LT3755 LINER [Linear Technology], LT3755 Datasheet - Page 17

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

a series resistor should always be used to increase the
slew rate on the VC pin to maintain tighter regulation of
LED current during fast transients on the input supply to
the converter.
Board Layout
The high speed operation of the LT3755 demands careful
attention to board layout and component placement. The
Exposed Pad of the package is the only GND terminal of
the IC and is also important for thermal management of
the IC. It is crucial to achieve a good electrical and thermal
contact between the Exposed Pad and the ground plane of
the board. To reduce electromagnetic interference (EMI), it
is important to minimize the area of the high dV/dt switching
node between the inductor, switch drain and anode of the
Schottky rectifi er. Use a ground plane under the switching
node to eliminate interplane coupling to sensitive signals.
The lengths of the high dI/dt traces: 1) from the switch
node through the switch and sense resistor to GND, and
2) from the switch node through the Schottky rectifi er and
APPLICATIONS INFORMATION
8V TO
L1: WÜRTH ELEKTRONIK 744870220
M1: VISHAY SILICONIX SI754DP
D1: DIODES INC. - PDS5100
M2: VISHAY SILICONIX SI2318DS
40V
V
IN
D2
0.01μF
C1
4.7μF
50V
INTV
CC
100k
10k
187k
1M
0.001μF
28.7k
400kHz
SHDN/UVLO
V
CTRL
OPENLED
PWM
SS
R
V
REF
C
T
30k
LT3755
V
20W SEPIC LED Driver
GND
IN
PWMOUT
INTV
SENSE
GATE
ISN
ISP
FB
CC
C2
4.7μF
10V
25k
22μH
L1A
511k
M1
0.015Ω
100V
1μF
C4
L1B
fi lter capacitor to GND should be minimized. The ground
points of these two switching current traces should come
to a common point then connect to the ground plane under
the LT3755. Likewise, the ground terminal of the bypass
capacitor for the INTV
the GND of the switching path. Typically this requirement
will result in the external switch being closest to the IC,
along with the INTV
the compensation network and other DC control signals
should be star connected to the underside of the IC. Do
not extensively route high impedance signals such as FB
and VC, as they may pick up switching noise. In particular,
avoid routing FB and PWMOUT in parallel for more than
a few millimeters on the board. Since there is a small
variable DC input bias current to the ISN and ISP inputs,
resistance in series with these pins should be minimized
to avoid creating an offset in the current sense threshold.
Likewise, minimize resistance in series with the SENSE
input to avoid changes (most likely reduction) to the switch
current limit threshold.
100V
D1
5A
0.1Ω
M2
37551 TA04a
1A
20W
LED
STRING
C3
4.7μF
50V
CC
100
95
90
85
80
CC
bypass capacitor. The ground for
LT3755/LT3755-1
0
regulator should be placed near
V
I
LED
OUT
= 1A
= 18V
10
Effi ciency vs V
V
IN
20
(V)
IN
30
37551 TA04b
17
37551fa
40