GMS77C1001 datasheet(34/44 Pages) HYNIX

34 / 44 page

GMS77C1000/GMS77C1001

July. 2001 Ver. 1.1

cy is a function of the supply voltage, the resistor(R) and

capacitor(C) values, and the operating temperature.

In addition, the oscillator frequency will vary from unit to

unit due to normal manufacturing process variations. Fur-

thermore, the difference in lead frame capacitance between

package types also affects the oscillation frequency, espe-

cially for low C values. The external R and C component

tolerances contribute to oscillator frequency variation as

well.

The user also needs to take into account variation due to

tolerance of external R and C components used.

Figure 13-3 shows how the R is connected to the

GMS77C100X. For Rext values below 2.2 k

Ω, the oscilla-

tor operation may become unstable, or stop completely.

For very high Rext values (e.g., 1 M

Ω) the oscillator be-

comes sensitive to noise, humidity and leakage. Thus, we

recommend keeping Rext between 3 k

Ω and 100 kΩ. Ta-

ble 13-3 shows recommended value of Rext and Cext.

Although the oscillator will operate with no external ca-

pacitor (Cext = 0 pF), it is recommend using values above

20 pF for noise and stability reasons. With no or small ex-

ternal capacitance, the oscillation frequency can vary dra-

matically due to changes in external capacitances, such as

PCB trace capacitance or package lead frame capacitance.

The Electrical Specifications sections show R frequency

variation from part to part due to normal process variation.

Also, see the Electrical Specifications sections for variation of os-

cillator frequency due to VDD for given Rext/Cext values as well

as frequency variation due to operating temperature for given R,

C, and VDD values.

The oscillator frequency, divided by 4, is available on the

XOUT pin, and can be used for test purposes or to synchro-

nize other logic.

Cext

Rext

Average FXIN @ 5V, 25°C

0pF

3.3K

10K

100K

7.48MHz

6.36MHz

4.04MHz

529KHz

20pF

3.3K

10K

100K

4.60MHz

3.62MHz

2.14MHz

249KHz

100pF

3.3K

10K

100K

1.75MHz

1.31MHz

734KHz

80KHz

300pF

3.3K

10K

100K

702KHz

510KHz

283KHz

30KHz

TABLE 13-3 RC OSCILLATION FREQUENCIES

FIGURE 13-3 RC OSCILLATION MODE

Rext

Internal

VDD

XIN

XOUT

Clock

FXIN/4

Cext

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