COMPARISON BULLETIN

The NVE SM124 and Infineon TLE4998S are both programmable linear magnetic sensors with microcontroller interfaces. The advantages of NVE’s groundbreaking new SM124 Smart Magnetometer over the Infineon part are summarized below:

	Technology	Interface	Accuracy  (–40–125°C)	Max.  Update Rate	Power Supply	Packages
Infineon  TLE4998S	Old-fashioned Hall-effect	Modified SENT	±2.6 mT	800 Hz	4.5 to 5.5V  44 mW	5 x 4 mm SOIC8,   5 x 4 mm SSO4, or 4 x 4 mm SSO3
NVE SM124	GMR	Industry Standard I²C	±0.1 mT	10 kHz	2.2 to 3.6V 25 mW	2.5 x 2.5 mm  leadless TDFN6

Convenient Magnetic Orientation
Unlike Infineon’s awkward, old-fashioned Hall-effect sensor, the SM124 uses GMR, which is sensitive in-plane for easy mechanical interfaces and convenient noncontact current sensing. Infineon sensors come in clunky SOIC8s that need to be mounted perpendicular to the magnet, and archaic SSO packages.

Twenty Times More Sensitive
The SM124’s high sensitivity (1 mT linear range) make it compatible with small, low-cost magnets, and it can detect strong magnets more than 50 mm away. The most sensitive TLE4998S range is 50 mT, not because applications need high field, but because of the low sensitivity and high noise of Hall effect elements. Infineon requires more expensive magnets and much smaller airgaps.

If you really do need a higher-field range, you can use our 10 mT SM225.

25 Times More Accurate
The SM124 has straightforward accuracy specifications: ±5% (0.05 mT) for 0 to 85°C, and ±10% (0.1 mT) over the full –40 to 125°C range. That covers all error sources, including temperature dependence, nonlinearity, offset, hysteresis, and noise.

The TLE4998S datasheet identifies a number of error sources:
  • Sensitivity drift: ±150 ppm/°C, or ±1.25 mT for the most sensitive (50 mT) range over –40 to 125°C
  • Nonlinearity: ±0.1% of the range, or ±0.05 mT for the 50 mT range
  • Magnetic offset: ±0.4 mT
  • Offset temperature sensitivity: ±5 µT/°C, or ±0.83 mT over the –40 to 125°C temperature range
  • Hysteresis: 0.01 mT
  • Noise: 2.5 LSB of rms output noise, or ±0.07 mT for 12 bits on the most sensitive range
  • Power-on error: ±1% after 20 ms, or ±0.01 mT for a 1 mT field

That adds up to more than ±2.6 mT, far worse than the SM124’s 0.1 mT accuracy.

At Least Twelve Times Faster
The SM124’s transmission time is a few microseconds and the update rate is 10 kHz. That’s especially important for AC current sensing. The interface is built for speed. With just one byte per sample with very little overhead, a microcontroller can read the SM124 quickly and still do everything else it has to. Additionally, magnetic noise is negligible, so filtering, which reduces the response time, is often unnecessary.

The TLE4998S transmission time depends on the data values being sent and the sensor’s internal oscillator frequency. Accounting for the Infineon part’s 20% oscillator tolerance, transmission time can be as long as 1.2 milliseconds. That’s barely 800 samples per second if the microcontroller isn’t doing anything else.

In addition to fast updates, the SM124 is up, running, and accurate in just 1 millisecond. The Infineon parts are slow to power up. A ±5% error is specified after 2 milliseconds and ±1% after 20 milliseconds. Presumably the errors continue drifting down with time, but that isn't specified.

Reliable I²C Interface
The SM124 uses a fast, reliable industry-standard I²C interface, compared to Infineon’s noncompliant “SPC” SENT interface.

Infineon tries to overcome inherent SENT limitations with “synchronous” and “ID selection” modes, but these need custom software and make the part incompatible with industry standards.

On the other hand, I²C hardware and software support is ubiquitous, and the SM124’s elegant architecture dramatically simplifies firmware, streamlines system development, and allows high-speed communication. For example, here’s everything to read an SM124 with an Arduino:

  #include <Wire.h> //I2C library
  int field; //Magnetic field (0-100 corresponds to 0-10 Oe)
  void setup() {
    Wire.begin(); //Join I2C bus as Master (SM124 is a Slave)
}
  void loop() {
    Wire.requestFrom(36,1); //1 data byte from SM124 at I2C addr. 36; default to mag field
    field = Wire.read(); //Read sensor (data always valid so a “While” loop isn’t needed)
}

That’s it. No sychronization, edge detection, accounting for variable data length, concatenation, bit masking, scaling, or calculating polynomial checksums for every nibble.

3V Supply; Lower Power
The SM124 has a modern, versatile 2.2 to 3.6 volt supply and 25 milliwatts or less, compared to 5 volts and 44 milliwatts for the Infineon parts. Even the “extended range” TLE4998S only works down to 4.1 volts.

Low Parts Count
The only external part the SM124 needs is a bypass capacitor. The Infineon part needs a bypass capacitor, an output pullup resistor, a capacitor on the output, and an RC filter between the output and the microcontroller input. Component values depend on speeds, voltages, and impedances.

A Real Operating Temperature Range
All SM124 operations work over the full –40 to 125°C temperature range. The Infineon parts can only be programmed at room temperature (the specification is 10°C to 30°C).

<Questions or Comments>