This reference design utilizes the LM61495 synchronous buck regulator, with internal top and bottom FETs, which is configured as a synchronous inverting buck-boost converter. The design generates an output of –8 V, capable of delivering 2.7-A continuous (4-A peak) of current to the load, from a +12 V, ±10% input. The design is built on the PMP23241A PCB, which is a 4-layer board with 1-oz copper for each of the four layers. The board is 76.2 mm × 68.6 mm. The actual design size is approximately 17.0 mm × 30.5 mm, excluding the input bulk capacitor, C1.

• Very small design size
• Regulator includes integrated FETs
• High efficiency
• Regulator features spread-spectrum switching (dithering) for improved EMI performance
• Converter generates a negative output voltage from a positive input voltage

• Active antenna system mMIMO (AAS)
• Macro remote radio unit (RRU)

Top of Board

Bottom of Board

• Power supplies (one to provide the main converter power)
• Electronic Load (isolated or floating)
• DMMs
• Oscilloscope

All voltage measurements were made relative to the 0-V common GND. When taking measurements, make sure to connect the GND clips of the oscilloscope to the GND (that is, 0-V) connection. Do not connect the oscilloscope GND clips to the –V_OUT node. Though this –V_OUT is the reference for the GND pins of the regulator IC, the output is no longer considered 0-V common GND.

In the inverting buck-boost topology, the voltage potential between the VIN and GND pins of the converter or regulator is the sum of the magnitudes of V_IN and V_OUT voltages. For example, with a nominal input voltage of +12 V, the total voltage potential exhibited by the LM61495 is: |+12 V| + |–8 V| = 20 V. The LM61495 has a maximum recommended supply voltage of 36 V. Therefore, do not apply an input voltage greater than 28 V_IN to the converter, preferably lower, to provide an extra buffer to accommodate for switching voltage spikes.