LT3519EMS-1 查看數據表（PDF） - Linear Technology

零件编号

产品描述 (功能)

生产厂家

LT3519EMS-1

LED Driver with Integrated Schottky Diode

Linear Technology 

LT3519/LT3519-1/LT3519-2

APPLICATIONS INFORMATION

Dimming Control

There are two methods to control the current source for

dimming using the LT3519/LT3519-1/LT3519-2. The first

method, PWM Dimming, uses the PWM pin to modulate

the current source between zero and full current to achieve

a precisely programmed average current. To make this

method of current control more accurate, the switch de-

mand current is stored on the internal VC node during the

quiescent phase when PWM is low. This feature minimizes

recovery time when the PWM signal goes high. To obtain

best PWM dimming performance, it is necessary to use

an external disconnect switch in the LED current path to

prevent the output capacitor from discharging during the

PWM signal low phase. For best product of analog and PWM

dimming, the minimum PWM low or high time should be at

least six switching cycles (3μs for fSW = 2MHz). Maximum

PWM period is determined by the system. The maximum

PWM dimming ratio (PWMRATIO) can be calculated from

the maximum PWM period (tMAX) and the minimum PWM

pulse width (tMIN) as follows:

PWMRATIO

=

tMAX

tMIN

Example:

tMAX = 9ms, tMIN = 3μs (fSW = 2MHz)

PWMRATIO

=

9ms

3µs

=

3000

:1

The second method of dimming control, Analog Dim-

ming, uses the CTRL pin to linearly adjust the current

sense threshold during the PWM high state. When the

CTRL pin voltage is less than 1V but more than 100mV,

the LED current is:

ILED

=

VCTRL – 100mV

4 • RSENSE

When VCTRL is higher than 1.2V, the LED current is clamped

to be:

ILED

=

250mV

RSENSE

When VCTRL is more than 1V but less than 1.2V, the

LED current is in the nonlinear region of VISP-VISN

Threshold vs VCTRL as shown in the Typical Performance

Characteristics.

The LED current programming feature through the CTRL

pin possibly increases the total dimming range by a factor

of ten. In order to have the accurate LED current, precision

resistors are preferred (1% is recommended). The CTRL

pin should not be left open. Tie to VREF if not used.

Programming Output Voltage (Constant Voltage

Regulation) or Open LED/Overvoltage Threshold

For a boost application, the output voltage can be set by

selecting the values of R1 and R2 (see Figure 1) according

to the following equation:

VOUT

=

⎛

⎝⎜

R1

R2

+

1⎞⎠⎟

•

1.22V

VOUT

R1

LT3519/

LT3519-1/ FB

LT3519-2

R2

3519 F01

Figure 1. FB Resistor Divider for Boost LED Driver

3519fa

9

Share Link: