LT3743(RevB) Ver la hoja de datos (PDF) - Linear Technology

Número de pieza

componentes Descripción

Fabricante

LT3743
(Rev.:RevB)

High Current Synchronous Step-Down LED Driver with Three-State Control

Linear Technology 

LT3743

PIN FUNCTIONS (QFN/TSSOP)

GND (Pins 1, 5, 9, 20, 21, Exposed Pad Pin 29/Pins 2, 7,

11, 22, 27, Exposed Pad Pin 29): Ground. The exposed

pad must be soldered to the PCB.

EN/UVLO (Pin 2/Pin 4): Enable Pin. The EN/UVLO pin

acts as an enable pin and turns on the internal current

bias core and subregulators at 1.55V. The pin does

not have any pull-up or pull-down, requiring a voltage

bias for normal part operation. Full shutdown occurs at

approximately 0.5V.

VREF (Pin 3/Pin 5): Buffered 2V Reference Capable of

0.5mA Drive.

CTRL_T (Pin 4/Pin 6): The thermal control input to reduce

the regulated current level for both current levels (CTRL_L

and CTRL_H).

CTRL_H (Pin 6/Pin 8): The CTRL_H pin sets the high level

regulated output current and overcurrent. The maximum

input voltage is internally clamped to 1.5V. The overcurrent

set point is equal to the high level regulated current level

set by the CTRL_H pin with an additional 23mV offset

between the SENSE+ and SENSE– pins.

CTRL_L (Pin 7/Pin 9): The CTRL_L pin sets the low level

regulated output current. It is not recommended that the

CTRL_L voltage be higher than the CTRL_H voltage.

SS (Pin 8/Pin 10): Soft-Start Pin. Place an external capaci-

tor to ground to limit the regulated current during start-up

conditions. The SS pin has a 5.5μA charging current. This

pin controls both of the regulated inputs determined by

CTRL_L and CTRL_H.

FB (Pin 10/Pin 12): Feedback Pin for Overvoltage Protec-

tion. The feedback voltage is 1V. Overvoltage/Open LED

is sensed through the FB pin. When the feedback voltage

exceeds 1.3V, the overvoltage lockout prevents switching

and connects both output capacitors to discharge the

inductor current.

SENSE+ (Pin 11/Pin 13): SENSE+ is the inverting input of

the average current mode loop error amplifier. This pin is

connected to the external current sense resistor, RS. The

voltage drop between SENSE+ and SENSE– referenced to

the voltage drop across an internal resistor produces the

input voltages to the current regulation loop.

SENSE– (Pin 12/Pin 14): SENSE– is the noninverting input

of the average current mode loop error amplifier. The refer-

ence current, based on CTRL_L or CTRL_H flows out of the

pin to the output (LED) side of the sense resistor, RS.

VCL (Pin 13/Pin 15): VCL provides the necessary compen-

sation for the average current loop stability during low level

current regulation. Typical compensation values are 15k to

80k for the resistor and 2nF to 10nF for the capacitor.

VCH (Pin 14/Pin 16): VCH provides the necessary com-

pensation for the average current loop stability during

high level current regulation. Typical compensation values

are 15k to 80k for the resistor and 2nF to 10nF for the

capacitor.

RT (Pin 15/Pin 17): A resistor to ground sets the switching

frequency between 200kHz and 1MHz. When using the

SYNC function, set the frequency to be 20% lower than

the SYNC pulse frequency. This pin is current limited to

60μA. Do not leave this pin open.

SYNC (Pin 16/Pin 18): Frequency Synchronization Pin.

This pin allows the switching frequency to be synchronized

to an external clock. The RT resistor should be chosen to

operate the internal clock at 20% slower than the SYNC

pulse frequency. The synchronization range is 240kHz to

1.2MHz. This pin should be grounded when not in use.

CTRL_SEL (Pin 17/Pin 19): The CTRL_SEL pin selects

between the high current control, CTRL_H and the low

current control, CTRL_L. When high, the VCH pin is

connected to the error amp output and the PWMGH gate

signal is high. When low, the VCL pin is connected to the

error amp output and the PWMGL gate signal is high. This

pin is used for current level dimming of the LED. This pin

should be grounded when not in use.

PWM (Pin 18/Pin 20): The input pin for PWM dimming

of the LED. When low, all switching is terminated and the

output caps are disconnected. This pin should be pulled

to VCC_INT when not in use.

PWMGH (Pin 19/Pin 21): The PWMGH output pin drives

the gate of an external FET to connect one of the switching

regulator output capacitors to the load. The driver pull-up

impedance is 3.2Ω and pull-down impedance is 1.75Ω.

3743fb

9

Share Link: