EM78P257
OTP ROM
Table 18 RC Oscillator Frequencies
Cext
Rext
Average Fosc 5V,25°C
3.18 MHz
Average Fosc 3V,25°C
2.75MHz
3.3k
5.1k
10k
2.1 MHz
2.0MHz
20 pF
1.14 MHz
1.12 MHz
100k
118 KHz
121 KHz
3.3k
5.1k
10k
1.25 MHz
830 KHz
435 KHz
46KHz
1.20 KHz
815 KHz
440 KHz
48 KHz
100 pF
300 pF
100k
3.3k
5.1k
10k
560 KHz
370 KHz
195 KHz
20 KHz
545 KHz
360 KHz
195 KHz
21 KHz
100k
<Note>
1. Measured on DIP packages.
2. Design reference only
3. The frequency drift about ±30%.
4. RC Oscillator Mode with Internal Capacitor
If both precision and cost are taken into consideration, EM78P257A/B also offers a special oscillation mode,
which is equipped with an internal capacitor and an external resistor connected to Vcc. The internal capacitor
functions as temperature compensator. In order to obtain more accurate frequency, a precise resistor is
recommended.
Vcc
Rext
OSCI
EM78P257A/B
Fig. 21 Circuit for Internal C Oscillator Mode
Table 19 R Oscillator Frequencies
Rext
Average Fosc 5V,25°C
4.3 MHz
Average Fosc 3V,25°C
4.3 MHz
51k
100k
300k
2.5 MHz
2.4 MHz
800KHz
800 KHz
<Note>
1. Measured on DIP packages.
2. Design reference only
This specification is subject to change without prior notice.
49
07.27.2004 (V1.4)
ELAN [ ELAN MICROELECTRONICS CORP ]
