SN74LVC1404_07 Datasheet, PDF (8/17 Pages) Texas Instruments – OSCILLATOR DRIVER FOR CRYSTAL OSCILLATOR OR CERAMIC RESONATOR

SN74LVC1404
OSCILLATOR DRIVER
FOR CRYSTAL OSCILLATOR OR CERAMIC RESONATOR
SCES469D – AUGUST 2003 – REVISED JANUARY 2007
APPLICATION INFORMATION
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Figure 3 shows a typical application of the SN74LVC1404 in a Pierce oscillator circuit. The output voltage can
be conditioned further by connecting OSCOUT to the Schmitt-trigger input inverter. The Schmitt-trigger input
inverter produces a rail-to-rail voltage waveform. The recommended load for the crystal, shown in this example,
is 16 pF. The value of the recommended load (C_L) can be found in the crystal manufacturer's data sheet. Values
of
C₁
and
C₂
are
chosen
so
that
C
L
+
C₁C₂
C₁ ) C
2
and
C₁
≈
C₂.
R_s
is
the
current-limiting
resistor,
and
the
value
depends on the maximum power dissipation of the crystal. Generally, the recommended value of R_s is specified
in the crystal manufacturer's data sheet and, usually, this value is approximately equal to the reactance of C₂ at
resonance
frequency,
i.e.,
R_s
+
XC
2
.
R_F
is
the
feedback
resistor
that
is
used
to
bias
the
inverter
in
the
linear
region of operation. Usually, the value is chosen to be within 1 MΩ to 10 MΩ.
CTRL⁽¹⁾
XIN
XOUT
R_F ≅ 2.2 MΩ
OSCOUT
C_LOAD
R_LOAD
C₁ ≅ 32 pF
C_L ≅ 16 pF
R_s ≅ 1 kΩ
C₂ ≅ 32 pF
A
Optional Signal-Conditioning Stage
Y
C_LOAD
R_LOAD
A) Logic Diagram View
(1) CTRL should be tied to logic high during normal operation of the oscillator circuit. To disable the oscillator circuit, connect CTRL to logic low.
Figure 3. Oscillator Circuit
8
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