AN_6612_007
78M6612 Hardware Design Guidelines
Rev 2
17
6 Timing Reference
This section is both a design and troubleshooting guide for using the low-power crystal oscillator interface
on the 78M6612.
The 78M6612 typically uses a crystal oscillator as the clock source. Another option is to use an external
canned oscillator. The main advantages of a crystal oscillator are frequency accuracy, stability, low cost,
high reliability, and low power consumption.
To avoid common problems with crystal oscillators and to achieve high reliability, it is important to pay
attention to the components and their values, and the layout. This section shows how these elements
affect such factors as stability, temperature variation, start-up time, and noise immunity. It also contains
suggestions for solving problems in these areas.
6.1 Oscillator Connections and Components Selection
Figure 18 shows the recommended connection of the crystal oscillator.
XIN
XOUT
C1
C2
32.768 kHz
Y1
Figure 19: 78M6612 Crystal Oscillator Connection
Typical values for C1 and C2 are 27 pF for a crystal load capacitance value of 12.5 pF.
The crystal output (XOUT) driver strength is internally limited to reduce the power dissipation.
