LT3591EDDB#PBF Linear Technology, LT3591EDDB#PBF Datasheet - Page 11

• Manufacturer Part Number: LT3591EDDB#PBF
• Manufacturer: Linear Technology

Specifications of LT3591EDDB#PBF

• Operating Supply Voltage (typ): 3.3/5/9V
• Number Of Segments: 10
• Operating Temperature (min): -40C
• Operating Temperature (max): 85C
• Operating Temperature Classification: Industrial
• Package Type: DFN EP
• Pin Count: 8
• Mounting: Surface Mount
• Operating Supply Voltage (min): 2.5V
• Operating Supply Voltage (max): 12V
• Lead Free Status / RoHS Status: Compliant

APPLICATIONS INFORMATION
LOW INPUT VOLTAGE APPLICATIONS
The LT3591 can be used in low input voltage applications.
The input supply voltage to the LT3591 must be 2.5V or
higher. However, the inductor can be run off a lower battery
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.
The LEDs can be driven straight from the battery, resulting
in higher effi ciency.
Figure 10 shows six LEDs powered by two AA cells. The
battery is connected to the inductor and the chip is powered
off a 3.3V logic supply voltage.
2 AA CELLS
2V TO 3.2V
3.3V
Figure 10. 2 AA Cells to Six White LEDs
C1
1 F
C1
1 F
C1: TAIYO YUDEN EMK107BJ105MA
C2: MURATA GRM31CR71H475KA12L
L1: TAIYO YUDEN NR4018T150M
15 H
L1
DIMMING CONTROL
V
SW
SHUTDOWN AND
IN
LT3591
CTRL
GND
CAP
LED
R
10
SENSE
3591 F10
C2
4.7 F
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,
proper layout of high frequency switching paths is essential.
Minimize the length and area of all traces connected to
the switching node pin (SW). Keep the sense voltage pins
(CAP and LED) away from the switching node. Place C
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.
SW
Figure 11. Recommended Component Placement
V
IN
L1
C
IN
1
2
3
4
3591 F11
GND
9
C
8
7
6
5
OUT
CTRL
CAP
LED
R
SENSE
LT3591
11
OUT
3591f