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| XR-4151 ...the analog plus company TM Voltage-to-Frequency Converter June 1997-3 FEATURES D Single Supply Operation (+8V to +22V) D Pulse Output Compatible with All Logic Forms D Programmable Scale Factor (K) D Linearity $0.05% Typical-precision Mode D Temperature Stability $100% ppm/C Typical D High Noise Rejection D Inherent Monotonicity D Easily Transmittable Output D Simple Full Scale Trim D Single-Ended Input, Referenced to Ground D Also Provides Frequency-to-Voltage Conversion D 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 ORDERING INFORMATION Part No. XR-4151P XR-4151CP XR-4151MD APPLICATIONS D Voltage-to-Frequency Conversion D A/D and D/A Conversion D Data Transmission D Frequency-to-Voltage Conversion D Transducer Interface D System Isolation voltage. The XR-4151 is useful in a wide range of applications including A/D and D/A conversion and data transmission. Package 8 Lead 300 Mil PDIP 8 Lead 300 Mil PDIP 8 Lead 4.4mm EIAJ SOP Operating Temperature Range -40C to +85C 0C to +70C 0C to +70C BLOCK DIAGRAM GND 4 VCC SCFA 8 2 INPV TRSH CSO 7 6 1 RC Comp One Shot Switch 3 OUTL 5 Figure 1. Block Diagram Rev. 2.01 E1979 EXAR Corporation, 48720 Kato Road, Fremont, CA 94538 z (510) 668-7000 z FAX (510) 668-7017 1 XR-4151 PIN CONFIGURATION CSO SCFA OUTL GND 1 2 3 4 8 7 6 5 VCC INPV TRSH RC CSO SCFA OUTL GND 1 2 3 4 8 7 6 5 VCC INPV TRSH RC 8 Lead PDIP (0.300") 8 Lead SOP (EIAJ, 4.4mm) PIN DESCRIPTION Pin # 1 2 3 4 5 6 7 8 Symbol CSO SCFA OUTL GND RC TRSH INPV VCC I I I O Type O I O Description Current Source Output. Scale Factor Input. Logic Output. Supply Ground. One Shot Timing Input. Comparator Input. Input Voltage. Positive Supply. Rev. 2.01 2 XR-4151 ELECTRICAL CHARACTERISTICS Test Conditions: VCC = 15V, TA = +25C, Unless Otherwise Specified Parameter 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 Input Comparator Offset Voltage Offset Current Input Bias Current Common Mode Range1 One-Shot Threshold Voltage, Pin 5 Input Bias Current, Pin 5 Reset VSAT Current Source Output Current Change With Voltage Off Leakage Reference Voltage Logic Output VSAT VSAT Off Leakage 0.50 0.30 1.0 0.15 0.10 0.1 V V A Pin 3, 1=3.0mA Pin 3, 1=2.0mA 1.70 2.5 50 2.08 138.7 1.0 0.15 1.9 A A nA V Pin 1, V=0, RS=14.0k Pin 1, V=0V to V=10V Pin 1, V=0V Pin 2 0.63 0.70 -500 0.5 0.667 -100 0.15 xVCC nA V Pin 5= 2.2mA 0 10 $100 -300 VCC -3 5 $50 -100 0 to VCC -2 mV nA nA V Min. 2.0 2.0 2.0 0.90 0.92 Max. 6.0 7.5 7.4 1.10 1.08 Typ. 3.5 4.5 4.5 1.00 1.00 $100 0.2 0.2 Unit mA mA mA kHz/V kHz/V ppm/C %/V %/V Conditions 8V < VCC < 15V 15V < VCC < 22V 15V < VCC < 22V Circuit of Figure 2, VI=10V RS=14.0K Circuit of Figure 2, VI=10V Circuit of Figure 2, VI=1.0V 8V < VCC < 18V -0.9 0.9 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 Power Supply . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22V Output Sink Current . . . . . . . . . . . . . . . . . . . . . . . 20mA Internal Power Dissipation . . . . . . . . . . . . . . . . 500mW Input Voltage . . . . . . . . . . . . . . . . . . . . . . -0.2V to +VCC Output Short Circuit to Ground . . . . . . . . . Continuous SYSTEM DESCRIPTION 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 14kW 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 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. Rev. 2.01 4 XR-4151 VCC 0.1F RS 12K 5K Voltage VI Input 0.01F 5 RO VCC 6.8K CO 0.01F CB 1F RB 100K 4 1 100K COMP 7 6 One Shot SW RL 5.1K 3 Frequency fo Output 2 CS 8 VL XR-4151 fo T f0=KVI, Where K=0.486 T=1.1@RO@CO 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. 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 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 .01F. VCC 0.1F RS Full Scale Trim 12K 2 CS RL 5.1K One Shot RO 6.8K 0.01F VI RB 100K 2 1 12 5 CO VCC 4 SW 3 Frequency fo 8 VL 7 6 VCC 5.1K 10K VCC comp 1 XR-4151 Output CI 2nF 1N914 100 LM747 VEE Offset Adjust 25K VCC 100K VEE 100K 100K Figure 3. Precision Voltage to Frequency Converter Rev. 2.01 6 XR-4151 Frequency-to-Voltage Conversion 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 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. 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 = 0.1F the ripple will be about 100mV. Response time constant R = RBCI. For RB = 100k and CI = 0.1F, R= 10msec. VCC VCC R1 C2 0.1F 8 10K 10K R2 RS 14K 2 COMP CS VL RL 5.1K 3 Frequency Input fI 5V P-P Square Wave 22nF C1 R3 10K R4 5.1K VCC 7 6 One Shot 5 4 SW Pulse fo Output Voltage Output 1 XR-4151 RO 6.8K 0.01F CO CB 1F RB 100K VO Up to 10V Design Equations VO = fI/K, Where K=0.486 T = 1.1@RO/CO RS RB@RO@CO Hz V Figure 4. Frequency to Voltage Converter Rev. 2.01 7 XR-4151 Precautions 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. 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 protected from accidental shorts to ground or supply voltages. Permanent damage may occur if the current in pin 2 exceeds 5mA. 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 0.01F. This is necessary for operation above 10kHz. VCC 0.1F RS Full Scale Trim 12K 5K VCC VCC Frequency fI Input 0 CI RB 5pF VCC 1 12 100K VO -10 LM747 Figure 5. Precision Frequency-to-Voltage Converter Rev. 2.01 8 XR-4151 Programming the XR-4151 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. 1. Set RS = 14k or use a 12K resistor and 5K pot as shown in the figures. (The only exception to this is Figure 3). 2. Set T = 1.1R0C0 = 0.75[1/fo] where fo is the desired full scale frequency. For optimum performance make 6.8k > R0 > 680k and 0.001F < C0 < 1.0F. 3. a) For the circuit of Figure 2 make CB = 10-2 [1/fo] Farads. Smaller values of CB will give a faster response time, but will also increase the frequency offset and nonlinearity. 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. 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. b) For the precision mode circuit of Figure 3, set RB = VIO/100A where VIO is the full scale input voltage. Alternately, the operational amplifier inverting input (summing node) can be used as a current input with the full scale input current IIO = -100A. 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. Design Example I. Design a precision VFC (from Figure 4) with fo = 100kHz and VIO = -10V. 1. Set RS = 14.0k. 2. T = 0.75 [1/105] = 7.5sec. Let R0 = 6.8k and C0 = 0.001F. 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/sec. 4. RB = 10V/100A = 100k. II. Design a precision VFC with fo = 1Hz and VIO = 10V. 1. Let RS = 14.0k. 2. T = 0.75 [1/1] = 0.75 sec. Let R0 = 680k and C0 = 1.0F. 3. CI = 5 x 10-5 [1/1]F = 50F. 4. RB = 100k. 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. 1. Set RS = 14.0k. 2. T = 0.75 [1183.3] = 9msec. Let R0 = 82k and CO = 0.1F. 3. Since this FVC must operate from 8.0V, we shall make the full scale output voltage at pin 6 equal to 5.0V. 4. RB = 5V/100A = 50k. 5. Output response time constant is R 200msec. Therefore, CB R/RB = (200 x 10-3)/(50 x 103) = 4F. Worst case ripple voltage is VR = (9ms x 135A)/4F = 304mV. 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 1 D A L 5 4 E1 E A2 A1 Seating Plane eA eB C B e B1 INCHES SYMBOL A A1 A2 B B1 C D E E1 e eA eB L MIN 0.145 0.015 0.015 0.014 0.030 0.008 0.348 0.300 0.240 MAX 0.210 0.070 0.195 0.024 0.070 0.014 0.430 0.325 0.280 MILLIMETERS MIN 3.68 0.38 2.92 0.36 0.76 0.20 8.84 7.62 6.10 MAX 5.33 1.78 4.95 0.56 1.78 0.38 10.92 8.26 7.11 0.100 BSC 0.300 BSC 0.310 0.115 0 0.430 0.160 15 2.54 BSC 7.62 BSC 7.87 2.92 0 10.92 4.06 15 Note: The control dimension is the inch column Rev. 2.01 11 XR-4151 8 LEAD EIAJ SMALL OUTLINE (4.4 mm EIAJ SOP) Rev. 1.00 D 8 1 5 E 4 H C Seating Plane A1 e B L A2 A INCHES SYMBOL A A1 A2 B C D E e H L MIN 0.057 0.002 0.055 0.012 0.004 0.193 0.169 MAX 0.071 0.008 0.063 0.020 0.008 0.201 0.177 MILLIMETERS MIN 1.45 0.05 1.40 0.30 0.10 4.90 4.30 MAX 1.80 0.20 1.60 0.50 0.20 5.10 4.50 0.050 BSC 0.236 0.012 0 0.252 0.030 10 1.27 BSC 6.00 0.30 0 6.40 0.76 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 |
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