XC888LM datasheet(82/144 Pages) INFINEON

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XC886/888CLM

Functional Description

Data Sheet

V0.9, 2006-12

Table 25 shows the VCO range for the XC886/888.

3.8.1

Recommended External Oscillator Circuits

The oscillator circuit, a Pierce oscillator, is designed to work with both, an external crystal

oscillator or an external stable clock source. It basically consists of an inverting amplifier

and a feedback element with XTAL1 as input, and XTAL2 as output.

When using a crystal, a proper external oscillator circuitry must be connected to both

pins, XTAL1 and XTAL2. The crystal frequency can be within the range of 4 MHz

to 12 MHz. Additionally, it is necessary to have two load capacitances

X1 and CX2, and

depending on the crystal type, a series resistor

X2, to limit the current. A test resistor RQ

may be temporarily inserted to measure the oscillation allowance (negative resistance)

of the oscillator circuitry.

Q values are typically specified by the crystal vendor. The CX1

and

X2 values shown in Figure 25 can be used as starting points for the negative

resistance evaluation and for non-productive systems. The exact values and related

operating range are dependent on the crystal frequency and have to be determined and

optimized together with the crystal vendor using the negative resistance method.

Oscillation measurement with the final target system is strongly recommended to verify

the input amplitude at XTAL1 and to determine the actual oscillation allowance (margin

negative resistance) for the oscillator-crystal system.

When using an external clock signal, the signal must be connected to XTAL1. XTAL2 is

left open (unconnected).

The oscillator can also be used in combination with a ceramic resonator. The final

circuitry must also be verified by the resonator vendor.Figure 25 shows the

recommended external oscillator circuitries for both operating modes, external crystal

mode and external input clock mode.

Table 25

VCO Range

VCOmin

VCOmax

VCOFREEmin

VCOFREEmax

Unit

150

200

MHz

100

150

MHz

XC888LM Datasheet(PDF) 82 Page - Infineon Technologies AG

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