Fujitsu MB3773 User manual

DS04-27401-7E
FUJITSU SEMICONDUCTOR
DATA SHEET
ASSP
Power Supply Monitor
with Watch-Dog Timer
MB3773
■DESCRIPTION
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.
■FEATURES
• Precision voltage detection (VS= 4.2 V ±2.5 %)
• Detection threshold voltage has hysteresis function
• Low voltage output for reset signal (VCC = 0.8 V Typ)
• 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
(DIP-8P-M01) (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,itisadvisedthatnormal precautionsbetakentoavoidapplicationofanyvoltagehigherthanmaximumratedvoltages
to this high impedance circuit.

MB3773
2
■
■■
■PIN ASSIGNMENT
CT
RESET
CK
GND
RESET
VS
VREF
VCC
1
2
3
4
8
7
6
5
CT
RESET
CK
GND
RESET
VS
VREF
VCC
1
2
3
4
8
7
6
5
(TOP VIEW)
(SIP-8P-M03)
(DIP-8P-M01)
(FPT-8P-M01)
(FRONT VIEW)

MB3773
3
■
■■
■BLOCK DIAGRAM
CT
+
_
+
_
82
7
3
1
4
5
GND
RESET
VS
VCC
R
S
Q
:= 1.24 V
:= 40 kΩ
:= 1.24 V
:= 10 µA
:= 1.2 µA
:= 100
kΩ
Watch
Dog
Timer
P.G
+
_
Reference Voltage Generator +
_
Reference AMP.
VREF
6
COMP.O
RESET
:= 10 µA
Inhibit
CK
COMP.S

MB3773
4
■
■■
■FUNCTIONAL DESCRIPTIONS
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 µs interval.
However 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 iscomparatorfor turning on/offthe outputand,compare thevoltageof theCrterminal andthethreshold
voltage. Because the RESET/RESET outputs have built-in pull-up circuit, there is no need to connect to external
pull-up resistor when connected to a high impedance load such as CMOS logic IC.
(It corresponds to 500 kΩat 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.

MB3773
5
RESET
VCC
VSH
VSL
0.8 V
CK
CT
TCK
TPR TWD
TWR TPR
(1) (2) (3)(4)(5) (5) (6)(7) (8)(9) (10) (11) (12)
•
••
•MB3773 Basic Operation
VCC
RESET
RESET
CK
Logic Circuit TPR (ms) := 1000 · CT(µF)
TWD (ms) := 100 · CT(µF)
TWR (ms) := 20 · CT(µF)
Example : CT=0.1 µF
TRR (ms) := 100 (ms)
TWD (ms) := 10 (ms)
TWR (ms) := 2 (ms)
RESET
RESET
CK
GND
CT
VCC

MB3773
6
■
■■
■OPERATION SEQUENCE
(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 CTstarts.
At this time, the output is being reset.
(3) When CTbegins charging, RESET goes “High” and RESET goes “Low”.
After TPR reset of the output is released.
Reset hold time: TPR (ms) := 1000 ×CT(µF)
After releasing reset, the discharge of CTstarts, and watch-dog timer operation starts.
TPR 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 CT.
(5) C changes from the charge into the discharge when the voltage of CTreaches 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 CTfalls on threshold ( := 0.4 V) of reset on, RESET goes
“Low” and RESET goes “High”.
Discharge time of CTuntil reset is output: TWD is watch-dog timer monitoring time.
TWD (ms) := 100 ×CT(µF)
Because the charging time of CTis added at accurate time from stop of the clock and getting to the output
of reset of the clock, TWD becomes maximum TWD +TWR by minimum TWD.
(7) Reset time in operating watch-dog timer:TWR is charging time where the voltage of CTgoes up to off
threshold ( := 1.4 V) for reset.
TWR (ms) := 20 ×CT(µF)
Reset of the output is released after CTreaches an off threshold for reset, and CTstarts 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 VSL ( := 4.2 V) , reset is output. CTis rapidly discharged of at the same time.
(9) When Vcc goes up to VSH, the charge with CTis started.
When Vcc is momentarily low,
After falling VSL 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 CTis 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 VSL or less, (8) to (10) is repeated.
(11) While power supply is off, when Vcc becomes VSL or less, reset is output.
(12) The reset output is maintained until Vcc becomes 0.8 V when Vcc falls on 0 V.

MB3773
7
■
■■
■ABSOLUTE MAXIMUM RATINGS
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
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.
Parameter Symbol Rating Unit
Min Max
Supply voltage VCC −0.3 +18 V
Input voltage VS−0.3 VCC +0.3 ( ≤+18) V
VCK −0.3 +18 V
RESET, RESET Supply voltage VOH −0.3 VCC +0.3 ( ≤+18) V
Power dissipation (Ta ≤+85 °C) PD200 mW
Storage temperature TSTG −55 +125 °C
Parameter Symbol Value Unit
Min Max
Supply voltage VCC +3.5 +16 V
RESET, RESET sink current IOL 020mA
VREF output current IOUT −200 +5 µA
Watch clock setting time tWD 0.1 1000 ms
CK Rising/falling time tFC, tRC 100 µs
Terminal capacitance CT0.001 10 µF
Operating ambient temperature Ta −40 +85 °C

MB3773
8
■
■■
■ELECTORICAL CHARACTERISTICS
(1) DC Characteristics (VCC =5 V, Ta =+25 °C)
Parameter Symbol Condition Value
Unit
Min Typ Max
Supply current ICC Watch dog timer operating 600 900 µA
Detection voltage
VSL VCC 4.10 4.20 4.30
V
Ta =−40 °C to +85 °C 4.05 4.20 4.35
VSH 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
Reference voltage VREF 1.227 1.245 1.263 V
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 ∆VREF2 IOUT =−200 µA to +5 µA−5 +5mV
CK threshold voltage VTH Ta =−40 °C to +85 °C 0.8 1.25 2.0 V
CK input current IIH VCK =5.0 V 01.0
µA
IIL VCK =0.0 V −1.0 −0.1 
CTdischarge current ICTD Watch dog timer operating
VCT =1.0 V 71014µA
High level output voltage VOH1 VSopen, IRESET =−5 µA4.54.9V
VOH2 VS=0 V, IRESET =−5 µA4.54.9
Output saturation voltage
VOL1 VS=0 V, IRESET =3 mA 0.2 0.4
V
VOL2 VS=0 V, IRESET =10 mA 0.3 0.5
VOL3 VSopen, IRESET =3 mA 0.2 0.4
VOL4 VSopen, IRESET =10 mA 0.3 0.5
Output sink current IOL1 VS=0 V, VRESET =1.0 V 20 60 mA
IOL2 VSopen, VRESET =1.0 V 20 60 
CTcharge current ICTU Power on reset operating
VCT =1.0 V 0.5 1.2 2.5 µA
Min supply voltage for RESET VCCL1 VRESET =0.4 V,
IRESET =0.2 mA 0.8 1.2 V
Min supply voltage for RESET VCCL2 VRESET =VCC −0.1 V,
RL(pin 2 −GND) =1 MΩ0.8 1.2 V

MB3773
9
(2)AC Characteristics (VCC =5 V, Ta =+25 °C)
* : Output rising/falling time are measured at 10 %to 90 %of voltage.
Parameter Symbol Condition Value Unit
Min Typ Max
VCC input pulse width TPI VCC 8.0 µs
CK input pulse width TCKW CK 3.0 µs
CK input frequency TCK 20 µs
Watch dog timer watching time TWD CT=0.1 µF 5 10 15 ms
Watch dog timer reset time TWR CT=0.1 µF123ms
Rising reset hold time TPR CT=0.1 µF, VCC 50 100 150 ms
Output propagation
delay time from VCC
TPD1 RESET, RL=2.2 kΩ,
CL=100 pF 210
µs
TPD2 RESET, RL=2.2 kΩ,
CL=100 pF 310
Output rising time* tRRL=2.2 kΩ,
CL=100 pF 1.0 1.5 µs
Output falling time* tFRL=2.2 kΩ,
CL=100 pF 0.1 0.5
5 V
4 V
or

MB3773
10
■■■■TYPICAL CHARACTERISTIC CURVES
(Continued)
6.0
5.0
4.0
3.0
2.0
1.0
01.02.03.04.05.06.07.0
Ta =+85 °C
Ta =+25 °C
Ta =−40 °C
4.50
4.44
4.30
4.20
4.10
4.00
−40−20020406080100
VSH
VSL
400
300
200
0 2.0 10.0 12.0 14.0 16.04.0 6.0 8.0 18.0
100
Ta =−40 °C
Ta =+25 °C
Ta =+85 °C
CT =0.1µF
400
300
200
100
0 2.0 10.0 12.0 14.0 16.04.06.08.018.0
CT=0.1µF
Ta =−40 °C
Ta =+25 °C
Ta =+85 °C
500
6.0
5.0
4.0
3.0
2.0
1.0
01.02.03.04.05.06.07.0
Ta = −40 °C, +25 °C, +85 °C
(RESET, RESET terminal)
Supply current vs. Supply voltage
Supply voltage VCC(V) Supply voltage VCC (V)
Output voltage vs. Supply voltage
(RESET terminal)
Supply voltage VCC (V)
Pull up 2.2 kΩ
Output voltage vs. Supply voltage
(RESET terminal)
Detection voltage
(VSH, VSL) vs. Temperature
Temperature Ta ( °C)
Outputsaturationvoltage
vs. Output sink current
(RESETterminal)
Output sink current IOL2(mA)
Output saturation voltage
vs. Output sink current
(RESET terminal)
Output sink current IOL8(mA)
Pull up 2.2 kΩ
Supply current ICC (mA)
Output voltage VRESET(V)
Detection voltage VSH, VSL (V)
Output voltage VRESET (V)
Output saturation voltage VOL2(mV)
Output saturation voltage VOL2 (mV)
0.65
0.75
0.55
0.45
0.35
0.25
0.15
04.02.06.08.010.012.014.016.018.020.0
Ta =−40 °C
Ta =−40 °C
Ta =+25 °C
Ta =+85 °C
CT=0.1 µF
Ta =+25 °CTa =+85 °C

MB3773
11
(Continued)
Ta =+25 °C
Ta =+85 °C
Ta =−40 °C
CT=0.1 µF
5.0
4.5
4.0 0−5−10−15
5.0
4.5
4.0 0−5−10−15
CT=0.1 µF
Ta =+25 °C
Ta =+85 °C
Ta =−40 °C
1.246
1.244
1.242
1.240
1.238
1.236
1.234
03.05.07.09.013.011.017.019.021.015.0
Ta =−40 °C
Ta =+25 °C
Ta =+85 °C
CT=0.1 µF
Ta =+85 °C
1.255
1.250
1.245
1.240
0−40−80−120−160−200−240
CT=0.1 µF
Ta =+25 °C
Ta =−40 °C
−20020−40
1.27
1.25
1.26
1.24
1.23
1.22
1.21
406080100 −20020−40406080100
160
140
120
100
80
60
0
40
CT=0.1 µF
VCC =5 V
Reference voltage
vs. Reference current
High level output voltage
vs. High level output current
(RESET terminal)
High level output voltage
vs. High level output current
(RESET terminal)
Reference voltage
vs. Supply voltage
Supply voltage VCC(V) Reference current IREF(µA)
Reference voltage
vs. Temperature
Temperature Ta ( °C)
Rising reset hold time
vs. Temperature
Temperature Ta ( °C)
High level output current IOH2(µA) High level output current IOH8(µA)
High level output voltage VOH2(V)
High level output voltage VOH8 (V)
Reference voltage VREF(V)
Reference voltage VREF(V)
Reference voltage VREF(V)
Rising reset hold time TPR (ms)

MB3773
12
(Continued)
3
2
1
0−40−20200406080100
CT=0.1 µF
VCC =5 V
−40−20200406080100
16
14
12
10
8
6
4
0
CT=0.1 µF
VCC=5 V
10 6
10 5
10 4
10 3
10 2
10 1
10 0
10 −1
10 −2
10 −3
10 −3 10 −2 10 −1 10 0 10 1 10 2
Ta =−40 °C
Ta =
+25 °C
+85 °C
10
− 3
10
− 2
10
− 1
10 0 10 1 10 2
102
101
100
10−1
10−2
10−3
Ta =+25 °C
+85 °C
Ta =
−40 °C
10 6
10 5
10 4
10 3
10 2
10 1
10 0
10 −1
10 −2
10 −3
10 −3 10 −2 10 −1 10 0 10 1 10 2
Ta =−40 °C
Ta =+25 °C+85 °C
CTterminal capacitance
vs. Rising reset hold time
Watchdog timer watching time
vs. Temperature
Temperature Ta ( °C)
Reset time vs.
Temperature
Temperature Ta ( °C)
C T t erminal capacitance C T (µF)
(At watch dog timer)
CTterminal capacitance
vs. Reset time
CTterminal capacitance
vs.
Watchdog timer watching time
C T t erminalcapacitanceC T (µF)
(at watch dog timer)
C T terminal capacitance C T (µF)
Reset time T
WR
(ms)
Watch dog timer
watching time T
WD
(ms)
Rising reset hold time T
PR
(ms)
Reset time T
WR
(ms)
Watch dog timer
watching time T
WD
(ms)

MB3773
13
■
■■
■APPLICATION CIRCUIT
EXAMPLE 1: Monitoring 5V Supply Voltage and Watchdog Timer
VCC (5V)
MB3773
RESET
RESET
CKGND
Logic circuit
Notes : •Supply voltage is monitored using VS.
•Detection voltage are VSH and VSL.
CT
1
2
3
4
8
7
6
5
EXAMPLE 2: 5V Supply Voltage Monitoring (external fine-tuning type)
VCC (5V)
1
2
3
4
8
7
6
5
MB3773
RESET
RESET
CKGND
Logic circuit
Notes : •Vs detection voltage can be adjusted externally.
•Based on selecting R1and R2values that are sufficiently lower than the resistance of the IC’s
internal voltage divider, the detection voltage can be set according to the resistance ratio of
R1and R2(See the table below.)
R1
R2
CT
R1(kΩ
ΩΩ
Ω)R
2(kΩ
ΩΩ
Ω) Detection voltage: VSL (V) Detection voltage: VSH (V)
10 3.9 4.4 4.5
9.1 3.9 4.1 4.2

MB3773
14
EXAMPLE 3: With Forced Reset (with reset hold)
VCC
1
2
3
4
8
7
6
5
MB3773
RESET
RESET
CK GND
Logic circuit
Note : Grounding pin 7 at the time of SW ON sets RESET (pin 8) to Low and RESET (pin 2) to High.
SW
VCC
1
2
3
4
8
7
6
5
MB3773
RESET
RESET
CK GND
Logic circuit
Note : Feeding the signal to terminal RESIN and turning on Tr sets the RESET terminal to Low and
the RESET terminal to High.
10 kΩ
Tr
RESIN
10 kΩ
Cr
CT
(a)
(b)

MB3773
15
EXAMPLE 4: Monitoring Two Supply Voltages (with hysteresis, reset output and NMI)
VCC1 (5 V)
1
2
3
4
8
7
6
5
MB3773 RESET
RESET
CK
GND
Comp. 2
Example : Comp. 1, Comp. 2
: MB4204, MB47393
NMI or port
R6
+
_
+
_
VCC2(12 V)
180 kΩ
R4
30 kΩ
R3
5.1 kΩ
R2
1.2 kΩ
R1
4.7 kΩ
R5
Comp. 1
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.
•Use VCC1 ( =5 V) to power the comparators (Comp. 1 and Comp. 2) in the external circuit shown
above.
•The detection voltage of the VCC2 ( =12 V) supply voltage is approximately 9.2 V/9.4 V and has
a hysteresis width of approximately 0.2 V.
VCC2 detection voltage and hysteresis width can be found using the following formulas:
→Detection voltage
→Hysteresis width VHYS =V2H −V2L
R3+(R4// R5)
R4// R5×VREF
V2L =R3+R5
R5×VREF
(Approximately 9.4 V in the above illustration)
(Approximately 9.2 V in the above illustration)
CT
Logic circuit
V2H =
10 kΩ

MB3773
16
EXAMPLE 5: Monitoring Two Supply Voltages (with hysteresis and reset output)
VCC1(5 V)
1
2
3
4
8
7
6
5
MB3773
RESET
RESET
CK GND
Comp. 2
Example : Comp. 1, Comp. 2
: MB4204, MB47393
20 kΩ
R6
+
_
+
_
VCC2 (12 V)
180 kΩ
R4
30 kΩ
R3
5.1 kΩ
R2
1.2 kΩ
R1
4.7 kΩ
R5
Comp. 1
Notes : •When either 5 V or 12 V supply voltage decreases below its detection voltage (VSL),
the MB3773 RESET terminal is set to High and the MB3773 RESET terminal is set to Low.
•Use VCC1 ( =5 V) to power the comparators (Comp. 1 and Comp. 2) in the external circuit shown
above.
•The detection voltage of the VCC2 ( =12 V) supply voltage is approximately 9.2 V/9.4 V and has a
hysteresiswidthofapproximately 0.2V.Fortheformulasfor findinghysteresiswidthanddetection
voltage, see section 4.
Logic circuit
Diode
CT

MB3773
17
EXAMPLE 6: Monitoring Low voltage and Overvoltage Monitoring (with hysteresis)
VCC (5 V)
1
2
3
4
8
7
6
5
MB3773
RESET
RESET
CK GND
Comp. 2
Example : Comp. 1, Comp. 2
: MB4204, MB47393
20 kΩ
R6
_
+
180 kΩ
R4
30 kΩ
R3
5.6 kΩ
R6
1.2 kΩ
R1
4.7 kΩ
R5
Comp. 1
Notes : •Comp. 1 and Comp. 2 are used to monitor for overvoltage while the MB3773 is used to monitor
for low voltage. Detection voltages V1L/V1H at the time of low voltage are approximately 4.2 V/4.3 V.
Detection voltages V2L/V2H at the time of overvoltage are approximately 6.0 V/6.1 V.
For the formulas for finding hysteresis width and detection voltage, see EXAMPLE 4.
•Use VCC ( =5 V) to power the comparators (Comp. 1 and Comp. 2) in the external circuit shown
above.
Logic circuit
Diode
RESET
0V1L V1H V2L V2H VCC
+
_
CT

MB3773
18
EXAMPLE 7: Monitoring Supply Voltage Using Delayed Trigger
VCC
1
2
3
4
8
7
6
5
MB3773
RESET
RESET
CK GND
Logic circuit
Note : Adding voltage such as shown in the figure to VCC increases the minimum input pulse
width by 50 µs (C1=1000 pF).
C1
VCC
5V
4V
CT

MB3773
19
(Continued)
EXAMPLE 8: Stopping Watch-dog Timer (Monitoring only supply voltage)
(a) Using NPN transistor
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 CTterminal voltage to VREF.
The supply voltage is constantly monitored even while the watch-dog timer is inhibited.
For this reason, a reset signal is output at the occurrence of either instantaneous disruption or a sudden drop
to low voltage.
Note that in application examples (a) and (b), the hold signal is inactive when the watch-dog timer is inhibited at
the time of resetting.
If the hold signal is active when tie microprocessor is reset, the solution is to add a gate, as in examples (c)
and (d).
VCC(5 V)
1
2
3
4
8
7
6
5
MB3773
RESET
RESET
CK
GND
Logic circuit
R2=1 kΩ
HALT
R1=1 MΩ
(b) Using PNP transistor
VCC (5 V)
1
2
3
4
8
7
6
5
MB3773
RESET
RESET
CK
GND
Logic circuit
R2=1 kΩ
HALT
R1=51 kΩ
CT
CT

MB3773
20
(Continued)
(c) Using NPN transistor
VCC (5 V)
1
2
3
4
8
7
6
5
CT
MB3773
RESET
RESET
CK
GND
Logic circuit
R2=1 kΩ
HALT
R1=1 MΩ
(d) Using PNP transistor
VCC (5 V)
1
2
3
4
8
7
6
5
CT
MB3773
RESET
RESET
CK
GND
Logic circuit
R2=1 kΩ
HALT
R1=51 kΩ