LT3755 LINER [Linear Technology], LT3755 Datasheet - Page 8

• Manufacturer Part Number: LT3755
• Description: 40VIN, 75VOUT LED Controller
• Manufacturer: LINER [Linear Technology]

PIN FUNCTIONS
LT3755/LT3755-1
SYNC (Pin 9/Pin 3, LT3755-1 Only): The SYNC pin is used
to synchronize the internal oscillator to an external logic
level signal. The R
an internal switching frequency 20% slower than the SYNC
pulse frequency. Gate turn-on occurs a fi xed delay after
the rising edge of SYNC. For best PWM performance, the
PWM rising edge should occur at least 200ns before the
SYNC rising edge. Use a 50% duty cycle waveform to
drive this pin. This pin replaces OPENLED on LT3755-1
option parts. If not used, tie this pin to GND.
SS (Pin 10/Pin 4): Soft-Start Pin. This pin modulates
oscillator frequency and compensation pin voltage (VC)
clamp. The soft-start interval is set with an external capaci-
tor. The pin has a 10μA (typical) pull-up current source
to an internal 2.5V rail. The soft-start pin is reset to GND
by an undervoltage condition (detected by SHDN/UVLO
pin) or thermal limit.
RT (Pin 11/Pin 5): Switching Frequency Adjustment Pin.
Set the frequency using a resistor to GND (for resistor
values, see the Typical Performance curve or Table 1). Do
not leave the RT pin open.
SHDN/UVLO (Pin 12/Pin 6): Shutdown and Undervoltage
Detect Pin. An accurate 1.22V falling threshold with ex-
ternally programmable hysteresis detects when power is
OK to enable switching. Rising hysteresis is generated by
the external resistor divider and an accurate internal 2μA
pull-down current. Above the 1.24V (nominal) threshold
(but below 6V), SHDN/UVLO input bias current is sub-μA.
8
T
resistor should be chosen to program
(MSOP/QFN)
Below the falling threshold, a 2μA pull-down current is
enabled so the user can defi ne the hysteresis with the
external resistor selection. An undervoltage condition
resets soft-start. Tie to 0.4V, or less, to disable the device
and reduce V
SHDN/UVLO to a voltage higher than V
INTV
GATE Driver and PWMOUT Driver. Supplied from V
regulates to 7V (typical). INTV
a 4.7μF capacitor placed close to the pin. Connect INTV
directly to V
V
bypassed with a 0.22μF (or larger) capacitor placed close
to the IC.
SENSE (Pin 15/Pin 9): The current sense input for the
control loop. Kelvin connect this pin to the positive ter-
minal of the switch current sense resistor, R
source of the NFET. The negative terminal of the current
sense resistor should be connected to the GND plane
close to the IC.
GATE (Pin 16/Pin 10): N-Channel FET Gate Driver Output.
Switches between INTV
shutdown, fault or idle states.
Exposed Pad (Pin 17/Pin 17): Ground. This pin also serves
as current sense input for control loop, sensing negative
terminal of current sense resistor. Solder the Exposed Pad
directly to ground plane.
IN
(Pin 14/Pin 8): Input Supply Pin. Must be locally
CC
(Pin 13/Pin 7): Regulated Supply for Internal Loads,
IN
IN
if V
quiescent current below 1μA. Do not tie
IN
is always less than or equal to 7V.
CC
and GND. Driven to GND during
CC
must be bypassed with
IN
.
SENSE
, in the
IN
37551fa
and
CC