2.3 Measure Current Draw of MSP430 MCU
The following steps assume that the target F5529 is to be powered from the USB host, not from an external power source.
- Remove the 3V3 jumper in the isolation jumper block. Attach an ammeter across this jumper.
- Consider the effect that the backchannel UART and any circuitry attached to the F5529 may have on current draw. Maybe these should be disconnected, or their current sinking and sourcing capability at least considered in the final measurement.
- Make sure there are no floating input I/Os. These cause unnecessary extra current draw. Every I/O should either be driven out or, if an input, should be pulled or driven to a high or low level.
- Begin target F5529 execution.
- Measure the current. (Keep in mind that if the current levels are fluctuating, it may be difficult to get a stable measurement. It is easier to measure quiescent states.)
This measurement does not include USB current, which is sourced through the 5V jumper instead. USB current levels can vary widely, depending on whether the connection is active or suspended, how much bus activity is happening, how long the cable is, and other factors.
If you are trying to achieve the LPM3 values shown in the F5529 data sheet and are having trouble, download the F5529 code examples and see MSP430F552x_LPM3_01.c, adjusting the I/O settings for your application.