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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 that may result from its use. no license is granted by implication or otherwise under any patent or patent rights of analog devices. a ADE7757 * one technology way, p.o. box 9106, norwood, ma 02062-9106, usa. tel: 781/329-4700www.analog.com fax: 781/326-8703 ? analog devices, inc., 2002 rev. 0 energy metering ic with integrated oscillator features on-chip oscillator as clock source high accuracy, supposes 50 hz/60 hz iec 521/1036 less than 0.1% error over a dynamic range of 500 to 1 the ADE7757 supplies average real power on the frequency outputs f1 and f2 the high frequency output cf is intended for calibration and supplies instantaneous real power the logic output revp can be used to indicate a poten- tial misw iring or negative power direct drive for electromechanical counters and two phase stepper motors (f1 and f2) proprietary adcs and dsp provide high accuracy over large variations in environmental conditions and time on-chip power supply monitoring on-chip creep protection (no load threshold) on-chip reference 2.5 v 8% (20 ppm/ c typical) with external overdrive capability single 5 v supply, low power (20 mw typical) low cost cmos process ac input only * u.s. patents 5,745,323, 5,760,617, 5,862,069, 5,872,469; others pending. functional block diagram multiplier revp v2p v2n v1p hpf rclkin ref in/out f1 f2 cf scf s0 s1 phase correction 4k ...110101... signal processing block power supply monitor - adc v1n ADE7757 ...11011001... lpf 2.5v reference digital-to-frequency converter v dd agnd dgnd - adc internal oscillator general description the ADE7757 is a high accuracy electrical energy measurement 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 the shunt resistor and operates only with ac input. the ADE7757 specifications surpass the accuracy requirements as quoted in the iec1036 standard. due to the similarity between the ADE7757 and ad7755, the application note an-559 can be used as a basis for a description 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 environmental 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 calibra- tion purposes, provides instantaneous real power information. the ADE7757 includes a power supply monitoring circuit on the v dd supply pin. the ADE7757 will remain inactive until the supply voltage on v dd reaches approximately 4 v. if the supply falls below 4 v, the ADE7757 will also remain inactive and the f1, f2, and cf outputs will be in their nonactive modes. internal phase matching circuitry ensures that the voltage and current channels are phase matched while the hpf in the cur- rent 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 a 16-lead soic narrow-body package.
rev. 0 ?2? ADE7757especifications (v dd = 5 v 5%, agnd = dgnd = 0 v, on-chip reference, rcklin = 6.2 k 0.1% 15ppm/ c , = + , ) / , 165 mv), 25 = = ) 0.1 degrees( ) = ) 0.1 degrees( ) = = , ) = , = = = , ) 0.3 % reading typ v1 = 21.2 mv rms, v2 = 116.7 mv rms, v dd = 5 v 30 mv max v1p and v1n to agnd channel v2 maximum signal level 165 mv max v2p and v2n to agnd input impedance (dc) 320 k ? = , = ? ? / ) = , = ? ? / , 18 mv max see terminology section and typical performance characteristics. gain error 1 4% ideal typ external 2.5 v reference v1 = 21.2 mv rms, v2 = 116.7 mv rms oscillator frequency (osc) 450 khz nominal rcklin = 6.2 k ? ? / 12 % reading typ oscillator frequency stability 1 30 ppm/ / + 200 mv max temperature coefficient 20 ppm/ , , , , = 5% input low voltage, v inl 0.8 v max v dd = 5 v 5% input current, i in 1 , = , , = = , = = , = = , = = , ) , = , = +
rev. 0 ?3? ADE7757 timing characteristics 1, 2 parameter a, b versions unit test conditions/comments t 1 3 244 ms f1 and f2 pulsewidth (logic low) t 2 see table ii sec output pulse period. see transfer function section. t 3 1/2 t 2 sec time between f1 falling edge and f2 falling edge t 4 3, 4 173 ms cf pulsewidth (logic high) t 5 see table iii sec cf pulse period. see transfer function section. t 6 2 , , = ? , = = , , = ? ? / , = + , )
rev. 0 ADE7757 ?4? absolute maximum ratings 1 (t a = 25 , ) + + , , , + + + + , ) + + , / , ) ) ) ) , , %% error energy registered by ade true energy true energy = ? ) ) , , , ) / , ) ) , , ) ) ) ) ) ) , + + +
rev. 0 ?5? ADE7757 pin function descriptions pin no. mnemonic description 1v dd power supply. this pin provides the supply voltage for the circuitry in the ADE7757. the supply voltage should be maintained at 5 v , , ) , , ) , , , , , , , , , / / , , , , , ? , , , , , , , , ), , , , , , , average real power information. the logic outputs can be used to directly drive electromechanical counters and two phase stepper motors. see transfer function section. pin configuration 1 ADE7757 v dd v2p v2n v1n v1p f1 f2 cf dgnd revp 2 3 4 5 16 15 14 13 12 top view (not to scale) agnd ref in/out scf rclkin s0 s1 6 7 8 11 10 9
rev. 0 ADE7757 ?6? etypical performance characteristics current e a 0.5 0.01 0.1 1 10 100 % error e0.5 e0.4 e0.3 e0.2 e0.1 0 0.1 0.2 0.3 0.4 +85 c +25 c e40 c pf = 1 on-chip reference tpc 1. error as a % of reading over temperature with on-chip reference (pf = 1) current e a 0.01 0.1 1 10 100 % error e0.5 e0.3 e0.1 0.1 0.3 0.5 0.7 0.9 pf = 0.5 on-chip reference e40 c, pf = 0.5 +25 c, pf = 1.0 +85 c, pf = 0.5 e25 c, pf = 0.5 tpc 2. error as a % of reading over temperature with on-chip reference (pf = 0.5) current e a 0.01 0.1 1 10 100 % error e1.0 e0.8 e0.6 e0.4 e0.2 0.2 0.6 1.0 pf = 1 external reference +85 c e40 c +25 c 0 0.4 0.8 tpc 3. error as a % of reading over temperature with external reference (pf = 1) current e a 0.01 0.1 1 10 100 % error e1.0 e0.8 e0.6 e0.4 e0.2 0.2 0.6 1.0 pf = 0.5 external reference 0 0.4 0.8 +25 c, pf = 1.0 +85 c, pf = 0.5 +25 c, pf = 0.5 e40 c, pf = 0.5 tpc 4. error as a % of reading over temperature with external reference (pf = 0.5) 6.2k v2n 200 220v 150nf v2p 200 602k v1p v1n 350 40a to 40ma ref in/out 100nf 1 f 100nf 10 f v dd dgnd f1 f2 cf revp rclkin s0 s1 scf 10nf 10nf 10nf u3 ps2501-1 k7 k8 u1 ADE7757 10k v dd 200 200 150nf 150nf agnd 150nf v dd figure 2. test circuit for performance curves
rev. 0 ADE7757 ?7? frequency e hz 45 % error e0.5 e0.4 e0.3 e0.2 e0.1 0.1 0.3 0.5 0 0.2 0.4 50 55 60 65 pf = e0.5 pf = +0.5 pf = +1.0 tpc 5. error as a % of reading over input frequency current e a 0.01 % error e1.0 e0.8 e0.6 e0.4 e0.2 0.2 0.6 1.0 0 0.4 0.8 0.1 1 10 100 5.25v 4.75v 5.0v pf = 1 on-chip reference tpc 6. psr with internal reference current e a 0.01 0.1 1 10 100 5.25v 5.0v 4.75v pf = 1 external reference % error e1.0 e0.8 e0.6 e0.4 e0.2 0.2 0.6 1.0 0 0.4 0.8 tpc 7. psr with external reference mv e8 0 0.5 10 15 25 35 45 20 30 40 internal reference temperature = 25 c e7 e6 e5 e4 e3 e2 e1 8 7 6 5 4 3 2 1 0 distribution characteristics number points: 100 minimum: e4.319 maximum: 2.2828 mean: e1.04576552 std. dev: 1.300956604 tpc 8. channel v1 offset distribution mv e8 0 0.5 10 15 25 35 45 20 30 40 internal reference temperature = 25 c e6 e4 e2 8 6 4 2 0 e10 e12 e14 e16 e18 e20 10 distribution characteristics number points: 100 minimum: e9.82923 maximum: 0.472126 mean: 4.54036589 std. dev: 1.89694475 tpc 9. channel v2 offset distribution % e8 0 0.5 10 15 25 35 20 30 40 e6 e4 e2 8 6 4 2 0 e10 e12 e14 e16 e18 e20 10 12 14 16 18 20 distribution characteristics number points: 100 minimum: e6.15% maximum: 9.96% mean: 0% std. dev: 2.84% external reference temperature = 25 c tpc 10. part-to-part cf distribution from mean
rev. 0 ADE7757 ?8? theory of operation the two adcs digitize the voltage signals from the current and voltage sensors. these adcs are 16-bit sigma-delta with an oversampling rate of 450 khz. this analog input structure greatly simplifies sensor interfacing by providing a wide dynamic range for direct connection to the sensor and also simplifies the antialiasing filter design. a high-pass filter in the current channel removes any dc component from the current signal. this elimi- nates any inaccuracies in the real power calculation due to off- sets in the voltage or current signals. because the hpf is always enabled, the ic will operate only with ac input (see hpf and offset effects section). the real power calculation is derived from the instantaneous power signal. the instantaneous power signal is generated by a direct multiplication of the current and voltage signals. in order to extract the real power component (i.e., the dc component), the instantaneous power signal is low-pass filtered. figure 3 illustrates the instantaneous real power signal and shows how the real power information can be extracted by low-pass filtering the instantaneous power signal. this scheme correctly calculates real power for sinusoidal current and voltage waveforms at all power factors. all signal processing is carried out in the digital domain for superior stability over temperature and time. time time adc adc ch1 ch2 multiplier lpf f1 f2 digital-to- frequency cf digital-to- frequency instantaneous real power signal instantaneous power signal e p(t) hpf figure 3. signal processing block diagram the low frequency outputs (f1, f2) of the ADE7757 are gener- ated 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.g., by a counter) to generate real energy information. conversely, due to its high output frequency and hence shorter integration time, the cf output frequency is proportional to the instantaneous real power. this is useful for system calibration, which can be done faster under steady load conditions. power factor considerations the method used to extract the real power information from the instantaneous power signal (i.e., by low-pass filtering) is still valid even when the voltage and current signals are not in phase. figure 4 displays the unity power factor condition and a dpf (displacement power factor) = 0.5, i.e., current signal lagging the voltage by 60 , , ) vi ? ? ? ? ? ? ) ? ? )
rev. 0 ADE7757 ?9? nonsinusoidal voltage and current the real power calculation method also holds true for nonsinusoidal current and voltage waveforms. all voltage and current waveforms in practical applications will have some har- monic content. using the fourier transform, instantaneous voltage and current waveforms can be expressed in terms of their harmonic content. vt v v h t hh h () sin( ) =+ + ? ) v(t) is the instantaneous voltage v 0 is the average value v h is the rms value of voltage harmonic h, and h is the phase angle of the voltage harmonic. it i i h t hh h () sin( ) =+ + ? ) i ( t ) is the instantaneous current i 0 is the dc component i h is the rms value of current harmonic h, and h is the phase angle of the current harmonic. using equations 1 and 2, the real power p can be expressed in terms of its fundamental real power ( p 1 ) and harmonic real power ( p h ). ppp h =+ pv i 111 1 111 = =? ? ) pvi hhhh hhh = =? ? ) , , ) ) + ? ? + + , , , , ) + ? ? + + , , , )
rev. 0 ADE7757 ?10? typical connection diagrams figure 7 shows a typical connection diagram for channel v1. a shunt is the current sensor selected for this example because of its low cost compared to other current sensors such as the ct (current transformer). this ic is ideal for low current meters. v1p v1n c f c f r f r f 30mv shunt agnd phase neutral figure 7. typical connection for channel v1 figure 8 shows a typical connection for channel v2. typically, the ADE7757 is biased around the neutral wire, and a resistor divider is used to provide a voltage signal that is proportional to the line voltage. adjusting the ratio of r a , r b , and r f is also a convenient way of carrying out a gain calibration on a meter. v2p v2n c f phase neutral r f 165mv c f r f r b r a * * r a >> r b + r f figure 8. typical connections for channel v2 power supply monitor the ADE7757 contains an on-chip power supply monitor. the power supply (v dd ) is continuously monitored by the ADE7757. if the supply is less than 4 v, the ADE7757 becomes inactive. this is useful to ensure proper device operation at power-up and power-down. the power supply monitor has built in hyster- esis and filtering that provide a high degree of immunity to false triggering from noisy supplies. as can be seen from figure 9, the trigger level is nominally set at 4 v. the tolerance on this trigger level is within , , , ) ) vtviti vi vivi tiv t vi t os os os os os os cos( ) cos( ) cos( ) cos( ) cos( ) ? ? + {} + {} = ++ + + ) ? ? ? ? /
rev. 0 ADE7757 ?11? the hpf in channel v1 has an associated phase response that is compensated for on-chip. figures 11 and 12 show the phase error between channels with the compensation network acti- vated. the ADE7757 is phase compensated up to 1 khz as shown. this will ensure correct active harmonic power calcula- tion even at low power factors. frequency e hz 0.30 phase e degrees 0.25 0.20 0.15 0.10 0.05 0 e0.05 e0.10 0 100 200 300 400 500 600 700 800 900 1000 figure 11. phase error between channels (0 hz to 1 khz) frequency e hz 0.30 phase e degrees 0.25 0.20 0.15 0.10 0.05 0 e0.05 e0.10 40 45 50 55 60 65 70 figure 12. phase error between channels (40 hz to 70 hz) digital-to-frequency conversion as previously described, the digital output of the low-pass filter after multiplication contains the real power information. how- ever, since this lpf is not an ideal brick wall filter implemen- tation, the output signal also contains attenuated components at the line frequency and its harmonics, i.e., cos(hwt) where h = 1, 2, 3, . . . and so on. the magnitude response of the filter is given by: hf f () . = + ) , ) ) , , ) ) , , /) ) ? ) ) , , ) ) , , , , , ,
rev. 0 ADE7757 ?12? interfacing the ADE7757 to a microcontroller for energy measurement the easiest way to interface the ADE7757 to a microcontroller is to use the cf high frequency output with the output frequency scaling set to 2048 , = = = ) , ? , , average frequency average power counter time == energy average power time counter time time counter === , , , , , , , , , , ) ? , ? ? , ? ) ) , , = = freq vv f v rms rms ref = ? freq = output frequency on f1 and f2 ( h z) v 1 rms =d ifferential rms voltage signal on channel v1 (volts) v 2 rms =d ifferential rms voltage signal on channel v2 (volts) v ref =t he reference voltage (2.5 v ) ) f 1-4 =o ne of four possible frequencies selected by using the logic inputs s0 and s1?ee table i.
rev. 0 ADE7757 ?13? table i. f 1e4 frequency selection f 1e4 at nominal s1 s0 osc relation 1 osc(hz) 2 00 osc/2 19 0.86 01 osc/2 18 1.72 10 osc/2 17 3.44 11 osc/2 16 6.86 1 f 1e4 is a binary fraction of the internal oscillator frequency (osc). 2 values are generated using the nominal frequency of 450 khz. example in this example, with ac voltages of , f 1? = osc /2 19 hz , s 0 = s 1 = 0 v 1 rms = 0.03 / 2 v v 2 rms = 0.165/ 2 v v ref = 2.5 v (nominal reference value). note: if the on-chip reference is used, actual output frequencies may vary from device to device due to reference tolerance of freq f . =. f=. = ) ) , = , = = ) , , , , , , , , ) ) , = , = , = , = , = , = , = , = , ) , / ) , / / ) ) , ) , )
rev. 0 ADE7757 ?14? table v. f1 and f2 frequency with half-scale ac inputs frequency on f1 and f2e s1 s0 f 1e4 (hz) * ch1 and ch2 half-scale ac input * 00 0.86 0.051 * , , , ) , / , ), ) = = , = , ) , )
rev. 0 ADE7757 ?5 outline dimensions 16-lead standard small outline package narrow body (rn-16) dimensions shown in millimeters and (inches) controlling dimensions are in millimeters; inch dimensions (in parentheses) are rounded-off millimeter equivalents for reference only and are not appropriate for use in design compliant to jedec standards ms-012ac 16 9 8 1 4.00 (0.1575) 3.80 (0.1496) 10.00 (0.3937) 9.80 (0.3858) 1.27 (0.0500) bsc pin 1 6.20 (0.2441) 5.80 (0.2283) seating plane 0.25 (0.0098) 0.10 (0.0039) 0.51 (0.0201) 0.33 (0.0130) 1.75 (0.0689) 1.35 (0.0531) 8 0 0.50 (0.0197) 0.25 (0.0098) 45 1.27 (0.0500) 0.40 (0.0157) 0.25 (0.0098) 0.19 (0.0075)
?16? c02898?0?8/02(0) printed in u.s.a.

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