COMPARISON BULLETIN

The NVE SM225 and Allegro A1454 are both linear magnetic sensors with microcontroller interfaces. The advantages of NVE’s groundbreaking SM225 Smart TMR Magnetometer over the Allegro part are summarized below:

	Technology	Full-Scale  Sensitivity	Accuracy		Magnetic  Bandwidth	Package
			–40–125°C
			% of full-scale	Field
Allegro A1454	Old-fashioned  Hall-effect	50 mT or 100 mT	±7%	±3.5 mT	2 kHz	4.4 x 3 mm  TSSOP8
NVE SM225	TMR	15 mT	±4%	±0.6 mT	7.5 kHz	2.5 x 2.5 mm   leadless TDFN6

Convenient Magnetic Orientation
Unlike Allegro’s awkward, old-fashioned Hall-effect sensor elements, the SM225 uses TMR, which is sensitive in-plane for optimal current sensing and easy mechanical interfaces.

Three Times More Sensitive
The SM225’s high sensitivity (15 mT linear range) make it compatible with small, low-cost magnets, and it can detect strong magnets more than 50 mm away. Allegro requires more expensive magnets and much smaller airgaps. The most sensitive A1454 version is rated at 50 mT, not because applications need high field, but because of the low sensitivity and high noise of Hall effect elements.

More Accurate
Most accuracy specifications are a percentage of full scale, so because of its much higher sensitivity, the SM225 is at least three times more accurate in the range of interest.

Even as a percentage of full scale, the SM225 is much more accurate.

The SM225 accuracy is ±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.

If you need even more accuracy, you can use our ultraprecise SM324.

The A1454 has a sensitivity error of ±3% for –40°C to 85°C and ±6% for –40°C to 125°C, and a ±1% linearity sensitivity error for a total of 7% or 3.5 mT over the full temperature range—much worse than our 4% or 0.6 mT.

Five Times Faster
The SM225 update rate is 15 kHz with a magnetic bandwidth of more than 7.5 kHz, so sampling is not limited by internal bandwidth. That’s especially important for AC current sensing. The A1301 claims an update rate of 32 kHz, but that’s of little value since the internal bandwidth is only 2 kHz.

Lower Voltage
SM225 has a versatile 2.2 to 3.6 V supply range, compared to the A1454’s 2.65 V minimum supply voltage.

More Reliable Interface
The SM225 has a fast, reliable SPI interface versus the A1454’s slower I²C interface.

Unlimited Nodes
SM225’s industry-standard SPI interface has a chip select allowing an almost an unlimited number of sensors to be connected to one microcontroller.

The A1454 only allows 15 I²C interface addresses and two resistor voltage dividers are required to select them, which increases the parts count. You can program the address, but that isn’t very practical since you need to use the default address to reprogram a new address.

Smaller
The A1454 is in a TSSOP8 with a 4.4 x 3 mm body and a 6.4 x 3 mm footprint. The SM225 has one-third the footprint area with its 2.5 x 2.5 mm leadless TDFN.

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