LTH2 Marking, LT3465 datasheet(9/16 Pages) LINER

9 / 16 page

LT3465/LT3465A

3465afa

APPLICATIO S I FOR ATIO

inductors, which is usually the case for this application,

the peak inrush current can be simplified as follows:

⎛

⎝⎜

⎞

⎠⎟

–.

•

• exp –

•

Table 3 gives inrush peak currents for some component

selections.

Table 3. Inrush Peak Current

VIN (V)

r (

Ω)L (µH)

C (

µF)

IP (A)

0.5

0.22

0.38

0.5

0.70

3.6

0.5

0.22

0.26

0.5

0.60

LED Current and Dimming Control

The LED current is controlled by the feedback resistor (R1

in Figure 1) and the feedback reference voltage.

ILED = VFB/RFB

The CTRL pin controls the feedback reference voltage as

shown in the Typical Performance Characteristics. For

CTRL higher than 1.8V, the feedback reference is 200mV,

which results in full LED current. CTRL pin can be used as

dimming control when CTRL voltage is between 200mV to

1.5V. In order to have accurate LED current, precision

resistors are preferred (1% is recommended). The for-

mula and table for RFB selection are shown below.

RFB = 200mV/ILED-Full

(1)

Table 4. RFB Resistor Value Selection

FULL ILED (mA)

R1 (

Ω)

40.0

20.0

13.3

10.0

The filtered PWM signal can be considered to be an

adjustable DC voltage. It can be used to adjust the CTRL

voltage source in dimming control. The circuit is shown in

Figure 6. The corner frequency of R1 and C1 should be

IIN 50mA/DIV

VIN = 3.6V

200

µs/DIV

3465 F05

4 LEDs, 20mA

L = 22

µH

C = 0.22

µF

VOUT 5V/DIV

VFB 100mV/DIV

CTRL 5V/DIV

Figure 5. Start-Up Waveforms

Inrush Current

The LT3465 and LT3465A have a built-in Schottky diode.

When supply voltage is applied to the VIN pin, the voltage

difference between VIN and VOUT generates inrush current

flowing from input through the inductor and the Schottky

diode to charge the output capacitor to VIN. The maximum

current the Schottky diode in the LT3465 and LT3465A

can sustain is 1A. The selection of inductor and capacitor

value should ensure the peak of the inrush current to be

below 1A. The peak inrush current can be calculated

as follows:

⎛

⎝⎜

⎞

⎠⎟

⎡

⎣

⎢

⎤

⎦

⎥

⎛

⎝⎜

⎞

⎠⎟

⎡

⎣

⎢

⎤

⎦

⎥

= +

()

–.

•

• exp –

• arctan

• sin arctan

•

–

•

where L is the inductance, r is the resistance of the

inductor and C is the output capacitance. For low DCR

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.

LTH2 Marking, LT3465 Datasheet(PDF) 9 Page - Linear Technology

LT3465 Datasheet(HTML) 9 Page - Linear Technology

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

Datasheet Download

Link URL