EM78P257AP datasheet(49/91 Pages) EMC

49 / 91 page

EM78P257

OTP ROM

This specification is subject to change without prior notice.

07.27.2004 (V1.4)

Table 18 RC Oscillator Frequencies

Cext

Rext

Average Fosc 5V,25

°C

Average Fosc 3V,25

°C

3.3k

3.18 MHz

2.75MHz

5.1k

2.1 MHz

2.0MHz

10k

1.14 MHz

1.12 MHz

20 pF

100k

118 KHz

121 KHz

3.3k

1.25 MHz

1.20 KHz

5.1k

830 KHz

815 KHz

10k

435 KHz

440 KHz

100 pF

100k

46KHz

48 KHz

3.3k

560 KHz

545 KHz

5.1k

370 KHz

360 KHz

10k

195 KHz

300 pF

100k

20 KHz

21 KHz

<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.

OSCI

EM78P257A/B

Vcc

Rext

Fig. 21 Circuit for Internal C Oscillator Mode

Table 19 R Oscillator Frequencies

Rext

Average Fosc 5V,25

°C

Average Fosc 3V,25

°C

51k

4.3 MHz

100k

2.5 MHz

2.4 MHz

300k

800KHz

800 KHz

<Note>

1. Measured on DIP packages.

2. Design reference only

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