R5101G データシートの表示（PDF） - RICOH Co.,Ltd.

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R5101G

Microprocessor power management with Watchdog Timer

RICOH Co.,Ltd. 

n OPERATION

¬ When VDD is turned on and Input Voltage reaches Vstart (nearly equal 0.8V), the output of RESET pin

becomes “L” level.

- An External Capacitor starts to be charged through the CD pin when an Output Voltage of the Voltage

Regulator, VOUT, crosses the Released Voltage , +VDET , from Lower to Higher . The VRESET is kept “L” level

until Voltage of the CD pin , VCD , reaches to the Vref2H , about 1.0V , and after that the VRESET becomes to

“H” level.

\ tPR : Time interval between the timing of starting edge of forcing voltage to VDD pin and the timing of

reverse the voltage level of VRESET .

tPR can be set by connecting an external capacitor to CD pin, tPR can be calculated as shown below;

tPR (ms) » 13000´ CD (mF) ; CD means a value of an external capacitor connected to CD pin.

® When the voltage level of VCD reaches to the Vref2H, the external capacitor starts to be charged through

the CTW pin and the watchdog timer begins to operate.

¯ The operation mode for the external capacitor changes from charging mode to discharging mode through

CTW pin when the voltage level of CTW pin , VCTW , reaches to the Vref2H.

° While the CTW pin is on the discharging mode, if a clock pulse is entered (synchronous with a rising edge

of the pulse), the operation mode of CTW pin changes from charging mode to discharging mode. And

the external capacitor connected to CTW pin is charged until its voltage level reaches to Vref2H.

± While the CTW pin is on the discharging mode, if VCTW level drops to Vref2L, about 0.2V without clock

pulse to CLK pin, the voltage level of Reset pin becomes from “H” to “L”.

\ Watch Time of the watchdog timer , tWD , : Discharging Time of CTW pin level from Vref2H to Vref2L

tWD can be set by connecting an external capacitor to CW pin, tWD can be calculated as shown below;

tWD (ms) » 10000´ CW (mF); Cw means a value of an external capacitor connected to Cw pin.

² CTW pin is changed to charging mode from discharging mode when the Reset signal is generated.

\ Reset time of the watchdog timer , tWR , : Time interval between Charging time of the CTW pin from Vref2L

to Vref2H. tWR can be calculated by the next equation as shown below;

tWR (ms) » tWD/10

³ The Output Voltage level of Reset pin becomes from “H” to “L”, or a Reset signal is generated when an

output voltage of the Voltage Regulator drops to a level at equal or less than -Vdet.

´ The watchdog timer will be halted when a Voltage level of CE pin becomes to “L”. In this case, only the

watchdog timer is stopped and monitoring the output voltage is continued. After that, if the voltage level of CE

pin becomes to “H”, CTW pin starts to be on charging mode.

Rev. 1.10

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