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Fujitsu MB3773 Datasheet

Power supply monitor with watch-dog timer.
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Power Supply Monitor
with Watch-Dog Timer
MB3773 generates the reset signal to protect an arbitrary system when the power-supply voltage momentarily is
intercepted or decreased. It is IC for the power-supply voltage watch and "Power on reset" is generated at the
normal return of the power supply. MB3773 sends the microprocessor the reset signal when decreasing more
than the voltage, which the power supply of the system specified, and the computer data is protected from an
accidental deletion.
In addition, the watchdog timer for the operation diagnosis of the system is built into, and various microprocessor
systems can provide the fail-safe function. If MB3773 does not receive the clock pulse from the processor for an
specified period, MB3773 generates the reset signal.
• Precision voltage detection (V
• Detection threshold voltage has hysteresis function
• Low voltage output for reset signal (V
• Precision reference voltage output (V
• With built-in watchdog timer of edge trigger input.
• External parts are few.(1 piece in capacity)
• The reset signal outputs the positive and negative both theories reason.
This device contains circuitry to protect the inputs against damage due to high static voltages or electric fields.
However, it is advised that normal precautions be taken to avoid application of any voltage higher than maximum rated voltages
to this high impedance circuit.
= 4.2 V
2.5 %)
= 0.8 V Typ)
= 1.245 V


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   Summary of Contents for Fujitsu MB3773

  • Page 1

    In addition, the watchdog timer for the operation diagnosis of the system is built into, and various microprocessor systems can provide the fail-safe function. If MB3773 does not receive the clock pulse from the processor for an specified period, MB3773 generates the reset signal.

  • Page 2: Table Of Contents


  • Page 3: Block Diagram

    BLOCK DIAGRAM 1.24 V Reference Voltage Generator COMP.S 40 k Inhibit 1.24 V 1.2 A COMP.O 10 A Watch Timer RESET MB3773 Reference AMP. 10 A RESET...

  • Page 4

    Comp.S is comparator including hysteresis. it compare the reference voltage and the voltage of Vs, so that when the voltage of Vs terminal falls below approximately 1.23 V, reset signal outputs. Instantaneous breaks or drops in the power can be detected as abnormal conditions by the MB3773 within a 2 s interval.

  • Page 5: C T

    MB3773 Basic Operation RESET RESET 0.8 V RESET (1) (2) Logic Circuit (ms) : = 1000 · C RESET (ms) : = RESET (ms) : = Example : C (3)(4)(5) (6) (7) (8)(9) MB3773 ( F) 100 · C ( F) 20 ·...

  • Page 6: C T

    (10) Reset of the output is released after T After that, when Vcc becomes V (11) While power supply is off, when Vcc becomes V (12) The reset output is maintained until Vcc becomes 0.8 V when Vcc falls on 0 V.

  • Page 7

    No warranty is made with respect to uses, operating conditions, or combinations not represented on the data sheet. Users considering application outside the listed conditions are advised to contact their FUJITSU representatives beforehand. Rating Symbol...

  • Page 8: Reset

    MB3773 ELECTORICAL CHARACTERISTICS (1) DC Characteristics Parameter Supply current Detection voltage Hysteresis width Reference voltage Reference voltage change rate Reference voltage output loading change rate CK threshold voltage CK input current discharge current High level output voltage Output saturation voltage...

  • Page 9

    0.1 F 0.1 F 0.1 F, V RESET, R 2.2 k , 100 pF RESET, R 2.2 k , 100 pF 2.2 k , 100 pF 2.2 k , 100 pF to 90 of voltage. MB3773 5 V, Ta Value Unit...

  • Page 10

    MB3773 TYPICAL CHARACTERISTIC CURVES Supply current vs. Supply voltage 0.75 0.65 0.55 0.45 0.35 0.25 0.15 8.0 10.0 12.0 14.0 16.0 18.0 20.0 Supply voltage V Output voltage vs. Supply voltage (RESET terminal) Pull up 2.2 k 85 C 25 C...

  • Page 11

    1.255 25 C 85 C 1.250 40 C 0.1 F 1.245 1.240 Reference current I Rising reset hold time MB3773 (RESET terminal) 0.1 F 25 C 85 C 40 C ( A) 0.1 F 25 C 85 C 40 C ( A) vs.

  • Page 12

    MB3773 (Continued) Reset time vs. Temperature (At watch dog timer) Temperature Ta ( C) terminal capacitance Watchdog timer watching time 40 C 25 C erminal capacitance C 0.1 F terminal capacitance vs. Reset time (at watch dog timer) 25 C...

  • Page 13

    Detection voltage are V EXAMPLE 2: 5V Supply Voltage Monitoring (external fine-tuning type) (5V) MB3773 Notes : Vs detection voltage can be adjusted externally. Based on selecting R internal voltage divider, the detection voltage can be set according to the resistance ratio of and R (See the table below.)

  • Page 14

    MB3773 EXAMPLE 3: With Forced Reset (with reset hold) Note : Grounding pin 7 at the time of SW ON sets RESET (pin 8) to Low and RESET (pin 2) to High. Note : Feeding the signal to terminal RESIN and turning on Tr sets the RESET terminal to Low and the RESET terminal to High.

  • Page 15

    Example : Comp. 1, Comp. 2 : MB4204, MB47393 Notes : The 5 V supply voltage is monitored by the MB3773. The 12 V supply voltage is monitored by the external circuit. Its output is connected to the NMI terminal and, when voltage drops, Comp. 2 interrupts the logic circuit.

  • Page 16

    : MB4204, MB47393 Notes : When either 5 V or 12 V supply voltage decreases below its detection voltage (V the MB3773 RESET terminal is set to High and the MB3773 RESET terminal is set to Low. Use V 5 V) to power the comparators (Comp. 1 and Comp. 2) in the external circuit shown above.

  • Page 17

    MB3773 1.2 k 5.6 k Notes : Comp. 1 and Comp. 2 are used to monitor for overvoltage while the MB3773 is used to monitor for low voltage. Detection voltages V Detection voltages V For the formulas for finding hysteresis width and detection voltage, see EXAMPLE 4.

  • Page 18

    MB3773 EXAMPLE 7: Monitoring Supply Voltage Using Delayed Trigger Note : Adding voltage such as shown in the figure to V width by 50 s (C MB3773 increases the minimum input pulse 1000 pF). Logic circuit RESET RESET...

  • Page 19

    These are example application circuits in which the MB3773 monitors supply voltage alone without resetting the microprocessor even if the latter, used in standby mode, stops sending the clock pulse to the MB3773. • The watch-dog timer is inhibited by clamping the C The supply voltage is constantly monitored even while the watch-dog timer is inhibited.

  • Page 20

    MB3773 (Continued) (c) Using NPN transistor (5 V) (d) Using PNP transistor (5 V) MB3773 =1 M =1 k MB3773 =51 k =1 k Logic circuit RESET RESET HALT Logic circuit RESET RESET HALT...

  • Page 21

    EXAMPLE 9: Reducing Reset Hold Time ( 5 V) MB3773 (a) T reduction method Notes : RESET is the only output that can be used. Standard T and T Formulas: T (ms) : = 100 (ms) : = 100 (ms) : = 16 The above formulas become standard values in determining T Reset hold time is compared below between the reduction circuit and the standard circuit.

  • Page 22

    MB3773 EXAMPLE 10: Circuit for Monitoring Multiple Microprocessor RESET RESET RESET RESET *: Microprocessor Notes : connects from FF1 and FF2 outputs Q Depending on timing, these connections may not be necessary. Example : R Output RESET RESET and Q 2.2 k...

  • Page 23

    Description of Application Circuits Using one MB3773, this application circuit monitors multiple microprocessor in one system. Signals from each microprocessor are sent to FF1, FF2 and FF3 clock inputs. Figure 2 shows these timings. Each flip-flop operates using signals sent from microprocessor as its clock pulse. When even one signal stops, the relevant receiving flip-flop stops operating.

  • Page 24

    MB3773 EXAMPLE 11: Circuit for Limiting Upper Clock Input Frequency Notes : This is an example application to limit upper frequency f the microprocessor. If the CK cycle sent from the microprocessor exceeds f (The lower frequency has already been set using C When a clock pulse such as shown below is sent to terminal CK, a short T from reaching the CK input threshold level ( : = 1.25 V), and will cause a reset signal to be output.

  • Page 25

    - Applying a negative voltage of 0.3 V or less to an LSI may generate a parasitic transistor, resulting in malfunction. ORDERING INFORMATION Part number MB3773P MB3773PS MB3773PF to 1 M resistors in series. Package 8-pin plastic DIP (DIP-8P-M01) 8-pin plastic SIP (SIP-8P-M03) 8-pin plastic SOP (FPT-8P-M01) MB3773 Remarks...

  • Page 26: Package Dimensions

    8-pin plastic DIP (DIP-8P-M01) 4.36(.172)MAX 3.00(.118)MIN +0.30 0.99 –0 +.012 .039 –0 +0.35 0.89 –0.30 +.014 .035 –.012 1994 FUJITSU LIMITED D08006S-2C-3 +0.40 9.40 –0.30 +.016 .370 –.012 6.20±0.25 1 PIN INDEX (.244±.010) 0.51(.020)MIN 0.25±0.05 (.010±.002) 0.46±0.08 (.018±.003) +0.30 1.52 –0...

  • Page 27

    (.019±.003) 0.10(.004) 0.10(.004) 2002 FUJITSU LIMITED F08002S-c-6-7 Note 1 : *1 : These dimensions include resin protrusion. Note 2 : *2 : These dimensions do not include resin protrusion. Note 3 : Pins width and pins thickness include plating thickness.

  • Page 28

    MB3773 (Continued) 8-pin plastic SIP (SIP-8P-M03) INDEX-1 INDEX-2 +0.30 0.99 –0 +.012 .039 –0 2.54(.100) 1994 FUJITSU LIMITED S08010S-3C-2 +0.15 19.65 –0.35 +.006 .774 –.014 6.20±0.25 (.244±.010) 8.20±0.30 (.323±.012) 4.00±0.30 (.157±.012) +0.30 1.52 0.50±0.08 –0 +.012 (.020±.003) .060 –0 Dimensions in mm (inches) .

  • Page 29

    Fujitsu or any third party or does Fujitsu warrant non-infringement of any third-party’s intellectual property right or other right by using such information.

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