EM78P458/459
OTP ROM
3.3k
5.1k
10k
510 KHz
340 KHz
175 KHz
19 KHz
470 KHz
320 KHz
170 KHz
19 KHz
300 pF
100k
<Note> 1. Measured on DIP packages.
2. Design reference only
4. RC Oscillator Mode with Internal Capacitor
If both precision and cost are taken into consideration, EM78P257A/B also offers a special oscillation
mode. It 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
EM78P458
EM78P459
Fig. 21 Circuit for Internal C Oscillator Mode
Table 15 R Oscillator Frequencies
Rext
51k
100k
300k
Average Fosc 5V,25°C
2.22 MHz
Average Fosc 3V,25°C
2.17 MHz
1.15 MHz
375 KHz
1.14 MHz
370 KHz
<Note> 1. Measured on DIP packages.
2. Design reference only
4.13 Power-on Considerations
Any microcontroller is not warranted to start proper operation before the power supply stabilizes in
steady state.
EM78P458/459 POR voltage range is 1.2V~1.8V. Under customer application, when power is OFF,
Vdd must drop to below 1.2V and remains OFF for 10us before power can be switched ON again.
This way, the EM78P458/459 will reset and work normally. The extra external reset circuit will work
well if Vdd can rise at very fast speed (50 ms or less). However, under most cases where critical
This specification is subject to change without prior notice.
48
06.25.2004 (V1.4)
ELAN [ ELAN MICROELECTRONICS CORP ]
