ADE7912 datasheet(25/44 Pages) AD

25 / 44 page

Data Sheet

ADE7912/ADE7913

Rev. 0 | Page 25 of 44

Figure 38. 3-Phase Meter Using Two ADE7912/ADE7913 Devices in Delta

Configuration

Figure 39. SPI Connections Between Three ADE7912/ADE7913 Devices and a

Microcontroller

ADE7912/ADE7913 CLOCK

Provide a digital clock signal at the XTAL1 pin to clock the

ADE7912/ADE7913. The frequency at which the ADE7912/

ADE7913 are clocked at XTAL1 is called CLKIN. The ADE7912/

ADE7913 are specified for CLKIN = 4.096 MHz, but frequencies

between 3.6 MHz and 4.21 MHz are acceptable.

Alternatively, a 4.096 MHz crystal with a typical drive level of

0.5 mW and an equivalent series resistance (ESR) of 20 Ω can

be connected across the XTAL1 and XTAL2 pins to provide a

clock source for the ADE7912/ADE7913 (see Figure 40).

The total capacitance, TC, at the XTAL1 and XTAL2 pins is

TC = C1 + CP1 = C2 + CP2

where:

C1 and C2 are the ceramic capacitors between XTAL1 and GND

and between XTAL2 and GND, respectively.

CP1 and CP2 are the parasitic capacitors of the wires

connecting the crystal to the ADE7912/ADE7913.

The load capacitance, LC, of the crystal is equal to half the total

capacitance, TC, because it is the capacitance of the series

circuit composed by C1 + CP1 and C2 + CP2.

CP2

CP1

Therefore, the value of the C1 and C2 capacitors as a function of

the load capacitance of the crystal is

C1 = C2 = 2 × LC − CP1 = 2 × LC − CP2

In the case of the ADE7912/ADE7913, the typical total

capacitance, TC, of the XTAL1 and XTAL2 pins is 40 pF

(see Table 1). Select a crystal with a load capacitance of

Assuming the parasitic capacitances, CP1 and CP2, are equal to

20 pF, select Capacitors C1 and C2 equal to 20 pF.

Figure 40. Crystal Circuitry

CS_A

CS_C

SCLK

MOSI

MISO

I/O

MICROCONTROLLER

4.096MHz

CRYSTAL

ISOLATION

BARRIER

V1P

V2P

GNDMCU

GNDISO_C

V1P

V2P

GNDMCU

GNDISO_A

XTAL2

XTAL1

SCLK

MOSI

MISO

XTAL2

XTAL1

SCLK

MOSI

MISO

PHASE A

ADE7912/ADE7913

PHASE C

ADE7912/ADE7913

CLKOUT/

DREADY

CLKOUT/

DREADY

LOAD

ADE7912/

ADE7913

PHASE A

ADE7912/

ADE7913

PHASE B

ADE7912/

ADE7913

PHASE C

SCLK

MOSI

MISO

SCLK

MOSI

MISO

SCLK

MOSI

MISO

CS_A

CS_B

SCLK

MOSI

MISO

CS_C

MICROCONTROLLER

10kΩ

VDD

ADE7912/

ADE7913

XTAL1

XTAL2

CP1

CP2

ADE7912 Datasheet(PDF) 25 Page - Analog Devices

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