Description

The LTC®3129 is a high efficiency, 200mA buck-boost DC/DC converter with a wide VIN and VOUT range. It includes an accurate RUN pin threshold to allow predictable regulator turn-on and a maximum power point control (MPPC) capability that ensures maximum power extraction from non-ideal power sources such as photovoltaic panels.

The LTC3129 employs an ultralow noise, 1.2MHz PWM switching architecture that minimizes solution footprint by allowing the use of tiny, low profile inductors and ceramic capacitors. Built-in loop compensation and soft-start simplify the design. For high efficiency operation at light loads, automatic Burst Mode operation can be selected, reducing the quiescent current to just 1.3µA.

Additional features include a power good output, less than 10nA of shutdown current and thermal shutdown.

The LTC3129 is available in thermally enhanced 3mm × 3mm QFN and 16-lead MSOP packages. For fixed output voltage options, seethefunctionallyequivalentLTC3129-1, which eliminates the need for an external feedback divider.

 

Introduction

TheLTC3129is a 1.3µA quiescent current, monolithic, current mode, buck-boost DC/DC converter that can operate over a wide input voltage range of 1.92Vto 15Vandprovide up to 200mA to the load. Internal, low RDS(ON) N-channel 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 stepdown operating modes are seamless and free oftransients and sub-harmonic switching, making this product ideal for noise sensitive applications. The LTC3129 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 response to load transients.

Burst Mode capability is also included in the LTC3129 and is user-selected via the PWM input pin. In Burst Mode operation, the LTC3129 provides exceptional efficiency at light output loading conditions by operating the converter only when necessary to maintain voltage regulation. The

Burst Mode quiescent current is a miserly 1.3µA. At higher loads, the LTC3129 automatically switches to fixed frequency PWM mode when Burst Mode operation is selected. (Please refer to the Typical Performance Characteristics curves for the mode transition point at different input and output voltages.) If the application requires extremely low noise, continuous PWM operation can also be selected via the PWM pin.

A MPPC (maximum power point control) function is also provided that allows the input voltage to the converter to be servo’d to a programmable point for maximum power when operating from various non-ideal power sources such as photovoltaic cells. The LTC3129 also features an accurate RUN comparator threshold with hysteresis, allowing the buck-boost DC/DC converter to turn on and off at user-selected VIN voltage thresholds. With a wide voltage range, 1.3µA Burst Mode current and programmable RUN and MPPC pins, the LTC3129 is well suited for many diverse applications .

 

PWM Mode Operation

If the PWM pin is high or if the load current on the converter is high enough to command PWM mode operation with PWM low, the LTC3129 operates in a fixed 1.2MHz PWM mode using an internally compensated average current mode control loop. PWM mode minimizes output voltage ripple and yields a low noise switching frequency spectrum. A proprietary switching algorithm provides seamless transitions between operating modes and eliminates discontinuities in the average inductor current, inductor ripple current and loop transfer function throughout all modes of operation. These advantages result in increased efficiency, improved loop stability and lower output voltage ripple in comparison to the traditional buck-boost converter.

The topology of the LTC3129 power stage which is comprised of four N-channel DMOS switches and their associated gate drivers. In PWM mode operation both switch pins transition on every cycle independent of the input and output voltages. In response to the internal control loop command, an internal pulse width modulator generates the appropriate switch duty cycle to maintain regulation of the output voltage.