Datasheet

S0340-01
XI XO
R
1
C
L2
C
L1
TLK105
TLK106
SLLSEB8A –AUGUST 2012–REVISED MARCH 2013 www.ti.com
7.2.2 Crystal
The use of a 25MHz, parallel, 20pF-load crystal is recommended if a crystal source is desired. Figure 7-2
shows a typical connection for a crystal resonator circuit. The load capacitor values will vary with the
crystal vendors; check with the vendor for the recommended loads.
The oscillator circuit is designed to drive a parallel-resonance AT-cut crystal with a minimum drive level of
100μW and a maximum of 500μW. If a crystal is specified for a lower drive level, a current limiting resistor
must be placed in series between XO and the crystal.
As a starting point for evaluating an oscillator circuit, if the requirements for the crystal are not known, set
the values for C
L1
and C
L2
at 33pF, and R
1
should be set at 0Ω. Specifications for a 25MHz crystal are
listed in Table 7-3.
Figure 7-2. Crystal Oscillator Circuit
Table 7-1. 25MHz Oscillator Specification
PARAMETER TEST CONDITIONS MIN TYP MAX UNIT
Frequency 25 MHz
Frequency Tolerance Operational Temperature ±50 ppm
Frequency Stability 1 year aging ±50 ppm
Rise / Fall Time 10%–90% 8 nsec
Jitter (Short term) Cycle-to-cycle 50 psec
Jitter (Long term) Accumulative over 10 ms 1 nsec
Symmetry Duty Cycle 40% 60%
Load Capacitance 15 30 pF
Table 7-2. 50MHz Oscillator Specification
PARAMETER TEST CONDITIONS MIN TYP MAX UNIT
Frequency 50 MHz
Frequency Tolerance Operational Temperature ±50 ppm
Frequency Stability 1 year aging ±50 ppm
Rise / Fall Time 10%–90% 6 nsec
Jitter (Short term) Cycle-to-cycle 50 psec
Jitter (Long term) Accumulative over 10 ms 1 nsec
Symmetry Duty Cycle 40% 60%
Table 7-3. 25MHz Crystal Specification
PARAMETER TEST CONDITIONS MIN TYP MAX UNIT
Frequency 25 MHz
Frequency Tolerance Operational Temperature ±50 ppm
At 25°C ±50 ppm
Frequency Stability 1 year aging ±5 ppm
Load Capacitance 10 40 pF
36 Design Guidelines Copyright © 2012–2013, Texas Instruments Incorporated
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