LTC3119IUFD#PBF

The LTC3119IUFD#PBF from Analog Devices is a high-efficiency, 18V, 2A bidirectional buck-boost DC/DC converter that combines a unique 4-switch architecture with bidirectional power flow capability. The device can operate from an input voltage as low as 2.2V to as high as 18V, producing a regulated output between 2.2V and 18V regardless of the input-to-output voltage relationship. The bidirectional capability allows the same component to function as either a step-up or step-down converter, with power flowing in either direction depending on the system requirements. This is particularly valuable in battery backup applications where the converter must charge the backup battery from the main supply (forward mode) and then supply power from the battery back to the system (reverse mode) when the main supply fails. The 4-switch topology enables seamless transitions between buck, boost, and buck-boost operating modes without output voltage discontinuity, maintaining regulation even when the input voltage passes through the output voltage level. Operating at a default switching frequency of 1MHz (adjustable 500kHz to 1.5MHz), the LTC3119 achieves up to 95% efficiency while keeping external inductor and capacitor sizes small. The forced continuous conduction mode eliminates the pulse-skipping behavior that creates output noise in discontinuous mode, making the device suitable for noise-sensitive applications. The LTC3119 is available in a compact 28-lead QFN package (4mm x 5mm).

The LTC3119IUFD#PBF operates as a 4-switch buck-boost converter with bidirectional power flow. Key subsystems include: (1) 4-Switch Bridge – four N-channel MOSFETs arranged in an H-bridge configuration between the input and output; depending on the VIN/VOUT relationship, different pairs of switches are modulated to implement buck, boost, or buck-boost operation; (2) Seamless Mode Transition – the control logic continuously monitors VIN and VOUT and transitions between operating modes without output discontinuity; in buck mode (VIN > VOUT), switches A and B are modulated while C is on and D is off; in boost mode (VIN < VOUT), switches C and D are modulated while A is on and B is off; in buck-boost mode (VIN near VOUT), all four switches are modulated; (3) Bidirectional Control – the DIR pin selects the power flow direction; when DIR selects forward mode, power flows from the VIN side to the VOUT side; when DIR selects reverse mode, the power flow reverses, allowing the output to supply the input; this enables a single converter to handle both battery charging and backup supply functions; (4) Current Mode Control – peak current mode control provides cycle-by-cycle current limiting and simplifies loop compensation; the average inductor current is regulated to maintain the desired power flow; (5) Frequency Synchronization – an internal oscillator runs at 1MHz default but can be synchronized to an external clock or adjusted via the RT pin for EMI optimization.

• Battery backup: forward mode charges 12V SLA from 24V supply; reverse mode provides 12V output when main supply fails
• Supercapacitor ride-through: charges supercap from 5V rail; discharges supercap back to 5V during power interruption
• Automotive battery balancer: transfers energy between 12V and 48V battery systems bidirectionally
• Industrial UPS: single converter handles both battery charging and backup supply functions