DESCRIPTION The is a signal conditioning circuit for use with Linear Variable Differential Transformers (LVDTs) and Rotary Variable Differential Transformers (RVDTs). The chip includes a low distortion, amplitude-stable sine wave oscillator with programmable frequency to drive the primary of the LVDT/RVDT, a synchronous demodulator to convert the LVDT/RVDT output amplitude and phase to position information, and an output amplifier to provide amplification and filtering of the demodulated signal. PIN CONFIGURATIONS F, N Packages AMP OUT IN IN DEMOD OUT 8 V T REF FEEDBACK FEATURES Low distortion Single supply V to 0V, or dual supply ±.V to ±0V Oscillator frequency khz to 0kHz Capable of ratiometric operation Low power consumption (8mV typ) APPLICATIONS LVDT signal conditioning RVDT signal conditioning LPDT signal conditioning Bridge circuits GND AMP OUT IN IN DEMOD OUT GND / 8 R T 9 0 TOP VIEW D Package 8 9 R T V C T FEEDBACK 0 / TOP VIEW NOTE:. SOL released in large SO package only. ORDERING INFORMATION DESCRIPTION TEMPERATURE RANGE ORDER CODE DWG # 8-Pin Plastic Dual In-Line Package (DIP) 0 to 0 NEN 00A -Pin Small Outline Large (SOL) Package 0 to 0 NED 0B 8-Pin Plastic Dual In-Line Package (DIP) 0 to 8 SAN 00A 8-Pin Ceramic Dual In-Line Package (CERDIP) to SEF 08A -Pin Ceramic Dual In-Line Package (CERDIP) 0 to 8 SAD 08B ABSOLUTE MAXIMUM RATINGS SYMBOL PARAMETER RATING UNIT V CC Supply voltage 0 V T A Split supply voltage ±0 V Operating temperature range NE SA SE 0 to 0 0 to 8 to T STG Storage temperature range to P D Power dissipation 90 mw NOTES:. For derating, see typical power dissipation versus load curves (Figure ). August, 99 90 8-00
BLOCK DIAGRAM FEEDBACK C T R T V IN IN AMP OUT 8 AUX AMP SINE CONV HRONOUS DEMODULATOR / GND/V DOMOD OUT NOTE: Pin numbers are for F, N packages. PIN DEFINITIONS FOR D, F AND N PACKAGES PIN NO. D F, N SYMBOL Amp Out Auxiliary Amplifier Out. IN Auxiliary Amplifier non-inverting input. IN Auxiliary Amplifier inverting input. DEFINITION Input to Synchronous Demodulator from the LVDT/RVDT secondary. DEMOD OUT Pulsating DC output from the Synchronous Demodulator output. This voltage should be filtered before use. Synchronizing input for the Synchronizing Demodulator. This input should be connected to the or output. Sync is referenced to /. GND Device return. Should be connected to system ground or to the negative supply. 8 8 NC No internal connection. -- 9 NC No internal connection. -- 0 NC No internal connection. 9 R T A temperature stable 8kΩ resistor should be connected between this pin and Pin. 0 / A high impedance source of one half the potential applied to. The LVDT/RVDT secondary return should be to this point. A bypass capacitor with low impedance at the oscillator frequency should also be connected between this pin and ground. Oscillator sine wave output that is 80 out of phase with the signal. The LVDT/RVDT primary is usually connected between and pins. Oscillator sine wave output. The LVDT/RVDT primaries are usually connected between and pins. FEEDBACK Usually connected to the output for unity gain, a resistor between this pin and, and one between this pin and ground can provide for a change in the oscillator output pin amplitudes. Reference voltage input for the oscillator and sine converter. This voltage MUST be stable and must not exceed V supply voltage. C T Oscillator frequency-determining capacitor. The capacitor connected between this pin and ground should be a temperature-stable type. 8 V Positive supply connection. August, 99 90
DC ELECTRICAL CHARACTERISTICS V = = 0V, T A = 0 to 0 for NE, T A = to for SE, T A = 0 to 8 for SA, Frequency = khz, unless otherwise noted. SYMBOL PARAMETER TEST CONDITIONS NE SA/SE Min Typ Max Min Typ Max V CC Supply current.9 0.9 8 ma I REF Reference current. 8. 8 ma Reference voltage range V V V P D Power dissipation 8 80 8 0 mw Oscillator Section Oscillator output R L = Ω 8.8 8.8 V RMS THD Sine wave distortion No load.. % Initial amplitude error T A = 0. ± 0. ± % Tempco of amplitude 0.00 0.0 0.00 0.0 %/ Init. accuracy of oscillator freq. T A = ±0.9 ± ±0.9 ± % Temperature coeff. of frequency 0.0 0.0 %/ Voltage coeff. of frequency.. %/V( ) Min () Load 00 0 00 0 Ω Demodulator Section r Linearity error V P-P input ±0.0 ±0. ±0.0 ±0. %FS Maximum demodulator input V P-P V OS Demodulator offset voltage ±. ± ±. ± mv TCV OS Demodulator offset voltage drift µv/ C I BIAS Demodulator input current 00 00 na V R/ accuracy ±0. ± ±0. ± % Auxiliary Output Amplifier V OS Input offset voltage ±0. ± ±0. ± mv I BIAS Input bias current 00 0 00 0 na I OS Input offset current 0 0 0 0 na A V Gain 00 8 00 8 V/mV SR Slew rate.. V/µs GBW Unity gain bandwidth product A V =.. MHz Output voltage swing R L = Ω 8. 8. V Output short circuit current to ground or to V CC T A = 00 00 ma NOTES:. This is temperature coefficient of frequency for the device only. It is assumed that C T and R T are fixed in value and C T leakage is fixed over the operating temperature range.. Minimum load impedance for which distortion is guaranteed to be less than %. UNIT August, 99 90
DEFINITION OF TERMS Oscillator Output Sine Wave Distortion Initial Amplitude Error Initial Accuracy of Oscillator Frequency Tempco of Oscillator Amplitude Tempco of Oscillator Frequency RMS value of the AC voltage at the oscillator output pin. This output is referenced to / and is a function of. The Total Harmonic Distortion (THD) of the oscillator output with no load. This is not a critical specification in LVDT/RVDT systems. This figure could be % or more without affecting system performance. A measure of the interchangeability of parts, not a characteristic of any one part. It is the degree to which the oscillator output of a number of samples will vary from the median of that sample. Another measure of the interchangeability of individual parts. This is the degree to which the oscillator frequency of a number of samples will vary from the median of that sample with a given timing capacitor. A measure of how the oscillator amplitude varies with ambient temperature as that temperature deviates from a ambient. A measure of how the oscillator frequency varies with ambient temperature as that temperature deviates from a ambient. Voltage Coefficient of Oscillator Frequency The degree to which the oscillator frequency will vary as the reference voltage ( ) deviates from 0V. Min () Load Minimum load impedance for which distortion is guaranteed to be less than %. Linearity Error Maximum Demodulator Input The degree to which the DC output of the demodulator/amplifier combination matches a change in the AC signal at the demodulator input. It is measured as the worst case nonlinearity from a straight line drawn between positive and negative fullscale end points. The maximum signal that can be applied to the demodulator input without exceeding the specified linearity error. APPLICATION INFORMATION.V frequency (R T.k) C T DEVICE POWER DISSIPATION (mw) 000 000 800 00 00 00 00 00 00 00 = V = 0V V 0V V PD MAX (N PACKAGE) AT T A = 0, T J(MAX) = 0 PD MAX (SO PACKAGE) AT T A = 8, T J(MAX) = 0 PD MAX (F PACKAGE) AT T A =, T J(MAX) = PD MAX (F PACKAGE) AT T A =, T J(MAX) = 0 0. 0. 0. 0.8 LOAD (kω) Figure. Device Power Dissipation vs Load at August, 99 90
8 I CC f (%) 0 I(mA) 0 8 8 I REF 8 0 8 0 V CC = (V) 0 0 0 8 T A () Figure. Oscillator Frequency Variation With Voltage (Normalized to = V CC = 0V) T A = Figure. I REF and I CC vs Temperature ( = V CC = 0V) 0 I CC I(mA) 0 I REF 0 0 0 V CC = (V) Figure. I REF and I CC vs Voltage (T A = ) August, 99 90