ADE7953 datasheet(25/68 Pages) AD

25 / 68 page

Data Sheet

ADE7953

Rev. A | Page 25 of 68

ACTIVE ENERGY CALCULATION

As described in the Active Power Calculation section, power

is defined as the rate of energy flow. This relationship can be

expressed mathematically as shown in Equation 8.

P =

(8)

where:

is power.

is energy.

Conversely, energy is given as the integral of power.

∫

= Pdt

(9)

The ADE7953 achieves the integration of the active power

signal in two stages. In the first stage, the active power signals

are accumulated in an internal 48-bit register every 143 μs

(6.99 kHz) until an internal fixed threshold is reached. When

this threshold is reached, a pulse is generated and is accumu-

lated in 24-bit, user-accessible accumulation registers. The

internal threshold results in a maximum accumulation rate

of approximately 206.9 kHz with full-scale inputs. This process

occurs simultaneously on Current Channel A and Current

Channel B, and the resulting readings can be read in the 24-bit

AENERGYA (Address 0x21E and Address 0x31E) and

AENERGYB (Address 0x21F and Address 0x31F) registers.

Both stages of the accumulation are signed and, therefore,

negative energy is subtracted from positive energy.

This discrete time accumulation, or summation, is equivalent

to integration in continuous time. Equation 10 expresses this

relationship.

⎭

⎬

⎫

⎩

⎨

⎧

∑

∫

∞

→

P(nT)

Lim

P(t)dt

(10)

where:

is the discrete time-sampled number.

is the sample period.

The discrete time sample period (T) for the accumulation

registers in the ADE7953 is 4.83 μs (1/206.9 kHz). This is

illustrated in Figure 46, which shows the energy register

roll-over rates with full-scale inputs.

0x000000

0x7FFFFF

0x3FFFFF

0x400000

0x800000

AENERGYx[23:0]

39.9

19.95

59.85

TIME (Seconds)

xWGAIN = 0x200000

xWGAIN = 0x400000

xWGAIN = 0x600000

Figure 46. Energy Register Roll-Over Time for Active Energy

Note that the energy register contents roll over to full-scale

negative (0x800000) and continue to increase in value when the

power or energy flow is positive. Conversely, if the power is

negative, the energy register underflows to full-scale positive

(0x7FFFFF) and continues to decrease in value.

AENERGYA and AENERGYB are read-with-reset registers

by default. This means that the contents of these registers are

reset to 0 after a read operation. This feature can be disabled

by clearing Bit 6 (RSTREAD) of the LCYCMODE register

(Address 0x004).

The ADE7953 includes two sets of interrupts that are triggered

when the active energy register is half full (positive or negative)

or when an overflow or underflow condition occurs. The first

set of interrupts is associated with the Current Channel A active

energy, and the second set of interrupts is associated with the

Current Channel B active energy. These interrupts are disabled

by default and can be enabled by setting the AEHFA and

AEOFA bits in the IRQENA register (Address 0x22C and

Address 0x32C) for Current Channel A, and the AEHFB and

AEOFB bits in the IRQENB register (Address 0x22F and

Address 0x32F) for Current Channel B.

Active Energy Integration Time Under Steady Load

The discrete time sample period (T) for the accumulation

registers is 4.83 μs (1/206.9 kHz). With full-scale sinusoidal

signals on the analog inputs and the AWGAIN and BWGAIN

registers set to 0x400000, a pulse is generated and added to

the AENERGYA and AENERGYB registers every 4.83 μs. The

maximum positive value that can be stored in the 24-bit

AENERGYA and AENERGYB registers is 0x7FFFFF before

the register overflows. The integration time under these

conditions can be calculated as follows:

Time

= 0x7FFFFF × 4.83 μs = 40.5 sec

(11)

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