Efficiently Power that Op Amp

Efficiency versus load current with Vout = -5V

In many applications, such as temperature sensing, two supply voltages are needed to power an op amp in the system—one positive and one negative.   This dual supply is needed by the amplifier in order to properly measure signals very close to or even below ground.  If the negative supply input of the op amp was just grounded and a single, positive supply voltage used, these signals would not be processed properly.  Both a negative and positive voltage are critical for amplifiers that see these use cases.

Once the positive and negative voltage levels have been decided (such as +/- 5V), the next question turns to the current required on each.  In many simple or battery-powered applications, this current drawn by the amplifier is quite low.  The good news from this fact is that the likely already-existing 5-V rail in the system is not further burdened by another device drawing power from it.  The bad news is that an entirely new voltage rail is needed to provide a regulated -5V.  To make matters more difficult, this negative rail is generally more cumbersome to design and implement due to the negative voltages and lack of dedicated solutions in the market for generating them.  Finally, the very low output power typically leads to relatively low conversion efficiency.

Enter TI Designs to save the day!  With PMP9752, you have a proven, explained, and documented solution to this challenge.  The TPS62120 or TPS62122 (which may already be in your BOM as a buck converter!) is used, not as a buck converter, but as an inverting buck-boost converter.  The same device fulfills two different roles.  Giving 80% efficiency for most of the load current range and requiring just 6 external components, this is a small and efficient solution to the need for a regulated, low current negative rail in industrial systems.

What are you powering that requires a +/- rail?