LT3519EMS-1 Просмотр технического описания (PDF) - Linear Technology

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LT3519EMS-1

LED Driver with Integrated Schottky Diode

Linear Technology 

LT3519/LT3519-1/LT3519-2

PIN FUNCTIONS

GND (Pins 1, 8, 9, 16): Power Ground and Signal Ground.

Tie to GND plane for best thermal performance.

OPENLED (Pin 2): Open LED Status Pin. The OPENLED

pin asserts if the FB input is greater than the FB regulation

threshold minus 60mV (typical). The pin must have an

external pull-up resistor to function. When the PWM input

is low and the converter is idle, the OPENLED condition

is latched to the last valid state when the PWM input was

high. When the PWM input goes high again, the OPENLED

pin will be updated. This pin may be used to report an

open LED fault.

PWM (Pin 3): Pulse Width Modulated Input. A signal

low disables the oscillator and turns off the main switch.

PWM has an internal pull-down resistor. Tie PWM pin to

VREF if not used.

SHDN/UVLO (Pin 4): Shutdown and Undervoltage Lockout

Pin. An accurate 1.22V falling threshold with externally

programmable hysteresis detects when power is okay to

enable switching. Rising hysteresis is generated by the

external resistor divider and an accurate internal 2.2μA

pull-down current. Above the 1.25V (nominal) rising

threshold (but below 6V), SHDN/UVLO input bias current

is sub-μA. Below the falling threshold, a 2.2μA pull-down

current is enabled so the user can define the hysteresis

with external resistor selection. Tie to 0.4V or less to dis-

able device and reduce VIN quiescent current below 1μA.

Pin may be tied to VIN, but do not tie it to a voltage higher

than VIN if VIN is less than 6V.

VIN (Pin 5): Input Supply Pin. This pin must be locally

bypassed with a 1μF ceramic capacitor (or larger) placed

close to it.

SW (Pin 6): Switch Pin. Connect the inductor at this pin.

Minimize the trace at this pin to reduce EMI.

ANODE (Pin 7): Internal Schottky Anode Pin.

CATHODE (Pin 10): Internal Schottky Cathode Pin.

ISP (Pin 11): Current Sense Resistor Positive Pin. This

input is the noninverting input of the internal current sense

amplifier. Input bias current increases with VISP–VISN

increase.

ISN (Pin 12): Current Sense Resistor Negative Pin. This

input is the inverting input of the internal current sense

amplifier.

FB (Pin 13): Voltage Loop Feedback Pin. It is used to

connect to output resistor divider for constant voltage

regulation or open LED protection. The internal trans-

conductance amplifier will regulate FB to 1.22V (nominal)

through the DC/DC converter. If the FB input is regulating

the loop, the OPENLED pull-down is asserted. This action

may signal an open LED fault. Do not leave the FB pin

open. If not used, connect to GND.

CTRL (Pin 14): Current Sense Threshold Voltage Adjust-

ment Pin. This pin sets the threshold voltage across the

sense resistor between ISP and ISN. Connect directly to

the VREF pin or a voltage above 1.2V for full-scale thresh-

old of 250mV, or use a voltage between 0.1V and 1.0V to

linearly adjust the threshold. A voltage between 1.0V and

1.2V transitions to the full-scale threshold. Tie CTRL pin

to the VREF pin if not used.

VREF (Pin 15): Reference Output Pin. Typically 2V. This

pin can supply up to 100μA.

3519fa

6

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