Datasheet LTC3129 (Analog Devices) - 10

LTC3129
operaTion INTRODUCTION PWM MODE OPERATION
The LTC3129 is a 1.3µA quiescent current, monolithic, cur- If the PWM pin is high or if the load current on the converter rent mode, buck-boost DC/DC converter that can operate is high enough to command PWM mode operation with over a wide input voltage range of 1.92V to 15V and provide PWM low, the LTC3129 operates in a fixed 1.2MHz PWM up to 200mA to the load. Internal, low RDS(ON) N-channel mode using an internally compensated average current power switches reduce solution complexity and maximize mode control loop. PWM mode minimizes output voltage efficiency. A proprietary switch control algorithm allows the ripple and yields a low noise switching frequency spec- buck-boost converter to maintain output voltage regulation trum. A proprietary switching algorithm provides seamless with input voltages that are above, below or equal to the transitions between operating modes and eliminates dis- output voltage. Transitions between the step-up or step- continuities in the average inductor current, inductor ripple down operating modes are seamless and free of transients current and loop transfer function throughout all modes of and sub-harmonic switching, making this product ideal operation. These advantages result in increased efficiency, for noise sensitive applications. The LTC3129 operates improved loop stability and lower output voltage ripple in at a fixed nominal switching frequency of 1.2MHz, which comparison to the traditional buck-boost converter. provides an ideal trade-off between small solution size and Figure 1 shows the topology of the LTC3129 power stage high efficiency. Current mode control provides inherent which is comprised of four N-channel DMOS switches and input line voltage rejection, simplified compensation and their associated gate drivers. In PWM mode operation rapid response to load transients. both switch pins transition on every cycle independent of Burst Mode capability is also included in the LTC3129 and the input and output voltages. In response to the internal is user-selected via the PWM input pin. In Burst Mode control loop command, an internal pulse width modulator operation, the LTC3129 provides exceptional efficiency at generates the appropriate switch duty cycle to maintain light output loading conditions by operating the converter regulation of the output voltage. only when necessary to maintain voltage regulation. The Burst Mode quiescent current is a miserly 1.3µA. At higher CBST1 CBST2 L loads, the LTC3129 automatically switches to fixed fre- quency PWM mode when Burst Mode operation is selected. BST1 VIN SW1 SW2 VOUT BST2 (Please refer to the Typical Performance Characteristics VCC VCC curves for the mode transition point at different input and A D output voltages.) If the application requires extremely low noise, continuous PWM operation can also be selected VCC VCC via the PWM pin. B C A MPPC (maximum power point control) function is also PGND PGND provided that allows the input voltage to the converter to LTC3129 3129 F01 be servo'd to a programmable point for maximum power when operating from various non-ideal power sources
Figure 1. Power Stage Schematic
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 program- mable RUN and MPPC pins, the LTC3129 is well suited for many diverse applications. 3129fc 10 For more information www.linear.com/LTC3129 Document Outline Features Applications Typical Application Description Absolute Maximum Ratings Pin Configuration Order Information Electrical Characteristics Typical Performance Characteristics Pin Functions Block Diagram Operation Applications Information Typical Applications Package Description Revision History Typical Application Related Parts