Fujitsu MB3773 User Manual

FUJITSU SEMICONDUCTOR

DATA SHEET

ASSP

Power Supply Monitor with Watch-Dog Timer

MB3773

DESCRIPTION

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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.

DS04-27401-7E

In addition, the watchdog timer for the operation diagnosis of the system is b uilt 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.

FEATURES

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• Precision voltage detection (VS = 4.2 V ± 2.5 %)

• Detection threshold voltage has hysteresis function

• Low voltage output for reset signal (V

• Precision reference voltage output (VR = 1.245 V ± 1.5%)

• 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.

PACKAGES

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(DIP-8P-M01)

CC = 0.8 V Typ)

(FPT-8P-M01)

(SIP-8P-M03)

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.

MB3773

PIN ASSIGNMENT

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(TOP VIEW)

RESET

(FRONT VIEW)

C T

RESET

GND

(DIP-8P-M01)

(FPT-8P-M01)

RESET

V S

V REF

V CC

GND

V CC

V REF

V S

RESET

(SIP-8P-M03)

BLOCK DIAGRAM

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:= 100

kΩ

:= 1.24 V

COMP.S

VCC

Reference Voltage Generator

:= 1.2 µA

:= 1.24 V

COMP.O

:= 10 µA

MB3773

Reference AMP.

10 µA

REF

:= 40 kΩ

Inhibit

Watch Dog Timer

P.G

GND

RESET

MB3773

FUNCTIONAL DESCRIPTIONS

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Comp.S is comparator including h ysteresis. it compare the ref erence voltage and the v oltage 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 µs interval. Howev er because momentary breaks or drops of this duration do not cause problems in actual systems in some cases, a delayed trigger function can be created by connecting capacitors to the Vs terminal. Comp.O is comparator f or turning on/off the output and, compare the voltage of the Cr terminal and the threshold voltage. Because the RESET/RESET pull-up resistor when connected to a high impedance load such as CMOS logic IC. (It corresponds to 500 kΩ at Vcc = 5 V.) when the voltage of the CK terminal changes from the “high” level into the “Low” level, pulse generator is sent to the watch-dog timer by generating the pulse momentarily at the time of drop from the threshold level. When power-supply voltages fall more than detecting voltages, the watch-dog timer becomes a interdiction. The Reference amplifier is a op-amp to output the reference voltage. If the comparator is put up outside, two or more power-supply voltage monitor and overvoltage monitor can be done. If it uses a comparator of the open-collector output, and the output of the comparator is connected with the Vs terminal of MB3773 without the pull-up resistor, it is possible to voltage monitor with reset-hold time.

outputs have b uilt-in pull-up circuit, there is no need to connect to external

••••

MB3773 Basic Operation

VCC

MB3773

VCC

0.8 V

VSH

VSL

VCC

Logic Circuit

TPR (ms) := 1000 · CT (µF)

RESET RESET

GND

RESET RESET CK

WD (ms) := 100 · CT (µF)

WR (ms) := 20 · CT (µF)

Example : C

T = 0.1 µF

RR (ms) := 100 (ms)

WD (ms) := 10 (ms)

WR (ms) := 2 (ms)

RESET

TCK

TPR

(1) (2) (3)(4)(5) (5) (6)(7) (8)(9) (10) (11) (12)

TWD TWR TPR

MB3773

OPERATION SEQUENCE

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(1) When Vcc rises to about 0.8 V, RESET goes “Low” and RESET goes “High”.

The pull-up current of approximately 1 µA (Vcc = 0.8 V) is output from RESET.

(2) When Vcc rises to VSH ( := 4.3V) , the charge with CT starts.

At this time, the output is being reset.

(3) When C

After T Reset hold time: T After releasing reset, the discharge of C T

T begins charging, RESET goes “High” and RESET goes “Low”.

PR reset of the output is released.

PR (ms) := 1000 × CT (µF)

T starts, and watch-dog timer operation starts.

PR is not influenced by the CK input.

(4) C changes from the discharge into the charge if the clock (Negative edge) is input to the CK terminal

while discharging C

(5) C changes from the charge into the discharge when the voltage of C

T reaches a constant

threshold ( := 1.4 V) . (4) and (5) are repeated while a normal clock is input by the logic system.

(6) When the clock is cut off, gets, and the voltage of C

T falls on threshold ( := 0.4 V) of reset on, RESET goes

“Low” and RESET goes “High”. Discharge time of C

WD (ms) := 100 × CT (µF)

Because the charging time of C of reset of the clock, T

(7) Reset time in operating watch-dog timer:T

T until reset is output: TWD is watch-dog timer monitoring time.

T is added at accurate time from stop of the clock and getting to the output

WD becomes maximum TWD + TWR by minimum TWD.

WR is charging time where the voltage of CT goes up to off

threshold ( := 1.4 V) for reset.

WR (ms) := 20 × CT (µF)

Reset of the output is released after C

T reaches an off threshold for reset, and CT starts the discharge,

after that if the clock is normally input, operation repeats (4) and (5) , when the clock is cut off, operation repeats (6) and (7) .

(8) When Vcc falls on V

SL ( := 4.2 V) , reset is output. CT is rapidly discharged of at the same time.

(9) When Vcc goes up to V

SH, the charge with CT is started.

When Vcc is momentarily low, After falling V

SL or less Vcc, the time to going up is the standard value of the Vcc input pulse width in VSH or

more. After the charge of C

T is discharged, the charge is started if it is TPI or more.

(10) Reset of the output is released after TPR, after Vcc becomes VSH or more, and the watch-dog timer starts.

After that, when Vcc becomes V

(11) While power supply is off, when Vcc becomes V

SL or less, (8) to (10) is repeated.

SL or less, reset is output.

(12) The reset output is maintained until Vcc becomes 0.8 V when Vcc falls on 0 V.

ABSOLUTE MAXIMUM RATINGS

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MB3773

Parameter Symbol

Unit

Min Max

Rating

Supply voltage V

CC − 0.3 + 18 V

S − 0.3 VCC + 0.3 ( ≤ +18) V

Input voltage

CK − 0.3 + 18 V

RESET, RESET Supply voltage VOH − 0.3 VCC + 0.3 ( ≤ +18) V Power dissipation (Ta ≤ +85 °C) P Storage temperature T

D  200 mW

STG − 55 + 125 °C

WARNING: Semiconductor devices can be permanently damaged by application of stress (voltage, current,

temperature, etc.) in excess of absolute maximum ratings. Do not exceed these ratings.

RECOMMENDED OPERATING CONDITIONS

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Value

Parameter Symbol

Unit

Min Max

Supply voltage V

CC + 3.5 + 16 V

RESET, RESET

REF

output current IOUT − 200 + 5 µA Watch clock setting time t CK Rising/falling time t

sink current IOL 020mA

WD 0.1 1000 ms

tRC  100 µs Terminal capacitance CT 0.001 10 µF Operating ambient temperature Ta − 40 + 85 °C

WARNING: The recommended operating conditions are required in order to ensure the normal operation of the

semiconductor device. All of the device’s electrical characteristics are warranted when the device is operated within these ranges.

Always use semiconductor devices within their recommended operating condition ranges. Operation outside these ranges may adversely affect reliability and could result in device failure.

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.

MB3773

ELECTORICAL CHARACTERISTICS

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(1) DC Characteristics

Parameter Symbol Condition

(

VCC = 5 V, Ta = + 25 °C)

Value

Min Typ Max

Unit

Supply current I

CC Watch dog timer operating  600 900 µA

VCC 4.10 4.20 4.30

Ta = − 40 °C to + 85 °C 4.05 4.20 4.35

Detection voltage

VCC 4.20 4.30 4.40

Ta = − 40 °C to + 85 °C 4.15 4.30 4.45

Hysteresis width VHYS VCC 50 100 150 mV

 1.227 1.245 1.263

Reference voltage V

REF

Ta = − 40 °C to + 85 °C 1.215 1.245 1.275 Reference voltage change rate ∆VREF1 VCC = 3.5 V to 16 V  310mV Reference voltage output

loading change rate CK threshold voltage V

∆V

REF2 IOUT = − 200 µA to + 5 µA − 5  + 5mV

TH Ta = − 40 °C to + 85 °C 0.8 1.25 2.0 V

IIH VCK = 5.0 V  01.0

CK input current

T discharge current ICTD

IL VCK = 0.0 V − 1.0 − 0.1 

Watch dog timer operating

CT = 1.0 V

71014µA

µA

High level output voltage

Output saturation voltage

Output sink current

charge current ICTU

Min supply voltage for RESET

Min supply voltage for RESET V

OH1 VS open, IRESET

= − 5 µA4.54.9 VOH2 VS = 0 V, IRESET = − 5 µA4.54.9 V

OL1 VS = 0 V, IRESET = 3 mA  0.2 0.4 OL2 VS = 0 V, IRESET = 10 mA  0.3 0.5

V VOL3 VS VOL4 VS

OL1 VS = 0 V, VRESET = 1.0 V 20 60 

I IOL2 VS

VCCL1

CCL2

open, IRESET = 3 mA  0.2 0.4 open, IRESET = 10 mA  0.3 0.5

open, VRESET = 1.0 V 20 60 

Power on reset operating V

CT = 1.0 V

VRESET = 0.4 V, I

RESET = 0.2 mA

VRESET = VCC − 0.1 V, R

L (pin 2 − GND) = 1 MΩ

0.5 1.2 2.5 µA

 0.8 1.2 V

(2)AC Characteristics

Parameter Symbol Condition

MB3773

(

VCC = 5 V, Ta = + 25 °C)

Value

Min Typ Max

Unit

input pulse width TPI

CK input pulse width T CK input frequency T

CKW

CK  20 µs

VCC

5 V 4 V

8.0 µs

3.0 µs

Watch dog timer watching time TWD CT = 0.1 µF 5 10 15 ms Watch dog timer reset time T

Rising reset hold time T

Output propagation delay time from V

Output rising time* t

Output falling time* t

WR CT = 0.1 µF123ms

TPD1

PD2

CT = 0.1 µF, VCC RESET, RL = 2.2 kΩ,

L = 100 pF

RESET, RL = 2.2 kΩ, C

L = 100 pF

RL = 2.2 kΩ, C

L = 100 pF

RL = 2.2 kΩ, C

L = 100 pF

50 100 150 ms

 210

 310

 1.0 1.5

 0.1 0.5

* : Output rising/falling time are measured at 10 % to 90 % of voltage.

µs

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