LT3756-1 LINER [Linear Technology], LT3756-1 Datasheet - Page 8

• Manufacturer Part Number: LT3756-1
• Description: 60VIN LED Controller with Internal PWM Generator
• Manufacturer: LINER [Linear Technology]

pin FuncTions
LT3761
PWMOUT (Pin 1): 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 over-
voltage condition—will toggle if the FB input is greater
than the FB regulation voltage (V
The PWMOUT pin is driven from INTV
with gate cut-off voltage higher than 1V is recommended.
FB (Pin 2): Voltage Loop Feedback Pin. FB is intended for
constant-voltage regulation or for LED protection and open
LED detection. The internal transconductance amplifier with
output V
DC/DC converter. If the FB input exceeds the regulation
voltage, V
and ISN has dropped below the C/10 threshold of 25mV
(typical), the OPENLED pull-down is asserted. This action
may signal an open LED fault. If FB is driven above the FB
overvoltage threshold, the PWMOUT and GATE pins 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): Connection Point for the Negative Terminal
of the Current Feedback Resistor. The constant output
current regulation can be programmed by I
R
R
is typically 20μA flowing into the pin. Below INTV
ISN bias current decreases until it flows out of the pin.
ISP (Pin 4): Connection Point for the Positive Terminal of
the Current Feedback Resistor. Input bias current depends
upon CTRL pin voltage. When it is greater than INTV
it flows into the pin. Below INTV
decreases until it flows out of the pin. If the difference
between ISP and ISN exceeds 600mV (typical), then an
overcurrent event is detected. In response to this event,
the GATE and PWMOUT pins are driven low to protect
the switching regulator, a 1.5mA pulldown on PWM and
a 9mA pulldown on the DIM/SS pin are activated for 4µs.
V
Used to Stabilize the Switching Regulator Control Loop
with an RC Network. The V
PWM is low. This feature allows the V
8
C
LED
LED
(Pin 5): Transconductance Error Amplifier Output Pin
). If ISN is greater than INTV
when CTRL > 1.2V or I
C
will regulate FB to 1.25V (nominal) through the
FB
, minus 50mV and the voltage between ISP
C
pin is high impedance when
LED
FB
= (CTRL – 100mV)/(4 •
CC
) plus 60mV (typical).
CC
, input bias current
, ISP bias current
C
CC
pin to store the
. Use of a FET
LED
= 250mV/
CC
CC
,
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): Current Sense Threshold Adjustment Pin.
Constant current regulation point V
V
1.2V the V
the full-scale value of 250mV. For 1V ≤ CTRL ≤ 1.2V, the
dependence of V
from a linear function to a constant value, reaching 98% of
full-scale value by CTRL = 1.1V. Do not leave this pin open.
V
This pin drives a resistor divider for the CTRL pin, either
for analog dimming or for temperature limit/compensation
of LED load. It can be bypassed with 10nF or greater, or
less than 50pF . Can supply up to 185µA (typical).
PWM (Pin 8): A signal low turns off switcher, idles the
oscillator and disconnects the V
loads. PWMOUT pin follows the PWM pin, except in fault
conditions. The PWM pin can be driven with a digital
signal to cause pulse width modulation (PWM) dimming
of an LED load. The digital signal should be capable of
sourcing or sinking 200μA at the high and low thresholds.
During start-up when DIM/SS is below 1V, the first rising
edge of PWM enables switching which continues until
V
PWM pin to GND invokes a self-driving oscillator where
internal pull-up and pull-down currents set a duty ratio
for the PWMOUT pin for dimming LEDs. The magnitude
of the pull-up/down currents is set by the current in the
DIM/SS pin. The capacitor on PWM sets the frequency of
the dimming signal. For hiccup mode response to output
short-circuit faults, connect this pin as shown in the ap-
plication titled Boost LED Driver with Output Short-Circuit
Protection. If not used, connect the PWM pin to INTV
OPENLED (Pin 9): An open-drain pull-down on this pin
asserts if the FB input is greater than the FB regulation
voltage (V
CTRL
REF
ISP-ISN
(Pin 7): Voltage Reference Output Pin, Typically 2V.
plus an offset for 0V ≤ CTRL ≤ 1V. For CTRL >
≥ 25mV or SS ≥ 1V. Connecting a capacitor from
FB
ISP-ISN
) minus 50mV (typical) AND the difference
ISP-ISN
current regulation point is constant at
upon CTRL voltage transitions
C
pin from all internal
ISP-ISN
is one-fourth
3761f
CC
.