LT3466 데이터 시트보기 (PDF) - Linear Technology

부품명

상세내역

일치하는 목록

LT3466

Dual Full Function White LED Step-Up Converter with Built-In Schottky Diodes

Linear Technology 

LT3466

APPLICATIO S I FOR ATIO

Table 3. Inrush Peak Current

VIN (V)

5

L (µH)

15

5

33

5

47

5

68

9

47

12

33

COUT (µF)

0.47

1.00

2.2

1.00

0.47

0.22

IP (A)

0.78

0.77

0.95

0.53

0.84

0.93

Typically peak inrush current will be less than the value

calculated above. This is due to the fact that the DC

resistance in the inductor provides some damping result-

ing in a lower peak inrush current.

PROGRAMMING LED CURRENT

The LED current of each LED string can be set indepen-

dently by the choice of resistors RFB1 and RFB2 respec-

tively (Figure 2). The feedback reference is 200mV. In

order to have accurate LED current, precision resistors are

preferred (1% is recommended).

RFB1

=

200mV

ILED1

RFB2

=

200mV

ILED2

Table 4. RFB Value Selection

ILED (mA)

5

10

15

20

25

RFB (Ω)

40.2

20.0

13.3

10.0

8.06

Most White LEDs are driven at maximum currents of

15mA to 20mA.

DIMMING CONTROL

There are two different types of dimming control circuits.

The LED current in the two drivers can be set indepen-

dently by modulating the CTRL1 and CTRL2 pins

respectively.

12

Using a DC Voltage

For some applications, the preferred method of brightness

control is a variable DC voltage to adjust the LED current.

The CTRL pin voltage can be modulated to set the dimming

of the respective LED string. As the voltage on the CTRL

pin increases from 0V to 1.6V, the LED current increases

from 0 to ILED. As the CTRL pin voltage increases beyond

1.6V, it has no effect on the LED current.

The LED current can be set by:

ILED ≈ (200mV/RFB), when VCTRL > 1.6V

ILED ≈ (VCTRL/5 • RFB), when VCTRL < 1V

Feedback voltage variation versus control voltage is given

in the Typical Performance Characteristics graphs.

Using a Filtered PWM Signal

A variable duty cycle PWM can be used to control the

brightness of the LED string. The PWM signal is filtered

(Figure 8) by an RC network and fed to the CTRL1, CTRL2

pins.

The corner frequency of R1, C1 should be much lower than

the frequency of the PWM signal. R1 needs to be much

smaller than the internal impedance in the CTRL pins,

which is 100kΩ.

R1

PWM 10k

10kHz TYP

LT3466

CTRL1,2

C1

1µF

3466 F08

Figure 8. Dimming Control Using a Filtered PWM Signal

LOW INPUT VOLTAGE APPLICATIONS

The LT3466 can be used in low input voltage applications.

The input supply voltage to the LT3466 must be 2.7V or

higher. However, the inductors can be run off a lower

battery voltage. This technique allows the LEDs to be

powered off two alkaline cells. Most portable devices have

a 3.3V logic supply voltage which can be used to power the

LT3466. The LEDs can be driven straight from the battery,

resulting in higher efficiency.

3466fa

Share Link: