MPLAB REAL ICE Power Monitor

September 23, 2013

Jack Ganssle-September 23, 2013

Microchip is one of the pioneers in developing MCUs that sip tiny amounts of current. They are also well-known for the huge number of development kits shipped each year. One of these products is the REAL ICE, a $500 tool that gives engineers a number of ways to develop and debug code for Microchip's processors.

They recently introduced an add-on for the REAL ICE. The Power Monitor (Figure 1 below) is a $380 circuit board that goes between the ICE and the target board, and it eponymously measures the power used by either the target board or just the board's MCU. (Like so many such tools, the name is a misnomer. The unit measures current, not power.)

Figure 1. The Power Monitor is between the REAL ICE and the target board.

Specs are scarce. The datasheet indicates that it can monitor up to an amp, but is silent about the low end. When I configured the MPLAB X IDE to use the Power Monitor, it gave me two options for power ranges: 1 mA to 1 A, and 1 uA to 9 mA. That's a huge range, but it will not be of much help for profiling the low-power sleep modes available on Microchip's XLP MCUs.

The company tells me the accuracy varies between 1 to 5%, the latter being for low-end measurements. They are apparently tweaking the software to add filters to improve those numbers, but I don't see the need. Most people will use the product to find where the code consumes the most current; 10 or even 20% errors probably aren't that important.

Microchip also tells me that there are no bandwidth-limiting filters. The ADC samples at 500 KSPS, which is fabulous resolution compared to many other similar products.

The Current Monitor unsurprisingly feeds Vdd to the board being tested, and lets you select a voltage from 1.25 to 5V in 0.125 increments, all under software control. I like that fine-grained control since in battery-powered applications one must account for the varying battery voltage vs. state of charge.

Unlike the other current-measuring devices I've reviewed, this only works with Microchip's MCUs. However, it handles every one of those.

There's no manual, but the help file has a reasonable amount of (poorly-written) documentation. It's impossible to navigate unless one enters via Help's "Contents" tab, and then selects "MPLAB REAL IDEA In-Circuit Emulator/Reference/Emulator Accessories/MPLAB REAL ICE Power Monitor."

The unit does come with a single-page sheet that takes one through the setup process. Don't read it; the help file has useful screen shots that makes setup a breeze.

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