Designing buck/boost regulators puts a high demand on PCB layout. With the LTM4712, Analog Devices provides a one-stop-shop solution for power management. The part's input voltage range of 5 V to 35 V makes it ideally suited to situations where power comes from a widely fluctuating input. The output voltage ranges from 1V to 36V. The regulator is furthermore able to operate at high efficiency when the input and output voltage are the same.

The LTM4712 maximum output current can reach up to 12 amperes, ensuring that the switching regulator can power demanding applications such as FPGA circuits. All of this takes place with very high efficiency. The figure shows that efficiency rarely falls below 94%, usually about 96%. These values makes the LTM4712 one of the most efficient regulators currently on the market.

PCB layout ensures quick design success

Control the LTM4712 working frequency with an external resistor. Analog provides a switching range of 100 to 600 kHz, permitting designers to keep the working frequency clear of frequency bands occupied by sensitive components. The inductor resides in the modules, leading to a simplified PCB design. Any MLCC capacitor can be used to provide output capacitance. A connection between the pins COMPa and COMPb enables default stabilizing behavior. Should a different mode of operation be required, connect a CRC network between the two compensation pins. Its values are ideally determined by LTPowerCad, a workstation-based application that can be downloaded for free from the Analog Devices website via the URL https://www.analog.com/en/lp/ltpowercad.html.

Additional external components permit the fine-tuning of regulator behavior. For example, the SS pin can be used to enable a soft-start behavior where the LTM4712 output voltage is slowly ramped up to the value set up using the external programming resistor. Furthermore, the switching frequency is selectable via the FREQ pin - the part permits ranges from 100 to 600 kHz using the resistor values shown in the table.

In particular, the FB pin emits a defined current, permitting the calculation of the resistor's value using Ohm's Law.

Higher current by parallelizing regulator modules

While the LTM4712 maximum output current of up to 12 amperes should be sufficient for most designs, advanced designs might require additional current on a single power rail. In this case, the LTM4712 can be cascaded by designing a group of building blocks and connecting the synchronization pins.

The resulting design is then phase-synchronized for a minimal amount of ripple and EMI permissions. Should input redundancy be required, the modules can also be paired up using a special regimen described in the datasheet.

In this mode, the failure of individual modules is not problematic as long as the maximum current-bearing capacity of all the modules is not exceeded. This ensures that the failure of one voltage input source does not lead to a catastrophic system failure.

PCB layout and component purchasing

Analog Devices provide the SKUs LTM4712EY#PBF and LTM4712IY#PBF. Both sell a 16×16 pin BGA housing, which uses multiple pins in parallel so as to enable maximum current output. The layout is optimized to permit two-layer printed circuit boards.

Conclusion

With the LTM4712, Analog Devices provides an easy-to-use boost/buck regulator. If an application must deal with widely differing input voltages, deploying this part greatly simplifies the design of the power electronics component. Thus, our recommendation is always given.