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參數(shù)資料
| 型號(hào)： | HA1848P |
| 廠商： | Hitachi,Ltd. |
| 英文描述： | Watchdog Timer |
| 中文描述： | 看門狗定時(shí)器 |
| 文件頁數(shù)： | 7/13頁 |
| 文件大?。?/td> | 59K |
| 代理商： | HA1848P |
HA1835P/HA1848P
7
Functional Description
Voltage Regulator
The HA1835P, and HA1848P supplies 5 V regulated output from a wide V
CC
input range (V
CC
= 6 V to
17.5 V). The external PNP transistor should be selected according to the supply current demand of the
system. Connect a more than 100
μ
F capacitor between Vout and GND to realize the 5 V regulated output.
The resistor connected from the Vadj terminal to the Vout or GND terminal fine tunes the output voltage.
A resistor between Vadj and the Vout decreases the output voltage, and a resistor between Vadj and GND
increases the output voltage.
5
Vout
7.14
5
Vout
7.14
Vout
5
R (Vout
Vadj)
≈
(k
)
R (Vadj
GND)
≈
(k
)
Current Limiter
To protect the external transistor from overcurrent, connect a current-sense resistor between the CS
terminal and the V
CC
terminal. The value of this resistor should be:
0.3 V
Iout (Limit)
R
SC
≈
(at Ta = 25
°
C)
Power-On Reset
The HA1835P, and HA1848P can output a reset pulse to start the microcomputer at power on (figure 6).
The external resistor R
R
and capacitor C
R
determine the power-on reset timing.
Note that
RES
and RES are open-collector terminals. They should therefore be connected to a pull-up
resistor of about 5 k
.
Watchdog Timer
The watchdog timer is a fail-safe function. It can reset the microcomputer system if the system runs out of
control. It does this be monitoring a pulse output by the system's software. It uses a bandpass filter to
determine whether the pulse frequency is within the system's normal frequency band (figure 7, 8). External
resistor and capacitor Rf and Cf determine the frequency range of the bandpass filter. If the pulse
frequency is not within the frequency band, the HA1835P, and HA1848P outputs a reset pulse.
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