ADE7754AR datasheet(13/44 Pages) AD

13 / 44 page

REV. PrG 01/03

PRELIMINARY TECHNICAL DATA

ADE7754

– 13 –

VOLTAGE CHANNEL ADC

Figure 10 shows the ADC and signal processing chain for the

Input VA in voltage channel (same for VB and VC).

VAP

ADC

x1, x2, x4

GAIN[6:5]

0.5V

GAIN

Analog

Input Range

TO ACTIVE &

REACTIVE ENERGY

CALCULATION

-100% to +100% FS

LPF1

27E9h

D817h

LPF Output

word Range

TO VOLTAGE RMS AND

WAVEFORM SAMPLING

60Hz

2838h

D7C8h

50Hz

Figure 10 – ADC and signal processing in voltage

channel

For Energy measurements, the output of the ADC (1 bit) is

passed directly to the multiplier and is not filtered. This

solution avoids a wide bits multiplier and does not affect the

accuracy of the measurement. A HPF is not required to

remove any DC offset since it is only required to remove the

offset from one channel to eliminate errors in the Power

calculation.

In the voltage channel, the samples may also be routed to the

WFORM register (WAVMODE to select VA, VB or VC and

sampling frequency). However before being passed to the

Waveform register, the ADC output is passed through a

single pole, low pass filter with a cutoff frequency of 260Hz.

The plots in Figure 11 show the magnitude and phase

response of this filter. The filter output code of any inputs of

the voltage channel swings between D70Bh (-10,485d) and

28F5h (+10,485d) for full scale sinewave inputs.

This has the effect of attenuating the signal. For example if

the line frequency is 60Hz, then the signal at the output of

LPF1 will be attenuated by 3%.

dBs

()

(

)

== −

260

0 974

0 2

Note LPF1 does not affect the power calculation since it is

used only in the Waveform sample mode.

When in waveform sample mode, one of four output sample

rates can be chosen by using bits 3 and 4 of the WAVMode

13.5kSPS, 6.5kSPS or 3.3kSPS. The interrupt request

output IRQ signals a new sample availability by going active

low. The voltage waveform register is a 2-complement 16-bit

the waveform data from the voltage input is located in the 16

LSB of the Waveform register. The sign of the 16-bit voltage

input value is not extended to the upper byte of the waveform

waveform samples are transferred from the ADE7754 one

byte (8-bits) at a time, with the most significant byte shifted

out first. The timing is the same as that for the current

channels and is shown in Figure 9.

ZERO CROSSING DETECTION

The ADE7754 has rising edge zero crossing detection

circuits for each of voltage channels (VAP, VBP, or VCP).

Figure 12 shows how the zero cross signal is generated from

the output of the ADC of the voltage channel.

AP, VBP, VCP

ADC

PGA

x1, x2, x4

REFERENCE

GAIN[6:5]

MULTIPLIER

-100% to +100% FS

IRQ

13 degrees @ 60Hz

0.95

1.0

ZERO

CROSS

Zero Crossing

Detection

Read RSTATUS

LPF1

f-3dB = 260Hz

Figure 12– Zero cross detection on Voltage Channel

The zero crossing interrupt is generated from the output of

LPF1. LPF1 has a single pole at 260Hz (CLKIN = 10MHz).

As a result there will be a phase lag between the analog input

signal of the voltage channel and the output of LPF1. The

phase response of this filter is shown in the Voltage channel

Sampling section of this data sheet. The phase lag response

of LPF1 results in a time delay of approximately 0.6ms (@

60Hz) between the zero crossing on the analog inputs of

Voltage channel and the falling of IRQ.

When one phase crosses zero from negative to positive values

(rising edge), the corresponding flag in the Interrupt Status

output will also appear if the corresponding ZX bit in the

Interrupt Mask register is set to logic one.

The flag in the Interrupt status register is reset to 0 when the

Interrupt status register with reset (RSTATUS) is read. Each

phase has its own interrupt flag and mask bit in the interrupt

−60°

−40°

−20°

0°

Frequency (Hz)

−40

−20

(60Hz ; −13°)

(60Hz ; −0.2dB)

Figure 11 – Magnitude & Phase response of LPF1

ADE7754AR 数据表(PDF) 13 Page - Analog Devices

ADE7754AR 数据表(HTML) 13 Page - Analog Devices

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44

数据表下载