LT3755 datasheet(7/24 Pages) LINER

7 / 24 page

LT3755/LT3755-1

37551fa

PIN FUNCTIONS

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

for Driving LED Load Disconnect NMOS or Level Shift. This

pin also serves a protection function for the FB overvoltage

condition—will toggle if the FB input is greater than the FB

regulation voltage (VFB)plus60mV(typical).ThePWMOUT

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. The LED cur-

rent can be programmed by ILED = 100mV/RLED when

VCTRL > 1.2V or ILED = VCTRL –100mV/(10 • RLED). If ISN

is greater than 2.9V, input bias current is typically 20μA.

Below 3V, ISN is an input to the short-circuit protection

feature that forces GATE to 0V if ISN is more than 150mV

(typ) below ISP.

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

nal of the Current Feedback Resistor. Input bias current for

this pin is typically 30μA. ISP is an input to the short-circuit

protection feature when ISP is less than 3.1V.

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.

CTRL (Pin 6/Pin 16): Current Sense Threshold Adjustment

Pin. Regulating threshold VISP – VISN is 1/10th VCTRL plus

an offset. CTRL linear range is from GND to 1.1V. Connect

CTRL to VREF for the 100mV default threshold. Do not

leave this pin open.

VREF (Pin 7/Pin 1): Voltage Reference Output Pin, Typically

2V. This pin drives a resistor divider for the CTRL pin, either

for analog dimming or for temperature limit/compensation

of LED load. Can supply up to 100μA.

PWM (Pin 8/Pin 2): A signal low turns off switcher, idles

oscillator and disconnects VC pin from all internal loads.

PWMOUT pin follows PWM pin. PWM has an internal

pull-down resistor. If not used, connect to INTVCC.

OPENLED (Pin 9/Pin 3, LT3755 Only): An open-drain

pull-down on OPENLED asserts if the FB input is greater

than the FB regulation threshold minus 50mV (typical).

To function, the pin requires an external pull-up resistor.

When the PWM input is low and the DC/DC converter is

idle, the OPENLED condition is latched to the last valid

state when the PWM input was high. When PWM input

goes high again, the OPENLED pin will be updated. This

pin may be used to report an open LED fault.

(MSOP/QFN)

LT3755 Datasheet(PDF) 7 Page - Linear Technology

LT3755 Datasheet(HTML) 7 Page - Linear Technology

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

Datasheet Download

Link URL