LTC3118 datasheet(13/40 Pages) LINER

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LTC3118

3118fa

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operaTion

Introduction

The LTC3118 is a dual-input, current mode, monolithic

buck-boost DC/DC converter that can operate over a wide

input voltage range of 2.2V to 18V. The output voltage

can be programmed between 2V to 18V and deliver more

than 2A of load current. The LTC3118 operates from either

VIN1 or VIN2 depending on the state of the SEL pin. If SEL

is commanded to be a logic high, VOUT will be powered

from the highest valid input voltage. If SEL is a logic low,

VOUT will be powered from VIN1 (priority mode) assuming

sufficient input voltage is present. Internal, low RDS(ON)

N-channel power switches reduce the solution complexity

and maximize efficiency.

A proprietary switch algorithm allows the buck-boost

converter to maintain output voltage regulation with in-

put voltages that are above, below or equal to the output

voltage. Transitions between the step-up or step-down

operating modes are seamless and free of transients and

subharmonicswitching,makingthisproductidealfornoise

sensitive applications. The LTC3118 operates at a fixed

nominal switching frequency of 1.2MHz, which provides

an ideal trade-off between small solution size and high

efficiency. Current mode control provides inherent input

line voltage rejection, simplified compensation and rapid

responsetoloadtransients.BurstModeoperationcapabil-

ity is also included in the LTC3118 and is user-selected

via the MODE input pin. In Burst Mode operation, the

LTC3118 provides exceptional efficiency at light output

loads by operating the converter only when necessary to

maintain voltage regulation. At higher loads, the LTC3118

automatically transitions to fixed frequency PWM mode

when Burst Mode operation is selected.

For 5V VOUT applications, the input quiescent currents in

Burst Mode operation can be reduced with the internal

LDO regulator bootstrapped to the output voltage. If the

applicationrequiresextremelylownoise,continuousPWM

operation can also be selected via the MODE pin. The

LTC3118 also features accurate, resistor programmable

RUN comparator thresholds with hysteresis for each VIN.

This allows the buck-boost DC/DC converter to turn on

and off at user-selected voltage thresholds depending on

the power source for each VIN. With a wide voltage range

and high efficiency, the LTC3118 is well suited for many

demanding power systems.

Power Stage Topology

Figure 1 shows the topology of the dual-input LTC3118

power stage switches and their associated gate drivers.

The LTC3118 integrates independent switch paths from

VIN1 to SW1 and VIN2 to SW1 to provide isolation between

theselectedinputandtheinactiveinput.Thisconfiguration

allows conversion from either input source, regardless of

their respective voltage levels, enabling ideal diode or VIN1

priority modes (see SEL pin description).

Figure 1. LTC3118 Dual

-Input Power Stage

3118 F01

VIN1

VOUT

VCC

PUMP1

A1ON

BST1

CM1

VIN2

A2ON

SW1

SW2

BST1

CM2

BST2

PGND

BON

CON

DON

PUMP2

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