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Low Cost, Low Power,
True RMS-to-DC Converter
AD8436
Data Sheet
FEATURES
FUNCTIONAL BLOCK DIAGRAM
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:
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
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
CAVG CCF
VCC
AD8436
100kΩ
SUM
RMS
IGND
8kΩ
100kΩ
RMS CORE
VEE
16kΩ
OUT
10pF
IBUFGN
10kΩ
10kΩ
IBUFIN–
–
IBUFIN+
+
FET OP AMP
+
DC BUFFER
OBUFIN+
OBUFIN–
16kΩ
OGND
–
IBUFOUT
OBUFOUT
10033-001
Product
Overview
Figure 1.
GENERAL DESCRIPTION
other battery-powered applications.
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 waveforms, 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.
Rev. D
GREATER INPUT DYNAMIC RANGE
AD8436
ΔΣ SOLUTION
100µV
1mV
10mV
100mV
1V
3V
10033-002
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
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, 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.
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