ADE7978 datasheet(42/125 Pages) AD

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ADE7978/ADE7933/ADE7932/ADE7923

Data Sheet

Rev. D | Page 42 of 125

Figure 57 shows the ADC and signal processing chain for the

temperature sensor when the ADE7933/ADE7932 monitor

Phase A. The temperature measurement is characterized by

offset and gain errors. The offset information is calculated

during the manufacturing process and is stored with a sign

opposite of the calculated sign into the ADE7933/ADE7932 and

ADE7923.

The ADE7978 reads the offset information using the bit stream

communication (see the Bit Stream Communication Between

the ADE7978 and the ADE7933/ADE7932 section for more

information). The ADE7978 then stores this information in the

8-bit signed ATEMPOS, BTEMPOS, CTEMPOS, and NTEMPOS

registers. The offset information is shifted left by 11 bits before

it is added to the temperature datapath.

The 24-bit signed temperature gain registers (ATGAIN, BTGAIN,

CTGAIN, and NTGAIN) can be used for gain compensation to

change the temperature waveform by ±100%. For example, if

0x400000 is written to these registers, the ADC output is scaled

up by 50%. To scale the output by −50%, write 0xC00000 to the

registers. Equation 10 describes mathematically the function of

the temperature waveform gain registers.

Temperature Waveform =

(10)

ADC Output ×













Gain

Temp

Contents

The temperature measurements are also used in the current

channel datapath for the temperature compensation of the current

gain (see the Current Waveform Gain Registers section). A simple

approach to implement the temperature measurement is to leave

the temperature gain registers at their default values so that the

temperature compensation path uses the temperature

measurements without any gain correction.

The temperature measurement results are stored in the 24-bit

signed ATEMP, BTEMP, CTEMP, and NTEMP registers 1.024 sec

after the temperature sensor measurement is started by setting

the VT_A, VT_B, VT_C, and VT_N pins low. These registers

are updated at an 8 kSPS rate. The VT_A, VT_B, VT_C, and

VT_N pins must be kept low for at least 1.024 sec for the

temperature measurement results to be stored in the ATEMP,

BTEMP, CTEMP, and NTEMP registers.

The microcontroller can obtain the temperature measurements

expressed in °C units by applying the following formula:

Temperature(°C) = 8.72101 × 10−5 × TEMP − 306.47 (11)

The serial ports of the ADE7978 work with 32-, 16-, or 8-bit

words, whereas the DSP works with 28-bit words. Like the

SAGLVL register shown in Figure 69, the 24-bit signed ATEMP,

BTEMP, CTEMP, and NTEMP registers are transmitted as 32-bit

registers with the eight MSBs padded with zeroes.

AIGAIN TEMPERATURE

COMPENSATION

ATEMP TEMPERATURE

RANGE

DIGITAL

LPF

DIGITAL LPF

WITH 10Hz

CORNER

BIT 0 (VA2_EN) IN

CONFIG3 REGISTER

CLEARED TO 0

ADE7978

VT_A

+0.2472V

VIN

TEMPERATURE SENSOR CHARACTERISTIC

+0.3672V

+0.3098V

+25°C

+85°C

–40°C

3,055,500

4,488,800

3,800,800

VOLTAGE CHANNEL DATA RANGE

WHEN TEMPERATURE SENSOR IS SELECTED

+25°C

+85°C

–40°C

ATEMPOS[7:0]

211

ATGAIN[23:0]

REFERENCE

PHASE A

ADE7933

Σ-Δ

MODULATOR

V2P

VIN

TEMPERATURE

SENSOR

Figure 57. Temperature Measurement Datapath

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