74aup1z125 NXP Semiconductors, 74aup1z125 Datasheet - Page 20

• Manufacturer Part Number: 74aup1z125
• Description: Low-power X-tal Driver With Enable And Internal Resistor
• Manufacturer: NXP Semiconductors

Philips Semiconductors
74AUP1Z125_1
Product data sheet
13.1.1 Design
Figure 12
circuit is basically a Pierce oscillator circuit in which the crystal is operating at its
fundamental frequency and is tuned by the parallel load capacitance of C
C
drive-limiting resistor and is set to approximately the same value as the reactance of C
the crystal frequency (R
rail-to-rail output of X2. This keeps the drive level into the crystal within drive specifications
(the designer should verify this). Overdriving the crystal can cause damage.
The internal 1 M resistor provides negative feedback and sets a bias point of the inverter
near mid-supply, operating the 74AUP1GU04 in the high gain linear region.
To calculate the values of C
C
capacitance of the circuit (for the 74AUP1Z125 this is equal to an input capacitance
of 5 pF).
Fig 11. Average I
C
2
L
are in series with the crystal. They should be approximately equal. R
L
is the load capacitance as specified by the crystal manufacturer, C
(1) (a) = resonance
(2) (b) = anti-resonance
(3) (c) = load resonance
=
C
-------------------
C
(a)
(b)
(c)
1
1
shows the recommended way to connect a crystal to the 74AUP1Z125. This
+
C
L
C
C
2
2
+
C
C
C
CC
C
0
0
0
s
C
as a function of V
L
Rev. 01 — 3 August 2006
1
= X
C
R
C
R
C
R
L
L
L
1
1
1
1
1
1
1
1
1
1
C1
and C
Low-power X-tal driver with enable and internal resistor
). This will result in an input to the crystal of 50 % of the
+
0
+
0
+
0
2
, the designer can use the formula:
CC
R
1
R
L
f
r
f r
f
L
f
L
R
p
© Koninklijke Philips Electronics N.V. 2006. All rights reserved.
f
f
a
a
f
74AUP1Z125
a
resistance
resistance
resistance
reactance
reactance
reactance
s
is the stray
1
1
is the
and C
mnb104
f
f
f
2
. C
20 of 27
1
and
1
at