Why am I unable to achieve the low supply currents listed in the datasheet?
Answer
The shutdown currents listed in the datasheet can be achieved after all peripherals that have an enable/disable bit have been turned off. There are a number things to check that may be affecting your current measurements:
Check that LEDs and switches have been disconnected from the Port I/O pins. On most Target Boards, these components can be disconnected by removing the shorting blocks from the associated headers. For example, on the 'F33x Target Board, all shorting blocks on J3 should be removed when measuring supply current.
Verify that peripherals enabled on reset have been disabled. This includes most peripherals associated with the power supply such as voltage regulators and supply monitors. For example, all USB microcontrollers have the voltage regulator and VDD Monitor enabled after each reset.
Verify that the USB Debug Adapter is not connected. On some target boards, this can result in a supply current increase of approximately 30uA.
Check for any pull-down resistors (For example, IDAC resistors). All Port I/O have weak pullups, and if external pull-downs are used, this could result in a current of a few uA. If a pin does have a pull-down resistor, it can be configured into Analog mode to disable its weak pull-up.
If using an 'F9xx device, see Application Note 358 for more details on how to reduce power consumption.
Measuring Supply Current