LTC3534 datasheet(11/34 Pages) AD

11 / 34 page

LTC3114-1

Rev. D

For more information www.analog.com

PIN FUNCTIONS

PLDO (Pin 11): Internal LDO Regulator Output. PLDO is

the output of the internal linear regulator that generates

the LDO rail from VIN. PLDO is also used as the supply

connection to the power switch gate drivers. Pins PLDO

and LDO must be connected together in the application.

BST2 (Pin 12): Flying Capacitor Pin for SW2. This pin

must be connected to SW2 through a 68nF capacitor.

BST2 is used to generate the gate driver rail for power

switch D. Make the PCB trace from BST2 to the boost

capacitor as short and direct as possible.

BST1 (Pin 13): Flying Capacitor Pin for SW1. This pin

must be connected to SW1 through a 68nF capacitor.

BST1 is used to generate the gate driver rail for power

switch A. Make the PCB trace from BST2 to the boost

capacitor as short and direct as possible.

PVIN (Pin 14): Power Input for the Buck-Boost Converter.

A 10µF or larger capacitor must be connected between

PVIN and GND as close to the IC as possible. The bypass

capacitor ground connection should via directly down to

the PCB ground plane. Pins PVIN and VIN must be con-

nected together in the application.

SW1 (Pin 15): Buck-Boost Power Converter Switch

Pin. This pin is connected to one side of the buck-boost

inductor.

MODE (Pin 16): Burst Mode/PWM Mode Control Pin.

Forcing MODE high causes the IC to operate in continu-

ous fixed frequency PWM mode. The nominal switching

frequency in PWM mode is 1.2MHz. Forcing MODE low

enables Burst Mode operation. Burst Mode operation

improves efficiency at light loads by only activating the

buck-boost converter as needed to maintain the nominal

regulated output voltage. If MODE is low, the converter

will automatically transition to PWM mode if the load cur-

rent increases.

OPERATION

INTRODUCTION

The LTC3114-1 is a monolithic, current mode, buck-boost

DC/DC converter that can operate over a wide voltage

range of 2.2V to 40V and provide up to 1A to the load.

Internal, low RDS(ON) N-channel DMOS power switches

reduce solution complexity and maximize efficiency. A

proprietary switch control algorithm allows the buck-

boost converter to maintain output voltage regulation with

input 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

subharmonic switching, making this product ideal for

noise sensitive applications. The LTC3114-1 operates at a

fixed nominal switching frequency of 1.2MHz, which pro-

vides an ideal trade-off between small solution size and

high efficiency. Current mode control provides inherent

input line voltage rejection, simplified compensation and

rapid response to load transients. Burst Mode capability

is also included in the LTC3114-1 and is user selected

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

LTC3114-1 provides exceptional efficiency at light output

loading conditions by operating the converter only when

necessary to maintain voltage regulation. At higher loads,

the LTC3114-1 automatically switches to fixed frequency

PWM mode when Burst Mode operation is selected. For

5V VOUT applications, the quiescent current in Burst Mode

operation can be as low as 20µA with the internal LDO

regulator bootstrapped to the output voltage. If the appli-

cation requires extremely low noise, continuous PWM

operation can also be selected via the MODE pin. The

LTC3114-1 also features an accurate RUN comparator

threshold with hysteresis. This allows the buck-boost

DC/DC converter to turn on and off at user-selected VIN

voltage thresholds. With a wide voltage range and pro-

grammable output current or monitoring capabilities,

the LTC3114-1 is well suited for many demanding power

conversion needs.

PROGRAMMABLE AVERAGE OUTPUT CURRENT

The LTC3114-1 includes the ability to program an accu-

rate average output current from the buck-boost DC/DC

converter. Whether the application is driving high power

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