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RC4152
Voltage-to-Frequency Converters
Features
* * * * * * * * * * * 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
* Signal isolation: - VFC--opto-isolaton--FVC - ADC with opto-isolation * Signal encoding: - FSK modulation/demodulation - Pulse-width modulation * Frequency scaling * DC motor speed control
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. 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.
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
Functional Block Diagram
4152
Switched Current Source Output Switched Reference Output Open Collector Output
1
Switched Current Source
Voltage Reference Open Loop Comparator
8 -VS
2
Switched Voltage Reference
7
Comparator Inputs
3
Precision One Shot
6
Ground
4
Open Collector Logic Output Transistor
4152-01
5
One Shot Timing
Rev. 1.0.1
PRODUCT SPECIFICATION
RC4152
Pin Assignments
IOUT 1 RS 2 FOUT 3 GND 4 8 +VS 7 VIN 6 VTH 5 CO
4152-02
Pin Descriptions
Pin 1 2 3 4 5 6 7 8 Function Switched Current Source Output (IOUT) Switched Voltage Reference (RS) Logic Output (Open Collector) (FOUT) Ground (GND) One-Shot R, C Timing (CO) Threshold (VTH) Input Voltage (VlN) +VS
Absolute Maximum Ratings
Parameter Supply Voltage Internal Power Dissipation Input Voltage Output Sink Current (Frequency Output) Output Short Circuit to Ground Storage Temperature Range Operating Temperature Range RC4152 RV4152N 0 -25 +70 +85 C C -65 -0.2 Min. Typ. Max. +22 500 +VS 20 Continuous +150 C Units V mW V mA
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 Max. Junction Temp. Max. PD TA<50C Therm. Res qJC Therm. Res qJC For TA>50C Derate at +125C 468 mW -- 160C/W 6.25 mW/C Small Outline SO-8 +125C 300mW -- 240C/W 4.17mW/C
2
RC4152
PRODUCT SPECIFICATION
Electrical Characteristics
(VS = +15V, and TA = +25C unless otherwise noted) Parameters Power Supply Requirements (Pin 8) Supply Current Supply Voltage Input Comparator (Pins 6 and 7) VOS Input Bias Current Input Offset Current Input Voltage Range One Shot (Pin 5) Threshold Voltage Input Bias Current Saturation Voltage Drift of Timing vs. Temperature2 I = 2.2 mA T = 75 ms over the specified temperature range 1)1 RS = 16.7K over specified temperature range Off State Pin 1 = 0V to +10V 1.0 2.0 over specified temperature range ISINK = 3 mA ISINK = 10 mA Off State 1.0 Hz to 10 kHz FOUT = 10 kHz, over specified temperature range +138 50 0.10 1.0 2.5 2.25 50 0.1 0.8 0.1 0.007 75 1.0 0.05 150 2.5 100 0.5 50 100 mA ppm/C %/V nA mA V ppm/C V V mA % ppm/C 0.65 0.67 -50 0.1 30 100 0.69 -500 0.5 50 VS nA V ppm/C ppm/V 0 2.0 -50 30 VS-2 10 -300 100 VS-3 mV nA nA V VS = +15V +7.0 2.5 +15 6.0 +18 mA V Test Conditions Min. Typ. Max. Units
Timing Drift vs. Supply Voltage Switched Current Source (pin Output Current Drift vs. Temperature2 Drift vs. Supply Voltage Leakage Current Compliance Reference Voltage (Pin 2) VREF Drift vs. Temperature2 Logic output (Pin 3) Saturation Voltage Leakage Current Nonlinearity Error (Voltage Sourced Circuit of Figure 3) Temperature Drift (Voltage Sourced Circuit of Figure 3) Voltage2
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
10 KHz Current-Sourced VFC Nonlinearity vs. Input Voltage +0.01 +0.005 NL (% Error) 0 -0.005 -0.01 -0.015 0 1 2 3 4 5 VIN (V) 6 7 8 9 10 NL (% Error) +0.06 +0.03 0 -0.03 -0.06 -0.09 0 1 2 3 4 5 VIN (V) 6 7 8 9 10 100 KHz Current-Sourced VFC Nonlinearity vs. Input Voltage
10 KHz Voltage-Sourced VFC Nonlinearity vs. Input Voltage +0.01 +0.005 NL (% Error) NL (% Error) 0 -0.005 -0.01 -0.015 0 1 2 3 4 5 VIN (V) 10 KHz Precision VFC Nonlinearity vs. Input Frequency +0.01 +0.005 NL (% Error) NL (% Error) 0 -0.005 -0.01 -0.015 0 1 2 3 4 5 6 7 8 9 10 +0.12 +0.08 +0.04 0 -0.04 -0.08 0 1 6 7 8 9 10 +0.10 +0.05 0 -0.05 -0.10 -0.15 0 1
100 KHz Voltage-Sourced VFC Nonlinearity vs. Input Voltage
2
3
4
5 VIN (V)
6
7
8
9
10
100 KHz Precision VFC Nonlinearity vs. Input Frequency
2
3
4
5
6
7
8
9
10
FIN (kHz)
FIN (kHz)
4
4152-03
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 I OUT RB Switched Current Source
4152 1
Voltage Reference Open Loop Comparator +VS
8
100K V IN 0 to +10V
2
RS Current Setting Resistor RS = 16.7K
Switched Voltage Reference
7
0.01 m F
3
Precision One Shot
6
RO
R LOAD
Ground
4
F OUT
Open Collector Output
Open Collector Logic Output Transistor
5
CO
One Shot Timing
4152-04
Figure 1. Single Supply VFC
5
PRODUCT SPECIFICATION
RC4152
Applications
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. 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 DC to 10 kHz DC to 100 kHz
1 T = ------------F OUT TP V IN ----------- = I OUT ----T RB V REF I OUT = ------------RS where TP = 1.1 R O C O
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
CI 0.05 mF
RB 100 kW
0 to -10V 0 to 1.0 kHz 0.1 KHz/V 6.8 kW 0.1 mF 0 to -10V 0 to 10 kHz 1.0 KHz/V 6.8 kW 0.01 mF
0.005 mF 100 kW 100 kW
0 to -10V 0 to 100 kHz 10 KHz/V 6.8 kW 0.001 mF 500 pF
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 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.
RO 6.8 kW 6.8 kW 6.8 kW
CO 0.1 mF 0.01 mF 0.001 mF
RB 100 kW 100 kW 100 kW
CB 10 mF 10 mF 10 mF
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.
Precision Current Sourced VFC
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. 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.
Single Supply FVC
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.
6
RC4152
PRODUCT SPECIFICATION
CI 0.005 mF 1N914 -VS +VS V IN 0 to -10V RB 100K 2 3 1 R S = 16.7K R B+ 100 k W 4 7 OP-27 RL 10k W 6 8 100W
+VL
Offset Adjust
RL 5.1K 2 FOUT Output Frequency 0 FO 10kHz
+VS +VS
1 3 I OUT +V 8 FOUT R S S 4152 4 Gnd 7 VFC VTH VIN CO 5 CO 0.01 mF 6 5k W +VS RO 6.8 k W
10 k W
1 mF
4152-05
Figure 2. Precision Current Sourced VFC
CI 0.005 mF 1N914 -V S +VS V IN 0 to -10V RB 100K 3 1 R S = 16.7K RB+ 100 k W +VS +VS 1 2 IOUT R S 3 +VS 8 FOUT 4152 4 VFC 7 Gnd CO VTH VIN 6 5 RZ 10k W 2 4 7 6 8 100W
OP-27
Offset Adjust
+VL RL 5.1K FOUT Output Frequency 0 FOUT 10kHz
10 k W
CO 0.01 mF
5 kW +VS RO 6.8 k W
1 mF
4152-06
Figure 3. Precision Voltage Sourced VFC
7
PRODUCT SPECIFICATION
RC4152
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. 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
Precision FVC
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.
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 0 to 1.0 kHz 0 to 10 kHz
CIN 0.02 mF
RO
CO
RB
CB
Ripple
6.8 kW 0.1 mF
100 kW 100 mF 1.0 mV 100 kW 10 mF 1.0 mV 1.0 mV
0.002 mF 6.8 kW 0.01 mF
0 to 100 kHz 200 pF
6.8 kW 0.001 mF 100 kW 1.0 mF
+15V 10 k W 10Y k W C IN 0.022 mF FIN Frequency Input 0 FIN 10kHz 10 k W +15V RB 100K V OUT CB 10 mF
4152-07
RO 6.8 kW
CO 0.01 m F 5 CO
7 VIN 6V TH +VS 5 kW 8 4152 VFC I OUT 1
Gnd
4
F OUT 3 RS 2
R S = 16.7K
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 5.0 VP-P Squarewave VIN 5 C O Gnd 4 3 4152 VFC 6 FOUT VTH I OUT R S +VS 1 2 8 5 kW R S = 16.7K 10 k W +15V CI 5 pF -VS +VS 4 2 7 6 OP-27 3 8 RB 100 k W 1 RZ 10 kW RB 100 k W CO 0.01 mF
100W VOUT Voltage Output -10V V O 0
Offset Adjust
+VS
4152-08
9
10
(3) (8) +VS Q41 M N S X U Q40 T Q32 I OUT (1) Q33 2K 3.6K 2K (2) RS Q27 Q26 6.2K 2K Q22 Q21 (6) VTH V IN Q1 (7) Q2 Q3 Q4 Q12 10K Q13 Q14 Q15 10K Q5 Q6 Q7 Q8 2K Q9 2K 2K Q10 Q11 Q17 Q16 Q18 Q19 Q20 10K (4) Gnd Q25 2K -VS 7.8K Q30 Q23 12K D39 D29 6.3V Q34 Q42 Q38 D43 Q35 15K Q36 Q37 Q28 Z Y R W FoUT V CO (5) 4152-09
PRODUCT SPECIFICATION RC4152
Schematic Diagram
RC4152
PRODUCT SPECIFICATION
Notes:
11
PRODUCT SPECIFICATION
RC4152
Ordering Information
Part Number RC4152N RC4152M RV4152N
Notes: N = 8-lead plastic DIP M = 8-lead plastic SOIC
Package N M N
Operating Temperature Range 0C to +70C 0C to 70C -25C to +85C
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.
www.fairchildsemi.com 6/25/98 0.0m 003 Stock#DS30004152 O 1998 Fairchild Semiconductor Corporation
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.

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