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TPS62913-IBB-EVM: Design notes for IBB

Part Number: TPS62913-IBB-EVM
Other Parts Discussed in Thread: TPS62913


I have questions about IBB.

Q1. I am thinking of inserting a fuse as a measure against burning. Where is the best place to place it?

Q2. Should the IBB phase compensation parameters be the same as for the positive power supply?

Q3. When multiple devices generate multiple negative voltages, how far should the devices be from each other in terms of heat dissipation?

Q4. I would like to know the advantages and disadvantages of CUK converter and IBB.



  • Koki, 

    Thank you for your questions. 

    The TPS62913 has a current limit feature so you may not need a fuse for conditions of excessive load.  However, this depends on your specific application and the conditions that you are trying to protect against, such as shorting the input to output and bypassing the TPS62913 protection, which in that case you would want the fuse on the input.

    The inverting buck boost configuration results in a right half plane zero (RHPZ) that requires the crossover to be ~4 times lower than that value.  With some converters, you can re-compensate to achieve this, but with the TPS62913 and the internal fixed frequency, the only way to do that is to increase the output capacitance.  This is what is shown in the TPS62913 Inverting Buck Boost EVM User Guide. More detail on the IBB topology can be found here:

    The spacing between devices for optimal heat dissipation depends on many factors such as board thickness, operating conditions, airflow, the application thermal targets, and the device performance.  The thermal performance of the TPS62913 can be calculated using the power dissipation in the device and estimating the temperature rise using the thermal parameter table in the datasheet.  

    Inverting outputs can be achieved with both CUK and IBB topologies.  The TI Power Topologies Handbook ( has all the design equations to compare each topology in detail. In my opinion, the main reasons to use an IBB topology is that you can use almost any buck converter, as long as the input voltage tolerance is wide enough to cover the actual input voltage minus the output voltage (i.e., you need a 17V converter to achieve 12Vin and -3.3Vout with some margin), and you only need a single inductor. Keep in mind that in the IBB configuration, you will have a reduced output current capability versus the rated current limit due to the configuration.  With the CUK, you need a controller that is capable of boost, SEPIC, or flyback configuration as well as two inductors. 

    I hope this helps.