Digi-Key offers a vast array of DC-DC switching voltage regulators which are designed to efficiently convert an input voltage to the desired output voltage. To help narrow the selection down to parts that perform the desired function, we list a parameter aptly named “Function”.
Most of the options under the “Function” parameter are fairly intuitive:
Ratiometric - Magnitude of output voltage is a function of the input voltage defined by some ratio (often about 2:1)
Example “Ratiometric” circuit using Microchip TC1240A
Step-Up - Magnitude of output voltage is greater than input voltage
Example “Step-Up” circuit using Maxim MAX1722
Step-Down - Magnitude of output voltage is less than input voltage
Example “Step-Down” circuit using Diodes Incorporated AP3211
A number of parts can perform more than one function depending on how they are configured. For example, we carry parts that can be configured as “Ratiometric” or as “Step-Up”. We list this under the “Function” parameter as “Ratiometric, Step-Up”. This description is still fairly obvious and intuitive.
However, we list some parts as “Step-Up, Step-Down” while we list other parts as “Step-Up/Step-Down”, which is somewhat confusing. Despite the seemingly redundant descriptions, there is actually a rationale for listing it this way.
When we list the function as “Step-Up, Step-Down” with the comma separating the two functions, we are stating that the part can be configured in one of two ways: either as a “Step-Up” function or as a “Step-Down” function, but not both simultaneously.
By contrast, when we list the function as “Step-Up/Step-Down” with the forward-slash in between, we are stating that the part is capable of regulating a fixed output voltage regardless of whether the input voltage is greater than or less than the output voltage without having to reconfigure the part. Such a part is particularly useful in battery-powered applications where the battery voltage is above the output voltage when fully charged, but which drops below the output voltage before it is fully depleted, thus allowing full battery utilization.
Example “Step-Up/Step-Down” circuit using Texas Instruments TPS63051