Specifications

transients may be anticipated, a blocking diode may be con-
nected in the power supply line to the IC as illustrated in
Figure 7(d). During these negative transients, the diode D1
will be reverse biased and prevent reverse currents flowing
in the IC. If these transients are short and the capacitor C1
is large enough, then the power to the IC can be sustained.
This is useful to prevent change of state or change of
charge in in systems connected to it.
Temperature Ranges and Packaging Considerations
The LM2907, LM2917 series devices are specified for oper-
ation over the temperature range
b
40
§
Cto
a
85
§
C.
The devices are normally packaged in molded epoxy, dual-
in-line packages. Other temperature ranges and other pack-
ages are availabe to special order. For reliability require-
ments beyond those of normal commercial application
where the cost of military qualification is not bearable, other
programs are available such as B
a
.
PART IIÐAPPLICATIONS
INTRODUCTION
The LM 2907, LM2917 series devices were designed not
only to perform the basic frequency to voltage function re-
quired in many systems, but also to provide the input and
output interface so often needed, so that low cost imple-
mentations of complete functions are available.
The concept of building blocks requires that a function be
performed in the same way as it can be mathematically de-
fined. In other words, a frequency to voltage converter will
provide an output voltage proportional to frequency which is
independent of the input voltage or other input parameters,
except the frequency. In the same way, the output voltage
will be zero when the input frequency is zero. These fea-
tures are built into the LM2907.
Applications for the device range from simple speed switch
for anti-pollution control device functions in automobiles, to
motor speed controls in industrial applications. The applica-
tions circuits which follow are designed to illustrate some of
the capabilities of the LM2907. In most cases, alternative
input or output configurations can be mixed and matched at
will and other variations can be determined from the de-
scription in Part I of this application note. For complete
specifications, refer to the data sheet.
Speed Switches
Perhaps the most natural application of the LM2907 is in
interfacing with magnetic pickups, such as the one illustrat-
ed in
Figure 8 to perform speed switching functions. As an
example, New York taxies are required to change the inten-
sity of the warning horn above and below 45 mph. Other
examples include an over-speed warning, where a driver
may set the desired maximum speed and have an audible
TL/H/7451–23
FIGURE 8. Typical Magnetic Pickup
TL/H/7451–24
TL/H/7451–25
FIGURE 9. Simple Speed Switch Load is Energized
when f
IN
l
1
2C1R1
FIGURE 10. RC Selection Chart
8