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RMS-to-DC converter targets limited space apps

Posted: 19 Aug 2011     Print Version  Bookmark and Share

Keywords:RMS  DC  converter 

Analog Devices Inc. (ADI) unveils the AD8436, an integrated true RMS-to-DC converter that offers wide usable dynamic range of 100µV to 3V and the ability to measure extremely low signal levels with high accuracy and no drop in settling time.


According to the company, the AD8436 precision monolithic true RMS-to-DC converter features AC conversion accuracy to better than ±0.5 per cent. Uniform settling for widely variant input values enables consistent conversion rates with results displayed promptly for near-zero and high-level AC inputs. The AD8436 is said to be immune to temperature, crest factor and supply voltage variations. Zero DC offset voltages at the converter output simplify calibration. This performance is packed into a compact package integrated with a FET input and precision DC buffer amplifiers and consumes only 300µA of power typical at ±2.4V. The AD8436 is said to be a good choice for remote, portable battery-powered instrumentation, energy and automotive applications where limited board space and outdoor environments are considerations.

RMS (root mean square) is a fundamental measurement of the magnitude of an AC and DC signal and is a better measure of the power in a signal than simple averaging. RMS-to-DC converters are used in applications where precise, low power measurement of AC/DC signals is the prime objective. The AD8436 system-on-a-chip design computes the precise DC equivalent of the RMS value and provides a level of linearity and accuracy across the entire input range that enables engineers to design systems with 90dB of dynamic range.

The AD8436 extends the crest-factor to 10—approximately double the current industry-standard digital solution—with minimal loss of accuracy. According to the company, it is particularly useful for high transit signals and can be used in designs currently using ADI's low-power, true RMS-to-DC converters such as the AD736 and AD737 with improved performances. The device is laser trimmed and characterized at 300mV RMS input and comes with dual supply voltage range of ±2.4V to ±18V and single supply voltage range of 4.8V to 36V.

According to the company, the AD8436 instantly computes true RMS value with fast and constant settling time at all input levels. It features input frequency range of 65kHz for additional 1 per cent error.

The AD8436A is available in full volume production now in a -40°C to 125°C temperature range version at a price of Rs.221.97 ($4.95) per 1000 units in 20-lead LFCSP 4x4mm packaging and the AD8436JZ is available in full volume production now in a 0°C to 70°C temperature range version at a price of Rs.132.29 ($2.95) per 1000 units in 20-lead LFCSP 4x4mm packaging.

Complementary components to the AD8436 in low noise, low power, precision applications include the AD7190 24bit Sigma Delta A/D converter and the ADR3433 micro power, high accuracy voltage references.

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