ADE7912 datasheet(21/41 Pages) AD

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Data Sheet

ADE7912/ADE7913

Rev. C | Page 21 of 41

TEMPERATURE SENSOR

The ADE7912/ADE7913 contain a temperature sensor that is

multiplexed with the V2P input of the voltage channel. Bit 3

(TEMP_EN) of the CONFIG register selects what the third

ADC of the ADE7913 measures. If the TEMP_EN bit is 0, the

default value, the ADC measures the voltage between the V2P

and VM pins. If the TEMP_EN bit is 1, the ADC measures the

temperature sensor. In the case of the ADE7912, the ADC always

measures the temperature sensor, and the state of the TEMP_EN

bit has no significance. In both the ADE7912 and the ADE7913,

the conversion result is stored in the V2WV register. The time it

takes for the temperature sensor measurement to settle after the

TEMP_EN bit is set to 1 is 5 ms.

In the microcontroller, the expression calculates the temperature

in degrees Celsius is:

Temperature =

Gain × V2WV + 8.72101 × 10−5 × TEMPOS × 211 − 306.47

where:

Temperature is the temperature value measured in degrees

Celsius.

Gain is equal to 8.72101 × 10−5 when Bit 7 (BW) in the

CONFIG register is 0 and 8.21015 × 10−5 when Bit 7 (BW) in

the CONFIG register is 1. See Table 10 for details on Bit 7 (BW)

significance in the context of ADC output frequency selection.

The temperature measurement accuracy is ±5°C.

TEMPOS is the 8-bit signed read-only register in which the

temperature sensor offset is stored. The offset information is

calculated during the manufacturing process, and it is stored

with the opposite sign. For example, if the offset is 5, −5 is

written into the ADE7912/ADE7913. One least significant bit

(LSB) of the TEMPOS register is equivalent to 211 LSBs of the

V2WV register.

Instead of using the default temperature gain value, the gain

can be calibrated as part of the overall meter calibration process.

Measure the temperature, TEMP, of every ADE7912/ADE7913

using a thermocouple. Call it temperature and express it in

degrees Celsius (see Equation 6). Read the V2WV register

containing the temperature sensor reading of every

ADE7912/ADE7913, and compute the gains as follows:

Temperature Gain = Gain =

(Temperature + 306.47)/(V2WV + (k × TEMPOS × 211)) (6)

where k = 1 when Bit 7 (BW) in CONFIG register is 0 and k =

1.062223 when Bit 7 (BW) in CONFIG register is 1.

PROTECTING THE INTEGRITY OF CONFIGURATION

REGISTERS

The configuration registers of the ADE7912/ADE7913 are either

user accessible registers (CONFIG, EMI_CTRL, SYNC_SNAP,

COUNTER0, and COUNTER1) or internal registers. The internal

registers are not user accessible, and they must remain at their

default values. To protect the integrity of all configuration

registers, a write protection mechanism is available.

By default, the protection is disabled and the user accessible

configuration registers can be written without restriction. When

the protection is enabled, no writes to any configuration register

are allowed. The registers can always be read, without restriction,

independent of the write protection state.

To enable the protection, write 0xCA to the 8-bit lock register

(Address 0xA). To disable the protection, write 0x9C to the

8-bit lock register. It is recommended that the write protection

be enabled after the CONFIG and EMI_CTRL registers are

initialized. If any user accessible register must be changed, for

example, during the synchronization process of multiple

ADE7912/ADE7913 devices, disable the protection, change the

value of the register, and then reenable the protection.

CRC OF CONFIGURATION REGISTERS

Every output cycle, the ADE7912/ADE7913 compute the CRC

of the CONFIG, EMI_CTRL, and TEMPOS registers, as well as

Bit 2 (IC_PROT) of the STATUS0 register, and Bit 7 of the

STATUS1 register. The CRC algorithm is called CRC-16-

CCITT. The 16-bit result is written in the CTRL_CRC register.

The input registers to the CRC circuit form a 64-bit array that is

introduced bit by bit into an LFSR-based generator, similar to

Figure 28 and Figure 29, with one byte at a time, least significant

byte first. Each byte is then processed with the most significant bit

first.

The formulas that govern the LFSR are as follows:

bi(0) = 1, where i = 0, 1, 2, …, 15, the initial state of the bits that

form the CRC. Bit b0 is the least significant bit, and Bit b15 is the

most significant bit.

gi, where i = 0, 1, 2, …, 15 are the coefficients of the generating

polynomial defined by the CRC-16-CCITT algorithm in

Equation 1 and Equation 2.

FB(j) = aj − 1 XOR b15(j − 1)

(7)

b0(j) = FB(j) AND g0

(8)

bi(j) = FB(j) AND gi XOR bi − 1(j − 1), i = 1, 2, 3, … , 15 (9)

Equation 7, Equation 8, and Equation 9 must be repeated for

j = 1, 2, … , 64. The value written into the CTRL_CRC register

contains Bit bi(64), i = 0, 1, …, 15. Because each ADE7912/

ADE7913 has a particular TEMPOS register value, each ADE7912/

ADE7913 has a different CTRL_CRC register default value.

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