SUPPLY VOLTAGE
MONITOR
ISSUE 3 – JANUARY 1998
DEVICE DESCRIPTION
The ZSM561 is a three terminal under
vo l ta ge mo ni t or ci rc ui t f or use i n
microprocessor systems. The threshold
voltage of the device has been set to 4.6 volts
making it ideal for 5 volt circuits.
Included in the device is a precise voltage
reference and a comparator with built in
hysteresis to prevent erratic operation. The
ZSM561 features an open collector output
capable of sinking at least l0mA which only
requires a single external resistor to
interface to following circuits.
Operation of the device is guaranteed from
one volt upwards, from this level to the
device threshold voltage the output is held
low providing a power on reset function.
Should the supply voltage, once established,
at any time drop below the threshold level
then the output again will pull low. Also
included is a 6 volt zener diode connected
between Vcc and Gnd. With just the addition
of a low cost external NPN transistor and
resistor, this zener allows the ZSM561 to
provide both regulator and supply monitor
functions
The device is available in a TO92 package for
through hole applications as well as SO8 and
SOT223 for surface mount requirements.
ZSM561
FEATURES
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
SO8, SOT223 and TO92 packages
Power on reset generator
Automatic reset generation
Low standby current
Guaranteed operation from 1 volt
Wide supply voltage range
Internal clamp diode to discharge
delay capacitor
4.6 volt threshold for 5 volt logic
20mV hysteresis prevents erratic operation
APPLICATIONS
Microprocessor systems
Computers
Computer peripherals
Instrumentation
Automotive
Battery powered equipment
SCHEMATIC DIAGRAM
4-364
ZSM561
ABSOLUTE MAXIMUM RATING
Input Supply Voltage
Supply Zener Current
Offstate Output Voltage
Onstate Output
Sink Current(
Note 1
)
Clamp Diode
Forward Current(
Note 1
)
-1 to 7V
25mA continuous
7V
Internally limited
100mA
Operating Junction
Temperature
Operating Temperature
Storage Temperature
Power Dissipation
TO92
SOT223
SO8
150°C
-40 to 85°C
-65 to 150°C
780mW
2W(
Note 2
)
780mW(
Note 2
)
TEST CONDITIONS
(T
amb
=25°C for typical values, T
amb
=-40 to 85°C for min/max values (Note3))
COMPARATOR
PARAMETER
Threshold Voltage
High state output (Vcc increasing)
Threshold Voltage
Low state output (Vcc decreasing)
Hysteresis
SYMBOL
V
IH
V
IL
V
H
4.5
4.5
0.01
MIN
TYP.
MAX.
UNITS
V
V
V
4.61
4.59
0.02
4.7
4.7
0.05
OUPUT
Output sink saturation:
(V
cc
=4.0V, I
sink
=8.0mA)
(V
cc
=4.0V, I
sink
=2.0mA)
(V
cc
=1.0V, I
sink
=0.1mA)
Onstate output sink current
(V
cc
, Output=4V)
Offstate output leakage current
(V
cc
, Output=5V)
Clamp diode forward voltage
(I
f
=10mA)
Propagation delay
(V
in
5V to 4V, R
l
=10k, T
amb
=25°C)
I
sink
I
oh
V
f
T
d
0.6
10
20
0.02
1.2
1.5
V
OL
0.46
0.15
1.0
0.4
0.25
60
0.5
1.5
V
V
V
mA
µA
V
µs
SUPPLY ZENER
Avalanche Voltage:(Icc=1mA)
Slope Resistance:
V
z
5.8
6
45
21
6.2
60
30
V
Ω
Ω
(Icc=15mA)
R
z
(Icc=15mA to 50mA)
TOTAL DEVICE
Operating input voltage range(Note 5)
Quiescent current (V
cc
=5V)
V
cc
I
q
1.0 to 7
135
200
V
µA
4-365
ZSM561
TYPICAL CHARACTERISTICS
4.70
50
40
4.65
Threshold Voltage (V)
Input Current (mA)
Upper Threshold
4.60
30
20
Lower Threshold
4.55
10
4.50
0
0
2
4
6
8
10
-40
-20
0
20
40
60
80
100
Temperature ( °C)
Input Voltage (V)
Input Current vs. Input Voltage
Threshold Voltage vs. Temperature
TIMING DIAGRAM
Vcc
Threshold
Voltage
1V
Output
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Output
Undefined
Output
Undefined
Note:
1. Maximum package power dissipation must be observed.
2. Maximum power dissipation for the SOT223 and SO8 packages is calculated assuming that
the device is mounted on a PCB measuring 2 inches square.
3. Low duty cycle pulse techniques are used during test to maintain junction temperatures as
close to ambient as possible
4. A time delayed reset can be accomplished with the additional Cd.
5. Operation above V
z
may be restricted by the supply current rating I
z
4-367
ZSM561
APPLICATION CIRCUITS
1
T
DY
=
RCd
ln
1
−
V
TH
(
mpu
)
V
in
T
DY
= Time (Seconds)
V
TH
= Microprocessor ResetThreshold
V
in
= Power Supply Voltage
R
B
=
(
V
INMIN
−
6
)
I
L
(
I
Q
+
)
h
FE
h
FE
= The minimum h
FE
that can be expected
from the pass transistor under worst case
conditions. (ie Lowest temperature and
minimum input voltage). For the ZTX690B a
value of 250 could be used.
V
INMIN
= The minimum input voltage provided
by the unregulated supply.
I
Q
= The ZSM561 quiescent current (ie 200
µA)
I
L
= Load current taken by the microprocessor
system.
4-368
Embedded System
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