MB3771
Power Supply Monitor
Description
The Cypress MB3771 is designed to monitor the voltage level of one or two power supplies (+5 V and an arbitrary voltage) in a
microprocessor circuit, memory board in large-size computer, for example.
If the circuit’s power supply deviates more than a specified amount, then the MB3771 generates a reset signal to the microprocessor.
Thus, the computer data is protected from accidental erasure.
Using the MB3771 requires few external components. To monitor only a +5 V supply, the MB3771 requires the connection of one
external capacitor. The level of an arbitrary detection voltage is determined by two external resistors. The MB3771 is available in an
8-pin Dual In-Line, Single In-Line Package or space saving Flat Package.
Features
■
■
■
■
■
■
■
■
■
■
Precision voltage detection
(V
SA
=
4.2 V
±
2.5
%)
User selectable threshold level with hysteresis (V
SB
= 1.23 V
±
1.5
%)
Monitors the voltage of one or two power supplies (5 V and an arbitrary voltage,
>1.23
V)
Usable as over voltage detector
Low voltage output for reset signal (V
CC
= 0.8 V Typ)
Minimal number of external components (one capacitor Min)
Low power dissipation (I
CC
= 0.35 mA Typ, V
CC
= 5 V)
Detection threshold voltage has hysteresis function
Reference voltage is connectable.
One type of package (SOP-8pin : 1 type)
Application
■
■
Industrial Equipment
Arcade Amusement etc.
Cypress Semiconductor Corporation
Document Number: 002-08511 Rev. *D
•
198 Champion Court
•
San Jose
,
CA 95134-1709
•
408-943-2600
Revised June 28, 2017
MB3771
Contents
Description ............................................................................. 1
Features .................................................................................. 1
Application ............................................................................. 1
Contents ................................................................................. 2
1. Pin Assignment ................................................................. 3
2. Block Diagram ................................................................... 3
3. Functional Descriptions .................................................... 4
4. Function Explanation ........................................................ 4
5. Absolute Maximum Ratings ............................................. 5
6. Recommended Operating Conditions ............................. 5
7. Electrical Characteristics .................................................. 6
7.1 DC Characteristics ..................................................... 6
7.2 AC Characteristics ...................................................... 7
8. Application Circuit ............................................................. 8
8.1 5V Power Supply Monitor ........................................... 8
8.2 5V Power Supply Voltage Monitor
(Externally Fine-Tuned Type) ........................................... 8
8.3 Arbitrary Voltage Supply Monitor ................................ 9
8.4 5 V and 12 V Power Supply Monitor (2 types of power
supply monitor VCC1 = 5 V, VCC2 =12 V) ..................... 10
8.5 5 V and 12 V Power Supply Monitor (RESET signal is
generated by 5 V, VCC1 = 5 V, VCC2 = 12 V) ............... 10
8.6 5 V Power Supply Monitor with forced RESET input
(VCC = 5 V) .................................................................... 11
8.7 5 V Power Supply Monitor with Non-inverted
RESET ............................................................................ 11
8.8 Supply Voltage Monitoring with Delayed Trigger ..... 11
8.9 Dual (Positive/Negative) Power Supply Voltage
Monitoring (VCC = 5 V, VEE = Negative Power Supply). 12
8.10 Reference Voltage Generation and Voltage Sagging
Detection ........................................................................ 12
8.11 Low Voltage and Over Voltage Detection
(VCC = 5 V) .................................................................... 14
8.12 Detection of Abnormal State of Power Supply System
(VCC = 5 V) .................................................................... 14
8.13 Back-up Power Supply System (VCC = 5 V) ......... 15
9. Typical Characteristics ................................................... 17
10. Notes on Use .................................................................. 19
11. Ordering Information ..................................................... 19
12. RoHS Compliance Information ..................................... 19
13. Package Dimensions ..................................................... 20
Document History ................................................................ 21
Sales, Solutions, and Legal Information ........................... 22
Document Number: 002-08511 Rev. *D
Page 2 of 22
MB3771
1. Pin Assignment
(TOP VIEW)
C
T
V
SC
OUT
C
GND
1
2
3
4
(
SOE008
)
8
7
6
5
RESET
V
SA
V
SB
RESIN
V
CC
2. Block Diagram
V
CC
5
≅
1.24 V
≅
1.24 V
≅
100 kΩ
V
SA
7
≅
40 kΩ
+
−
Comp. A
+
REFERENCE VOLTAGE
+
−
R
Q
≅
12
μA
≅
10
μA
2
V
SC
−
+
−
Comp. C
+
V
SB
/ RESIN 6
−
Comp. B
S
4
1
C
T
8
3
GND
RESET OUT
C
Document Number: 002-08511 Rev. *D
Page 3 of 22
MB3771
3. Functional Descriptions
Comparators Comp.A and Comp.B apply a hysteresis to the detected voltage, so that when the voltage at either the V
SA
or V
SB
pin
falls below 1.23 V the RESET output signal goes to “low” level.
Comp. B may be used to detect any given voltage(8.Application Circuit 8.3 : Arbitrary Voltage Supply Monitor), and can also be used
as a forced reset pin (with reset hold time) with TTL input (8.Application Circuit 8.6 : 5V Power Supply Monitor with forced RESET input
(V
CC
= 5 V) ).
Note that if Comp.B is not used, the V
SB
pin should be connected to the V
CC
pin (8.Application Circuit 8.1 : 5V Power Supply Monitor).
Instantaneous breaks or drops in the power supply can be detected as abnormal conditions by the MB3771 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 V
SA
or V
SB
pin (8.Application Circuit 8.8 : Supply Voltage Monitoring
with Delayed Trigger).
Because the RESET output has built-in pull-up resistance, there is no need to connect to external pull-up resistance when connected
to a high impedance load such as a CMOS logic IC.
Comparator Comp. C is an open-collector output comparator without hysteresis, in which the polarity of input/output characteristics
is reversed. Thus Comp. C is useful for over-voltage detection (8.Application Circuit 8.11 : Low Voltage and Over Voltage Detection
(V
CC
= 5 V) ) and positive logic RESET signal output (8.Application Circuit 8.7 : 5 V Power Supply Monitor with Non-inverted RESET),
as well as for creating a reference voltage (8.Application Circuit 8.10 : Reference Voltage Generation and Voltage Sagging Detection).
Note that if Comp. C is not used, the V
SC
pin should be connected to the GND pin (Application Circuit 1 : 5V Power Supply Monitor).
4. Function Explanation
V
HYS
V
S
V
CC
V
CC
C
T
1
2
3
4
8
7
6
5
RESET
0.8 V
t
T
PO
T
PO
RESET
t
(1)
(2)
(3)
(4) (5) (6)
(7)
(8)
1. When V
CC
rises to about 0.8V, RESET goes low.
2. When V
CC
reaches V
S
+V
HYS
, C
T
then begins charging. RESET remains low during this time
3. RESET goes high when CT begins charging.
T
PO
≈
C
T
× 10
5
(Refer to “C
T
pin capacitance vs. reset hold time” in “9.Typical Characteristics”.)
4. When V
CC
level drops lower then V
S
, then RESET goes low and C
T
starts discharging.
5. When V
CC
level reaches V
S
+ V
HYS
, then C
T
starts charging.
In the case of voltage sagging, if the period from the time V
CC
goes lower than or equal to V
S
to the time V
CC
reaches V
S
+V
HYS
again, is longer than t
PI
, (as specified in the 7.2.AC Characteristics), C
T
is discharged and charged successively.
6. After T
PO
passes, and V
CC
level exceeds V
S
+ V
HYS
, then RESET goes high.
7. Same as Point 4.
8. RESET remains low until V
CC
drops below 0.8V.
Document Number: 002-08511 Rev. *D
Page 4 of 22
MB3771
5. Absolute Maximum Ratings
Parameter
Power supply voltage
Input voltage
Symbol
V
CC
V
SA
V
SB
V
SC
Power dissipation
Storage temperature
P
D
Tstg
Rating
Min
Max
+20
V
CC
+
0.3
( < +20)
+20
+20
200
(Ta
Unit
V
V
V
V
mW
°C
−
0.3
−
0.3
−
0.3
−
0.3
–
≤
85°C)
−
55
+125
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.
6. Recommended Operating Conditions
Parameter
Power supply voltage
Output current
Symbol
V
CC
I
RESET
I
OUTC
Operating ambient temperature
Ta
Value
Min
3.5
0
0
Max
18
20
6
+85
Unit
V
mA
mA
°C
−
40
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 Cypress representatives beforehand.
Document Number: 002-08511 Rev. *D
Page 5 of 22
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