MCP39F521 datasheet(41/52 Pages) MICROCHIP

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DS20005442A-page 41

MCP39F521

8.7

Temperature Compensation

The MCP39F521 measures the indication of the

temperature sensor and uses the value to compensate

the temperature variation of the shunt resistance and

the frequency of the internal RC oscillator.

The same formula applies for Line Frequency, Current

RMS, Active Power and Reactive Power. The

temperature compensation coefficient depends on the

16-bit signed integer value of the corresponding

compensation register.

EQUATION 8-10:

When calibrating the temperature, the effect of the

compensation coefficients is minimal. The coefficients

need to be tuned when the difference between the

calibration temperature and the device temperature is

significant. It is recommended to use the default values

as starting points.

8.8

Retrieving Factory Default

Calibration Values

After user calibration and a Save to Flash command

has been issued, it is possible to retrieve the factory

default calibration values. This can be done by writing

0xA5A5 to the Calibration Register Delimiter, issuing a

Save

Flash

, and then resetting the part. This

procedure will retrieve all factory default calibration

values and will remain in this state until calibration has

been performed again, and a Save

Flash

command has been issued.

CAL

–









Where:

x = Uncompensated Output (corresponding to

Line Frequency, Current RMS, Active Power

and Reactive Power)

y = Compensated Output

c = Temperature Compensation Coefficient

(depending on the shunt's Temperature

Coefficient of Resistance or on the internal RC

oscillator temperature frequency drift). There

are three registers: one for Line Frequency

compensation, one for Current compensation,

and one for power compensation (Active and

Reactive)

T =

Thermistor Voltage (in 10-bit ADC units)

TCAL = Ambient Temperature Reference Voltage. It

should be set at the beginning of the

calibration procedure, by reading the

thermistor voltage and writing its value to the

ambient temperature reference voltage

M = 26 (for Line Frequency compensation)

= 27 (for Current, Active Power and Reactive

Power)

TemperatureCompensation Register

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