FB

2.8V/3.3V

SW1

SW2

EN

LM3668

PVIN

PGND

SYNC/MODE

VSEL

L = 2.8V

H = 3.3V

VIN = 2.5V - 5.5V

SGND

VOUT

VDD

C2

22 2F

C1

10 2F

2.2 2H

NC

LM3668

www.ti.com

SNVS449O – JUNE 2007 – REVISED APRIL 2015

9 Application and Implementation

NOTE

Information in the following applications sections is not part of the TI component

specification, and TI does not warrant its accuracy or completeness. TI’s customers are

responsible for determining suitability of components for their purposes. Customers should

validate and test their design implementation to confirm system functionality.

9.1 Application Information

9.1.1 MODE/SYNC Pin

If the MODE/SYNC pin is set high, the device is set to operate at PWM mode only. If MODE/SYNC pin is set low,

the device is set to automatically transition from PFM to PWM or PWM to PFM depending on the load current.

Do not leave this pin floating. The MODE/SYNC pin can also be driven by an external clock to set the desired

switching frequency between 1.6 MHz to 2.7 MHz.

9.1.2 VSEL Pin

switching between 2.8 V and 3.3 V or switching at maximum load.

9.2 Typical Application

Figure 46. LM3668 Typical Application Circuit

9.2.1 Design Requirements

9.2.1.1 Maximum Current

The LM3668 is designed to operate up to 1 A. For input voltages at 2.5 V, the maximum operating current is 600

mA and 800 mA for 2.7 V input voltage. In any mode it is recommended to avoid starting up the device at

minimum input voltage and maximum load. Special attention must be taken to avoid operating near thermal

shutdown when operating in boost mode at maximum load (1 A). A simple calculation can be used to determine

maximum power dissipation using the above formula is around 845 mW.

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