ADE7878 datasheet(31/92 Pages) AD

31 / 92 page

ADE7878

Rev. 0 | Page 31 of 92

used; therefore, it is not recommended to use the detection

circuit. In these cases, use the time intervals between phase

voltages to analyze the phase sequence (see the Time Interval

Between Phases section for details).

Figure 42 presents the case in which Phase A voltage is not

followed by Phase B voltage but by Phase C voltage. Every time

a negative-to-positive zero crossing occurs, Bit 19 (SEQERR) in

the STATUS1[31:0] register is set to 1 because such zero crossings

on Phase C, Phase B, or Phase A cannot come after zero crossings

from Phase A, Phase C, or respectively, Phase B zero crossings.

ZX B

ZX C

PHASE C

PHASE B

PHASE A

A, B, C PHASE

VOLTAGES AFTER

LPF1

BIT 19 (SEQERR) IN

STATUS1[31:0]

IRQ1

ZX A

STATUS1[19] SET TO 1

STATUS1[19] CANCELLED

BY A WRITE TO

STATUS1[31:0] WITH

SEQERR BIT SET

Figure 42. SEQERR Bit Set to 1 When Phase A Voltage Is Followed by

Phase C Voltage

Once a phase sequence error has been detected, the time

measurement between various phase voltages (see the Time

Interval Between Phases section) may help to identify which

phase voltage should be considered with another phase current

in the computational datapath. Bits[9:8] (VTOIA[1:0]),

Bits[11:10] (VTOIB[1:0]), and Bits[13:12] (VTOIC[1:0]) in the

CONFIG[15:0] register can be used to direct one phase voltage

to the datapath of another phase. See the Changing Phase

Voltage Datapath section for details.

Time Interval Between Phases

The ADE7878 has the capability to measure the time delay

between phase voltages, between phase currents, or between

voltages and currents of the same phase. The negative-to-positive

transitions identified by the zero-crossing detection circuit are

used as start and stop measuring points. Only one set of such

measurements is available at one time, based on Bits[10:9]

(ANGLESEL[1:0]) in the COMPMODE[15:0] register.

ZX C

ZX B

PHASE B

PHASE C

PHASE A

ZX A

Figure 43. Phase Sequence Detection

When the ANGLESEL[1:0] bits are set to 00, the default value,

the delays between voltages and currents on the same phase are

measured. The delay between Phase A voltage and Phase A

current is stored in the 16-bit unsigned ANGLE0[15:0] register

(see Figure 44 for details). In a similar way, the delays between

voltages and currents on Phase B and Phase C are stored in the

ANGLE1[15:0] and ANGLE2[15:0] registers, respectively.

PHASE A

CURRENT

ANGLE0

PHASE A

VOLTAGE

Figure 44. Delay Between Phase A Voltage and Phase A Current Is

Stored in ANGLE0[15:0]

When the ANGLESEL[1:0] bits are set to 01, the delays between

phase voltages are measured. The delay between Phase A voltage

and Phase C voltage is stored into ANGLE0[15:0]. The delay

between Phase B voltage and Phase C voltage is stored in the

ANGLE1[15:0] register, and the delay between Phase A voltage

and Phase B voltage is stored in the ANGLE2[15:0] register (see

Figure 45 for details).

When the ANGLESEL[1:0] bits are set to 10, the delays between

phase currents are measured. Similar to delays between phase

voltages, the delay between Phase A and Phase C currents is

stored into the ANGLE0[15:0] register, the delay between

Phase B and Phase C currents is stored in the ANGLE1[15:0]

stored into the ANGLE2[15:0] register (see Figure 45 for

details).

PHASE B

PHASE C

PHASE A

ANGLE2

ANGLE0

ANGLE1

Figure 45. Delays Between Phase Voltages (Currents)

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