MLX90251_12 Datasheet, PDF (13/20 Pages) Melexis Microelectronic Systems – Programmable Linear Hall Effect Sensor

MLX90251
Programmable Linear Hall Effect Sensor
10.7 Filter (FILTER)
The MLX90251 includes two programmable low-pass filters located within the chopper amplifier stages. The
two low-pass filters are controlled through a 4 bit parameter, FILTER. The FILTER value 0 corresponds to
minimum filtering, maximum speed (impulse response time), and maximum output noise. The value 15
provides the maximum filtering, minimum speed, and minimum output noise. It is important to note the noise
is also linked to the gain settings. The FILTER parameter needs to be adjusted to achieve optimal
performance. The next table shows typical values the cut-off frequency at -3 dB versus FILTER and RG
parameters. FILTER values from 8 to 11 are not used. For most applications FILTER values 7 or 15 are
recommended.
Cut-off frequency at -3 dB (Hz) – Typical
Filter
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
MLX90251-0
MLX90251-1
MLX90251-2
MLX90251-3
Rough Gain 0…3 Rough Gain 4…7 Rough Gain 8…11 Rough Gain 12…15
22900
14300
7000
3850
19500
11450
5550
2950
12300
10000
3000
2300
10400
6750
2100
1100
7450
3900
1500
850
5850
2900
1125
860
5700
2700
1350
715
5050
2550
1380
650
Not used
Not used
Not used
Not used
2200
840
565
250
1000
480
470
190
920
380
290
155
800
330
250
135
Table 11: Cut-off Frequency versus FILTER and RG Parameters
10.8 Sensitivity Temperature Compensation (TC, TCW, TC²)
The change in the device's Sensitivity versus temperature is defined as the Sensitivity Temperature
Compensation, TempCo. In an application the slope output transfer characteristic is often affected by
temperature. Fluctuations in temperature can cause variations in the air gap, mechanical alignment and
magnetic field. The Sensitivity Temperature Compensation feature compensates for these effects.
Three parameters, TC, TCW, TC² are used for adjustment of the TempCo. The TCW is used to adjust the
TempCo range, TC is for fine adjustment of the TempCo value, and TC² effects the TempCo linear response.
To simplify use of these parameters Melexis stores a look up table within the EEPROM of each device. The
look up table is optimized for each device by characterizing the unit over temperature at final test.
The value of TempCo is often determined by the magnet. In the application the TempCo is adjusted to
compensate for the temperature coefficient of the magnet. To adjust the value the look up table is read from
the device. The parameters are then calculated to match the desired value. The Melexis PTC hardware and
software tools contain built in functions for programming the TempCo.
3901090251
Rev 012
Page 13 of 20
Data Sheet
Oct/2012