Low Cost, Low Power,
True RMS-to-DC Converter
AD8436
FEATURES
FUNCTIONAL BLOCK DIAGRAM
CAVG CCF
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:
VCC
100kΩ
SUM
IGND
100kΩ
8kΩ
RMS CORE
RMS
VEE
OGND
OUT
1 MHz for −3 dB (300 mV)
65 kHz for additional 1% error
16kΩ
10pF
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
10kΩ
10kΩ
IBUFGN
IBUFIN–
IBUFIN+
–
+
FET OP AMP
IBUFOUT
High-Z FET separately powered input buffer
OBUFIN+
OBUFIN–
+
–
DC BUFFER
OBUFOUT
R
IN ≥ 1012 Ω, CIN ≤ 2 pF
16kΩ
Precision dc output buffer
Wide supply range
AD8436
Figure 1.
Dual: 2.4 V to 18 V
Single: 4.8 V to 36 V
Small size: 4 mm × 4 mm package
ESD protected
GENERAL DESCRIPTION
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
(see Figure 2) and temperatures. The ensured accuracy of ≤±±.ꢀ5
and ≤1± μV output offset result from the latest Analog Devices,
Inc., technology. The crest factor error is <±.ꢀ5 for CF values
between 1 and 1±.
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 <1±± μV and >3 V extends the dynamic
range with no external scaling, accommodating the most
demanding low signal conditions.
GREATER INPUT DYNAMIC RANGE
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.
AD8436
∆Σ SOLUTION
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-
100µV
1mV
10mV
100mV
1V
3V
Figure 2. Usable Dynamic Range of the AD8436 vs. ΔΣ
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, 2±-lead chip-scale package. The operating
temperature ranges are −4±°C to 12ꢀ°C and ±°C to 7±°C.
Rev. 0
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. Specifications subject to change without notice. No
license is granted by implication or otherwise under any patent or patent rights of Analog Devices.
Trademarks and registeredtrademarks arethe property of their respective owners.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781.329.4700
Fax: 781.461.3113
www.analog.com
©2011 Analog Devices, Inc. All rights reserved.
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