Datasheet

5
LT3491
3491fa
1
–
+
–
+
R
SW
5
V
IN
CAP
Q
S
DRIVER
Σ
OVERVOLTAGE
PROTECTION
RAMP
GENERATOR
OSCILLATOR
V
REF
1.25V
START-UP
CONTROL
SHDN
Q1
R
–
+
+
8
LED
3491 F01
CTRL
GND
PINS 2, 3, 4
7
6
–
+
A = 6.25
A1
R
C
C
C
A2
A3
PWM
COMP
PIN NUMBERS CORRESPOND TO THE 8-PIN SC70 PACKAGE
UU
U
PI FU CTIO S
SW (Pin 1/Pin 3): Switch Pin. Minimize trace area at this
pin to minimize EMI. Connect the inductor at this pin.
GND (Pins 2, 3, 4/Pin 2): Ground Pins. All three pins
should be tied directly to local ground plane.
V
IN
(Pin 5/Pin 1): Input Supply Pin. Must be locally
bypassed.
CTRL (Pin 6/Pin 6): Dimming and Shutdown Pin. Connect
this pin below 50mV to disable the driver. As the pin
voltage is ramped from 0V to 1.5V, the LED current ramps
from 0 to I
LED
( = 200mV/R
SENSE
). The CTRL pin must not
be left floating.
LED (Pin 7/Pin 5): Connection Point for the Anode of the
First LED and the Sense Resistor. The LED current can be
programmed by :
I
mV
R
LED
SENSE
=
200
CAP (Pin 8/Pin 4): Output of the Driver. This pin is
connected to the cathode of internal Schottky. Connect the
output capacitor to this pin and the sense resistor from
this pin to the LED pin.
EXPOSED PAD (NA/Pin 7): The Exposed Pad should be
soldered to the PCB ground to achieve the rated thermal
performance.
BLOCK DIAGRA
W
Figure 1. Block Diagram
(SC70/DFN)