Low Cost, Low Power,
True RMS-to-DC Converter
AD8436
Data Sheet
FEATURES
FUNCTIONAL BLOCK DIAGRAM
CAVG CCF
Delivers true rms or average rectified value of ac waveform
Fast settling at all input levels
Accuracy: 10 μV 0.25% of reading (B grade)
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
AD8436
100kΩ
SUM
IGND
100kΩ
8kΩ
RMS CORE
10pF
RMS
VEE
OGND
OUT
16kΩ
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
High-Z FET separately powered input buffer
RIN ≥ 1012 Ω, CIN ≤ 2 pF
10kΩ
10kΩ
IBUFGN
IBUFIN–
IBUFIN+
–
IBUFOUT
FET OP AMP
+
OBUFIN+
OBUFIN–
+
–
DC BUFFER
OBUFOUT
16kΩ
Precision dc output buffer
Wide power supply voltage range
Dual: 2.4 V to 18 V; single: 4.8 V to 36 V
4 mm × 4 mm LFCSP and 8 mm × 6 mm QSOP packages
ESD protected
Figure 1.
GENERAL DESCRIPTION
The AD8436 is a new generation, translinear precision, low
power, true rms-to-dc converter loaded with options. It
computes a precise dc equivalent of the rms value of ac wave-
forms, including complex patterns such as those generated by
switch mode power supplies and triacs. Its accuracy spans a
wide range of input levels (see Figure 2) 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 precision dc output buffer minimizes errors when driving
low impedance loads with extremely low offset voltages, thanks
to internal 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 demanding low level signal conditions and
allowing ample overrange without clipping
.
GREATER INPUT DYNAMIC RANGE
The AD8436 delivers 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 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.
AD8436
ΔΣ SOLUTION
100µV
1mV
10mV
100mV
1V
3V
Figure 2. Usable Dynamic Range of the AD8436 vs. ∆Σ
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; A and B
grades are available in a 20-lead QSOP package. The operating
temperature ranges are −40°C to 125°C for A and B grades and
0°C to 70°C for J grade.
Rev. B
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rightsof third parties that may result fromits 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 andregisteredtrademarks are the property of their respective owners.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781.329.4700 ©2011–2013 Analog Devices, Inc. All rights reserved.
Technical Support
www.analog.com
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