EM78P447S
OTP ROM
OSCI
Ext. Clock
OSCO
EM78P447S
Fig. 10 Crystal/Resonator Circuit
C1
OSCI
EM78P447S
XTAL
OSCO
C2
RS
Fig. 11 Crystal/Resonator Circuit
Table 10 Capacitor Selection Guide for Crystal Oscillator or Ceramic Resonator
Oscillator Type
Frequency Mode
Frequency
455 kHz
2.0 MHz
4.0 MHz
32.768kHz
100KHz
200KHz
455KHz
1.0MHz
2.0MHz
4.0MHz
C1(pF)
100~150
20~40
10~30
25
C2(pF)
100~150
20~40
10~30
15
Ceramic Resonators
HXT
LXT
HXT
25
25
25
25
Crystal Oscillator
20~40
15~30
15
20~150
15~30
15
15
15
For some applications that do not need a very precise timing calculation, the RC oscillator (Fig. 15) offers a lot of cost
savings. Nevertheless, it should be noted that the frequency of the RC oscillator is influenced by the supply voltage, the
values of the resistor (Rext), the capacitor (Cext), and even by the operation temperature. Moreover, the frequency also
changes slightly from one chip to another due to the manufacturing process variation.
In order to maintain a stable system frequency, the values of the Cext should not be less than 20pF, and that the value
of Rext should not be greater than 1 M ohm. If they cannot be kept in this range, the frequency is easily affected by noise,
This specification is subject to change without prior notice.
25
06.25.2003 (V1.1)
ELAN [ ELAN MICROELECTRONICS CORP ]
