COP8CCR9IMT7SLASHNOPB datasheet(30/111 Pages) TI1

30 / 111 page

COP8CBR9, COP8CCR9, COP8CDR9

SNOS535I – OCTOBER 2000 – REVISED MARCH 2013

www.ti.com

5.8.1

Oscillator

CKI is the clock input while G7/CKO is the clock generator output to the crystal. An on-chip bias resistor

connected between CKI and CKO is provided to reduce system part count. The value of the resistor is in

the range of 0.5M to 2M (typically 1.0M). Table 5-1 shows the component values required for various

standard crystal values. Resistor R2 is on-chip, for the high speed oscillator, and is shown for reference.

Figure 5-6 and Figure 5-6 shows the crystal oscillator connection diagrams. A ceramic resonator of the

required frequency may be used in place of a crystal if the accuracy requirements are not quite as strict.

High Speed Oscillator

Low Speed Oscillator

Figure 5-6. Crystal Oscillator

Table 5-1. Crystal Oscillator Configuration, TA = 25°C, VCC = 5V

(1)

CKI Freq.

R1 (k

Ω)

R2 (M

Ω)

C1 (pF)

C2 (pF)

(MHz)

On Chip

18–36

5.6

On Chip

100

100–156

0.455

32.768 kHz*

(1)

*Applies to connection to low speed oscillator on port pins L0 and L1 only.

**See Note below.

The crystal and other oscillator components should be placed in close proximity to the CKI and CKO pins

to minimize printed circuit trace length.

The values for the external capacitors should be chosen to obtain the manufacturer's specified load

capacitance for the crystal when combined with the parasitic capacitance of the trace, socket, and

package (which can vary from 0 to 8 pF). The guideline in choosing these capacitors is:

Manufacturer's specified load cap = (C1 * C2) / (C1 + C2) + Cparasitic

C2 can be trimmed to obtain the desired frequency. C2 should be less than or equal to C1.

NOTE

The low power design of the low speed oscillator makes it extremely sensitive to board

layout and load capacitance. The user should place the crystal and load capacitors within

1cm. of the device and must ensure that the above equation for load capacitance is strictly

followed. If these conditions are not met, the application may have problems with startup of

the low speed oscillator.

Functional Description

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