P1

P2

N1

+

-

VIN

Load

SW1

SW2

PGND

Sw1

Sw2

P1

P2

Control Logic

Switch

buffer

Switch

buffer

Buffer

Soft

Start

Ramp

Generator

FB

+

-

VREF

2 MHz

Oscillator

PFM

Generator

SYNC/

MODE

EN

SGND

VOUT

PFM_hi

PFM_low

NC

VDD

Error

Amp

VSEL

PWM

Comparator

N1

N2

LM3668-Q1

SNVSA84A – APRIL 2015 – REVISED MAY 2015

www.ti.com

7.2 Functional Block Diagram

7.3 Feature Description

7.3.1 Buck Operation

When the input voltage is greater than the output voltage, the device operates in buck mode where switch P2 is

always ON and P1 and N1 control the output. Figure 6 shows the simplified circuit for buck mode operation.

Figure 6. Simplified Circuit for Buck Operation

7.3.2 Boost Operation

When the input voltage is smaller than the output voltage, the device enters boost mode operation where P1 is

always ON, while switches N2 and P2 control the output. Figure 7 shows the simplified circuit for boost mode

operation.

8

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