Datasheet

LT3599
7
3599fe
PIN FUNCTIONS
CTRL: LED Current Control. If the CTRL pin is not used,
tie this pin to V
REF
.
DISABLE4: Allows Disabling Channel 4. Connect to V
REF
to disable channel 4. If channel 4 is disabled, the LED4 pin
should be connected to the LED3 pin. Connect DISABLE4
to ground to allow operation of channel 4.
Exposed Pad: Ground. The ground for the IC should be
soldered to a continuous copper ground plane under the
LT3599 die.
FB: Feedback Pin for Overvoltage Protection. Reference
voltage is 1.223V. Connect the resistive divider tap here.
Minimize trace area at FB. Set V
OUT
according to V
OUT
=
1.223(1 + R2/R1) when overvoltage protection occurs.
GND: Analog Ground. Tie directly to local ground plane.
Connect RT, I
SET
and T
SET
resistors between this local
ground plane and their respective pins.
I
SET
: Programs Led Current for Each String. A resistor
to ground programs LED currents between 30mA and
120mA.
LED1-4: LED String Output. Connect the bottom cathode
of each LED string to these pins.
OPENLED: Open LED Flag. An open-collector output when
any LED string opens.
NC: No Connect Pins. Can be left open or connected to
any ground plane.
PWM: Input Pin for PWM Dimming Control. Above 1V
allows converter switching, and below 0.4V disables
switching with V
C
pin level maintained. A PWM signal
driving the PWM pin provides accurate dimming control.
The PWM signal can be driven from 0V to 5V. If unused,
the pin should be connected to V
REF
.
RT : A Resistor to Ground Which Programs Switching
Frequency Between 200kHz and 2.1MHz. For SYNC func-
tion, choose the resistor to program a frequency 20%
slower than the SYNC pulse frequency. Do not leave this
pin open.
SHDN/UVLO: The SHDN/UVLO pin has an accurate 1.36V
threshold and can be used to program an undervoltage
lockout (UVLO) threshold for system input supply using a
resistor divider from supply to ground. A 4μA pin current
hysteresis allows programming of undervoltage lockout
(UVLO) hysteresis. 1.36V turns the part on and removes a
4μA sink current from the pin. SHDN/UVLO = 0V reduces
V
IN
current < 0.1μA. SHDN/UVLO can be directly connected
to V
IN
. Do not leave this pin open.
SHORTLED: Indicates a high side short (LED pin shorted
to V
OUT
). This is an open-collector output.
SS: Soft-Start Pin. Place a soft-start capacitor here. Upon
start-up, a 11μA current charges the capacitor. Use a larger
capacitor for a slower start-up.
SW: Switch Pin. This is the collector of the internal NPN
power switch. Minimize the metal trace area connected
to this pin to minimize EMI.
SYNC: Frequency Synchronization Pin. This input allows for
synchronizing the operating frequency to an external clock.
The R
T
resistor should be chosen to program a switching
frequency 20% slower than SYNC pulse frequency. This
pin should be grounded if this feature is not used.
T
SET
: Programs LT3599 junction temperature breakpoint,
beyond which LED currents will begin to decrease. An
internal V
PTAT
threshold (see Block Diagram) increases
with junction temperature. When V
PTAT
exceeds T
SET
pin
voltage, LED currents are decreased. If the function is not
required, connect T
SET
pin to V
REF
pin. If the T
SET
pin is
not used, tie this pin to V
REF
.
V
C
: Error Amplifi er Output Pin. Tie the external compensa-
tion network to this pin.
V
IN
: Input Supply Pin. Must be locally bypassed with a
capacitor to ground.
V
O_SW
: Drain of an Internal PMOS. The internal PMOS
disconnects the feedback resistors from the V
OUT
pin
during shutdown and when the PWM pin is low.
V
OUT
: Output Pin. This pin provides power to all LEDs.
V
REF
: Bandgap Voltage Reference. Internally set to 1.227V.
This pin can supply up to 100μA. Can be used to program
the CTRL pin voltage using resistor dividers to ground.