Voltage-to-Frequency and Frequency-to-Voltage CONVERTER

Size: px

Start display at page:

Download "Voltage-to-Frequency and Frequency-to-Voltage CONVERTER"

Stephen Atkinson
5 years ago
Views:

1 Voltage-to-Frequency and Frequency-to-Voltage CONVERTER FEATURES OPERATION UP TO 00kHz EXCELLENT LINEARITY ±0.0% max at 0kHz FS ±0.0% max at 00kHz FS V/F OR F/V CONVERSION MONOTONIC VOLTAGE OR CURRENT INPUT APPLICATIONS INTEGRATING A/D CONVERTER SERIAL FREQUEY OUTPUT ISOLATED DATA TRANSMISSION FM ANALOG SIGNAL MOD/DEMOD MOTOR SPEED CONTROL TACHOMETER R 0kΩ 0nF film T DESCRIPTION The voltage-to-frequency converter provides an output frequency accurately proportional to its input voltage. The digital open-collector frequency output is compatible with all common logic families. Its integrating input characteristics give the excellent noise immunity and low nonlinearity. Full-scale output frequency is determined by an external capacitor and resistor and can be scaled over a wide range. The can also be configured as a frequency-to-voltage converter. The is available in -pin plastic DIP, SO- surface-mount, and metal TO-00 packages. Commercial, industrial, and military temperature range models are available. Pull-Up Voltage 0V V PU +V CC +V.kΩ V PU 8mA 0 to 0V 0 to 0kHz Pinout shown is for DIP or SOIC packages. C 3.3nF NPO Ceramic International Airport Industrial Park Mailing Address: PO Box 00 Tucson, AZ 83 Street Address: 630 S. Tucson Blvd. Tucson, AZ 806 Tel: (20) 6- Twx: Cable: BBRCORP Telex: FAX: (20) Immediate Product Info: (800) Burr-Brown Corporation PDS-32F Printed in U.S.A. September, 993

2 SPECIFICATIONS At T A = +2 C and V CC = ±V, unless otherwise noted. KP, KU BM SM PARAMETER CONDITIONS MIN TYP MAX MIN TYP MAX MIN TYP MAX UNITS INPUT (V/F CONVERTER) F OUT = /. R C Voltage Range () Positive >0 +0.2mA * * * * V x R Negative >0 0 * * * * V Current Range () > * * * * ma Bias Current Inverting * * * * na Noninverting * * * * na Offset Voltage (2) * * * * mv Differential Impedance * * * * kω pf Common-mode Impedance * * * * MΩ pf INPUT (F/V CONVERTER) V OUT =. R C F IN Impedance * * * * kω pf Logic +.0 * * * * V Logic * * * * V Pulse-width Range 0. 0k/F MAX * * * * µs ACCURACY Linearity Error (3) 0.0Hz Oper Freq 0kHz ±0.00 ±0.00 () * * * * % of FSR () 0.Hz Oper Freq 00kHz ±0.02 ±0.0 * * * * % of FSR 0.Hz Oper Freq 00kHz ±0.0 * * % of FSR Offset Error Offset Votlage (2) * * * * mv Offset Drift (6) ±3 * * ppm of FSR/ C Gain Error (2) * * % of FSR Gain Drift (6) f = 0kHz ± ±0 ±00 ±0 ±0 ppm/ C Full Scale Drift f = 0kHz ± ±0 ±00 ±0 ±0 ppm of FSR/ C (offset drift and gain drift) (6, ) Power Supply f = DC, ±V CC = 2VDC Sensitivity to 8VDC ±0.0 * * % of FSR/% OUTPUT (V/F CONVERTER) (open collector output) Voltage, Logic 0 I SINK = 8mA * * * * * * V Leakage Current, Logic V O = V * * * * µa Voltage, Logic External Pull-up Resistor Required (see Figure ) V PU * * V Pulse Width For Best Linearity 0.2/F MAX * * s Fall Time I OUT = ma, C LOAD = 00pF 00 * * ns OUTPUT (F/V CONVERTER) V OUT Voltage I O ma 0 to +0 * * V Current V O VDC +0 * * ma Impedance Closed Loop * * Ω Capacitive Load Without Oscillation 00 * * pf DYNAMIC RESPONSE Full Scale Frequency 00 (8) * * khz Dynamic Range 6 * * decades Settling Time (V/F) to Specified Linearity for a Full Scale Step (9) * * Overload Recovery < 0% Overload (9) * * POWER SUPPLY Rated Voltage ± V Voltage Range ± ±20 * V Quiescent Current ±. ±6.0 * * * ma TEMPERATURE RANGE Specification C Operating C Storage C * Specification the same as KP. NOTES: () A 2% duty cycle (0.2mA input current) is recommended for best linearity. (2) Adjustable to zero. See Offset and Gain Adjustment section. (3) Linearity error is specified at any operating frequency from the straight line intersecting 90% of full scale frequency and 0.% of full scale frequency. See Discussion of Specifications section. Above 200kHz, it is recommended all grades be operated below +8 C. () ±0.0% of FSR for negative inputs shown in Figure. Positive inputs are shown in Figure. () FSR = Full Scale Range (corresponds to full scale frequency and full scale input voltage). (6) Exclusive of external components drift. () Positive drift is defined to be increasing frequency with increasing temperature. (8) For operations above 200kHz up to 00kHz, see Discussion of Specifications and Installation and Operation sections. (9) One pulse of new frequency plus µs. 2

3 ABSOLUTE MAXIMUM RATINGS Supply Voltage... ±22V Output Sink Current (F OUT )... 0mA Output Current (V OUT ) mA Voltage,... ±Supply Voltage, +... ±Supply Comparator... ±Supply Storage Temperature Range: BM, SM... 6 C to +0 C KP, KU... 2 C to +8 C PACKAGE INFORMATION PACKAGE DRAWING MODEL PACKAGE NUMBER () KP -Pin Plastic DIP 00 BM TO-00 Metal 00 SM TO-00 Metal 00 KU SO- SOI3 NOTE: () For detailed drawing and dimension table, please see end of data sheet, or Appendix D of Burr-Brown IC Data Book. ORDERING INFORMATION MODEL PACKAGE TEMPERATURE RANGE KP -Pin Plastic DIP 0 C to 0 C BM TO-00 Metal 2 C to +8 C SM TO-00 Metal C to +2 C KU SO- SOIC 0 C to +0 C PIN CONFIGURATIONS Top View In 2 +In M Package (TO-00) 0 Amp V OUT 9 +V CC In 2 P Package U Package (Epoxy Dual-in-line) Amp 3 +In V OUT V CC (Case) 3 Capacitor Switch One- shot 6 8 Common Comparator 3 V CC Capacitor 6 Switch One- shot V CC Common Comparator = no internal connection External connection permitted. The information provided herein is believed to be reliable; however, BURR-BROWN assumes no responsibility for inaccuracies or omissions. BURR-BROWN assumes no responsibility for the use of this information, and all use of such information shall be entirely at the user s own risk. Prices and specifications are subject to change without notice. No patent rights or licenses to any of the circuits described herein are implied or granted to any third party. BURR-BROWN does not authorize or warrant any BURR-BROWN product for use in life support devices and/or systems. 3

4 TYPICAL PERFORMAE CURVES At T A = +2 C and V CC = ±V, unless otherwise noted. Typical Linearity Error (% of FSR) LINEARITY ERROR vs FULL SCALE FREQUEY Duty Cycle = 2% at Full Scale T A = +2 C Linearity Error (Hz) LINEARITY ERROR vs OPERATING FREQUEY f FULL SCALE = 0kHz, 2% Duty Cycle T A = +2 C 0.00 k 0k 00k M.0 0 k 2k 3k k k 6k k 8k 9k 0k Full Scale Frequency (Hz) Operating Frequency (Hz) Full Scale Temp Drift (ppm of FSR/ C) FULL SCALE DRIFT vs FULL SCALE FREQUEY (SM, KP, KU) (BM) 0 k 0k 00k Full Scale Frequency (Hz) M

5 APPLICATION INFORMATION Figure shows the basic connection diagram for frequencyto-voltage conversion. R sets the input voltage range. For a 0V full-scale input, a 0kΩ input resistor is recommended. Other input voltage ranges can be achieved by changing the value of R. V R = FS 0.2mA () R should be a metal film type for good stability. Manufacturing tolerances can produce approximately ±0% variation in output frequency. Full-scale output frequency can be trimmed by adjusting the value of R see Figure 3. The full-scale output frequency is determined by C. Values shown in Figure are for a full-scale output frequency of 0kHz. Values for other full-scale frequencies can be read from Figure 2. Any variation in C tolerance, temperature drift, aging directly affect the output frequency. Ceramic NPO or silver-mica types are a good choice. For full-scale frequencies above 200kHz, use larger capacitor values as indicated in Figure 2, with R = 20kΩ. The value of the integrating capacitor,, does not directly influence the output frequency, but its value must be chosen within certain bounds. Values chosen from Figure 2 produce approximately 2.Vp-p integrator voltage waveform. If s value is made too low, the integrator output voltage can exceed its linear output swing, resulting in a nonlinear response. Using values larger than shown in Figure 2 is acceptable. Accuracy or temperature stability of is not critical because its value does not directly affect the output frequency. For best linearity, however, should have low leakage and low dielectric absorption. Polycarbonate and other film capacitors are generally excellent. Many ceramic types are adequate, but some low-voltage ceramic capacitor types may degrade nonlinearity. Electrolytic types are not recommended. FREQUEY OUTPUT PIN The frequency output terminal is an open-collector logic output. A pull-up resistor is usually connected to a V logic supply to create standard logic-level pulses. It can, however, be connected to any power supply up to +V CC. Output pulses have a constant duration and positive-going during the oneshot period. Current flowing in the open-collector output transistor returns through the Common terminal. This terminal should be connected to logic ground. f O T R 0kΩ 0nF film T Pull-Up Voltage 0V V PU +V CC +V.kΩ V PU 8mA 0 to 0V 0 to 0kHz Pinout shown is for DIP or SOIC packages. C 3.3nF NPO Ceramic FIGURE. Voltage-to-Frequency Converter Circuit.

6 FREQUEY-TO-VOLTAGE CONVERSION Figure shows the connected as a frequency-tovoltage converter. The capacitive-coupled input network C 3, R 6 and R allow standard V logic levels to trigger the comparator input. The comparator triggers the one-shot on the falling edge of the frequency input pulses. Threshold voltage of the comparator is approximately 0.V. For frequency input waveforms less than V logic levels, the R 6 /R voltage divider can be adjusted to a lower voltage to assure that the comparator is triggered. The value of C is chosen from Figure 2 according to the full-scale input frequency. smooths the output voltage waveform. Larger values of reduce the ripple in the output voltage. Smaller values of allow the output voltage to settle faster in response to a change in input frequency. Resistor R can be trimmed to achieve the desired output voltage at the full-scale input frequency. PRIIPLES OF OPERATION The operates on a principle of charge balance. The signal input current is equal to /R. This current is integrated by input op amp and, producing a downward ramping integrator output voltage. When the integrator output ramps to the threshold of the comparator, the one-shot is triggered. The ma reference current is switched to the integrator input during the one-shot period, causing the integrator output ramp upward. After the one-shot period, the integrator again ramps downward. The oscillation process forces a long-term balance of charge (or average current) between the input signal current and the reference current. The equation for charge balance is: I IN = I R(AVERAGE) (2) R = f O t OS (ma) (3) Capacitor Value 0nF nf 00pF 0pF k 33,000pF C = 30pF f FS (khz) R = 0kΩ Above 200kHz Full-Scale 66,000pF C = 30pF f FS (khz) R = 20kΩ 0k 00k Full Scale Frequency (Hz) M Where: f O is the output frequency t OS is the one-shot period, equal to t OS = 00 C (Farads) () The values suggested for R and C are chosen to produce a 2% duty cycle at full-scale frequency output. For full-scale frequencies above 200kHz, the recommended values produce a 0% duty cycle. FIGURE 2. Capacitor Value Selection. T +V Gain Trim 0kΩ 3kΩ kΩ f O 0MΩ Offset Trim 00kΩ ma Pinout shown is for DIP and SOIC packages. C 33nF FIGURE 3. Gain and Offset Voltage Trim Circuit. 6

7 2.V 0V 0V 0 to 0kHz 00pF 2kΩ 2.V f IN V Logic 2.2kΩ R 0kΩ V O 0 to 0V 00kΩ 0MΩ C 3.3nF FIGURE. Frequency-to-Voltage Converter Circuit. 2nF +V to 0kHz 0V to 0V R 0kΩ Nonlinearity may be higher than specified due to common-mode voltage on op amp input. C 60pF Pinout shown is for DIP or SOIC package. FIGURE. V/F Converter Negative Voltage.

Voltage-to-Frequency and Frequency-to-Voltage CONVERTER

Voltage-to-Frequency and Frequency-to-Voltage CONVERTER FEATURES OPERATION UP TO 500kHz EXCELLENT LINEARITY ±0.0% max at 0kHz FS ±0.05% max at 00kHz FS V/F OR F/V CONVERSION MONOTONIC VOLTAGE OR CURRENT