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TL/H/7451
LM2907 Tachometer/Speed Switch Building Block Applications AN-162
National Semiconductor
Application Note 162
June 1976
LM2907 Tachometer/Speed
Switch Building Block
Applications
INTRODUCTION
Frequency to voltage converters are available in a number
of forms from a number of sources, but invariably require
significant additional components before they can be put to
use in a given situation. The LM2907, LM2917 series of
devices was developed to overcome these objections. Both
input and output interface circuitry is included on chip so
that a minimum number of additional components is re-
quired to complete the function. In keeping with the systems
building block concept, these devices provide an output
voltage which is proportional to input frequency and provide
zero output at zero frequency. In addition, the input may be
referred to ground. The devices are designed to operate
from a single supply voltage, which makes them particularly
suitable for battery operation.
PART 1ÐGENERAL OPERATION PRINCIPLES
Circuit Description
Referring to
Figure 1,
the family of devices all include three
basic components: an input amplifier with built-in hysteresis;
a charge pump frequency to voltage converter; and a versa-
tile op amp/comparator with an uncommitted output transis-
tor. LM2917 incorporates an active zener regulator on-chip.
LM2907 deletes this option. Both versions are obtainable in
14-pin and in 8-pin dual-in-line molded packages, and to
special order in other packages.
LM2907N-8
TL/H/7451–1
LM2917N-8
TL/H/7451–2
LM2907N
TL/H/7451–3
LM2917N
TL/H/7451–4
FIGURE 1. Block Diagrams
C
1995 National Semiconductor Corporation RRD-B30M115/Printed in U. S. A.
