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ADE7753ARSRL 数据表(PDF) 11 Page - Analog Devices |
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ADE7753ARSRL 数据表(HTML) 11 Page - Analog Devices |
11 / 37 page ADE7753 –11– REV. PrF 10/02 PRELIMINARY TECHNICAL DATA ZERO CROSSING DETECTION The ADE7753 has a zero crossing detection circuit on Channel 2. This zero crossing is used to produce an external zero cross signal (ZX) and it is also used in the calibration mode - see Energy Calibration. The zero crossing signal is also used to initiate a temperature measurement on the ADE7753 - see Temperature Measurement. Figure 10 shows how the zero cross signal is generated from the output of LPF1. V2P V2N ADC 2 PGA2 1 x1, x2, x4, x8, x16 REFERENCE GAIN[7:5] V2 TO MULTIPLIER -63% to + 63% FS LPF1 f-3dB = 140Hz ZERO CROSS ZX V2 LPF1 ZX 23.2 8@ 60Hz 0.92 1.0 Figure 10– Zero cross detection on Channel 2 The ZX signal will go logic high on a positive going zero crossing and logic low on a negative going zero crossing on Channel 2. The zero crossing signal ZX is generated from the output of LPF1. LPF1 has a single pole at 156Hz (at CLKIN = 3.579545MHz). As a result there will be a phase lag between the analog input signal V2 and the output of LPF1. The phase response of this filter is shown in the Channel 2 Sampling section of this data sheet. The phase lag response of LPF1 results in a time delay of approximately 0.97ms (@ 60Hz) between the zero crossing on the analog inputs of Channel 2 and the rising or falling edge of ZX. The zero-crossing detection also drives one flag bit in the interrupt status register. An active low in the IRQ output will also appear if the corresponding bit in the Interrupt Enable register is set to logic one. The flag in the Interrupt status register as well as the IRQ output are reset to their default value when the Interrupt Status register with reset (RSTSTATUS) is read. Zero Crossing Timeout The zero crossing detection also has an associated time-out register ZXTOUT. This unsigned, 12-bit register is decremented (1 LSB) every 128/CLKIN seconds. The reg- ister is reset to its user programmed full scale value every time a zero crossing on Channel 2 is detected. The default power on value in this register is FFFh. If the register decrements to zero before a zero crossing is detected and the DISSAG bit in the Mode register is logic zero, the SAG pin will go active low. The absence of a zero crossing is also indicated on the IRQ pin if the ZXTO enable bit in the Interrupt Enable register is set to logic one. Irrespective of the enable bit setting, the ZXTO flag in the Interrupt Status register is always set when the ZXTOUT register is decremented to zero - see ADE7753 Interrupts. The Zerocross Time-out register can be written/read by the user and has an address of 1Dh - see Serial Interface section. The resolution of the register is 128/CLKIN seconds per LSB. Thus the maximum delay for an interrupt is 0.15 second (128/CLKIN × 212). Figure 11 shows the mechanism of the zero crossing time out detection when the line voltage stays at a fixed DC level for more than CLKIN/128 x ZXTOUT seconds. Channel 2 ZXTO detection bit ZXTOUT 16-bit internal register value Figure 11 - Zero crossingTime out detection PERIOD MEASUREMENT The ADE7753 provides also the period measurement of the line. The period register is an unsigned 15-bit register and is updated every period. The resolution of this register is 2.2ms/LSB when CLKIN=3.579545MHz, which represents 0.013% when the line frequency is 60Hz. When the line frequency is 60Hz, the value of the Period register is approximately 7576d. The length of the register enables the measurement of line frequencies as low as 13.9Hz. 40 45 50 55 60 65 70 -90.05 -90 -89.95 -89.9 -89.85 -89.8 -89.75 -89.7 FREQUENCY-Hz Figure 9– Combined phase response of the digital integra- tor and phase compensator (40Hz to 70Hz) Note that the integrator has a -20dB/dec attenuation and approximately -90° phase shift. When combined with a di/dt sensor, the resulting magnitude and phase response should be a flat gain over the frequency band of interest. However, the di/dt sensor has a 20dB/dec gain associated with it, and generates significant high frequency noise, a more effective anti-aliasing filter is needed to avoid noise due to aliasing— see Antialias Filter. When the digital integrator is switched off, the ADE7753 can be used directly with a conventional current sensor such as current transformer (CT) or a low resistance current shunt. |
类似零件编号 - ADE7753ARSRL |
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类似说明 - ADE7753ARSRL |
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