TC1278/TC1279
3-Pin Reset Monitors for 5V Systems
Features
•
•
•
•
•
•
Precision V
CC
Monitor for 5.0V System Supplies
250msec Minimum RESET Output Duration
Output Valid to V
CC
= 1.2V
V
CC
Transient Immunity
Small 3-Pin SOT-23B Package
No External Components
General Description
The TC1278/TC1279 are cost-effective system super-
visor circuits designed to monitor V
CC
in digital systems
and provide a reset signal to the host processor when
necessary. No external components are required.
The reset output is driven active within 5µsec of V
CC
falling through the reset voltage threshold. RESET is
maintained active for a minimum of 250msec after V
CC
rises above the reset threshold. The TC1278 has an
active-high RESET output while the TC1279 has an
active-low RESET output, and both devices have an
open drain output stage. The output is valid down to
V
CC
= 1.2V. Both devices are available in a 3-Pin SOT-
23B package.
Applications
•
•
•
•
Computers
Embedded Systems
Battery Powered Equipment
Critical
µP
Power Supply Monitoring
Device Selection Table
Part
Number
Order
Package
Temp.
Range
Typical Operating Circuit
V
CC
2
V
CC
1
RESET
V
CC
Processor
RESET
Input
TC1278-xENB Open Drain 3-Pin SOT-23B -40°C to +85°C
TC1279-xENB Open Drain 3-Pin SOT-23B -40°C to +85°C
NOTE:
“x” denotes a suffix for V
CC
threshold (see table below).
TC1279
GND
3
GND
Suffix
5
10
15
Reset V
CC
Threshold (V)
4.625
4.375
4.125
Package Type
3-Pin SOT-23B
RESET
1
TC1278-xENB
TC1279-xENB
V
CC
3
GND
2
NOTE:
3-Pin SOT-23B is equivalent to JEDEC TO-236
2002 Microchip Technology Inc.
DS21384B-page 1
©
TC1278/TC1279
1.0
ELECTRICAL
CHARACTERISTICS
*Stresses above those listed under "Absolute Maximum
Ratings" may cause permanent damage to the device. These
are stress ratings only and functional operation of the device
at these or any other conditions above those indicated in the
operation sections of the specifications is not implied.
Exposure to Absolute Maximum Rating conditions for
extended periods may affect device reliability.
Absolute Maximum Ratings*
Supply Voltage (V
CC
to GND) ..............................+6.0V
RESET, RESET...........................-0.3V to (V
CC
+ 0.3V)
Input Current, V
CC
...............................................20mA
Output Current, RESET....................................... 20mA
Power Dissipation (T
A
≤
70°C)
3-Pin SOT-23B (derate 4mW/°C above +70°C)
.................................................................230mW
Operating Temperature Range............. -40°C to +85°C
Storage Temperature Range .............. -65°C to +150°C
TC1278/TC1279 ELECTRICAL SPECIFICATIONS
Recommended DC Operating Conditions:
T
A
= -40°C to +85°C unless otherwise noted. Typical values are at T
A
= +25°C.
Symbol
V
CC
Symbol
V
OL
I
OL
I
CC1
I
CC2
V
CCTP-5
Parameter
Supply Voltage
Min
1.2
Typ
—
Max
5.5
Units
V
Device
Test Conditions
Note 1
DC Electrical Characteristics:
T
A
= -40°C to +85°C unless otherwise noted. Typical values are at T
A
= +25°C.
Parameter
Low Level @ RESET
RESET
Output Current @ 0.4 Volts
Operating Current
Operating Current
V
CC
Trip Point (TC1278/9-5)
Min
—
+8
—
—
—
—
4.50
4.25
4.00
—
3
Typ
—
—
0.9
—
—
0.9
4.625
4.375
4.125
9
6
Max
0.4
—
2.0
40
40
2.0
4.74
4.49
4.24
—
9
Units
V
mA
mA
µA
µA
mA
V
V
V
pF
kΩ
TC1278
TC1279
TC1278
TC1279
TC1278
TC1279
Test Conditions
Note 1
Note 2
V
CC
> V
CCTP(MAX)
V
CC
> V
CCTP(MAX)
V
CC
< V
CCTP(MIN)
V
CC
< V
CCTP(MIN)
Note 1
Note 1
Note 1
V
CCTP-10
V
CC
Trip Point (TC1278/9-10)
V
CCTP-15
V
CC
Trip Point (TC1278/9-15)
C
OUT
R
P
Symbol
t
RST
t
RPD1
t
RPD2
t
F
t
R
t
RPU1
t
RPU2
Note
1:
2:
Output Capacitance
Internal Pull-Up Resistor
AC Electrical Characteristics:
T
A
= -40°C to +85°C unless otherwise noted. Typical values are at T
A
= +25°C.
Parameter
RESET Active Time
V
CC
Detect to RESET
V
CC
Detect to RESET
V
CC
Slew Rate
(4.75V-4.00V)
V
CC
Slew Rate
(4.00V-4.75V)
V
CC
Detect to RESET
V
CC
Detect to RESET
Min
250
—
—
300
0
250
250
Typ
350
2
2
—
—
350
350
Max
450
5
5
—
—
450
450
Units
msec
µsec
TC1279
µsec
TC1278
µsec
nsec
msec TC1279
msec TC1278
Figure 3-2
Figure 3-4
Figure 3-2, Figure 3-4
Figure 3-1, Figure 3-3
Figure 3-1
Figure 3-3
Test Conditions
All voltages referenced to ground.
A 1kΩ external resistor may be required in some applications for proper operation of the microprocessor reset control circuit when using
the TC1279. V
CC
= 1.8V.
©
DS21384B-page 2
2002 Microchip Technology Inc.
TC1278/TC1279
2.0
PIN DESCRIPTIONS
The descriptions of the pins are listed in Table 2-1.
TABLE 2-1:
Pin No.
(3-Pin SOT-23B)
1
PIN FUNCTION TABLE
Symbol
RESET (TC1279)
Description
RESET output remains low while V
CC
is below the reset voltage threshold, and for
350msec (250msec min.) after V
CC
rises above reset threshold. The output stage of the
TC1279 is open drain.
RESET output remains high while V
CC
is below the reset voltage threshold, and for
350msec (250msec min.) after V
CC
rises above reset threshold. The output stage of the
TC1278 is open drain.
Supply voltage (1.2V to 5.5V).
Ground.
1
RESET (TC1278)
2
3
V
CC
GND
2002 Microchip Technology Inc.
DS21384B-page 3
©
TC1278/TC1279
3.0
3.1
APPLICATIONS INFORMATION
Operation – Power Monitor
FIGURE 3-3:
Timing Diagram –
Power Up (TC1278)
t
R
The TC1278/TC1279 provide the function of detecting
out-of-tolerance power supply conditions and warning
a processor-based system of impending power failure.
When V
CC
is detected as out-of-tolerance, the RESET
signal is asserted. On power-up, RESET is kept active
for approximately 350msec after the power supply has
reached the selected tolerance. This allows the power
supply and microprocessor to stabilize before RESET
is released.
V
CCTP(MAX)
V
CCTP(MIN)
V
CCTP
V
CC
t
RPU2
FIGURE 3-1:
Timing Diagram –
Power Up (TC1279)
RESET
t
R
V
OL
4.75V
4.00V
V
CCTP
FIGURE 3-4:
Timing Diagram –
Power Down (TC1278)
t
F
V
CC
t
RPU
1
V
CC
4.74V
V
CCTP
V
OH
4.00V
RESET
t
RPD2
FIGURE 3-2:
Timing Diagram –
Power Down (TC1279)
t
F
V
OH
RESET SLEWS WITH V
CC
RESET
V
CC
4.75V
V
CCTP
4.00V
t
RPD1
RESET
V
OL
©
DS21384B-page 4
2002 Microchip Technology Inc.
TC1278/TC1279
3.2
V
CC
Transient Rejection
FIGURE 3-5:
The TC1278/TC1279 provides accurate V
CC
monitor-
ing and reset timing during power-up, power-down,
and brownout/sag conditions, and rejects negative-
going transients (glitches) on the power supply line.
Figure 3-5 shows the maximum transient duration vs.
maximum negative excursion (overdrive) for glitch
rejection. Any combination of duration and overdrive
that lays under the curve will not generate a reset
signal. Combinations above the curve are detected as
a brownout or power-down. Transient immunity can be
improved by adding a capacitor in close proximity to the
V
CC
pin of the TC1278/TC1279.
MAXIMUM TRANSIENT DURATION (µsec)
5
MAXIMUM TRANSIENT
DURATION VS.
OVERDRIVE FOR GLITCH
REJECTION AT 25°C
V
CC
V
CCTP
Overdrive
Duration
T
A
°C
4
3
2
TC1278/9
1
0
1
5
1000
100
RESET COMPARATOR OVERDRIVE,
[
V
CCTP
- V
CC
]
(mV)
2002 Microchip Technology Inc.
DS21384B-page 5
©
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