Analog Devices AD636KH, AD636KD, AD636JH, AD636JD, AD636JCHIP Datasheet

a		Low Level,
		True RMS-to-DC Converter
		AD636

FEATURES

True RMS-to-DC Conversion 200 mV Full Scale

Laser-Trimmed to High Accuracy 0.5% Max Error (AD636K) 1.0% Max Error (AD636J)

Wide Response Capability:

Computes RMS of AC and DC Signals

1 MHz –3 dB Bandwidth: V RMS >100 mV Signal Crest Factor of 6 for 0.5% Error

dB Output with 50 dB Range

Low Power: 800 mA Quiescent Current

Single or Dual Supply Operation Monolithic Integrated Circuit Low Cost

Available in Chip Form

				PIN CONNECTIONS &
			FUNCTIONAL BLOCK DIAGRAM
								IOUT
VIN	1		ABSOLUTE	14	+VS		RL		BUF IN
NC			VALUE				10kV
	2	AD636		13	NC		AD636	+	–	BUF OUT
					COMMON			BUF
–V	3		SQUARER	12	NC			CURRENT
S			DIVIDER					MIRROR
									10kV
CAV	4			11	NC
dB	5		CURRENT	10	COMMON			SQUARER
						+VS		DIVIDER		dB
			MIRROR
BUF OUT	6	+		9	RL			ABSOLUTE
			10kV
								VALUE
BUF IN	7	BUF		8	IOUT
		–10kV					V		CAV
							IN

NC = NO CONNECT	–V
	S

PRODUCT DESCRIPTION

The AD636 is a low power monolithic IC which performs true rms-to-dc conversion on low level signals. It offers performance which is comparable or superior to that of hybrid and modular converters costing much more. The AD636 is specified for a signal range of 0 mV to 200 mV rms. Crest factors up to 6 can be accommodated with less than 0.5% additional error, allowing accurate measurement of complex input waveforms.

The low power supply current requirement of the AD636, typically 800 µA, allows it to be used in battery-powered portable instruments. A wide range of power supplies can be used, from

± 2.5 V to ±16.5 V or a single +5 V to +24 V supply. The input and output terminals are fully protected; the input signal can exceed the power supply with no damage to the device (allowing the presence of input signals in the absence of supply voltage) and the output buffer amplifier is short-circuit protected.

The AD636 includes an auxiliary dB output. This signal is derived from an internal circuit point which represents the logarithm of the rms output. The 0 dB reference level is set by an externally supplied current and can be selected by the user to correspond to any input level from 0 dBm (774.6 mV) to –20 dBm (77.46 mV). Frequency response ranges from 1.2 MHz at a 0 dBm level to over 10 kHz at –50 dBm.

The AD636 is designed for ease of use. The device is factorytrimmed at the wafer level for input and output offset, positive and negative waveform symmetry (dc reversal error), and fullscale accuracy at 200 mV rms. Thus no external trims are required to achieve full-rated accuracy.

AD636 is available in two accuracy grades; the AD636J total error of ± 0.5 mV ± 0.06% of reading, and the AD636K

REV. B

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 which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of Analog Devices.

is accurate within ± 0.2 mV to ± 0.3% of reading. Both versions are specified for the 0°C to +70°C temperature range, and are offered in either a hermetically sealed 14-pin DIP or a 10-lead TO-100 metal can. Chips are also available.

PRODUCT HIGHLIGHTS

1.The AD636 computes the true root-mean-square of a complex ac (or ac plus dc) input signal and gives an equivalent dc output level. The true rms value of a waveform is a more useful quantity than the average rectified value since it is a measure of the power in the signal. The rms value of an ac-coupled signal is also its standard deviation.

2.The 200 millivolt full-scale range of the AD636 is compatible with many popular display-oriented analog-to-digital converters. The low power supply current requirement permits use in battery powered hand-held instruments.

3.The only external component required to perform measurements to the fully specified accuracy is the averaging capacitor. The value of this capacitor can be selected for the desired trade-off of low frequency accuracy, ripple, and settling time.

4.The on-chip buffer amplifier can be used to buffer either the

input or the output. Used as an input buffer, it provides accurate performance from standard 10 MΩ input attenuators. As an output buffer, it can supply up to 5 milliamps of output current.

5.The AD636 will operate over a wide range of power supply

voltages, including single +5 V to +24 V or split ± 2.5 V to

± 16.5 V sources. A standard 9 V battery will provide several hundred hours of continuous operation.

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

Tel: [phone]	World Wide Web Site: http://www.analog.com
Fax: [phone]	© Analog Devices, Inc., 1999

AD636–SPECIFICATIONS (@ +258C, and +VS = +3 V, –VS = –5 V, unless otherwise noted)

Model	AD636J				AD636K
	Min	Typ	Max	Min	Typ	Max	Units
TRANSFER FUNCTION	VOUT =	avg. ( VIN )2		VOUT = avg. ( VIN )2
CONVERSION ACCURACY							mV ± % of Reading
Total Error, Internal Trim1, 2			60.5 61.0			60.2 60.5
vs. Temperature, 0°C to +70°C			± 0.1 ± 0.01			± 0.1 ± 0.005	mV ± % of Reading/°C
vs. Supply Voltage		± 0.1 ± 0.01			± 0.1 ± 0.01		mV ± % of Reading/V
dc Reversal Error at 200 mV		± 0.2			± 0.1		% of Reading
Total Error, External Trim1		± 0.3 ± 0.3			± 0.1 ± 0.2		mV ± % of Reading
ERROR VS. CREST FACTOR3
Crest Factor 1 to 2	Specified Accuracy			Specified Accuracy
Crest Factor = 3		–0.2			–0.2		% of Reading
Crest Factor = 6		–0.5			–0.5		% of Reading
AVERAGING TIME CONSTANT		25			25		ms/µF CAV
INPUT CHARACTERISTICS
Signal Range, All Supplies
Continuous rms Level		0 to 200			0 to 200		mV rms
Peak Transient Inputs			± 2.8			± 2.8
+3 V, –5 V Supply							V pk
± 2.5 V Supply			± 2.0			± 2.0	V pk
± 5 V Supply			± 5.0			± 5.0	V pk
Maximum Continuous Nondestructive			± 12			± 12
Input Level (All Supply Voltages)							V pk
Input Resistance	5.33	6.67	8	5.33	6.67	8	kΩ
Input Offset Voltage			± 0.5			± 0.2	mV
FREQUENCY RESPONSE2, 4
Bandwidth for 1% Additional Error (0.09 dB)
VIN = 10 mV		14			14		kHz
VIN = 100 mV		90			90		kHz
VIN = 200 mV		130			130		kHz
± 3 dB Bandwidth
VIN = 10 mV		100			100		kHz
VIN = 100 mV		900			900		kHz
VIN = 200 mV		1.5			1.5		MHz
OUTPUT CHARACTERISTICS2			60.5			60.2
Offset Voltage, VIN = COM		± 10			± 10		mV
vs. Temperature							µV/°C
vs. Supply		± 0.1			± 0.1		mV/ V
Voltage Swing
+3 V, –5 V Supply	0.3	0 to +1.0		0.3	0 to +1.0		V
± 5 V to ± 16.5 V Supply	0.3	0 to +1.0		0.3	0 to +1.0		V
Output Impedance	8	10	12	8	10	12	kΩ
dB OUTPUT		± 0.3	60.5		± 0.1	60.2
Error, VIN = 7 mV to 300 mV rms							dB
Scale Factor		–3.0			–3.0		mV/dB
Scale Factor Temperature Coefficient		+0.33			+0.33		% of Reading/°C
		–0.033			–0.033		dB/°C
IREF for 0 dB = 0.1 V rms	2	4	8	2	4	8	µA
IREF Range	1		50	1		50	µA
IOUT TERMINAL							µA/V rms
IOUT Scale Factor		100			100
IOUT Scale Factor Tolerance	–20	± 10	+20	–20	± 10	+20	%
Output Resistance	8	10	12	8	10	12	kΩ
Voltage Compliance		–VS to (+VS			–VS to (+VS		V
		–2 V)			–2 V)
BUFFER AMPLIFIER
Input and Output Voltage Range	–VS to (+VS			–VS to (+VS
Input Offset Voltage, RS = 10k	–2 V)	± 0.8	62	–2 V)	± 0.5	61	V
							mV
Input Bias Current		100	300		100	300	nA
Input Resistance		108			108		Ω
Output Current	(+5 mA,			(+5 mA,
Short Circuit Current	–130 µA)	20		–130 µA)	20		mA
Small Signal Bandwidth		l			l		MHz
Slew Rate5		5			5		V/µs
POWER SUPPLY
Voltage, Rated Performance		+3, –5	± 16.5		+3, –5	± 16.5	V
Dual Supply	+2, –2.5			+2, –2.5			V
Single Supply	+5		+24	+5		+24	V
Quiescent Current6		0.80	1.00		0.80	1.00	mA

–2–

REV. B

AD636

Model		AD636J			AD636K
	Min	Typ	Max	Min	Typ	Max	Units
TEMPERATURE RANGE							°C
Rated Performance	0		+70	0		+70
Storage	–55		+150	–55		+150	°C
TRANSISTOR COUNT		62			62

NOTES

1Accuracy specified for 0 mV to 200 mV rms, dc or 1 kHz sine wave input. Accuracy is degraded at higher rms signal levels. 2Measured at Pin 8 of DIP (IOUT), with Pin 9 tied to common.

3Error vs. crest factor is specified as additional error for a 200 mV rms rectangular pulse trim, pulse width = 200 µs. 4Input voltages are expressed in volts rms.

5With 10 kΩ pull down resistor from Pin 6 (BUF OUT) to –VS. 6With BUF input tied to Common.

Specifications subject to change without notice.

All min and max specifications are guaranteed. Specifications shown in boldface are tested on all production units at final electrical test and are used to calculate outgoing quality levels.

ABSOLUTE MAXIMUM RATINGS1
Supply Voltage	±16.5 V
Dual Supply . . . . . . . . . . . . . . . . . . . . . . . .
Single Supply . . . . . . . . . . . . . . . . . . . . . . .	. . . . . . . . +24 V
Internal Power Dissipation2 . . . . . . . . . . . . .	. . . . . . .500 mW
Maximum Input Voltage . . . . . . . . . . . . . . . .	. . . . ±12 V Peak
Storage Temperature Range N, R . . . . . . . . .	–55°C to +150°C
Operating Temperature Range	0°C to +70°C
AD636J/K . . . . . . . . . . . . . . . . . . . . . . . . .
Lead Temperature Range (Soldering 60 sec) .	. . . . . . . +300°C
ESD Rating . . . . . . . . . . . . . . . . . . . . . . . . . .	. . . . . . . . 1000 V

NOTES

1Stresses above those listed under Absolute Maximum Ratings may cause permanent damage to the device. This is a stress rating only; functional operation of the device at these or any other conditions above those indicated in the operational section of this specification is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability.

210-Lead Header: θJA = 150°C/Watt.

14-Lead Side Brazed Ceramic DIP: θJA = 95°C/Watt.

METALIZATION PHOTOGRAPH

Contact factory for latest dimensions.

Dimensions shown in inches and (mm).

0.1315 (3.340)

COM	RL
10	9

+VS 14

8 IOUT

0.0807

(2.050)

	VIN	1a*
		1b*

3	4		5
–V	C	AV	dB
S

PAD NUMBERS CORRESPOND TO PIN NUMBERS FOR THE TO-116 14-PIN CERAMIC DIP PACKAGE.

NOTE

*BOTH PADS SHOWN MUST BE CONNECTED TO VIN.

7 BUF IN

6 BUF OUT

ORDERING GUIDE

	Temperature	Package	Package
Model	Range	Descriptions	Options
AD636JD	0°C to +70°C	Side Brazed Ceramic DIP	D-14
AD636KD	0°C to +70°C	Side Brazed Ceramic DIP	D-14
AD636JH	0°C to +70°C	Header	H-10A
AD636KH	0°C to +70°C	Header	H-10A
AD636J Chip	0°C to +70°C	Chip
AD636JD/+	0°C to +70°C	Side Brazed Ceramic DIP	D-14

STANDARD CONNECTION

The AD636 is simple to connect for the majority of high accuracy rms measurements, requiring only an external capacitor to set the averaging time constant. The standard connection is shown in Figure 1. In this configuration, the AD636 will measure the rms of the ac and dc level present at the input, but will show an error for low frequency inputs as a function of the filter capacitor, CAV, as shown in Figure 5. Thus, if a 4 F capacitor is used, the additional average error at 10 Hz will be 0.1%, at

3 Hz it will be 1%. The accuracy at higher frequencies will be according to specification. If it is desired to reject the dc input, a capacitor is added in series with the input, as shown in Fig-

ure 3; the capacitor must be nonpolar. If the AD636 is driven with power supplies with a considerable amount of high frequency ripple, it is advisable to bypass both supplies to ground with 0.1 F ceramic discs as near the device as possible. CF is an optional output ripple filter, as discussed elsewhere in this data sheet.

			CAV			CF
			– +			(OPTIONAL)
VIN	1		ABSOLUTE	14	+VS	10kV
						AD636	+	–
	2		VALUE	13			BUF		VOUT
		AD636					CURRENT
–V	3		SQUARER	12			MIRROR	10kV
S
			DIVIDER
	4			11	+VS		SQUARER
			CURRENT				DIVIDER
	5			10
			MIRROR
							ABSOLUTE
VOUT	6			9		VIN	VALUE
		+	10kV
	7	BUF		8
		–			CF	CAV
			10kV				–V
					(OPTIONAL)	–+
							S

Figure 1. Standard RMS Connection

REV. B

–3–