Epson C I - 4 5 Manual do Utilizador descarregar pdf (Página 5)

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The buffer inverter makes a reverse phase three times internally, therefore the output waveform will have some distortion.

Also, the buffer has more gain than the unbuffer, causing a higher drive level.

2.2. Determining the preliminary values

There is no general value for the oscillation circuit because the value must be changed due to the IC characteristics, printed

pattern layout, oscillation frequency, etc. In the case of a regular inverter, such as the TC74HCU04P, the following parameters

will generally assure suitable operation. If the IC has some built-in device, please choose each parameter close to the

following values:

Preliminary Parameters Rf [M

Ω

] Rd[k

Ω

] Cg [pF] Cd[pF]

20 to 60 [KHz] 20 500 10 10

60 to 165 [KHz] 10 300 10 10

5.5 to 24 [MHz] 1 0.5 10 10

A more exact value will be found with actual data from the circuit evaluation.

2.3. Useful board design for the evaluation

There are some parts positions that are useful for the evaluation even for parts that will not be used. Figure 2.3 shows five (5)

positions A, B, C, D1 and D2 which will be used for additional devices during the evaluation. The following explains the

purpose of these positions:

A: Used for putting a resistor in series with the crystal.

With this, measurement of oscillation allowance will

be easy.

B: Used for putting a resistor in series to increase Rf

if the device has a built - in Rf

C: Used for putting a resister in series to increase

Rd if the device has a built - in Rd.

D1, D2: Used for putting capacitors in parallel to increase

Cg and Cd if the device has them.

The printed patterns for these are shown bellow the circuit.

For A, B and C the line should continue through and will be

cut when the resistors are added.

Epson C I - 4 5 Manual do Utilizador Página 5