LT3486
PIN FUNCTIONS
SW1, SW2 (Pins 1, 16):
The SW Pins are the Collectors
of the Internal Power Transistors. Connect the inductors
and Schottky diodes to these pins. Minimize trace area at
these pins to minimize EMI.
V
IN
(Pin 2):
Input Supply Pin. Must be locally bypassed
with an X5R or X7R type ceramic capacitor.
OVP1, OVP2 (Pins 3, 14):
Output Overvoltage Protection
Pins. Connect these pins to the output capacitors. The
on-chip voltage detectors monitor the voltages at these
pins and limit it to 36V (typ) by turning off the respective
switcher and pulling its V
C
pin low.
R
T
(Pin 4):
Timing Resistor to Program the Switching
Frequency. The switching frequency can be programmed
from 200kHz to 2.5MHz.
V
C1
, V
C2
(Pins 5, 12):
The V
C
Pins are the Outputs of the
Internal Error Amplifier. The voltages at these pins control
the peak switch currents. Connect a resistor and capacitor
compensation network from these pin to ground.
FB1, FB2 (Pins 6, 11):
The LT3486 regulates the voltage
at each feedback pin to 200mV. Connect the cathode of the
lowest LED in the string and the feedback resistor (R
FB
)
to the respective feedback pin. The LED current in each
string can be programmed by:
I
LED
@
200mV/R
FB
, when V
CTRL
> 1.8V
I
LED
@
V
CTRL
/(5R
FB
), when V
CTRL
< 1V
CTRL1, CTRL2 (Pins 7, 10):
The CTRL pins are used to
provide dimming and shutdown control for the individual
switching converters. Connecting these to ground shuts
down the respective converter. As the voltages on these
pins is ramped from 0V to 1.8V, the LED current in each
converter ramps from 0 to I
LED
= (200mV/R
FB
). Any volt-
age above 1.8V does not affect the LED current.
PWM1, PWM2 (Pins 8, 9):
The PWM control pins can
be used to extend the dimming range for the individual
switching converter. The LED current in each string can
be controlled down to µA levels by feeding a PWM signal
to these pins. When the PWM pin voltage is taken below
0.4V, the respective converter is turned off and its V
C
pin
is disconnected from the internal circuitry. Taking it higher
than 0.9V resumes normal operation. Connect these pins
to 0.9V supply or higher, if not in use.
SHDN
(Pin 13):
Shutdown Pin for the Device. Connect it
to 1.6V or higher to enable device; 0.4V or less to disable
device.
REF (Pin 15):
The internal bandgap reference (1.25V)
is available at this pin. Bypass with a 0.1µF X5R or X7R
ceramic capacitor. Draw no more than 50µA from this pin.
Exposed Pad (Pin 17):
Ground. The exposed pad of the
package provides an electrical contact to ground and good
thermal connection to the printed circuit board (PCB).
Solder the exposed pad to the PCB system ground.
3486fe
6
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