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MITSUMI
System Reset (with built-in watchdog timer) MM1145
System Reset (with built-in watchdog timer)
Monolithic IC MM1145
Outline
This IC has a built-in watchdog timer, with 2 channels for a clock monitoring function that monitors the microcomputer and outputs an intermittent reset signal if the microcomputer runs wild. Also, it has a power supply voltage monitoring function (system reset function) which generates a reset signal if power supply voltage is momentarily interrupted or drops, and performs power ON reset during normal power supply recovery and when power is turned on.
Features
1. Built-in edge trigger input watchdog timer 2. 2 clock pulse monitoring 3. Power ON reset time (TPR) and watchdog timer monitoring time (TWD) can be set individually with external elements (R, C) 4. Excellent watchdog timer monitoring time (TWD) precision A type : 20% B type : 30% 5. Watchdog function stop pin allows use as system reset IC 6. Accurate power supply voltage drop detection 4.2V3.5% 7. Detection voltage has hysteresis 100mV typ. 0.14%/C 8. Low reset minimum voltage 9. Low current consumption 150A typ.
Package
SOP-8C (MM1145AF, MM1145BF)
Applications
Voltage detection for CPUs, microcomputers, etc. and clock pulse monitoring
Series Table
Model MM1145A MM1145B VSL 4.2 TPR 100ms 40ms TWD 50ms 110ms TWR 10ms 10ms
VSL : Reset detection voltage TPR : Reset hold time during Vcc rise TWD : Watchdog timer monitoring time TWR : Reset time
*CT=0.02F, RCT=1M
MITSUMI
System Reset (with built-in watchdog timer) MM1145
Pin Assignment
1 2 8 7 6 5 3 4 1 2 3 4 5 6 SOP-8C (TOP VIEW) 7 8 TC CK1 CK2 GND VCC RCT VS
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RESET
Pin Description
Pin No. Pin name 1 2 3 4 5 TC CK1 CK2 GND VCC RCT VS
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Function TWD, TWR, TPR time setting pins. Time determined by external capacitor. Clock input pin 1 Clock input from logic system Clock input pin 2 Clock input from logic system GND pin Power supply pin Detection voltage 4.2V Watchdog timer stop pin and TWD adjustment pin Operation modes : Operation Vcc, Stop GND
6
TWD time determined by external resistor RRCT and CT 7 8 Detection voltage adjustment pin RESET Reset output pin (low output)
Block Diagram
MITSUMI
System Reset (with built-in watchdog timer) MM1145
Absolute Maximum Ratings
Item Power supply voltage CK pin input voltage VS pin input voltage Voltage applied to RCT pin Voltage applied to RESET pin Allowable loss Storage temperature
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Symbol VCC max. VCK VVS VRCT VOH Pd TSTG
Rating -0.3~+7.5 < -0.3~VCC+0.3 ( = +7.5) -0.3~VCC+0.3 ( < +7.5) = < -0.3~VCC+0.3 ( = +7.5) -0.3~VCC+0.3 ( < +7.5) = 300 -40~+125
Units V V V V V mW C
Recommended Operating Conditions
Item Power supply voltage RESET sync current Clock monitoring time setting Power supply voltage rise and fall times Clock rise and fall times CT pin capacitance RCT pin resistance Operating temperature Symbol VCC IOL TWD tFV, tRV tFC, tRC CT RrCT TOP Rating +2.2~+7.0 0~4.0 1.95~10000 <300 <100 0.002~2 0.39~2 -25~+75 Units V mA ms s s F M C
Electrical Characteristics (DC)
Item Consumption current Detection voltage Detection voltage temperature coefficient Hysteresis voltage CK input threshold CK input current Output voltage (High) Symbol ICC VSL VSH VS T VHYS VTH IIH IIL VOH VOL1 Output voltage (Low) VOL2 IOL ICT1 ICT2 VCCL
(Except where noted otherwise, Ta=25C, Vcc=5.0V) Measurement conditions Min. 4.05 4.15 Typ. 150 4.20 4.30 0.01 50 0.8 VCK=5.0V VCK=0V I RESET =-1A, VS=OPEN I RESET =0.5mA, VS=0V I RESET =2.0mA, VS=0V V RESET =1.0V, VS=0V
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Max. 180 4.35 4.45
Units A V %/C
During watchdog timer operation VS=OPEN, VCC VS=OPEN, VCC VSH-VSL, VCC
100 1.2 0 -8.5 4.5 0.10 0.15
150 2 1 -4.5 0.20 0.35 0.30
mV V A V V mA
-14.5 4.0
Output sync current MM1145A CT charge current MM1145B MM1145A MM1145B Minimum operating power supply voltage to ensure RESET
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2 -0.40 -0.17 -0.21 -0.62
4 -0.48 -0.22 -0.31 -0.93 0.8 -0.60 -0.30 -0.62 -2.33 1.0
During watchdog timer operation During power ON reset operation V RESET =0.4V I RESET =0.1mA
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A A V
MITSUMI
System Reset (with built-in watchdog timer) MM1145
Electrical Characteristics (DC)
Item VCC input pulse width Symbol TPI TCKW1 TCKW2 TCK1 TCK2 TWD TWR TPR TPD tR tF
(Except where noted otherwise, Ta=25C, VCC=5.0V) (Except where noted otherwise, resistance unit is )
Measurement conditions VCC CK 5.0V 4.0V or or CT=0.02F, RRCT=1M CT=0.02F, RRCT=1M CT=0.02F RRCT=1M
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Min. 8 3 200 40 80 5 5 50 20
Typ.
Max.
Units s s s
CK input pulse width
CK input cycle 7 Watchdog timer MM1145A
*
50 110 10 10 100 40 2 2.0 0.2
60 140 15 15 150 60 10 4.0 1.0
monitoring time 1 MM1145B
ms ms ms s s s
*
Watchdog timer reset time 2
MM1145A MM1145B
*
Reset hold time for MM1145A power supply rise 3 MM1145B
*
VCC
Output delay time from VCC 4
*
RESET pin, RL=10k, CL=20pF RESET pin, RL=10k, CL=20pF
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Output rise time 5
* Output fall time 5 *
RESET pin, RL=10k, CL=20pF
Notes: 1 Monitoring time is the time from the last pulse (negative edge) of the timer clear clock pulse until reset pulse output. In other words, reset output is output if a clock pulse is not input during this time. 2 Reset time means reset pulse width. However, this does not apply to power ON reset. 3 Reset hold time is the time from when VCC exceeds detection voltage (VSHR) during power ON reset until reset release (RESET output high). 4 Output delay time is the time from when power supply voltage drops below detection voltage (VSL) until reset state occurs (RESET output low). 5 The voltage range when measuring output rise and fall time is 10~90%. 7 1 Set CK1 and CK2 input cycles within the following range. TCK1 < nTCK2* * * * * *
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2 TCK1, TCK2 < 200 s results in the following operation. = Discharge switches to charging with the CK2 pulse (negative edge) that inputs 200s after CT switches from charging to discharge by the CK2 pulse (negative edge). RESET output stays high while this operation is being repeated. (However, TCK1, TCK2 > 20s.) =
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MITSUMI
System Reset (with built-in watchdog timer) MM1145
Formula for CT Pin External Constant
Watchdog timer monitoring time (TWD), watchdog timer reset time (TWR) and reset hold time (TPR) during power supply rise can be changed by varying CT capacitance. TWD also can be changed with RRCT. The variable times are expressed by the following.
1. MM1145A TPR (ms) . . 5000 CT (F) = TWD (ms) . . 2500 CT (F) RRCT (M) = . TWR (ms) = 500 CT (F) . Example : when CT=0.02F, RRCT=1M TPR . . 100ms = TWD . . 50ms = TWR . . 10ms =
2. MM1145B . TPR (ms) = 2000 CT (F) . . TWD (ms) = 5500 CT (F) RRCT (M) . . TWR (ms) = 500 CT (F) . Example : when CT=0.02F, RRCT=1M . TPR = 40ms . . TWD = 110ms . . TWR = 10ms .
Formula for Watchdog Timer Monitoring Time (TWD) Adjustment
The ratio between TPR and TWD can be changed within the range below by adjusting TWD with RRCT. . TWD/TPR = 2.0 . 1. MM1145A RRCT (0.39 (M) < RRCT < 2 (M)) = = . TWD/TPR = 2.75 . 2. MM1145B RRCT (0.39 (M) < RRCT < 2 (M) = =
How to Use RCT Pin
Example 1 Example 2
1. Watchdog timer operates when RCT pin is open. 2. Watchdog timer stops operating when RCT pin is connected to ground.
Description of Operation
1. RESET goes low when VCC rises to approximately 0.8V. Approximately 1A (VCC=0.8V) of pull up current is output from RESET. 2. Capacitor CT charging starts when VCC rises to VSH (. . 4.3V). Output is in reset state at this time. = 3. Output reset is released (RESET goes high) after a certain time (TPR), from when CT starts charging until . discharge (the time from when CT voltage reaches a certain threshold value VT1 ( = 1.4V) until CT voltage . . 0.2V). drops to a certain threshold value VT2 ( = . Reset hold time : TPR is as follows. . TPR (ms) = 5000 CT (F) . CT charging starts again after reset release, and watchdog timer operation begins. Clock input during power ON reset time (TPR) will cause mis-operation. 4. If CK1 and CK2 are input in that order (or simultaneously) during CT charging, CK2 negative edge trigger causes the TC pin to switch from charging to discharge. 5. Discharge switches to charging when CT voltage drops to threshold value VT2 (. . 0.2V). Steps 4 and 5 are = repeated while a normal clock is input from the logic system.
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MITSUMI
System Reset (with built-in watchdog timer) MM1145
6. Operation is as follows if either clock CK1 or CK2 ceases (the figure shows CK1). Output goes to reset state (RESET goes low) when CT voltage reaches reset ON threshold value VT1 (. . 1.4V). = The formula for CT charging time (TWD : watchdog timer monitoring time) until reset is output is as follows. TWD (ms) . . 2500 CT (F) = 7. Watchdog timer reset time TWR is the discharge time until CT voltage drops to reset OFF threshold value VT2 from reset ON threshold value VT1. The formula is as follows. TWR (ms) . . 500 CT (F) = After reset OFF threshold value is reached, output reset is released and CT starts charging. Thereafter, steps 4 and 5 are repeated if a normal clock is input, and when one of the clocks ceases, 6 and 7 are repeated. In the same way, 6 and 7 are repeated if both clocks CK1 and CK2 cease. 8. Reset is output when VCC drops to VSL (. . 4.2V). CT is charged simultaneously. = 9. CT charging starts when VCC rises to VSH. When VCC drops momentarily, CT charging begins after the charge is first discharged, if the time from VCC dropping below VSL until it rises to VSH is longer than the VCC input pulse width standard value TPI. 10.Output reset is released after VCC goes above VSH and after TPR, and the watchdog timer starts. 11.Watchdog timer operation can be stopped by switching RCT voltage from high to low. (Clocks CK1 and CK2 are invalid. Regardless of status, TC pin voltage discharges quickly and goes to 0V.) This operation can be applied from any timing. In this state the IC functions as a reset IC with power ON reset. 12.Watchdog timer operation re-starts when RCT voltage switches to high. 13.When power is OFF, reset is output if VCC goes below VSL. 14.When Vcc drops to 0V, reset output is held until VCC reaches 0.8V.
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Measuring Circuit
Measuring Circuit 1
MITSUMI
System Reset (with built-in watchdog timer) MM1145
Measuring Circuit 2
Timing Chart
VCC
VH VL 0.8
RCT
CK1 CK2
CT
TPR VT1 VT2 TWD TWR
RESET
1 2 3 4 5 6 7 8 9 10 11 12 13 14
Basic Circuit Diagram

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