LT3754 datasheet(8/28 Pages) LINER

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LT3754

3754f

PIN FUNCTIONS

LEDx (Pin 1-8,17-24): 16 LED Driver Outputs. Each output

contains an open collector constant current sink. LED

currents are programmable from 10mA to 50mA using

a single resistor at the ISET pin. Channel matching is

±2% with an absolute current accuracy of ±3%. Connect

the cathode of each LED string to an LED pin. Connect

the anode of each LED string to VOUT. Channels can be

paralleled for greater LED current or individually disabled

(connect LED to VOUT).

SENSE (Pin 9): The Current Sense Input for the Control

Loop. Connect this pin to the sense resistor in the source

of the external power MOSFET.

GATE (Pin 10): Drives the gate of an N-channel MOSFET

from 0V to INTVCC.

INTVCC (Pin 11): A 7V LDO supply generated from VIN and

used to power the GATE driver and some control circuitry.

Must be bypassed with a 4.7μF capacitor to GND.

VIN (Pin 12): Input Supply Pin. Must be locally bypassed

with a 1μF capacitor to ground.

SHDN/UVLO(Pin13): TheSHDN/UVLOpinhasanaccurate

1.476Vthresholdandcanbeusedtoprogramanundervoltage

lockout (UVLO) threshold for system input supply using

a resistor divider from supply to ground. A 2.4μA pin

current hysteresis allows programming of UVLO hysteresis.

SHDN/UVLO above 1.476V turns the part on and removes

a 2.4μA sink current from the pin. SHDN/UVLO < 0.7V

reduces VIN current < 20μA. If the shutdown function is not

required, it should be forced above 1.476V or connected

directly to VIN.

FAULT (Pin 14): Active low if any or all LED strings have

an open fault or if any/all LED pins have been shorted to

VOUT. If fault(s) removed, FAULT ﬂag returns high. Fault

status is only updated during PWM high state and latched

during PWM low.

SYNC (Pin 15): Allows synchronization of boost converter

switching frequency to an external clock. RT resistor should

be programmed for fOSC 20% below SYNC frequency. If

unused, connect to GND.

VOUT (Pin16): Boosted Output Voltage of the Converter.

Connect a capacitor from this pin to ground. Connect the

anode of each LED (string) to VOUT.

RT (Pin 25): A resistor to ground programs switching

frequency fOSC between 0.1MHz and 1MHz.

VC (Pin 26): Output of Both Transconductance Error

Ampliﬁers for the Converter Regulation Loop. The most

commonly used gm error ampliﬁer (LED) regulates VOUT

to ensure no LED pin falls below 1V. The other gm error

ampliﬁer (OVP) is activated if all LEDs fail open and a

regulated maximum VOUT is required. Connect a resistor

and capacitor in series from the VC pin to ground.

PWM (Pin 27): Input Pin for PWM Dimming Control. Above

1.4V allows converter switching and below 0.7V disables

switching. The PWM signal can be driven from 0V to 6V.

If unused, connect to VREF.

OVPSET (Pin 28): Programs maximum allowed VOUT

regulation level if all LEDs are open circuit.

CTRL (Pin 29): CTRL pin voltage below 1V controls

maximum LED current. CTRL voltage can be set by a

resistor divider from VIN,VREForanexternalvoltagesource.

LED current derating versus temperature is achievable

if the voltage programmed at the CTRL pin has a negative

temperature coefﬁcient using an external resistor divider

from VREF pin with temperature dependent resistance.

TSET (Pin 30): Programs LT3754 junction temperature

breakpoint past which LED current will begin to derate.

VREF (Pin 31): 1.485V Reference Output Pin. This pin

can supply up to 150μA. Can be used to program CTRL,

TSET and OVPSET pin voltages using resistor dividers to

ground.

ISET(Pin32):ResistortoGroundProgramsLEDpincurrent.

See Table 6 in the Applications Information Section.

Exposed Pad (Pin 33): GND. The ground for the IC and

the converter. The package has an exposed pad (Pin 33)

underneath the IC which is the best path for heat out of the

package. Pin 33 should be soldered to a continuous copper

ground plane under the device to reduce die temperature

and increase the power capability of the LT3754.

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