XR-4151 ...the analog plus Voltage-to-Frequency Converter company TM June 1997-3 FEATURES APPLICATIONS Single Supply Operation (+8V to +22V) Voltage-to-Frequency Conversion Pulse Output Compatible with All Logic Forms A/D and D/A Conversion Programmable Scale Factor (K) Data Transmission Linearity 0.05% Typical-precision Mode Frequency-to-Voltage Conversion Temperature Stability 100% ppm/°C Typical Transducer Interface High Noise Rejection System Isolation Inherent Monotonicity Easily Transmittable Output Simple Full Scale Trim Single-Ended Input, Referenced to Ground Also Provides Frequency-to-Voltage Conversion Direct Replacement for RC/RV/RM-4151 GENERAL DESCRIPTION The XR-4151 is a device designed to provide a simple, low-cost method for converting a DC voltage into a proportional pulse repetition frequency. It is also capable of converting an input frequency into a proportional output voltage. The XR-4151 is useful in a wide range of applications including A/D and D/A conversion and data transmission. ORDERING INFORMATION Part No. Package Operating Temperature Range XR-4151P 8 Lead 300 Mil PDIP -40°C to +85°C XR-4151CP 8 Lead 300 Mil PDIP 0°C to +70°C XR-4151MD 8 Lead 4.4mm EIAJ SOP 0°C to +70°C BLOCK DIAGRAM GND 4 VCC 8 SCFA 2 INPV 7 TRSH 6 CSO 1 Comp One Shot RC Switch 3 OUTL 5 Figure 1. Block Diagram Rev. 2.01 1979 EXAR Corporation, 48720 Kato Road, Fremont, CA 94538 (510) 668-7000 FAX (510) 668-7017 1 XR-4151 PIN CONFIGURATION CSO SCFA OUTL GND 1 8 2 7 3 6 4 5 VCC INPV TRSH RC PIN DESCRIPTION Symbol Type 1 CSO O Current Source Output. 2 SCFA I Scale Factor Input. 3 OUTL O Logic Output. 4 GND Description Supply Ground. 5 RC I One Shot Timing Input. 6 TRSH I Comparator Input. 7 INPV I Input Voltage. 8 VCC O Positive Supply. 1 8 VCC SCFA OUTL GND 2 7 3 6 4 5 INPV TRSH RC 8 Lead SOP (EIAJ, 4.4mm) 8 Lead PDIP (0.300”) Pin # CSO Rev. 2.01 2 XR-4151 ELECTRICAL CHARACTERISTICS Test Conditions: VCC = 15V, TA = +25°C, Unless Otherwise Specified Parameter Min. Max. Typ. Unit 2.0 2.0 2.0 6.0 7.5 7.4 3.5 4.5 4.5 mA mA mA 0.90 0.92 1.10 1.08 1.00 1.00 kHz/V kHz/V Circuit of Figure 2, VI=10V RS=14.0K 100 ppm/°C Circuit of Figure 2, VI=10V 0.9 0.2 0.2 %/V %/V Circuit of Figure 2, VI=1.0V 8V < VCC < 18V Offset Voltage 10 5 mV Offset Current 100 50 nA Supply Current XR-4151MD, CP XR-4151P Conversion Accuracy Scale Factor XR-4151MD, CP XR-4151P Drift With Temperature Drift With VCC XR-4151MD, CP XR-4151P -0.9 Conditions 8V < VCC < 15V 15V < VCC < 22V 15V < VCC < 22V Input Comparator Input Bias Current Common Mode Range1 -300 -100 nA 0 VCC -3 0 to VCC -2 V 0.63 0.70 0.667 xVCC -500 -100 nA 0.5 0.15 V Pin 5= 2.2mA 138.7 µA Pin 1, V=0, RS=14.0kΩ 2.5 1.0 µA Pin 1, V=0V to V=10V One-Shot Threshold Voltage, Pin 5 Input Bias Current, Pin 5 Reset VSAT Current Source Output Current Change With Voltage Off Leakage 50 0.15 nA Pin 1, V=0V 2.08 1.9 V Pin 2 VSAT 0.50 0.15 V Pin 3, 1=3.0mA VSAT 0.30 0.10 V Pin 3, 1=2.0mA Off Leakage 1.0 0.1 µA Reference Voltage 1.70 Logic Output Notes 1 Input Common Mode Range includes ground. Bold face parameters are covered by production test and guaranteed over operating temperature range. Specifications are subject to change without notice Rev. 2.01 3 XR-4151 ABSOLUTE MAXIMUM RATINGS Input Voltage . . . . . . . . . . . . . . . . . . . . . . -0.2V to +VCC Output Short Circuit to Ground . . . . . . . . . Continuous Power Supply . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22V Output Sink Current . . . . . . . . . . . . . . . . . . . . . . . 20mA Internal Power Dissipation . . . . . . . . . . . . . . . . 500mW SYSTEM DESCRIPTION precision switched current source. The voltage comparator compares a positive input voltage applied at pin 7 to the voltage at pin 6. If the input voltage is higher, the comparator will fire the one-shot. The output of the one-shot is connected to both the logic output and the precision switched current source. During the one-shot period, T, the logic output will go low and the current source will turn on with current 1. At the end of the one shot period the logic output will go high and the current source will shut off. At this time the current source has injected an amount of charge Q = IOT into the network RB-CB. If this charge has not increased the voltage VB such that VB > VI, the comparator again fires the one-shot and the current source injects another, Q, into the RB-CB network. This process continues until VB > VI. When this condition is achieved, the current source remains off and the voltage VB decays until VB is again equal to VI. This completes one cycle. The VFC will now run in a steady state mode. The current source charges the capacitor CB at a rate such that VB >VI. Since the discharge rate of capacitor CB is proportional to VB /RB, the frequency at which the system runs will be proportional to the input voltage. The XR-4151 is a precision voltage-to-frequency converter featuring 0.05% conversion linearity (precision mode), high noise rejection, monotonicity, and single supply operation from 8V to 22V. An RC network on Pin 5 gets the maximum full wave frequency. Input voltage on Pin 7 is compared with the voltage on Pin 6 (which is generally controlled by the current source output, Pin 1). Frequency output is proportioned to the voltage on Pin 7. The current source is controlled by the resistance on Pin 2 (nominally 14k with I = 1.9 V/R. The output is an open collector at Pin 3. PRINCIPLES OF OPERATION Single Supply Mode Voltage-to-Frequency Converter In this application, the XR-4151 functions as a stand alone voltage-to-frequency converter operating on a single positive power supply. Refer to the functional block diagram and Figure 2, the circuit connection for single supply voltage-to-frequency conversion. The XR-4151 contains a voltage comparator, a one-shot, and a Rev. 2.01 4 XR-4151 VCC 0.1µF 8 RS 12K CS 2 VL 5K Voltage COMP 100K 7 VI Input SW One Shot 6 RL 5.1K 3 Frequency fo 0.01µF 5 4 Output 1 XR-4151 VCC fo T RO CB 6.8K CO 0.01µF 1µF f0=KVI, Where K=0.486 T=1.1@RO@CO RB 100K RS RB@RO@CO kHz V Figure 2. Voltage-to-Frequency Converter TYPICAL APPLICATIONS Single Supply Voltage-to-Frequency Converter Figure 2 shows the simplest type of VFC that can be made with the XR-4151. The input voltage range is from 0 to +10V, and the output frequency is from 0 to 10kHz. The full scale frequency can be tuned by adjusting RS, the output current set resistor. This circuit has the advantage of being simple and low in cost, but it suffers from inaccuracy due to a number of error sources. Linearity error is typically 1%. A frequency offset will also be introduced by the input comparator offset voltage. Also, response time for this circuit is limited by the passive integration network RBCB. For the component values shown in Figure 2, response time for a step change input from 0 to +10V will be 135msec. For applications which require fast response time and high accuracy, use the circuit of Figure 3. Rev. 2.01 5 XR-4151 Precision Voltage-to-Frequency Converter In this application (Figure 3) the XR-4151 is used with an operational amplifier integrator to provide typical linearity of 0.05% over the range of 0 to -10V. Offset is adjustable to zero. Unlike many VFC designs which lose linearity below 10mV, this circuit retains linearity over the full range of input voltage, all the way to 0V. error due to the current source output conductance is eliminated. The diode connected around the operational amplifier prevents the voltage at pin 7 of the XR-4151 from going below 0. Use a low-leakage diode here, since any leakage will degrade the accuracy. This circuit can be operated from a single positive supply if an XR-3403 ground-sensing operational amplifier is used for the integrator. In this case, the diode can be left out. Note that even though the circuit itself will operate from a single supply, the input voltage is necessarily negative. For operations above 10kHz, bypass pin 6 of the XR-4151 with .01µF. Trim the full scale adjust pot at VI = -10V for an output frequency of 10kHz. The offset adjust pot should be set for 10Hz with an input voltage of -10mV. The operational amplifier integrator improves linearity of this circuit over that of Figure 2 by holding the output of the source, Pin 1, at a constant 0V. Therefore, the linearity VCC 0.1µF RS Full Scale Trim 8 12K CS 2 7 6 VL RL 5.1K comp SW One Shot VCC 5.1K 10K RO VCC 6.8K 5 4 1 Frequency fo 3 XR-4151 CO CI 0.01µF VI Output 2nF VCC RB 1 12 100K 2 100K VEE LM747 VEE Offset Adjust 100K 100K Figure 3. Precision Voltage to Frequency Converter Rev. 2.01 6 1N914 100 25K VCC XR-4151 Frequency-to-Voltage Conversion amplitudes and frequencies. The passive integrator network RBCB filters the current pulses from the pin 1 output. For less output ripple, increase the value of CB. The XR-4151 can be used as a frequency-to-voltage converter. Figure 4 shows the single-supply FVC configuration. With no signal applied, the resistor bias networks tied to pins 6 and 7 hold the input comparator in the off state. A negative going pulse applied to pin 6 (or positive pulse to pin 7) will cause the comparator to fire the one-shot. For proper operation, the pulse width must be less than the period of the one-shot, T = 1.1 R0C0. For a 5Vpp square-wave input the differentiator network formed by the input coupling capacitor and the resistor bias network will provide pulses which correctly trigger the one-shot. An external voltage comparator can be used to “square-up” sinusoidal input signals before they are applied to the XR-4151. Also, the component values for the input signal differentiator and bias network can be altered to accommodate square waves with different For increased accuracy and linearity, use an operational amplifier integrator as shown in Figure 5, the precision FVC configuration. Trim the offset to give -10mV out with 10Hz in and trim the full scale adjust for -10V out with 10kHz in. Input signal conditioning for this circuit is necessary just as for the single supply mode and the scale factor can be programmed by the choice of component values. A tradeoff exists between the amount of output ripple and the response time, through the choice or integration capacitor C1. If C1 = 0.1µF the ripple will be about 100mV. Response time constant τR = RBCI. For RB = 100kΩ and CI = 0.1µF, τR= 10msec. VCC VCC 10K R1 10K R2 C2 0.1µF 8 RS 14K CS 2 VL COMP 7 Frequency Input 6 22nF C1 fI 5V P-P Square Wave R3 10K VCC 3 5 R4 5.1K RL 5.1K SW One Shot 4 1 Pulse fo XR-4151 Output Voltage Output RO CB 6.8K 1µF VO Up to 10V RB 100K 0.01µF CO Design Equations VO = fI/K, Where K=0.486 T = 1.1@RO/CO Figure 4. Frequency to Voltage Converter Rev. 2.01 7 RS RB@RO@CO Hz V XR-4151 Precautions protected from accidental shorts to ground or supply voltages. Permanent damage may occur if the current in pin 2 exceeds 5mA. 1. The voltage applied to comparator input pins 6 and 7 should not be allowed to go below ground by more than 0.3V. 2. Pins 3 and 5 are open-collector outputs. Shorts between these pins and VCC can cause overheating and eventual destruction. 4. Avoid stray coupling between pins 5 and 7; it could cause false triggering. For the circuit of Figure 2, bypass pin 7 to ground with at least 0.01µF. This is necessary for operation above 10kHz. 3. Reference voltage terminal pin 2 is connected to the emitter of an NPN transistor and is held at approximately 1.9V. This terminal should be VCC 0.1µF RS Full Scale Trim 8 12K CS 2 5K VCC VCC Frequency fI Input 0<f1<10kHz COMP 10K 7 10K SW One Shot 6 3 5.1K 5 22nF 10K VCC 4 RO 1 XR-4151 CO 6.8K 0.01µF CI RB 100K 5pF Voltage Output VCC 1 - 100K -10<VO<0 Offset Adjust 25K 100K 100K Figure 5. Precision Frequency-to-Voltage Converter Rev. 2.01 8 VO LM747 VEE VEE 100K 12 2 + VCC XR-4151 Programming the XR-4151 2. T = 0.75 [1/105] = 7.5µsec. The XR-4151 can be programmed to operate with a full scale frequency anywhere from 1.0Hz to 100kHz. In the case of the VFC configuration, nearly any full scale input voltage from 1.0V and up can be tolerated if proper scaling is employed. Here is how to determine component values for any desired full scale frequency. Let R0 = 6.8kΩ and C0 = 0.001µF. 3. CI = 5 x 10-5 [1/105] = 500pF. Op amp slew rate must be at least SR = 135 x 10-6 [1/500pF] = 0.27V/µsec. 1. Set RS = 14kΩ or use a 12K resistor and 5K pot as shown in the figures. (The only exception to this is Figure 3). 4. RB = 10V/100µA = 100kΩ. II. Design a precision VFC with fo = 1Hz and VIO = 10V. 2. Set T = 1.1R0C0 = 0.75[1/fo] where fo is the desired full scale frequency. For optimum performance make 6.8kΩ > R0 > 680kΩ and 0.001µF < C0 < 1.0µF. 2. T = 0.75 [1/1] = 0.75 sec. 3. a) For the circuit of Figure 2 make CB = 10-2 [1/fo] Farads. 3. CI = 5 x 10-5 [1/1]F = 50µF. 1. Let RS = 14.0kΩ. Let R0 = 680kΩ and C0 = 1.0µF. 4. RB = 100kΩ. Smaller values of CB will give a faster response time, but will also increase the frequency offset and nonlinearity. III. Design a single supply FVC to operate with a supply voltage of 9V and full scale input frequency fo = 83.3Hz. The output voltage must reach at least 0.63 of its final value in 200msec. Determine the output ripple. b) For the active integrator circuit make CI = 5 x 10-5 [1/fo] Farads. The operational amplifier integrator must have a slew rate of at least 135 x 10-6 [1/C1] volts per second where the value of C1 is in Farads. 1. Set RS = 14.0kΩ. 2. T = 0.75 [1183.3] = 9msec. Let R0 = 82kΩ and CO = 0.1µF. 4. a) For the circuit of Figure 3 keep the values of RB as shown and use an input attenuator to give the desired full scale input voltage. 3. Since this FVC must operate from 8.0V, we shall make the full scale output voltage at pin 6 equal to 5.0V. b) For the precision mode circuit of Figure 3, set RB = VIO/100µA where VIO is the full scale input voltage. 4. RB = 5V/100µA = 50kΩ. Alternately, the operational amplifier inverting input (summing node) can be used as a current input with the full scale input current IIO = -100µA. 5. Output response time constant is τR 200msec. Therefore, CB τR/RB = (200 x 10-3)/(50 x 103) = 4µF. 5. For the FVC’s, pick the value of CB or CI to give the optimum tradeoff between the response time and output ripple for the particular application. Worst case ripple voltage is VR = (9ms x 135µA)/4µF = 304mV. Design Example I. Design a precision VFC (from Figure 4) with fo = 100kHz and VIO = -10V. 1. Set RS = 14.0kΩ. Rev. 2.01 9 XR-4151 8 3 1 2 6 7 5 4 Figure 6. Equivalent Schematic Diagram Rev. 2.01 10 XR-4151 8 LEAD PLASTIC DUAL-IN-LINE (300 MIL PDIP) Rev. 1.00 8 5 1 4 E1 E D A2 A Seating Plane L α A1 B e INCHES SYMBOL eA eB B1 MILLIMETERS MIN MAX MIN MAX A 0.145 0.210 3.68 5.33 A1 0.015 0.070 0.38 1.78 A2 0.015 0.195 2.92 4.95 B 0.014 0.024 0.36 0.56 B1 0.030 0.070 0.76 1.78 C 0.008 0.014 0.20 0.38 D 0.348 0.430 8.84 10.92 E 0.300 0.325 7.62 8.26 E1 0.240 0.280 6.10 7.11 e 0.100 BSC 2.54 BSC eA 0.300 BSC 7.62 BSC eB 0.310 0.430 7.87 10.92 L 0.115 0.160 2.92 4.06 α 0° 15° 0° 15° Note: The control dimension is the inch column Rev. 2.01 11 C XR-4151 8 LEAD EIAJ SMALL OUTLINE (4.4 mm EIAJ SOP) Rev. 1.00 D 8 5 E 1 H 4 C A2 Seating Plane A α A1 e B L INCHES SYMBOL MILLIMETERS MIN MAX MIN A 0.057 0.071 1.45 1.80 A1 0.002 0.008 0.05 0.20 A2 0.055 0.063 1.40 1.60 B 0.012 0.020 0.30 0.50 C 0.004 0.008 0.10 0.20 D 0.193 0.201 4.90 5.10 E 0.169 0.177 4.30 4.50 e 0.050 BSC MAX 1.27 BSC H 0.236 0.252 6.00 6.40 L 0.012 0.030 0.30 0.76 α 0° 10° 0° 10° Note: The control dimension is the millimeter column Rev. 2.01 12 XR-4151 Notes Rev. 2.01 13 XR-4151 Notes Rev. 2.01 14 XR-4151 Notes Rev. 2.01 15 XR-4151 NOTICE EXAR Corporation reserves the right to make changes to the products contained in this publication in order to improve design, performance or reliability. EXAR Corporation assumes no responsibility for the use of any circuits described herein, conveys no license under any patent or other right, and makes no representation that the circuits are free of patent infringement. Charts and schedules contained herein are only for illustration purposes and may vary depending upon a user’s specific application. While the information in this publication has been carefully checked; no responsibility, however, is assumed for inaccuracies. EXAR Corporation does not recommend the use of any of its products in life support applications where the failure or malfunction of the product can reasonably be expected to cause failure of the life support system or to significantly affect its safety or effectiveness. Products are not authorized for use in such applications unless EXAR Corporation receives, in writing, assurances to its satisfaction that: (a) the risk of injury or damage has been minimized; (b) the user assumes all such risks; (c) potential liability of EXAR Corporation is adequately protected under the circumstances. Copyright 1979 EXAR Corporation Datasheet June 1997 Reproduction, in part or whole, without the prior written consent of EXAR Corporation is prohibited. Rev. 2.01 16