ADE9078 datasheet(26/108 Pages) AD

26 / 108 page

Data Sheet

ADE9078

Rev. 0 | Page 25 of 107

To select the appropriate capacitance value for the ceramic

capacitors, calculate CL1 and CL2, from the following expression:

CL = ((CL1 + CP1 + CIN1) × (CL2 + CP2 + CIN2))/( CL1 + CP1 +

CIN1 + CL2 + CP2 + CIN2)

(1)

Select CL1 and CL2 such that the total capacitance on each clock

pins is equal:

CL1 + CP1 + CIN1 = CL2 + CP2 + CIN2

(2)

Using Equation 1 and Equation 2, the values of CL1 and CL2 can

be calculated.

Load Capacitor Calculation Example

If a crystal with load capacitance specification of 12 pF is selected,

and the measured parasitic capacitances from the PCB traces

are CP1 = CP2 = 2 pF, Equation 1 implies,

CL = ((CL1 + CP1 + CIN1) × (CL2 + CP2 + CIN2))/(CL1 + CP1 +

CIN1 + CL2 + CP2 + CIN2)

12 pF = ((CL1 + 2 pF + 4 pF) × (CL2 + 2 pF + 4 pF))/(CL1 +

2 pF + 4 pF + CL2 + 2 pF + 4 pF)

Assuming CL1 = CL2, to satisfy Equation 2,

12 pF = ((CL1 + 6 pF) × (CL1 + 6 pF))/(CL1 + 6 pF + CL1 + 6 pF)

12 pF = ((CL1 + 6 pF) × (CL1 + 6 pF))/(2 × (CL1 + 6 pF))

12 pF = (CL1 + 6 pF)/2

Thus, CL1 = CL2 = 18 pF.

Based on this example, 18 pF ceramic capacitors are selected for CL1

and CL2. The user must verify the customized values based on care-

ful investigations on multiple devices over the temperature range.

POWER MANAGEMENT

Power Modes

The ADE9078 offers four operating modes: PSM0, PSM1, PSM2,

and PSM3. The entry into the power modes is controlled by the

PM1 and PM0 pins. These pins are checked continuously to

determine which operating mode to enter. Table 8 shows the

PMx pin configurations for each power mode.

Most applications use PSM0 (normal mode). If the user wants

to put the ADE9078 into a low power reset state, use PSM3.

PSM1 and PSM2, in combination with PSM3, enable low power

tamper detection and measurement, which is required in some

regions. These operating modes enable the user to check for a

tamper condition while minimizing power consumption—

because in tamper scenarios, a battery typically powers the

ADE9078.

The current peak detection mode, PSM2, checks if the input

currents are above a user set amplitude. The tamper

measurement mode, PSM1, allows the user to make key

measurements quickly for IRMS, VRMS, active power, and VAR

with a reduced power consumption compared to PSM0.

In the application, the host microcontroller creates a duty cycle

that puts the ADE9078 into PSM2, waits the required time to

receive a result indicated in Table 8, and then returns to PSM3.

This cycle continues once per minute until the tamper checking

cycle ends, which may be up to seven days in some applications. If a

tamper is detected in PSM2, PSM1 is entered and the key measure-

ments are made. After the time required for measurements has

elapsed, the host microcontroller reads the results via the SPI

interface and changes the PM1 and PM0 pins to put the device

back into PSM3. This cycle continues once per minute until the

tamper checking cycle ends, which may be up to seven days in

some applications. Figure 38 shows the functions available in

PSM2 and PSM1.

SINC4

AND

DECIMATION

AVDD

LDO

DVDD

LDO

SPI

1.25V

REFERENCE

TEMP

SENSOR

CF1

TO CF4

IRQ0

IRQ1

SPI

PM1

PM0

ADE9078

PGA

ADC

PGA

ADC

SAR

AVAILABLE IN PSM0

AVAILABLE IN PSM2

DISABLED IN PSM1

PGA

ADC

PGA

ADC

PGA

ADC

PGA

ADC

PGA

ADC

METROLOGY FEATURES

(PER PHASE)

IRMS, VRMS

ACTIVE POWER, VA

YX, ANGLE

WAVEFORM BUFFER

ENERGY/POWER/CF

ACCUMULATION

LINE FREQUENCY

ETC.

LOW

POWER

COMPARATOR

Figure 38. Functions Available in PSM1 and PSM2

As indicated in Table 8, the SPI is not available in PSM2. To check

whether the current inputs are above the user configured tamper

threshold, check the IRQ0 and IRQ1 pins (see the Measurements

(PSM2) section for more information).

One register is retained during PSM2 and PSM3: PSM2_CFG, as

shown in Table 8. Note that if PSM0 or PSM1 is entered, PSM2_CFG

returns to it default value and must be rewritten before reentering

PSM2 (see the Measurements (Normal Mode) section,

Measurements (PSM1) section, and Measurements (PSM2)

section for details on functionality in PSM0, PSM1, and PSM2).

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