ADE7757 Analog Devices, ADE7757 Datasheet

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ADE7757

Manufacturer Part Number
ADE7757
Description
Energy Metering IC with Integrated Oscillator
Manufacturer
Analog Devices
Datasheet

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a
Information furnished by Analog Devices is believed to be accurate and
reliable. However, no responsibility is assumed by Analog Devices for its
use, nor for any infringements of patents or other rights of third parties
which may result from its use. No license is granted by implication or
otherwise under any patent or patent rights of Analog Devices.
*U.S. Patents 5,745,323, 5,760,617, 5,862,069, 5,872,469; other pending.
REV. PrC.
The ADE7757 is a high accuracy electrical energy mea-
surement IC. It is a pin reduction version of AD7755
with an enhancement of a precise oscillator circuit that
serves as a clock source to the chip. The ADE7757
eliminates the cost of an external crystal or resonator,
thus reducing the overall cost of a meter built with this
IC. The chip directly interfaces with shunt resistor and
only operates with AC input.
PRELIMINARY TECHNICAL DATA
V2N
V2P
V1N
V1P
REFERENCE
2.5V
SUPPLY MONITOR
4kV
REF
POWER
V
ADC
ADC
DD
IN/OUT
...
...
AGND
RCLKIN
110101
11011001
OSCILLATOR
...
INTERNAL
CORRECTION
...
RESERVED
ADE7757
PHASE
MULTIPLIER
The ADE7757 specifications surpass the accuracy require-
ments as quoted in the IEC1036 standard. Due to the
similarity between the ADE7757 and AD7755, the Appli-
cation Note AN-559 can be used as a basis for a descrip-
tion of an IEC1036 low cost watt-hour meter reference
design.
The only analog circuitry used in the ADE7757 is in the
sigma-delta ADCs and reference circuit. All other signal
processing (e.g., multiplication and filtering) is carried
out in the digital domain. This approach provides superior
stability and accuracy over time and extreme environmen-
tal conditions.
The ADE7757 supplies average real power information on
the low frequency outputs F1 and F2. These outputs may
be used to directly drive an electromechanical counter or
interface with an MCU. The high frequency CF logic
output, ideal for calibration purposes, provides instanta-
neous real power information.
The ADE7757 includes a power supply monitoring circuit
on the V
mode until the supply voltage on V
mately 4 V. If the supply falls below 4 V, the ADE7757
will also reset and the F1, F2 and CF outputs will be in
their non-active modes.
Internal phase matching circuitry ensures that the voltage
and current channels are phase matched while the HPF in
the current channel eliminates dc offsets. An internal no-
load threshold ensures that the ADE7757 does not exhibit
creep when no load is present.
The ADE7757 is available in 16-lead SOIC narrow-body
package.
DIGITAL-TO-FREQUENCY
SCF S0 S1
HPF
CONVERTER
DD
supply pin. The ADE7757 will remain in reset
LPF
PROCESSING
CF
SIGNAL
BLOCK
DGND
F1
F2
DD
reaches approxi-

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ADE7757 Summary of contents

Page 1

... The ADE7757 includes a power supply monitoring circuit on the V mode until the supply voltage on V mately the supply falls below 4 V, the ADE7757 will also reset and the F1, F2 and CF outputs will be in their non-active modes. Internal phase matching circuitry ensures that the voltage and current channels are phase matched while the HPF in the current channel eliminates dc offsets ...

Page 2

PRELIMINARY TECHNICAL DATA 1, 2 ACCURACY 1 Measurement Error on Channel V1 1 Phase Error Between Channels V1 Phase Lead 37° (PF = 0.8 Capacitive) V1 Phase Lag 60° (PF = 0.5 Inductive Power Supply Rejection Output Frequency ...

Page 3

... The CF pulse is always 18 µs in the high frequency mode. See Frequency Outputs section and Table III. Specifications subject to change without notice ADE7757ARN EVAL-ADE7757EB REV. PrC and F2 Pulsewidth (Logic Low) sec Output Pulse Period. See Transfer Function Section sec Time Between F1 Falling Edge and F2 Falling Edge ...

Page 4

... The ideal frequency is obtained from the ADE7757 trans- fer function—see Transfer Function section. The gain error of the ADE7757 is defined as the differ- ence between the measured output frequency (minus the offset) and the ideal output frequency measured with a gain channel V1 ...

Page 5

... PRELIMINARY TECHNICAL DATA 1 V Power Supply. This pin provides the supply voltage for the circuitry in the ADE7757. The DD supply voltage should be maintained ± 5% for specified operation. This pin should be decoupled with a 10 µF capacitor in parallel with a ceramic 100 nF capacitor. 2,3 V2P, V2N Analog Inputs for Channel V2 (voltage channel). These inputs provide a fully differential input pair. The maximum differential input voltage is ± ...

Page 6

... PRELIMINARY TECHNICAL DATA TBD TBD TBD TBD TBD V DD VDD 602k V2P 150nF 220V 200 U1 ADE7757 200 V2N 150nF 40A TO RESERVED 40mA 200 V1P RCLKIN 150nF 500 200 V1N 150nF REF IN/OUT 100nF 1 F AGND DGND – 6 – 100nF ...

Page 7

PRELIMINARY TECHNICAL DATA TBD TBD REV. PrC. TBD – 7 – ...

Page 8

... 1+cos ( TIME The low frequency outputs (F1, F2) of the ADE7757 is generated by accumulating this real power information. This low frequency inherently means a long accumulation time between output pulses. Consequently, the resulting output frequency is proportional to the average real power. This average real power information is then accumulated (e ...

Page 9

... REV. PrC. ) and The output of the line voltage sensor is connected to the 1 ADE7757 at this analog input. Channel fully differen- tial voltage input with maximum peak differential signal of ±165 mV. Figure 14 illustrates the maximum signal levels that can be connected to the ADE7757 Channel V2. ...

Page 10

... The ADE7757 contains an on-chip power supply monitor. The power supply ( continuously monitored by the DD ADE7757. If the supply is less than 4 V, the ADE7757 will reset. This is useful to ensure proper device operation at power-up and power-down. The power supply monitor has built in hysteresis and filtering that provide a high degree of immunity to false triggering from noisy sup- plies ...

Page 11

... The average value of a sinusoidal signal is zero. Hence the frequency gener- ated by the ADE7757 is proportional to the average real power. Figure 21 shows the digital-to-frequency conver- sion for steady load conditions, i.e., constant voltage and current ...

Page 12

... ADE7757 output frequency is running asynchronously to the MCU timer. This would result in a one-in-twenty or 5% error in the power measurement. The ADE7757 calculates the product of two voltage signals (on Channel V1 and Channel V2) and then low-pass filters this product to extract real power information. This real power information is then converted to a frequency ...

Page 13

... The ADE7757 also includes a “no load threshold” and “start- up current” feature that will eliminate any creep effects in the meter. The ADE7757 is designed to issue a minimum output frequency. Any load generating a frequency lower than this minimum frequency will not cause a pulse to be issued on F1 ...

Page 14

PRELIMINARY TECHNICAL DATA Dimensions shown in inches and (mm). 16-Lead SOIC narrow-body 0.3937 (10.00) 0.3859 (9.80 0.1574 (4.00) 0.2440 (6.20) 0.1497 (3.80) 0.2284 (5.80 PIN 1 0.0688 (1.75) 0.050 (1.27) BSC 0.0532 (1.35) 0.0098 (0.25) 0.0192 ...

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