1

2

3

6

5

4

BOOST

GND

FB

SW

EN/DIM

1

4

3

2

8

5

6

7

SW

GND

VIN

EN/DIM

BOOST

GND

FB

NC

LM3405A

SNVS508B – OCTOBER 2007 – REVISED OCTOBER 2008

www.ti.com

These devices have limited built-in ESD protection. The leads should be shorted together or the device placed in conductive foam

during storage or handling to prevent electrostatic damage to the MOS gates.

CONNECTION DIAGRAMS

Figure 1. 6-Lead SOT Package

Figure 2. 8-Lead MSOP PowerPAD Package

See Package Number DDC0006A

See Package Number DGN0008A

SOT-6 Pin Descriptions

Pin No.

Name

Application Information

Boost voltage that drives the NMOS output switch. A bootstrap capacitor is connected between the BOOST and

1

BOOST

SW pins.

2

GND

Signal and power ground pin. Place the bottom resistor of the feedback network as close as possible to this pin.

3

FB

Feedback pin. Connect FB to external resistor divider to set output voltage.

Enable control input. Logic high enables operation. Toggling this pin with a periodic logic square wave of varying

4

EN/DIM

duty cycle at different frequencies controls the brightness of LEDs. Do not allow this pin to float or be greater than

5

VIN

Input supply voltage. Connect a bypass capacitor locally from this pin to GND.

6

SW

Switch pin. Connect this pin to the inductor, catch diode, and bootstrap capacitor.

MSOP8 PowerPAD Pin Descriptions

Pin No.

Name

Function

1

FB

Feedback pin. Connect FB to external resistor divider to set output voltage.

2, 7

GND

Signal and power ground pin. Place the bottom resistor of the feedback network as close as possible to this pin. Tie

pins 2, 7 and DAP to one GND plane.

3

NC

No Connection

4

BOOST

Boost voltage that drives the NMOS output switch. A bootstrap capacitor is connected between the BOOST and SW

pins.

5

SW

Switch pin. Connect this pin to the inductor, catch diode, and bootstrap capacitor.

6

VIN

Input supply voltage. Connect a bypass capacitor locally from this pin to GND.

8

EN/DIM

Enable control input. Logic high enables operation. Toggling this pin with a periodic logic square wave of varying

duty cycle at different frequencies controls the brightness of LEDs. Do not allow this pin to float or be greater than

DAP

Attach to power ground pin

2

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