GM5115H データシートの表示（PDF） - Genesis Microchip

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GM5115H

OnPanel LCD Panel Controller

Genesis Microchip 

*** Genesis Microchip Confidential ***

gm5115/25 Preliminary Data Sheet

The TCLK oscillator uses a Pierce Oscillator circuit. The output of the oscillator circuit,

measured at the TCLK pin, is an approximate sine wave with a bias of about 2 volts above

ground (see Figure 5). The peak-to-peak voltage of the output can range from 250 mV to 1000

mV depending on the specific characteristics of the crystal and variation in the oscillator

characteristics. The output of the oscillator is connected to a comparator that converts the sine

wave to a square wave. The comparator requires a minimum signal level of about 50-mV peak to

peak to function correctly. The output of the comparator is buffered and then distributed to the

gm5115/25 circuits.

3.3 Volts

~ 2 Volts

250 mV peak to peak

to

1000 mV peak to peak

time

Figure 5.

Internal Oscillator Output

One of the design parameters that must be given some consideration is the value of the loading

capacitors used with the crystal as shown in Figure 6. The loading capacitance (Cload) on the

crystal is the combination of CL1 and CL2 and is calculated by Cload = ((CL1 * CL2) / (CL1 + CL2)) +

Cshunt. The shunt capacitance Cshunt is the effective capacitance between the XTAL and TCLK

pins. For the gm5115/25 this is approximately 9 pF. CL1 and CL2 are a parallel combination of the

external loading capacitors (Cex), the PCB board capacitance (Cpcb), the pin capacitance (Cpin), the

pad capacitance (Cpad), and the ESD protection capacitance (Cesd). The capacitances are

symmetrical so that CL1 = CL2 = Cex + CPCB + Cpin + Cpad + CESD. The correct value of Cex must be

calculated based on the values of the load capacitances. Approximate values are provided in

Figure 6.

June 2002

12

C5115-DAT-01H

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