HMS77C1000A Datasheet, PDF (35/45 Pages) Hynix Semiconductor – 8-BIT SINGLE-CHIP MICROCONTROLLERS

HMS77C1000A/HMS77C1001A
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
HMS77C100XA. For Rext values below 2.2 kΩ, the oscil-
lator operation may become unstable, or stop completely.
For very high Rext values (e.g., 1 MΩ) the oscillator be-
comes sensitive to noise, humidity and leakage. Thus, we
recommend keeping Rext between 3 kΩ 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.
Cext
Rext
Average F_XIN @ 5V, 25°C
3.3K
0pF
5K
15K
100K
6.5MHz
5.4MHz
2.3MHz
400KHz
20pF
3.3K
5K
15K
100K
4.3MHz
3.5MHz
1.4MHz
240KHz
100pF
3.3K
5K
15K
100K
1.8MHz
1.5MHz
610KHz
100KHz
300pF
3.3K
5K
15K
100K
780KHz
630KHz
260KHz
42.5KHz
TABLE 13-3 RC OSCILLATION FREQUENCIES
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
X_OUT pin, and can be used for test purposes or to synchro-
nize other logic.
V_DD
R_ext
C_ext
F_XIN/4
X_IN
N
X_OUT
Internal
Clock
FIGURE 13-3 RC OSCILLATION MODE
32
Oct. 2001 Ver. 2.0