MCP39F511N datasheet(22/61 Pages) MICROCHIP

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 2015-2018 Microchip Technology Inc.

DS20005473B-page 22

MCP39F511N

5.4

RMS Current, RMS Voltage and

Apparent Power (S)

The MCP39F511N device provides true RMS

measurements. The MCP39F511N device has two

simultaneous sampling 24-bit A/D converters for the

current measurements. The root mean square

calculations are performed on 2N current and voltage

samples, where N is defined by the register

Accumulation Interval Parameter.

EQUATION 5-1:

RMS CURRENT AND

VOLTAGE

FIGURE 5-2:

RMS Current (Channel 1 or 2), Apparent Power (Channel 1 and 2) and Voltage

Calculation Signal Flow.

5.4.1

APPARENT POWER (S)

This 32-bit register is the output register for the final

apparent power indication. It is the product of RMS

current and RMS voltage as shown in Equation 5-2.

EQUATION 5-2:

APPARENT POWER (S)

5.4.2

APPARENT POWER DIVISOR

DIGITS

The

registers

AppPowerDivisorDigits1

and

AppPowerDivisorDigits2 are configurable by the user

depending on the precision of the RMS indications and

the

desired

precision

for ApparentPower1

ApparentPower2.

Because AppPowerDivisorDigits registers can be

higher than 4, it may result in a 32-bit divisor. To

improve the speed of this part of the calculation engine,

a method that uses only multiplications and right-bit

shifts was implemented. Therefore the following

equation applies:

EQUATION 5-3:

APPARENT POWER (S)

RMS



–



-----------------------------

RMS



–



------------------------------



OffsetCurrentRMS1,2:s32

CurrentRMS1,2:u32

Range:b32

÷2RANGE

VoltageRMS:u16

Range:b32

ApparentPower1,2:u32



ACCU

2N-1

÷ 2N



ACCU

-1

÷ 2N

GainCurrentRMS1,2:u16

GainVoltageRMS:u16

÷2RANGE

RMS



ApparentPower

RMS



AppPowerDivisorDigits

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