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LT3591

3591f

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 efﬁciency.

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.

CTRL

VIN

4.7

µF

C1: TAIYO YUDEN EMK107BJ105MA

C2: MURATA GRM31CR71H475KA12L

L1: TAIYO YUDEN NR4018T150M

µF

µH

µF

2 AA CELLS

2V TO 3.2V

3.3V

RSENSE

Ω

3591 F10

LT3591

SHUTDOWN AND

DIMMING CONTROL

CAP

LED

GND

Figure 10. 2 AA Cells to Six White LEDs

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 COUT

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 11. Recommended Component Placement

CIN

COUT

3591 F11

VIN

CTRL

LED

CAP

RSENSE

GND

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