LM2917 National Semiconductor, LM2917 Datasheet - Page 3

• Manufacturer Part Number: LM2917
• Description: LM2907/LM2917 Frequency to Voltage Converter
• Manufacturer: National Semiconductor

ZENER REGULATOR
Electrical Characteristics
Note 1 For operation in ambient temperatures above 25 C the device must be derated based on a 150 C maximum junction temperature and a thermal resistance
of 101 C W junction to ambient for LM2907-8 and LM2917-8 and 79 C W junction to ambient for LM2907-14 and LM2917-14
Note 2 Hysteresis is the sum
Note 3 V
I
Note 4 Be sure when choosing the time constant R1
maximum value for R1 is limited by the output resistance of pin 3 which is greater than 10 M
Note 5 Nonlinearity is defined as the deviation of V
C1
General Description
The op amp comparator is fully compatible with the ta-
chometer and has a floating transistor as its output This
feature allows either a ground or supply referred load of up
to 50 mA The collector may be taken above V
maximum V
The two basic configurations offered include an 8-pin device
with a ground referenced tachometer input and an internal
connection between the tachometer output and the op amp
non-inverting input This version is well suited for single
speed or frequency switching or fully buffered frequency to
voltage conversion applications
Test Circuit and Waveform
2
Symbol
I
3
e
are the two factors that cause the tachometer gain constant to vary from 1 0
1000 pF R1
OH
is equal to
CE
of 28V
e
68k and C2
Regulator Voltage
Series Resistance
Temperature Stability
TOTAL SUPPLY CURRENT
c
V
a
CC
V
Parameter
TH
b
e
1 V
b
0 22 mFd
(
BE
b
(Continued)
V
V
TH
OL
) offset voltage is their difference See test circuit
is equal to
c
OUT
V
C1 that R1 is such that the maximum anticipated output voltage at pin 3 can be reached with I
CC
(
e
CC
TL H 7942 – 6
pin 3) for f
c
12 V
V
up to a
CC
R
DC
b
DROP
Conditions
1 V
IN
T
A
BE
e
e
e
therefore V
3
5 kHz from a straight line defined by the V
25 C see test circuit (Continued)
470
The more versatile configurations provide differential ta-
chometer input and uncommitted op amp inputs With this
version the tachometer input may be floated and the op
amp becomes suitable for active filter conditioning of the
tachometer output
Both of these configurations are available with an active
shunt regulator connected across the power leads The reg-
ulator clamps the supply such that stable frequency to volt-
age and frequency to current operations are possible with
any supply voltage and a suitable resistor
OH
Tachometer Input Threshold Measurement
b
typically
V
OL
Min
e
V
CC
2 The difference V
7 56
10 5
Typ
a
3 8
1
OUT
OH
1 kHz and V
b
Max
15
6
V
OL
and the mirror gain
OUT
TL H 7942– 7
3 c
mV C
Units
mA
R1 The
10 kHz
V