COMPARISON BULLETIN

The NVE SM225 and Micronas HAL2420 are both programmable linear magnetic sensors. The advantages of NVE’s groundbreaking SM225 Smart TMR Magnetometer over the Micronas part are summarized below:
 

	Technology	Programming	Accuracy	Bandwidth	Response  Time	Power Supply	Package
Micronas HAL2420	Old-fashioned  Hall-effect	Proprietary off-line Programmer	±2 mT	2 kHz	600 µs	4.5 to 5.5V  50 mW	5 x 4 mm  SOIC8 or TO-92
NVE SM225	TMR	SPI Interface	±0.6 mT	7.5 kHz	67 µs	2.2 to 3.6V 25 mW	2.5 x 2.5 mm  leadless TDFN6

Convenient Magnetic Orientation
Unlike Micronas’ awkward, old-fashioned Hall-effect sensor elements, the SM225 uses TMR, which is sensitive in-plane for optimal current sensing and easy mechanical interfaces. Micronas sensors come in clunky SOIC8s that need to be mounted perpendicular to the magnet, and archaic TO-92 packages.

Three Times More Accurate
The SM225 straightforward accuracy specifications: ±2% (0.3 mT) for 0 to 125°C and ±4% (0.6 mT) for the full –40 to 125°C range. That covers all error sources, including sensitivity, offset, nonlinearity, hysteresis, noise, and supply variation.

The HAL2420 datasheet identifies three major magnetic error sources:
  • Magnetic offset: ±0.4 mT
  • Magnetic offset change over temperature: ±5 µT/K, or ±0.83 mT over the –40 to 125°C temperature range
  • Error in magnetic sensitivity: ±1.5% of 50 mT, or ±0.75 mT

Additional electrical errors include:
  • Nonlinearity of output voltage over temperature: ±0.3% or a minimum of ±0.018 mT at the most sensitive (6 mT) scale
  • Ratiometric error of output over temperature: ±0.25% or ±0.015 mT at the most sensitive scale
  • Offset drift over temperature range: 0.2% or ±0.012 mT

In addition the ADC required to redigitize Micronas’ analog output adds another layer of error.

That adds up to more than ±2 mT, far worse than the SM225’s 0.6 mT accuracy.

Ten Times Faster
The SM225 has a high-speed TMR sensor element and a 15 kHz sample rate, so the response time for full accuracy is just 67 µs. That’s especially important for AC current sensing. The HAL2420 has a slow Hall element, with a 600 µs response time specification, and even that is only to 90% of the final value, so there’s still a 10% error.

The SM225 also has a 7.5 kHz magnetic bandwidth, more than triple that of the HAL2420. That’s especially important for AC current sensing.

In addition to fast response and wide bandwidth, the SM225 is up, running, and accurate in just 1 millisecond. The Micronas parts take 8 ms for full accuracy.

In-Circuit Programmability
The SM225 has a fast, reliable SPI microcontroller interface. The sensor can be zeroed, calibrated, or parameters other changed in the application.

Digital Interface
The SM225’s SPI interface allows fast polling of digital field and temperature data from one or more sensors using ubiquitous SPI hardware and software support for virtually any microcontroller. The HAL2420’s analog output requires an ADC input for a microcontroller, which adds expense to the microcontroller and another layer of error sources.

The nonstandard Micronas programming interface requires a Micronas programmer, a PC, and a LabView programming environment, which is not practical for production.

3V Supply; Lower Power
The SM225 has a modern, versatile 2.2 to 3.6 volt supply and 25 milliwatts or less, compared to 5 volts and 50 milliwatts for the Micronas part. Less self-heating means less temperature drift and more accuracy.

Smaller
The HAL2420 surface-mount package is a SOIC8 with a 5 x 4 mm body and a 6 x 4 mm footprint. The SM225 has one-fourth the footprint area with its 2.5 x 2.5 mm leadless TDFN.

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