Datasheet

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LT3465/LT3465A

3465afa

, LTC and LT are registered trademarks of Linear Technology Corporation. ThinSOT is a

trademark of Linear Technology Corporation. All other trademarks are the property of their

respective owners.

APPLICATIO S

FEATURES

TYPICAL APPLICATIO

DESCRIPTIO

■

Inherently Matched LED Current

■

Drives Up to Six LEDs from a 3.6V Supply

■

No External Schottky Diode Required

■

1.2MHz Switching Frequency (LT3465)

■

2.4MHz Switching Frequency Above AM Broadcast

Band (LT3465A)

■

Range: 2.7V to 16V

■

OUT(MAX)

= 30V

■

Automatic Soft-Start (LT3465)

■

Open LED Protection

■

High Efficiency: 81% (LT3465) 79% (LT3465A)

Typical

■

Requires Only 0.22µF Output Capacitor

■

Low Profile (1mm) SOT-23

1.2MHz/2.4MHz White

LED Drivers with Built-in

Schottky in ThinSOT

■

Cellular Phones

■

PDAs, Handheld Computers

■

Digital Cameras

■

MP3 Players

■

GPS Receivers

The LT

3465/LT3465A are step-up DC/DC converters

designed to drive up to six LEDs in series from a Li-Ion cell.

Series connection of the LEDs provides identical LED

currents and eliminates the need for ballast resistors.

These devices integrate the Schottky diode required exter-

nally on competing devices. Additional features include

output voltage limiting when LEDs are disconnected, one-

pin shutdown and dimming control. The LT3465 has

internal soft-start.

The LT3465 switches at 1.2MHz, allowing the use of tiny

external components. The faster LT3465A switches at

2.4MHz. Constant frequency switching results in low input

noise and a small output capacitor. Just 0.22µF is required

for 3-, 4- or 5-LED applications.

The LT3465 and LT3465A are available in the low profile

(1mm) 6-lead SOT-23 (ThinSOT

) package.

Figure 1. Li-Ion Powered Driver for Four White LEDs

SW V

OUT

LT3465/

LT3465A

CTRL

3465A F01a

10Ω

1µF

0.22µF

C1, C2: X5R OR X7R DIELECTRIC

L1: MURATA LQH32CN220

22µH

3V TO 5V

SHUTDOWN

AND DIMMING

CONTROL

GND

LED CURRENT (mA)

EFFICIENCY (%)

3465A F01b

= 3.6V

4 LEDs

LT3465

LT3465A

Conversion Efficiency

Summary of content (16 pages)

PAGE 1
LT3465/LT3465A 1.2MHz/2.4MHz White LED Drivers with Built-in Schottky in ThinSOT U FEATURES DESCRIPTIO ■ The LT®3465/LT3465A are step-up DC/DC converters designed to drive up to six LEDs in series from a Li-Ion cell. Series connection of the LEDs provides identical LED currents and eliminates the need for ballast resistors. These devices integrate the Schottky diode required externally on competing devices.
PAGE 2
LT3465/LT3465A W W W AXI U U U W PACKAGE/ORDER I FOR ATIO U ABSOLUTE RATI GS (Note 1) TOP VIEW Input Voltage (VIN) ................................................. 16V SW Voltage ............................................................. 36V FB Voltage ................................................................ 2V CTRL Voltage .......................................................... 10V Operating Temperature Range (Note 2) .. – 40°C to 85°C Maximum Junction Temperature ...................
PAGE 3
LT3465/LT3465A U W TYPICAL PERFOR A CE CHARACTERISTICS Switch Saturation Voltage (VCESAT) 300 400 350 300 250 200 150 100 50 0 50 100 150 200 250 SWITCH CURRENT (mA) 300 250 24 21 200 150 18 15 12 100 9 6 50 3 350 0 1000 400 600 800 200 SCHOTTKY FORWARD DROP (mV) 0 1200 4 2 6 10 8 VIN (V) 12 3465A G02 3465A G01 VFB vs VCTRL 250 TA = 25°C 27 0 0 30 TA = 25°C IQ (µA) TA = 25°C SCHOTTKY FORWARD CURRENT (mA) SWITCH SATURATION VOLTAGE (mV) 450 Shutdown Quiescent Current (CTRL
PAGE 4
LT3465/LT3465A U W TYPICAL PERFOR A CE CHARACTERISTICS Quiescent Current (CTRL = 3V) Feedback Voltage Switching Current Limit 3.0 210 400 350 204 CURRENT LIMIT (mA) 2.5 206 2.0 202 IQ (mA) FEEDBACK VOLTAGE (mV) 208 200 1.5 198 1.0 196 194 –50°C 25°C 100°C 0.
PAGE 5
LT3465/LT3465A U U U PI FU CTIO S VOUT (Pin 1): Output Pin. Connect to output capacitor and LEDs. Minimize trace between this pin and output capacitor to reduce EMI. GND (Pin 2): Ground Pin. Connect directly to local ground plane. FB (Pin 3): Feedback Pin. Reference voltage is 200mV. Connect LEDs and a resistor at this pin. LED current is determined by the resistance and CTRL pin voltage: CTRL (Pin 4): Dimming Control and Shutdown Pin. Ground this pin to shut down the device.
PAGE 6
LT3465/LT3465A W BLOCK DIAGRA VIN FB 5 3 VREF 1.25V 200mV – + + 6 SW – A1 1 DRIVER RC + A2 R CC S Q1 Q OVERVOLTAGE PROTECT + Σ 0.2Ω 10k CTRL VOUT COMPARATOR – RAMP GENERATOR 40k 4 2 GND 1.2MHz* OSCILLATOR 3465A F02 *2.4MHz FOR LT3465A Figure 2.
PAGE 7
LT3465/LT3465A U W U U APPLICATIO S I FOR ATIO Operation Minimum Output Current The LT3465 uses a constant frequency, current mode control scheme to provide excellent line and load regulation. Operation can be best understood by referring to the block diagram in Figure 2. At the start of each oscillator cycle, the SR latch is set, which turns on the power switch Q1.
PAGE 8
LT3465/LT3465A U W U U APPLICATIO S I FOR ATIO skipping using a 1k resistor from FB to GND. The photo in Figure 3b details circuit operation driving three white LEDs at a 0.2mA load. Peak inductor current is less than 30mA. 85 EFFICIENCY (%) 75 Inductor Selection A 22µH inductor is recommended for most LT3465 applications. Although small size and high efficiency are major concerns, the inductor should have low core losses at 1.2MHz and low DCR (copper wire resistance).
PAGE 9
LT3465/LT3465A U W U U APPLICATIO S I FOR ATIO Soft-Start (LT3465) The LT3465 has an internal soft-start circuit to limit the input current during circuit start-up. The circuit start-up waveforms are shown in Figure 5. inductors, which is usually the case for this application, the peak inrush current can be simplified as follows: IP = ⎛ α π⎞ VIN – 0.6 • exp⎜ – • ⎟ L•ω ⎝ ω 2⎠ Table 3 gives inrush peak currents for some component selections. IIN 50mA/DIV Table 3.
PAGE 10
LT3465/LT3465A U W U U APPLICATIO S I FOR ATIO percent duty cycle sets the LED current to zero, while 100% duty cycle sets it to full current. Average LED current increases proportionally with the duty cycle of the PWM signal. With the PWM signal at the CTRL pin to turn the LT3465A on and off, the output capacitor is charged and discharged accordingly. This capacitor charging/ discharging affects the waveform at the FB pin.
PAGE 11
LT3465/LT3465A U W U U APPLICATIO S I FOR ATIO case. The Average FB Voltage vs PWM Duty Cycle curves of different PWM frequencies with different output capacitors are shown in Figures 7c and 7d respectively. For PWM frequency lower than 1kHz, the curves are almost linear. For PWM frequency higher than 10kHz, the curves show strong nonlinearity. Since the cause of the nonlinearity is the output capacitor charging/discharging, the output capacitance and output voltage also affect 200 COUT = 0.
PAGE 12
LT3465/LT3465A U W U U APPLICATIO S I FOR ATIO Open-Circuit Protection The LT3465 and LT3465A have an internal open-circuit protection circuit. In the cases of output open circuit, when the LEDs are disconnected from the circuit or the LEDs fail, the VOUT is clamped at 30V. The LT3465 and LT3465A will then switch at a very low frequency to minimize the input current. VOUT and input current during output open circuit are shown in the Typical Performance Characteristics.
PAGE 13
LT3465/LT3465A U TYPICAL APPLICATIO S Li-Ion to Two White LEDs 85 L1 22µH VIN = 3.6V 2 LEDs 80 3V TO 5V VOUT VIN CIN 1µF LT3465/ LT3465A FB CTRL GND COUT 1µF EFFICIENCY (%) 75 SW 70 65 60 R1 4Ω 3465A TA01a 55 CIN: TAIYO YUDEN JMK107BJ105 COUT: AVX 0603ZD105 L1: MURATA LQH32CN220 LT3465 LT3465A 50 10 0 30 20 LED CURRENT (mA) 40 50 3465A TA01b Li-Ion to Three White LEDs 85 L1 22µH VIN = 3.6V 3 LEDs 80 3V TO 5V VOUT VIN CIN 1µF LT3465/ LT3465A FB CTRL GND COUT 0.
PAGE 14
LT3465/LT3465A U TYPICAL APPLICATIO Li-Ion to Five White LEDs 85 L1 22µH 3V TO 5V VIN = 3.6V 5 LEDs 80 SW VOUT VIN CIN 1µF LT3465/ LT3465A FB CTRL GND COUT 0.
PAGE 15
LT3465/LT3465A U PACKAGE DESCRIPTIO S6 Package 6-Lead Plastic TSOT-23 (Reference LTC DWG # 05-08-1636) 0.62 MAX 2.90 BSC (NOTE 4) 0.95 REF 1.22 REF 3.85 MAX 2.62 REF 1.4 MIN 2.80 BSC 1.50 – 1.75 (NOTE 4) PIN ONE ID RECOMMENDED SOLDER PAD LAYOUT PER IPC CALCULATOR 0.30 – 0.45 6 PLCS (NOTE 3) 0.95 BSC 0.80 – 0.90 0.20 BSC 0.01 – 0.10 1.00 MAX DATUM ‘A’ 0.30 – 0.50 REF 0.09 – 0.20 (NOTE 3) 1.90 BSC S6 TSOT-23 0302 NOTE: 1. DIMENSIONS ARE IN MILLIMETERS 2. DRAWING NOT TO SCALE 3.
PAGE 16
LT3465/LT3465A U TYPICAL APPLICATIO Li-Ion to Six White LEDs 85 L1 47µH/22µH VIN = 3.6V 6 LEDs 80 3V TO 5V VOUT VIN CIN 1µF COUT 0.47µF LT3465/ LT3465A FB CTRL GND EFFICIENCY (%) 75 SW 70 65 60 R1 10Ω 3465A TA04a CIN: TAIYO YUDEN JMK107BJ105 COUT: TAIYO YUDEN GMK212BJ474 L1: MURATA LQH32CN470 (LT3465) L1: MURATA LQH32CN220 (LT3465A) 55 LT3465 LT3465A 50 0 5 15 10 LED CURRENT (mA) 20 3465A TA04b RELATED PARTS PART NUMBER DESCRIPTION LT1618 Constant Current, Constant Voltage, 1.