Datasheet

Data Sheet ADE7953
Rev. B | Page 43 of 72
ZERO-CROSSING DETECTION
The ADE7953 includes a zero-crossing (ZX) detection feature
on all three input channels. Zero-crossing detection allows
measurements to be synchronized to the frequency of the
incoming waveforms.
Zero-crossing detection is performed at the output of LPF1 to
ensure that no harmonics or distortion affect the accuracy of the
zero-crossing measurement. LPF1 is a single-pole filter with a
−3 dB cutoff of 80 Hz and is clocked at 223 kHz. The phase shift
of this filter therefore results in a time delay of approximately
2.2 ms (39.6°) at 50 Hz. To assure good resolution of the ZX
detection, LPF1 cannot be disabled. Figure 61 shows how the
zero-crossing signal is detected.
GAIN[23:0]
REFERENCE
HPFEN BIT
DSP
HPF
PGA ADC
IA, IB,
OR V
ZX
DETECTION
LPF1
IA, IB, OR V
39.6° OR 2.2ms @ 50Hz
0V
ZX
ZX
ZX
ZX
LPF1 OUTPUT
09320-127
Figure 61. Zero-Crossing Detection
The error in the ZX detection is 0.08° for 50 Hz systems and
0.09° for 60 Hz systems. The zero-crossing information is
available on both an output pin or via an interrupt.
ZERO-CROSSING OUTPUT PINS
By default, the voltage and current channel ZX information
is configured to be output on Pin 1 (ZX) and Pin 21 (ZX_I),
respectively. These dedicated output pins provide an unlatched
ZX indicator (see the Alternative Output Functions section).
Voltage Channel Zero Crossing
The voltage channel zero-crossing indicator is output on Pin 1
(ZX) by default. Figure 62 shows the operation of the ZX output.
ZX
2.2ms @ 50Hz
V
09320-131
Figure 62. Voltage Channel ZX Output
As shown in Figure 62, the ZX output pin goes high on the
positive-going edge of the voltage channel zero crossing and
low on the negative-going edge of the zero crossing. A delay
of approximately 2.2 ms should be expected on this pin due to
the time delay of LPF1.
Current Channel Zero Crossing
The current channel zero-crossing indicator is output on Pin 21
(ZX_I) by default. The ZX_I pin operates in a similar way to the
ZX pin (see Figure 62). The ZX_I pin goes high on the positive-
going edge of the current channel zero crossing and low on the
negative-going edge of the current channel zero crossing. By
default, the ZX_I pin is triggered based on Current Channel A.
The ZX_I pin can be configured to trigger based on Current
Channel B by setting the ZX_I bit (Bit 11) of the CONFIG
register (Address 0x102) to 1.
ZERO-CROSSING INTERRUPTS
Three interrupts are associated with zero-crossing detection, one
for each input channel: Current Channel A, Current Channel B,
and the voltage channel. The zero-crossing condition occurs
when either a positive or a negative zero-crossing transition
takes place. If this transition occurs on the voltage channel, the
ZXV bit (Bit 15) of the IRQSTATA register (Address 0x22D and
Address 0x32D) is set to 1. If this transition occurs on Current
Channel A, the ZXIA bit (Bit 12) of the IRQSTATA register is
set to 1. If this transition occurs on Current Channel B, the
ZXIB bit (Bit 12) of the IRQSTATB register (Address 0x230 and
Address 0x330) is set to 1. Figure 63 shows the operation of the
voltage channel zero-crossing interrupt.
ZXV (BIT 15) OF
IRQSTATA REGISTER
V
09320-032
Figure 63. Zero-Crossing Interrupt
As shown by the dotted line in Figure 63, the ADE7953 can be
configured to trigger a zero-crossing event on only the positive-
going or the negative-going zero crossing. The ZX_EDGE bits
(Bits[13:12]) of the CONFIG register (Address 0x102) set the
edge that triggers the zero-crossing event. These bits default to
00 (the zero-crossing event is triggered on both the positive-
going and negative-going edges). Changing the ZX_EDGE bits
affects the zero-crossing event on all three channels. Note that
changing the ZX_EDGE bits affects only the ZX status bits and
interrupts; the function of the ZX pin (Pin 1) and the ZX_I pin
(Pin 21) is not affected.