LT3760 Просмотр технического описания (PDF) - Linear Technology

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LT3760

8-Channel × 100mA LED Driver

Linear Technology 

LT3760

Pin Functions

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

LED current. CTRL voltage can be set by a resistor

divider from VIN, VREF or an external voltage source.

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 to GND with temperature dependent

resistance.

TSET (Pin 2): Programs LT3760 junction temperature

breakpoint past which LED current will begin to derate.

Program using a resistor divider from VREF to GND.

VREF (Pin 3): 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 GND.

ISET (Pin 4): Resistor to GND Programs LED pin current.

See Table 6 in the Applications Information Section.

NC (Pin 5): No Connect. Okay to leave open or to connect

to GND.

LEDx (Pins 6 to 9, 20 to 23): 8 LED Driver Outputs. Each

output contains an open collector constant current sink. LED

currents are programmable from 20mA to 100mA using a

single resistor at the ISET pin. 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).

PGND (Pins 10, 19, Exposed Pad Pin 29): Power grounds

for the IC and the converter. The package has an exposed

pad (Pin 29) underneath the IC which is the best path for

heat out of the package. Pin 29 should be soldered to

a continuous copper ground plane under the device to

reduce die temperature and increase the power capability

of the LT3760.

SENSE (Pin 11): 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 12): Drives the gate of an N-channel MOSFET

from 0V to INTVCC.

INTVCC (Pin 13): 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 PGND.

8

VIN (Pin 14): Input Supply Pin. Must be locally bypassed

with a 1µF capacitor to PGND.

SHDN/UVLO (Pin 15): The SHDN/UVLO pin has an accurate

1.476V threshold and can be used to program an under volt-

age lockout (UVLO) threshold for system input supply using

a resistor divider from supply to GND. A 2.4µA pin cur-

rent 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 con-

nected directly to VIN.

FAULT (Pin 16): Active low if any or all LED strings have

an open fault. If fault(s) removed, FAULT flag returns high.

Fault status is only updated during PWM high state and

latched during PWM low.

SYNC (Pin 17): 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 (Pin 18): Boosted Output Voltage of the Converter.

Connect a capacitor from this pin to PGND. Connect the

anode of each LED (string) to VOUT.

GND (Pin 24): Signal Ground.

RT (Pin 25): A resistor to GND programs switching fre-

quency 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 GND.

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 regu-

lation level if all LEDs are open circuit. Program using a

resistor divider from VREF to GND.

3760fc

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