LT3755 Просмотр технического описания (PDF) - Linear Technology

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LT3755

40VIN, 75VOUT LED Controllers

Linear Technology 

LT3755/LT3755-1/LT3755-2

Typical Performance Characteristics TA = 25°C, unless otherwise noted.

ISP/ISN Input Bias Current

vs CTRL Voltage

40

ISP

30

ISN

20

10

0

0

0.5

1

1.5

2

CTRL (V)

37551 G19

INTVCC Dropout Voltage

vs Current, Temperature

0

TA = –45°C

–0.5

TA = 25°C

–1.0

TA = 125°C

TA = 150°C

–1.5

–2.0

–2.5 VIN = 7V

0

5

10 15 20

LDO CURRENT (mA)

25 30

37551 G20

Pin Functions (MSOP/QFN)

PWMOUT (Pin 1/Pin 11): Buffered Version of PWM Signal

for Driving LED Load Disconnect NMOS or Level Shift.

This pin also serves in a protection function for the FB

overvoltage condition—will toggle if the FB input is greater

than the FB regulation voltage (VFB) plus 60mV (typical).

The PWMOUT pin is driven from INTVCC. Use of a FET with

gate cut-off voltage higher than 1V is recommended.

FB (Pin 2/Pin 12): Voltage Loop Feedback Pin. FB is

intended for constant-voltage regulation or for LED protec-

tion/open LED detection. The internal transconductance

amplifier with output VC will regulate FB to 1.25V (nominal)

through the DC/DC converter. If the FB input is regulating

the loop, the OPENLED pull-down is asserted. This ac-

tion may signal an open LED fault. If FB is driven above

the FB threshold (by an external power supply spike, for

example), the OPENLED pull-down will be de-asserted and

the PWMOUT pin will be driven low to protect the LEDs

from an overcurrent event. Do not leave the FB pin open.

If not used, connect to GND.

ISN (Pin 3/Pin 13): Connection Point for the Negative

Terminal of the Current Feedback Resistor. If ISN is greater

than 2.9V, the LED current can be programmed by ILED =

100mV/RLED whenVCTRL>1.2VorILED =(VCTRL –100mV)/

(10 • RLED) when VCTRL ≤ 1V. Input bias current is typi-

cally 25µA. Below 3V, ISN is an input to the short-circuit

protection feature that forces GATE to 0V if ISP exceeds

ISN by more than 150mV (typ).

ISP (Pin 4/Pin 14): Connection Point for the Positive

Terminal of the Current Feedback Resistor. Input bias

current is dependent upon CTRL pin voltage as shown

in the TPC. ISP is an input to the short‑circuit protection

feature when ISN is less than 3V.

VC (Pin 5/Pin 15): Transconductance Error Amplifier

Output Pin Used to Stabilize the Voltage Loop with an RC

Network. This pin is high impedance when PWM is low, a

feature that stores the demand current state variable for

the next PWM high transition. Connect a capacitor between

this pin and GND; a resistor in series with the capacitor is

recommended for fast transient response.

37551fd



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