ADE7759
PIN FUNCTION DESCRIPTIONS (continued)
Description
Pin No.
Mnemonic
12
ZX
Voltage Waveform (Channel 2) Zero Crossing Output. This output toggles logic high and low at
the zero crossing of the differential signal on Channel 2—see Zero Crossing Detection section.
13
14
15
SAG
This open drain logic output goes active low when either no zero crossings are detected or a low
voltage threshold (Channel 2) is crossed for a specified duration. See Line Voltage Sag Detec-
tion section.
IRQ
Interrupt Request Output. This is an active low open drain logic output. Maskable interrupts
include Active Energy register rollover, Active Energy register at half-full, zero crossing, SAG, and
arrivals of new waveform samples—See Interrupts section.
CLKIN
Master Clock for ADCs and Digital Signal Processing. An external clock can be provided at this
logic input. Alternatively, a parallel resonant AT crystal can be connected across CLKIN and
CLKOUT to provide a clock source for the ADE7759. The clock frequency for specified opera-
tion is 3.579545 MHz. Ceramic load capacitors of between 10 pF to 30 pF should be used with
the gate oscillator circuit. Refer to crystal manufacturers data sheet for load capacitance requirements.
16
CLKOUT
A crystal can be connected across this pin and CLKIN as described above to provide a clock source
for the ADE7759. The CLKOUT pin can drive one CMOS load when either an external clock is
supplied at CLKIN or a crystal is being used.
17
18
CS
Chip Select. Part of the 4-wire SPI Serial Interface. This active low logic input allows the ADE7759 to
share the serial bus with several other devices. See Serial Interface section.
SCLK
Serial Clock Input for the Synchronous serial interface. All serial data transfers are synchronized to
this clock—see Serial Interface section. The SCLK has a Schmitt-trigger input for use with a clock
source that has a slow edge transition time, e.g., opto-isolator outputs.
19
20
DOUT
DIN
Data Output for the Serial Interface. Data is shifted out at this pin on the rising edge of SCLK.
This logic output is normally in a high impedance state unless it is driving data onto the serial data
bus—see Serial Interface section.
Data Input for the Serial Interface. Data is shifted in at this pin on the falling edge of SCLK—see
Serial Interface section.
TERMINOLOGY
MEASUREMENT ERROR
nominal supplies (5 V) is taken. A second reading is obtained
with the same input signal levels when the supplies are varied 5%.
The error associated with the energy measurement made by the
ADE7759 is defined by the following formula:
Any error introduced is again expressed as a percentage of reading.
ADC OFFSET ERROR
Percentage Error =
This refers to the dc offset associated with the analog inputs to the
ADCs. It means that with the analog inputs connected to AGND
the ADCs still see a dc analog input signal. The magnitude of the
offset depends on the gain and input range selection—see
characteristic curves. However, when HPF1 is switched on, the
offset is removed from Channel 1 (current) and the power calcu-
lation is not affected by this offset. The offsets may be removed
by performing an offset calibration—see Analog Inputs section.
Energy registered by the ADE7759 –True Energy
True Energy
PHASE ERROR BETWEEN CHANNELS
The digital integrator and the HPF1 (High-Pass Filter) in Channel
1 have nonideal phase response. To offset this phase response
and equalize the phase response between channels, two phase
correction networks are placed in Channel 1: one for the digital
integrator and the other for the HPF1. Each phase correction
network corrects the phase response of the corresponding com-
ponent and ensures a phase match between Channel 1 (current)
and Channel 2 (voltage) to within 0.1° over a range of 45 Hz
to 65 Hz and 0.2° over a range 40 Hz to 1 kHz.
GAIN ERROR
The gain error in the ADE7759 ADCs is defined as the difference
between the measured ADC output code (minus the offset) and
the ideal output code—see Channel 1 ADC and Channel 2
ADC. It is measured for each of the input ranges on Channel 1
(0.5 V, 0.25 V and 0.125 V). The difference is expressed as a
percentage of the ideal code.
POWER SUPPLY REJECTION
This quantifies the ADE7759 measurement error as a percent-
age of reading when the power supplies are varied.
GAIN ERROR MATCH
The Gain Error Match is defined as the gain error (minus the offset)
obtained when switching between a gain of 1 (for each of the
input ranges) and a gain of 2, 4, 8, or 16. It is expressed as a
percentage of the output ADC code obtained under a gain of 1.
This gives the gain error observed when the gain selection is
changed from 1 to 2, 4, 8, or 16.
For the ac PSR measurement a reading at nominal supplies
(5 V) is taken. A second reading is obtained with the same input
signal levels when an ac (175 mV rms/120 Hz) signal is intro-
duced onto the supplies. Any error introduced by this ac signal
is expressed as a percentage of reading—see Measurement Error
definition above. For the dc PSR measurement a reading at
–8–
REV. 0
ADI [ ADI ]
