ADIAD8436高精度RMS到DC轉換解決方案
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ADI公司的AD8436是新一代跨導線性的高精度低功耗真正的RMS/DC轉換器，它能精確計算交流波形的rms值，包括由開關電源和TRIAC所產品的復數項。精度優于0.5%，輸出失調小于10uV，波峰因素（CF=1-10）時的誤差小于0.5%,輸入范圍滿刻度為100 μV rms 到3 V rms (8.5 V p-p)，雙電源電壓為 ±2.4 V到±18 V ，單電源電壓為4.8 V 到36 V，主要用在遙控，手持儀表，板空間受限和戶外環境的電源和汽車。本文介紹了AD8436主要特性，功能方框圖，RMS核方框圖，波峰因素測試電路圖，典型應用電路以及AD8436-EVALZ評估板電路圖和PCB布局圖。
The AD8436 is a new generation, translinear precision, low power, true rms-to-dc converter that is loaded with options. It computes a precise dc equivalent of the rms value of ac waveforms, including complex patterns such as those generated by switchmode power supplies and triacs. Its accuracy spans a wide range of input levels and temperatures. The ensured accuracy of ≤±0.5% and ≤10 μV output offset result from the latest Analog Devices, Inc., technology. The crest factor error is 0.5% for CF values between 1 and 10.
The AD8436 delivers instant true rms results at less cost than misleading peak, averaging, or digital solutions. There is no programming expense or processor overhead to consider, and the 4 mm × 4 mm package easily fits into those tight applications.
On-board buffer amplifiers enable the widest range of options for any rms-to-dc converter available, regardless of cost. For minimal applications, only a single external averaging capacitor is required. The built-in high impedance FET buffer provides an interface for external attenuators, frequency compensation, or driving low impedance loads. A matched pair of internal resistors enables an easily configurable gain-of-two or more, extending the usable input range even lower. The low power, precision input buffer makes the AD8436 attractive for use in portable multi- meters and other battery-powered applications. The precision dc output buffer offers extremely low offset voltages, thanks to bias current cancellation.
Unlike digital solutions, the AD8436 has no switching circuitry limiting performance at high or low amplitudes (see Figure 2). A usable response of 100 μV and >3 V extends the dynamic range with no external scaling, accommodating the most demanding low signal conditions.
The AD8436 operates from single or dual supplies of ±2.4 V (4.8 V) to ±18 V (36 V). A and J grades are available in a compact 4 mm × 4 mm, 20-lead chip-scale package. The operating temperature ranges are ?40°C to 125°C and 0°C to 70°C.
The AD8436 is a good choice for remote, portable battery-powered instrumentation, energy and automotive applications where limited board space and outdoor environments are considerations.
AD8436主要特性：
Computes true rms value instantly
Accuracy: ±10 μV ± 0.5% of reading
Wide dynamic input range
100 μV rms to 3 V rms (8.5 V p-p) full-scale input range
Larger inputs with external scaling
Wide bandwidth:
1 MHz for ?3 dB (300 mV)
65 kHz for additional 1% error
Zero converter dc output offset
No residual switching products
Specified at 300 mV rms input
Accurate conversion with crest factors up to 10
Low power: 300 μA typical at ±2.4 V
Fast settling at all input levels
High-Z FET separately powered input buffer
RIN ≥ 1012 Ω, CIN ≤ 2 pF
Precision dc output buffer
Wide supply range
Dual: ±2.4 V to ±18 V
Single: 4.8 V to 36 V
Small size: 4 mm × 4 mm package
ESD protected
圖1。AD8436功能方框圖
圖2。AD8436 RMS核方框圖
圖3。波峰因素測試電路圖
圖4。AD8436典型應用電路
AD8436-EVALZ評估板
The AD8436-EVALZ provides a platform to evaluate AD8436 performance. The board is fully assembled, tested and ready to use after the power and signal sources are connected. Figure 45 is a photograph of the board. Signal connections are located on the primary and secondary sides, with power and ground on the inner layers.
The AD8436-EVALZ offers many options, without sacrificing simplicity. The board is tested and shipped with a 10 μF averaging capacitor (CAVG), 3.3 μF low-pass filter capacitor (C8) and a 0.1 μF (COPT) capacitor to optimize crest factor performance. To evaluate minimum cost applications, remove C8 and COPT.
圖5。AD8436-EVALZ評估板外形圖
圖6。AD8436-EVALZ評估板電路圖
圖7。AD8436-EVALZ評估板元件布局圖
詳情請見：
http://www.analog.com/static/imported-files/data_sheets/AD8436.pdf
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