AD8436 View Datasheet(PDF) - Analog Devices

Part Name

Description

Manufacturer

AD8436

Low Cost, Low Power, True RMS-to-DC Converter

Analog Devices 

Data Sheet

FEATURES

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

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 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 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.

Rev. E

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Low Cost, Low Power,

True RMS-to-DC Converter

AD8436

FUNCTIONAL BLOCK DIAGRAM

CAVG CCF

SUM

RMS

AD8436

8kΩ

RMS CORE

10pF

VCC

100kΩ

100kΩ

VEE

16kΩ

IGND

OGND

OUT

IBUFGN

IBUFIN–

IBUFIN+

10kΩ

10kΩ

–

+

FET OP AMP

IBUFOUT

OBUFIN+

OBUFIN–

+

16kΩ

–

DC BUFFER

Figure 1.

OBUFOUT

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

AD8436

∆Σ SOLUTION

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, 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.

One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.

Tel: 781.329.4700 ©2011–2017 Analog Devices, Inc. All rights reserved.

Technical Support

www.analog.com

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