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RC4152 Datasheet(PDF) 5 Page - Fairchild Semiconductor

Part No. RC4152
Description  Voltage-to-Frequency Converters
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Maker  FAIRCHILD [Fairchild Semiconductor]
Homepage  http://www.fairchildsemi.com
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RC4152 Datasheet(HTML) 5 Page - Fairchild Semiconductor

 
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RC4152
PRODUCT SPECIFICATION
5
Principles of Operation
The RC4152 contains the following components: an open
loop comparator, a precision one-shot timer, a switched volt-
age reference, a switched current source, and an open collec-
tor 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 cur-
rent 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.
Figure 1. Single Supply VFC
4152-04
4152
1
2
3
4
5
6
7
8
+VS
Switched
Current
Source
Switched
Voltage
Reference
Voltage
Reference
Precision
One Shot
Open Collector
Logic Output
Transistor
Open Loop
Comparator
Ground
LOAD
R O
C
O
0.01 F
m
VIN
0 to +10V
C
Integrator
B
R
B
RS
Current Setting Resistor
R
S = 16.7K
R
I
OUT
F
Open Collector Output
OUT
One Shot
Timing
100K


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