LT3755/LT3755-1/LT3755-2
Typical perForMance characTerisTics
ISP/ISN Input Bias Current
vs CTRL Voltage
40
ISP
INPUT BIAS CURRENT (µA)
30
ISN
20
LDO DROPOUT (V)
0
T
A
= –45°C
–0.5
T
A
= 25°C
–1.0
T
A
= 125°C
T
A
= 150°C
–1.5
T
A
= 25°C, unless otherwise noted.
INTV
CC
Dropout Voltage
vs Current, Temperature
10
–2.0
V
IN
= 7V
0
5
10
15
20
LDO CURRENT (mA)
25
30
0
0
0.5
1
CTRL (V)
1.5
37551 G19
2
–2.5
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 (V
FB
) plus 60mV (typical).
The PWMOUT pin is driven from INTV
CC
. 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 I
LED
=
100mV/R
LED
when V
CTRL
> 1.2V or I
LED
= (V
CTRL
–100mV)/
(10 • R
LED
) when V
CTRL
≤ 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
LINEAR_DIMENSIONS [ LINEAR DIMENSIONS SEMICONDUCTOR ]
