MCP39F511 datasheet(50/62 Pages) MICROCHIP

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MCP39F511

DS20005393B-page 50

 2015 Microchip Technology Inc.

9.7

Temperature Compensation

MCP39F511

measures

the

indication

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 9-10:

At the calibration temperature, the effect of the com-

pensation 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.

9.8

Retrieving Factory Default

Calibration Values

After user calibration and a Save

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 delimiter register,

issuing a Save to 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 to 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,

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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