www.fairchildsemi.com RC4152 Voltage-to-Frequency Converters Features • • • • • • • • • • • • Signal isolation: – VFC—opto-isolaton—FVC – ADC with opto-isolation • Signal encoding: – FSK modulation/demodulation – Pulse-width modulation • Frequency scaling • DC motor speed control Single supply operation Pulse output DTL/TTL/CMOS compatible Programmable scale factor (K) High noise rejection Inherent monotonicity Easily transmittable output Simple full scale trim Single-ended input, referenced to ground V-F or F-V conversion Voltage or current input Wide dynamic range Description The RC4152 is a monolithic circuit containing all of the active components needed to build a complete voltage-tofrequency converter. Circuits that convert a DC voltage to a pulse train can be built by adding a few resistors and capacitors to the internal comparator, one-shot, voltage reference, and switched current source. Frequency-to-voltage converters (FVCs) and many other signal conditioning circuits are also easily created using these converters. Applications • • • • • • • Precision voltage-to-frequency converters Pulse-width modulators Programmable pulse generators Frequency-to-voltage converters Integrating analog-to-digital converters Long-term analog integrators Signal conversion: – Current-to-Frequency – Temperature-to-Frequency – Pressure-to-Frequency – Capacitance-to-Frequency – Frequency-to-Current The RC4151 was the first monolithic VFC available and offers guaranteed temperature and accuracy specifications. The converter is available in a standard 8-pin plastic DIP. Functional Block Diagram 4152 Switched Current Source Output 1 Switched Reference Output 2 Open Collector Output 3 Switched Current Source Voltage Reference 8 -VS Open Loop Comparator Switched Voltage Reference 7 Comparator Inputs 6 Precision One Shot Ground 4 5 Open Collector Logic Output Transistor One Shot Timing 4152-01 Rev. 1.0.1 PRODUCT SPECIFICATION RC4152 Pin Assignments Pin Descriptions Pin Function 8 +VS 1 Switched Current Source Output (IOUT) RS 2 7 VIN 2 Switched Voltage Reference (RS) 3 FOUT 3 6 VTH Logic Output (Open Collector) (FOUT) 4 Ground (GND) GND 4 5 CO 5 One-Shot R, C Timing (CO) 6 Threshold (VTH) 7 Input Voltage (VlN) 8 +VS IOUT 1 4152-02 Absolute Maximum Ratings Parameter Min. Typ. Supply Voltage Internal Power Dissipation Input Voltage -0.2 Output Sink Current (Frequency Output) Output Short Circuit to Ground Max. Units +22 V 500 mW +VS V 20 mA Continuous Storage Temperature Range -65 +150 °C 0 +70 °C -25 +85 °C Operating Temperature Range RC4152 RV4152N Note: 1. “Absolute maximum ratings” are those beyond which the safety of the device cannot be guaranteed. They are not meant to imply that the device should be operated at these limits. If the device is subjected to the limits in the absolute maximum ratings for extended periods, its reliability may be impaired. The tables of Electrical Characteristics provides conditions for actual device operation. Thermal Characteristics 8-Lead Plastic DIP Small Outline SO-8 Max. Junction Temp. +125°C +125°C Max. PD TA<50°C 468 mW 300mW Therm. Res qJC — — Therm. Res qJC 160°C/W 240°C/W 6.25 mW/°C 4.17mW/°C For TA>50°C Derate at 2 RC4152 PRODUCT SPECIFICATION Electrical Characteristics (VS = +15V, and TA = +25°C unless otherwise noted) Parameters Test Conditions Min. Typ. Max. Units 2.5 6.0 mA +15 +18 V VOS ±2.0 ±10 mV Input Bias Current -50 -300 nA Input Offset Current ±30 ±100 nA 0 VS-2 VS-3 V 0.65 0.67 0.69 VS -50 -500 nA I = 2.2 mA 0.1 0.5 V T = 75 ms over the specified temperature range ±30 ±50 ppm/°C Power Supply Requirements (Pin 8) Supply Current VS = +15V Supply Voltage +7.0 Input Comparator (Pins 6 and 7) Input Voltage Range One Shot (Pin 5) Threshold Voltage Input Bias Current Saturation Voltage Drift of Timing vs. Temperature2 Timing Drift vs. Supply Voltage Switched Current Source (pin Output Current Drift vs. ±100 ppm/V +138 mA 1)1 RS = 16.7K Temperature2 ±50 over specified temperature range Drift vs. Supply Voltage ±100 0.10 Leakage Current Off State Compliance Pin 1 = 0V to +10V 1.0 1.0 2.5 2.0 ppm/°C %/V 50 nA mA Reference Voltage (Pin 2) VREF 2.25 2.5 V Drift vs. Temperature2 over specified temperature range ±50 ±100 ppm/°C Logic output (Pin 3) Saturation Voltage ISINK = 3 mA 0.1 0.5 V ISINK = 10 mA 0.8 Leakage Current Off State 0.1 1.0 mA 0.007 0.05 % ±75 ±150 ppm/°C Nonlinearity Error (Voltage Sourced Circuit of Figure 3) Voltage2 Temperature Drift (Voltage Sourced Circuit of Figure 3) 1.0 Hz to 10 kHz FOUT = 10 kHz, over specified temperature range V Notes: 1. Temperature coefficient of output current source (pin 1 output) exclusive of reference voltage drift. 2. Guaranteed but not tested. 3 PRODUCT SPECIFICATION RC4152 Typical Performance Characteristics 100 KHz Current-Sourced VFC Nonlinearity vs. Input Voltage +0.01 +0.06 +0.005 +0.03 NL (% Error) NL (% Error) 10 KHz Current-Sourced VFC Nonlinearity vs. Input Voltage 0 -0.005 -0.01 0 -0.03 -0.06 -0.015 -0.09 0 1 2 3 4 5 6 7 8 9 10 0 1 2 3 4 +0.01 +0.10 +0.005 +0.05 0 -0.005 7 8 9 10 8 9 10 9 10 0 -0.05 -0.10 -0.01 -0.15 -0.015 0 1 2 3 4 5 6 7 8 9 10 0 1 2 3 4 VIN (V) 5 6 7 VIN (V) 10 KHz Precision VFC Nonlinearity vs. Input Frequency 100 KHz Precision VFC Nonlinearity vs. Input Frequency +0.01 +0.12 +0.005 +0.08 0 -0.005 +0.04 0 4152-03 NL (% Error) NL (% Error) 6 100 KHz Voltage-Sourced VFC Nonlinearity vs. Input Voltage NL (% Error) NL (% Error) 10 KHz Voltage-Sourced VFC Nonlinearity vs. Input Voltage -0.04 -0.01 -0.015 -0.08 0 1 2 3 4 5 6 FIN (kHz) 4 5 VIN (V) VIN (V) 7 8 9 10 0 1 2 3 4 5 6 FIN (kHz) 7 8 RC4152 PRODUCT SPECIFICATION Principles of Operation The RC4152 contains the following components: an open loop comparator, a precision one-shot timer, a switched voltage reference, a switched current source, and an open collector logic output transistor. These functional blocks are internally interconnected. Thus, by adding some external resistors and capacitors, a designer can create a complete voltage-to-frequency converter. The comparator’s output controls the one-shot (monostable timer). The one-shot in turn controls the switched voltage reference, the switched current source and the open collector output transistor. The functional block diagram shows the components and their interconnection. To detail, if the voltage at pin 7 is greater than the voltage at pin 6, the comparator switches and triggers the one-shot. When the one-shot is triggered, two things happen. First, the one-shot begins its timing period. Second, the one-shot’s output turns on the switched voltage reference, the switched current source and the open collector output transistor. The one-shot creates its timing period much like the popular 555 timer does, by charging a capacitor from a resistor tied to +VS. The one-shot senses the voltage on the capacitor (pin 5) and ends the timing period when the voltage reaches 2/3 of the supply voltage. At the end of the timing period, the capacitor is discharged by a transistor similar to the open collector output transistor. Meanwhile, during the timing period of the one-shot, the switched current source, the switched voltage reference, and the open collector output transistor all will be switched on. The switched current source (pin 1) will deliver a current proportional to both the reference and an external resistor, RS. The switched reference (pin 2) will supply an output voltage equal to the internal reference voltage (2.25V). The open collector output transistor we be turned on, forcing the logic output (pin 3) to a low state. At the end of the timing period all of these outputs will turn off. The switched voltage reference has produced an off-on-off voltage pulse, the switched current source has emitted a quanta of charge, and the open collector output has transmitted a logic pulse. To summarize, the purpose of the circuit is to produce a current pulse, well-defined in amplitude and duration, and to simultaneously produce an output pulse which is compatible with most logic families. The circuit's outputs show a pulse waveform in response to a voltage difference between the comparators inputs. Integrator CB 4152 I OUT 1 RB 2 RS Current Setting Resistor RS = 16.7K Switched Current Source Voltage Reference +VS 8 Open Loop Comparator Switched Voltage Reference 3 Ground FOUT 4 V IN 0.01 m F 0 to +10V 6 Precision One Shot R LOAD 100K 7 Open Collector Logic Output Transistor RO One Shot Timing 5 CO Open Collector Output 4152-04 Figure 1. Single Supply VFC 5 PRODUCT SPECIFICATION RC4152 Applications 1 T = ------------F OUT Single Supply VFC The stand-alone voltage-to-frequency converter is one of the simplest applications for the RC4152. This application uses only passive external components to create the least expensive VFC circuit (see Figure 1). The positive input voltage VIN is applied to the input comparator through a low pass filter. The one-shot will fire repetitively and the switched current source will pump out current pulses of amplitude VREF/RS and duration 1.1 ROCO into the integrator. Because the integrator is tied back to the inverting comparator input, a feedback loop is created. The pulse repetition rate will increase until the average voltage on the integrator is equal to the DC input voltage at pin 7. The average voltage at pin 6 is proportional to the output frequency because the amount of charge in each current pulse is precisely controlled. TP V IN ----------- = I OUT -----T RB where TP = 1.1 R O C O V REF I OUT = ------------RS By rearranging and substituting, V IN R S 1 F OUT = ------------- ------- ----------------------V REF R B 1.1R O C O Recommended component values for different operating frequencies are shown in the table below. Range Input VIN Output FO Scale Factor RO CO 0 to -10V 0 to 1.0 kHz 0.1 KHz/V 6.8 kW 0.1 mF Because the one-shot firing frequency is the same as the open collector output frequency, the output frequency is directly proportional to VIN. The external passive components set the scale factor. For best linearity, RS should be limited to a range of 12 kW to 20 kW The reference voltage is nominally 2.25V for the RC4152. Recommended values for different operating frequencies are shown in the table below. Operating Range DC to 1.0 kHz RO CO RB CB 6.8 kW 0.1 mF 100 kW 10 mF DC to 10 kHz 6.8 kW 0.01 mF 100 kW 10 mF DC to 100 kHz 6.8 kW 0.001 mF 100 kW 10 mF 0 to -10V 0 to 10 kHz 1.0 KHz/V 6.8 kW 0.01 mF CI 0.05 mF RB 100 kW 0.005 mF 100 kW 0 to -10V 0 to 100 kHz 10 KHz/V 6.8 kW 0.001 mF 500 pF 100 kW The graphs shown under Typical Performance Characteristics show nonlinearity versus input voltage for the precision current sourced VFC. The best linearity is achieved by using an op amp having greater than 1.0 V/ms slew rate, but any op amp can be used. Precision Voltage Sourced VFC This circuit is identical to the current sourced VFC, except that the current pulses into the integrator are derived directly from the switched voltage reference. This improves temperature drift at the expense of high frequency linearity. The single supply VFC is recommended for uses where dynamic range of the input is limited, and the input does not reach 0V. With 10 kHz values, nonlinearity will be less than 1.0% for a 10 mV to 10V input range, and response time will be about 135 ms. The switched current source (pin 1) output has been tied to ground, and RS has been put in series between the switched voltage reference (pin 2) and the summing node of the op amp. This eliminates temperature drift associated with the switched current source. The graphs under the Typical Performance Characteristics show that the nonlinearity error is worse at high frequency, when compared with the current sourced circuit. Precision Current Sourced VFC Single Supply FVC This circuit operates similarly to the single supply VFC, except that the passive R-C integrator has been replaced by an active op amp integrator. This increases the dynamic range down to 0V, improves the response time, and eliminates the nonlinearity error introduced by the limited compliance of the switched current source output. A frequency-to-voltage converter performs the exact opposite of the VFCs function; it converts an input pulse train into an average output voltage. Incoming pulses trigger the input comparator and fire the one-shot. The one-shot then dumps a charge into the output integrator. The voltage on the integrator becomes a varying DC voltage proportional to the frequency of the input signal. Figure 4 shows a complete single supply FVC. The integrator algebraically sums the positive current pulses from the switched current source with the current VIN/RB. To operate correctly, the input voltage must be negative, so that when the circuit is balanced, the two currents cancel. 6 RC4152 PRODUCT SPECIFICATION CI 0.005 mF 1N914 -VS +VS RB 100K V IN 0 to -10V 4 2 7 3 R S = 16.7K R B+ 100 k W RL 5.1K 8 RL 10k W 1 +VL 100W 6 OP-27 Offset Adjust +VS +VS 2 FOUT Output Frequency 0 FO 10kHz 1 3 I OUT +V 8 FOUT R S S 4152 4 Gnd 7 VFC VTH VIN CO 10 k W 6 5 5k W CO 0.01 mF 1 mF +VS RO 6.8 k W 4152-05 Figure 2. Precision Current Sourced VFC CI 0.005 mF 1N914 -V S +VS V IN 0 to -10V RB 100K 4 2 R S = 16.7K RZ 10k W RB+ 100 k W Output Frequency 0 FOUT 10kHz 100W Offset Adjust +VS +VL FOUT 6 8 3 1 RL 5.1K 7 OP-27 +VS 1 2 IOUT R S 3 +VS 8 FOUT 4152 4 VFC 7 Gnd CO VTH VIN 6 5 CO 0.01 mF 10 k W 5 kW 1 mF +VS RO 6.8 k W 4152-06 Figure 3. Precision Voltage Sourced VFC 7 PRODUCT SPECIFICATION RC4152 Precision FVC The input waveform must have fast slewing edges, and the differentiated input signal must be less than the timing period of the one-shot, 1.1 ROCO. A differentiator and divider are used to shape and bias the trigger input; a negative going pulse at pin 6 will cause the comparator to fire the one-shot. The input pulse amplitude must be large enough to trip the comparator, but not so large as to exceed the ICs input voltage ratings. Linearity, offset and response time can be improved by adding one or more op amps to form an active lowpass filter at the output. A circuit using a single pole active integrator is shown in Figure 5. The positive output current pulses are averaged by the inverting integrator, causing the output voltage to be negative. Response time can be further improved by adding a double pole filter to replace the single pole filter. Refer to the graphs under Typical Performance Characteristics that show nonlinearity error versus input frequency for the precision FVC circuit. The output voltage is directly proportional to the input frequency: 1.1R O C O R B V REF V OUT = --------------------------------------------- F IN ( Hz ) RS Output ripple can be minimized by increasing CB, but this will limit the response time. Recommended values for various operating ranges are shown in the following table. Input Operating Rage CIN RO CO 0 to 1.0 kHz 0.02 mF 0 to 10 kHz 0.002 mF 6.8 kW 0.01 mF 0 to 100 kHz 200 pF 6.8 kW 0.1 mF RB CB Ripple 100 kW 100 mF 1.0 mV 100 kW 10 mF 1.0 mV 6.8 kW 0.001 mF 100 kW 1.0 mF 1.0 mV +15V RO 6.8 kW 10 k W CO 0.01 m F 10Ÿ k W C IN 0.022 mF FIN Frequency Input 0 FIN 5 7 VIN CO 4152 VFC 6 V TH +VS 5 kW 8 Gnd 4 F OUT 3 RS I OUT 1 2 10kHz 10 k W +15V RB 100K V OUT R S = 16.7K CB 10 mF 4152-07 Figure 4. Single Supply FVC 8 RC4152 PRODUCT SPECIFICATION RO 6.8 k W +15V 10 k W 10 k W 7 CIN 0.022 mF FIN Frequency Input 0 FO 10kHz CO 0.01 mF 5 C O Gnd 4 3 4152 VFC 6 FOUT VTH I OUT R S +VS 1 2 8 5 kW VIN R S = 16.7K 5.0 VP-P Squarewave 10 k W +15V CI RB 100 k W 5 pF -VS +VS 4 2 7 6 OP-27 3 8 RB 100 k W 1 RZ 10 kW +VS 100W Offset Adjust VOUT Voltage Output -10V V O 0 4152-08 9 10 Q35 Q36 (7) (6) (2) (1) Q5 V IN VTH RS I OUT +VS (8) Q6 Q1 Q33 Q34 Q7 Q2 15K 2K Q26 6.2K Q4 Q8 Q25 Q27 7.8K 2K Q3 Q30 3.6K Q37 Q28 Q9 M Q41 Z Q10 N 2K Q22 Q23 R FoUT 2K 2K Q32 2K 2K Q11 Q21 Y (3) Q17 S Q16 Q12 (5) Q13 CO Q18 D29 6.3V X T Q19 Q14 U Q20 Q42 Q40 V Q15 Q38 12K W -VS Gnd 4152-09 (4) 10K 10K 10K D39 D43 PRODUCT SPECIFICATION RC4152 Schematic Diagram RC4152 PRODUCT SPECIFICATION Notes: 11 PRODUCT SPECIFICATION RC4152 Ordering Information Part Number Package Operating Temperature Range RC4152N N 0°C to +70°C RC4152M M 0°C to 70°C RV4152N N -25°C to +85°C Notes: N = 8-lead plastic DIP M = 8-lead plastic SOIC LIFE SUPPORT POLICY FAIRCHILD’S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT DEVICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT OF FAIRCHILD SEMICONDUCTOR CORPORATION. As used herein: 1. Life support devices or systems are devices or systems which, (a) are intended for surgical implant into the body, or (b) support or sustain life, and (c) whose failure to perform when properly used in accordance with instructions for use provided in the labeling, can be reasonably expected to result in a significant injury of the user. 2. A critical component in any component of a life support device or system whose failure to perform can be reasonably expected to cause the failure of the life support device or system, or to affect its safety or effectiveness. www.fairchildsemi.com 6/25/98 0.0m 003 Stock#DS30004152 Ó 1998 Fairchild Semiconductor Corporation