld Computers ■ Automotive
LT3466
Dual Full Function White LED Step-Up Converter with Built-In Schottky Diodes
DESCRIPTIO
LT®3466 is a dual full function step-up DC/DC converter specifically designed to drive up to 20 White LEDs (10 in series per converter) with a constant current. Series connection of the LEDs provides identical LED currents resulting in uniform brightness and eliminating the need for ballast resistors and expensive factory calibration.
The two independent converters are capable of driving asymmetric LED strings. The dimming of the two LED strings can also be controlled independently. The LT3466 is ideal for providing backlight for main and sub-displays in cell phones and other handheld devices.
The LT3466 operating frequency can be set with an external resistor over a 200kHz to 2MHz range. A low 200mV feedback voltage minimizes power loss in the current setting resistor for better efficiency. Additional features include output voltage limiting when LEDs are disconnected and internal soft-start.
The LT3466 is available in the 10-pin (3mm × 3mm × 0.75mm) DFN and 16-pin thermally enhanced TSSOP packages.
, LTC and LT are registered trademarks of Linear Technology Corporation.
TYPICAL APPLICATIO
3V TO 5V
1µF
L1 47µH
L2 47µH
LED1
2.2µF
SW1 VIN VOUT1
SW2 VOUT2
LT3466
2.2µF
LED2
FB1
FB2
CTRL1 RT GND CTRL2
10Ω
OFF ON 63.4k
SHUTDOWN
AND DIMMING
CONTROL 1
OFF ON
SHUTDOWN AND DIMMING CONTROL 2
10Ω
3466 F01a
Figure 1. Li-Ion Powered Driver for 8/8 White LEDs
EFFICIENCY (%)
Conversion Efficiency
85 VIN = 3.6V 8/8 LEDs
80
75
70
65
60
55
50 0
5
10
15
LED CURRENT (mA)
20
3466 F01b
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LT3466
U WW W
ABSOLUTE AXI U RATI GS (Note 1)
Input Voltage (VIN) ................................................... 24V SW1, SW2 Voltages ................................................ 44V
VOUT1, VOUT2 Voltages ............................................. 44V CTRL1, CTRL2 Voltages ........................................... 24V
FB1, FB2, RT Voltages ................................................ 2V Operating Temperature Range (Note 2) ... –40°C to 85°C
Maximum Junction Temperature ......................... 125°C Storage Temperature Range
DFN .................................................. –65°C to 125°C TSSOP .............................................. –65°C to 150°C Lead Temperature (Soldering, 10 sec, TSSOP) ..... 300°C
UW U PACKAGE/ORDER I FOR ATIO
TOP VIEW
VOUT1 1 SW1 2 VIN 3 SW2 4
VOUT2 5
10 FB1
9 CTRL1
11
8 RT
7 CTRL2
6 FB2
DD PACKAGE 10-LEAD (3mm × 3mm) PLASTIC DFN
TJMAX = 125°C, θJA = 43°C/W, θJC = 2.96°C/W EXPOSED PAD (PIN 11) IS GND MUST BE SOLDERED TO PCB
ORDER PART NUMBER
LT3466EDD
DD PART MARKING LBBH
Consult LTC Marketing for parts specified with wider operating temperature ranges.
TOP VIEW
GND 1 NC 2
VOUT1 3 SW1 4 VIN 5 SW2 6
VOUT2 7 GND 8
16 GND 15 FB1 14 CTRL1 13 NC 17 12 RT 11 CTRL2 10 FB2 9 GND
FE PACKAGE 16-LEAD PLASTIC TSSOP
TJMAX = 125°C, θJA = 38°C/W, θJC(PAD) = 10°C/W EXPOSED PAD (PIN 17) IS GND MUST BE SOLDERED TO PCB
ORDER PART NUMBER LT3466EFE
FE PART MARKING 3466EFE
ELECTRICAL CHARACTERISTICS The ● denotes specifications that apply over the full operating temperature
range, otherwise specifications are at TA = 25°C. VIN = 3V, VCTRL1 = 3V, VCTRL2 = 3V, unless otherwise specified.
PARAMETER
CONDITIONS
MIN TYP MAX UNITS
Minimum Operating Voltage
2.7
V
Maximum Operating Voltage
24
V
FB1 Voltage
● 192
200
208
mV
FB2 Voltage
● 192
200
208
mV
Offset Voltage (VOS) Between FB1 and FB2 Voltages FB1 Pin Bias Current FB2 Pin Bias Current Quiescent Current
VOS = |FB1 – FB2| VFB1 = 0.2V (Note 3) VFB2 = 0.2V (Note 3) VFB1 = VFB2 = 0.3V CTRL1 = CTRL2 = 0V
0
1.5
7.5
mV
10
50
nA
10
50
nA
5
7.5
mA
16
25
µA
Switching Frequency Oscillator Frequency Range
RT = 48.7k (Note 4)
0.8
1
1.2
MHz
200
2000
kHz
Nominal RT Pin Voltage Maximum Duty Cycle
RT = 48.7k
RT = 48.7k RT = 20.5k RT = 267k
0.54
V
● 90
96
%
92
%
99
%
3466fa
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LT3466
ELECTRICAL CHARACTERISTICS The ● denotes specifications that apply over the full operating temperature
range, otherwise specifications are at TA = 25°C. VIN = 3V, VCTRL1 = 3V, VCTRL2 = 3V, unless otherwise specified.
PARAMET.