tle4998 Infineon Technologies Corporation, tle4998 Datasheet - Page 12

• Manufacturer Part Number: tle4998
• Description: Programmable Linear Hall Sensor
• Manufacturer: Infineon Technologies Corporation

Cst can for example be found by calculating the average error with Cst set to one as illustrated in the
implementation example.
4.1
For a computing system, an iterative algorithm is a good way to solve for the new DSP parameters as the possible
parameter space is very small. This means we iterate through all coefficients and check where
satisfied best over temperature. One possible criterion is to minimize the root mean square error value
is given by
It is not necessary to determine the residual error for very small temperature steps, a good value is to look for the
maximum residual error every 10°C from the minimum required temperature to the maximum required
temperature (-40 °C to +150 °C are resonable limits). The following section illustrates the procedure on a practical
implementation example.
4.2
The implementation is separated into two parts:
•
•
•
The implementation uses Microsoft
other programming languages.
4.2.1
Precalibrated parameter set read from the sensor:
•
•
•
Valid ranges are: TL_dsppre: 0...511; TQ_dsppre: 0...255; TT_dsppre: 0...31.
Given user values in °C and ppm:
•
•
•
Valid ranges are: T0_user: -50...80, TC1_user: -0.001...0.0025, TC2_user: -0.000004...0.000004.
Last but not least we have the new setup values, we initialize partly:
•
•
•
(Valid ranges are: TL_dsp: 0...511, TQ_dsp: 0...255, TT_dsp: 0...31).
4.2.2
The first function calculates the user polynomial at a given temperature T:
Private Function S_user(ByVal T) As Double
Temperature Coefficient Setup Guide
User’s Manual
ε
rms
Initialization of several global variables (parameters etc.)
Subroutines for calculating all the different sensitivities
The iteration loop to calculate the parameter set
TL_dsppre (as stored in EEPROM)
TQ_dsppre (as stored in EEPROM)
TT_dsppre (as stored in EEPROM)
T0_user (user reference temperature)
TC1_user (user linear temperature coefficient)
TC2_user (user quadratic temperature coefficient)
TL_dsp (used as sweep variable, needs no initialization)
TQ_dsp (used as sweep variable, needs no initialization)
TT_dsp = TT_dsppre
S_user = 1 + TC1_user * (T - T0_user) + TC2_user * (T - T0_user) ^ 2
=
--- -
N
1
k
∑
Algorithm
Example Implementation in Visual Basic
Setup of Global Variables
Sensitivity Calculation Subroutines
N
=
1
⎛
⎝
–
1
+
-------------------------------------------------------------------------------- -
Cst S
⋅
DSP pre
S
DSP final
,
,
®
(
Visual Basic
T
k
) S
(
T
⋅
k
)
user
(
T
®
k
, this language should be easy to understand and to map into
)
⎞
⎠
2
TC Setup Part 2 - Calculating the New EEPROM Values
.
12
Temperature Coefficient Setup Guide
Rev 1.1, 2008-10-30
Equation (13)
ε
TLE4998
rms
, which
(15)
is