Low-Dropout (LDO) Linear Regulator Evaluation

Low-Dropout (LDO) Linear Regulator Evaluation Quick Bench-top Evaluation of ICs and Electronic Components Keysight B2900A Series of Precision Source/Measure Units facilitates quick DC evaluation of linear regulator such as LDO.

DC evaluation of Linear Regulators

• A linear regulator keeps the DC output voltage stable even if the input voltage is varying. This is called “line regulation.” Linear regulators also provide a wide range of output current sourcing capability at constant output voltage. This is called “load regulation.” As this document will show, SMUs (Source/Measure Units) are convenient instruments to characterize a linear regulator’s DC specifications
• This one-pager outlines an example of load regulation characterization for an off-the-shelf LDO linear regulator

Measurement example

• Load regulation

It is easy to estimate load regulation by measuring output voltage drift while sweeping an output source current over a specified range. A dual-channel SMU such as the B2902A or B2912A is an ideal choice for these types of measurements. In the example shown below, a user-selected constant voltage (2.7 V) is applied to the input using SMU1 while the output current source is being swept from -250 mA to 0 A using SMU2

Measurement result (not using “Sense” connection)

Sweeping from -250 mA to 0 A without connecting the “Sense” terminals results in a large drift at the output. This is due to the voltage drop in the test leads. To eliminate this effect, you need to connect both the “Sense” and “Force” leads to the DUT. In this 4-wire measurement case the ”Sense” and “Force” leads are shorted together at the test pin of the evaluation module. The “Sense” leads measure the voltage at the tip of leads, thereby eliminating the voltage drop across the “Force” leads.

Measurement result (using “Sense” connection)

By using the “Sense” leads we can plot the true LDO regulator drift characteristics on the panel of B2912A. This 4-wire measurement technique exhibits a very small drift that is consistent with the device datasheet. This illustrates a general principle that SMU measurements with significant current sourcing or sinking require the use of the “Sense” terminal to obtain correct measurement results.