LT3517(RevA) 데이터 시트보기 (PDF) - Linear Technology

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LT3517
(Rev.:RevA)

Full-Featured LED Driver with 1.5A Switch Current

Linear Technology 

LT3517

APPLICATIONS INFORMATION

performance, size and cost. The compensation resistor

and capacitor at VC are selected to optimize control loop

stability. For typical LED applications, a 10nF compensa-

tion capacitor at VC is adequate and a series resistor is not

required. A compensation resistor may be used to increase

the slew rate on the VC pin to maintain tighter regulation

of LED current during fast transients on VIN or CTRL.

Diode Selection

The Schottky diode conducts current during the interval

when the switch is turned off. Select a diode rated for

the maximum SW voltage. If using the PWM feature for

dimming, it is important to consider diode leakage, which

increases with the temperature, from the output during the

PWM low interval. Therefore, choose the Schottky diode

with sufficiently low leakage current. Table 3 has some

recommended component vendors.

Table 3. Schottky Diodes

PART NUMBER

Diodes Inc.

DFLS160

Zetex

ZLLS1000TA

International Rectifier

10MQ060N

VR (V)

60

40

60

IAVE (A)

1

1

1.5

Board Layout

The high speed operation of the LT3517 demands careful

attention to board layout and component placement. The

Exposed Pad of the package is the only GND terminal of

the IC and is also important for thermal management of

the IC. It is crucial to achieve a good electrical and thermal

contact between the Exposed Pad and the ground plane of

the board. To reduce electromagnetic interference (EMI),

it is important to minimize the area of the SW node. Use

a GND plane under SW and minimize the length of traces

in the high frequency switching path between SW and

GND through the diode and the capacitors. Since there is

a small DC input bias current to the ISN and ISP inputs,

resistance in series with these inputs should be minimized

and matched, otherwise there will be an offset. Finally, the

bypass capacitor on the VIN supply to the LT3517 should

be placed as close as possible to the VIN terminal of the

device.

Soft-Start

For many applications, it is necessary to minimize the

inrush current at start-up. The built-in soft-start circuit

significantly reduces the start-up current spike and

output voltage overshoot. A typical value for the soft-start

capacitor is 0.1μF.

3517fa

11

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