ST2100 datasheet(31/39 Pages) STMICROELECTRONICS

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ST2100

Clocking parameters

This section details clock related electrical specifications.

6.1

Master clock (MCLK)

The external circuit for generating the clock from a crystal oscillator is shown in Figure 4.

Figure 4. MCLK crystal connections

1. CL1 and CL2 are the load capacitors.

The value of the capacitors depends on the type of the selected crystal. To calculate the

value of the load capacitance, use Equation 1.

For this example, an Aker C2E-24.000-12-3030-X 24 MHz oscillator has been used.

Load capacitance CL:

Equation 1

CL = (CL1 × CL2 / CL1 + CL2) + CS

Where CL1 and CL2 are the load capacitors and CS is the circuit's stray capacitance.

In our application this implies:

Equation 2

CL1 = CL2 = Cext

Equation 3

Cext = (CL - CS) × 2

Example

For the Aker® C2E-24.000-12-3030-X crystal:

CL = 12 PF; with CS = 3 PF, Cext = CL1 = CL2 = 18 PF.

Note:

The ESR of the used quartz must be < 50

.

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