H838532H datasheet(112/508 Pages) RENESAS

112 / 508 page

Section 4 Clock Pulse Generators

Rev. 1.00 May 30, 2008 Page 92 of 484

REJ09B0436-0100

4.5

Note on Oscillators

Oscillator characteristics are closely related to board design and should be carefully evaluated by

the user, referring to the examples shown in this section. Oscillator circuit constants will differ

depending on the oscillator element, stray capacitance in its interconnecting circuit, and other

factors. Suitable constants should be determined in consultation with the oscillator element

manufacturer. Design the circuit so that the oscillator element never receives voltages exceeding

its maximum rating.

(Vss)

TEST

OSC1

OSC2

Vss

P17

Figure 4.10 Example of Crystal and Ceramic Oscillator Element Arrangement

Figure 4.11 (1) shows an example measuring circuit with the negative resistance suggested by the

oscillator manufacturer. Note that if the negative resistance of the circuit is less than that suggested

by the oscillator manufacturer, it may be difficult to start the main oscillator.

If it is determined that oscillation is not occurring because the negative resistance is lower than the

level suggested by the oscillator manufacturer, the circuit may be modified as shown in figure 4.11

(2) through (4). Which of the modification suggestions to use and the capacitor capacitance should

be decided based upon an evaluation of factors such as the negative resistance and the frequency

deviation.

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