LT3591
APPLICATIONS INFORMATION
LOW INPUT VOLTAGE APPLICATIONS
BOARD LAYOUT CONSIDERATIONS
As with all switching regulators, careful attention must be
paid to the PCB board layout and component placement.
To prevent electromagnetic interference (EMI) problems,
properlayoutofhighfrequencyswitchingpathsisessential.
Minimize the length and area of all traces connected to
the switching node pin (SW). Keep the sense voltage pins
The LT3591 can be used in low input voltage applications.
The input supply voltage to the LT3591 must be 2.5V or
higher.However,theinductorcanberunoffalowerbattery
voltage. This technique allows the LEDs to be powered off
two alkaline cells. Most portable devices have a 3.3V logic
supply voltage which can be used to power the LT3591.
TheLEDscanbedrivenstraightfromthebattery, resulting
in higher efficiency.
(CAP and LED) away from the switching node. Place C
OUT
next to the CAP pin. Always use a ground plane under the
switching regulator to minimize interplane coupling. Re-
commended component placement is shown in Figure 11.
Figure 10 shows six LEDs powered by two AA cells. The
batteryisconnectedtotheinductorandthechipispowered
off a 3.3V logic supply voltage.
C
IN
SHUTDOWN AND
V
IN
DIMMING CONTROL
CTRL
CAP
8
7
6
5
1
2
3
4
3.3V
CTRL CAP
V
IN
C1
1µF
LED
R
GND
9
SENSE
10Ω
LT3591
LED
L1
L1
15µH
SW
C2
4.7µF
2 AA CELLS
2V TO 3.2V
SW
R
SENSE
GND
C
OUT
C1
1µF
3591 F11
3591 F10
C1: TAIYO YUDEN EMK107BJ105MA
C2: MURATA GRM31CR71H475KA12L
L1: TAIYO YUDEN NR4018T150M
Figure 11. Recommended Component Placement
Figure 10. 2 AA Cells to Six White LEDs
3591f
11
Linear Systems [ Linear Systems ]
