LTC1232
Microprocessor
Supervisory Circuits
FEATURES
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■
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DESCRIPTIO
Guaranteed
Reset Assertion at V
CC
= 1V
8-Pin SO Plastic Package
2.0mA Maximum Supply Current
4.62V/4.37V Precision Voltage Monitor
Power OK/Reset Time Delay: 600ms
Minimum External Component Count
Superior Upgrade for DS1232
The LTC
®
1232 provides power supply monitoring,
watchdog timing and external reset for microprocessor
systems. A precise internal voltage reference and
comparator circuit monitor the power supply line. When
an out-of-tolerance condition occurs, the reset outputs
are forced to active states. The RST output is guaranteed
to remain logic low even with V
CC
as low as 1V.
The LTC1232 has an internal watchdog timer which forces
the reset outputs to active states when the Strobe input is
not forced low prior to a preset time-out period. The
watchdog timing can be set to operate on time-out periods
of typically 150ms, 600ms or 1.2 seconds.
The LTC1232 performs push-button reset control.
The LTC1232 debounces the push-button input
and guarantees an active reset pulse width of 250ms
minimum.
, LTC and LT are registered trademarks of Linear Technology Corporation.
APPLICATIO S
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Critical
µP
Power Monitoring
Intelligent Instruments
Computers and Controllers
Automotive Systems
TYPICAL APPLICATIO
RST Output Voltage vs
Supply Voltage
5
5V DC
PB RST
5V DC
TD
V
CC
100k
ST
MPU
(e.g. 6805)
I/O LINE
RESET
RST OUTPUT VOLTAGE (V)
4
3
LTC1232
TOL
GND
RST
RST
2
1
LTC1232 • TA01
0
0
1
U
3
4
2
SUPPLY VOLTAGE (V)
5
LTC1232 • TA02
U
U
1232fa
1
LTC1232
ABSOLUTE
(Note 1, 2 and 3)
AXI U
RATI GS
PACKAGE/ORDER I FOR ATIO
TOP VIEW
PB RST 1
TD 2
TOL 3
GND 4
8
7
6
5
V
CC
ST
RST
RST
Terminal Voltage
V
CC
....................................................... –0.3V to 7.0V
ST and RST .......................................... –0.3V to 7.0V
All Other Inputs and Outputs ...... –0.3V to V
CC
+0.3V
Power Dissipation .............................................. 500mW
Operating Temperature Range
LTC1232C ............................................... 0°C to 70°C
LTC1232I ........................................... –40°C to 85°C
Storage Temperature Range ................. –65°C to 150°C
Lead Temperature (Soldering, 10 sec).................. 300°C
ORDER
PART NUMBER
LTC1232CN8
LTC1232IN8
N8 PACKAGE
8-LEAD PDIP
T
JMAX
= 100°C,
θ
JA
= 130°C/W
TOP VIEW
PB RST 1
TD 2
TOL 3
GND 4
8
7
6
5
V
CC
ST
RST
RST
ORDER
PART NUMBER
LTC1232CS8
LTC1232IS8
S8 PART MARKING
1232
1232I
S8 PACKAGE
8-LEAD PLASTIC SO
T
JMAX
= 100°C,
θ
JA
= 180°C/W
Consult LTC Marketing for parts specified with wider operating tempera-
ture ranges.
PRODUCT SELECTIO GUIDE
PINS
LTC1232
LTC690
LTC691
LTC694
LTC695
LTC699
LTC1235
8
8
16
8
16
8
16
RESET
X
X
X
X
X
X
X
WATCHDOG
TIMER
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
BATTERY
BACKUP
POWER
FAIL
WARNING
RAM
WRITE
PROTECT
PUSH-BUTTON
RESET
X
CONDITIONAL
BATTERY
BACKUP
2
U
1232fa
W
U
U
W W
U
W
LTC1232
RECO
SYMBOL
V
CC
V
IH
V
IL
over the full operating temperature. V
CC
= full operating range.
PARAMETER
Supply Voltage
ST and PB RST Input High Level
ST and PB RST Input Low Level
E DED OPERATI G CO DITIO S
CONDITIONS
DC ELECTRICAL CHARACTERISTICS
temperature. V
CC
= full operating range.
SYMBOL
I
IL
I
OH
I
OL
I
CC
V
CCTP
V
CCTP
V
HYS
V
RST
PARAMETER
Input Leakage
Output Current at 2.4V
Output Current at 0.4V
Supply Current
V
CC
Trip Point
V
CC
Trip Point
V
CC
Trip Point Hysteresis
RST Output Voltage at V
CC
= 1V
I
SINK
= 10µA
CONDITIONS
(Note 3)
(Note 5)
(Note 5)
(Note 4)
TOL = GND
TOL = V
CC
The
●
denotes the specifications which apply over the full operating
MIN
●
●
●
●
●
●
AC CHARACTERISTICS
V
CC
= full operating range.
SYMBOL
t
PB
t
RST
t
ST
t
RPD
t
f
t
RPU
t
R
t
TD
PARAMETER
PB RST = V
IL
RESET Active Time
ST Pulse Width
V
CC
Detect to RST and RST
V
CC
Slew Rate 4.75V–4.25V
V
CC
Detect to RST and RST
(Reset Active Time)
V
CC
Slew Rate 4.25V–4.75V
ST Pin Detect to RST and RST
(Watchdog Time-Out Period)
Input Capacitance
Output Capacitance
The
●
denotes the specifications which apply over the full operating temperature.
CONDITIONS
●
●
●
●
●
t
R
= 5µs
TD = GND
TD = Floating
TD = V
CC
C
IN
C
OUT
Note 1:
Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 2:
All voltage values are with respect to GND.
Note 3:
The PB RST pin is internally pulled up to V
CC
with an internal
impedance of 10k typical. The TD pin has internal bias current.
Note 4:
Measured with outputs open.
Note 5:
The RST pin is an open drain output.
U
U
U
U WW
The
●
denotes the specifications which apply
MIN
●
●
●
TYP
5
MAX
5.5
V
CC
+0.3
0.8
UNITS
V
V
V
4.5
2
–0.3
TYP
MAX
1
UNITS
µA
mA
mA
–1
–1
2
–13
6
0.5
4.5
4.25
4.62
4.37
40
4
2
4.74
4.49
mA
V
V
mV
200
mV
MIN
40
250
20
TYP
MAX
UNITS
ms
610
1000
ms
ns
100
300
250
0
60
250
500
150
610
1200
5
5
250
1000
2000
610
1000
ns
µs
ms
ns
ms
ms
ms
pF
pF
●
●
●
●
●
1232fa
3
LTC1232
TI I G DIAGRA S
Push-Button Reset
PB RST
V
IL
t
PB
RST
RST
V
IH
V
IL
LTC1232 • TD01
Strobe Input
t
ST
t
TD
LTC1232 • TD02
BLOCK DIAGRA
V
CC
TOL
8
6
3
RST
5%, 10%
SWITCH
OSC
PB RST
1
LEVEL SENSE
AND
DEBOUNCE
LEVEL SENSE
ST
7
TD
2
TIME-OUT
SELECTION
4
W
W
UW
Power Down
V
IH
t
RST
V
CC
4.75V
4.25V
t
F
4.50V
t
RPD
RST
RST
V
OH
V
OL
LTC1232 • TD03
Power Up
t
R
V
CC
4.50V
4.75V
4.25V
t
RPU
RST
RST
V
OH
V
OL
LTC1232 • TD04
+
C1
–
1.3V
RESET PULSE
GENERATOR
5
RST
WATCHDOG
TIMER
LTC1232 • BD01
1232fa
LTC1232
TYPICAL PERFOR A CE CHARACTERISTICS
V
CC
Trip Point vs Temperature
4.63
TOL = GND
4.62
V
CC
TRIP POINT (V)
V
CC
TRIP POINT (V)
4.61
4.60
4.59
4.58
4.57
–50 –25
4.37
RESET ACTIVE TIME (ms)
50
25
75
0
TEMPERATURE (˚C)
Time-Out Period vs Temperature
696
WATCHDOG TIME-OUT PERIOD (ms)
V
CC
= 5V
TD = NO CONNECTION
672
648
624
600
576
552
–50 –25
RST OUTPUT VOLTAGE (V)
4
5
50
25
75
0
TEMPERATURE (˚C)
PI FU CTIO S
V
CC
:
5V Supply Input. The V
CC
pin should be bypassed
with a 0.1µF capacitor.
GND:
Ground Pin.
PB RST:
Logic Input to be Directly Connected to a Push-
Button. The PB RST input requires an active low signal
which is debounced and timed for a minimum of 40ms.
When this condition is satisfied, the reset pulse generator
forces the reset outputs to active states. The reset outputs
remain in active states for a minimum of 250ms after
PB RST is released from logic low level.
TOL:
Input to Select 5% or 10% Variation on V
CC
. When
TOL is connected to GND, the reset pulse generator forces
the reset outputs to active states as V
CC
falls below 4.75V
(4.62V typical). When TOL is connected to V
CC
, the reset
pulse generator forces the reset outputs to active states as
V
CC
falls below 4.5V (4.37V typical).
TD:
Time-Out Delay. TD is a three-level input to select three
different time-out periods. The time-out period is set by
the TD input to be 150ms with TD connected to GND,
600ms with TD left floating, and 1.2 seconds with TD
connected to V
CC
.
1232fa
U W
100
V
CC
Trip Point vs Temperature
4.38
TOL = V
CC
672
648
624
600
576
696
Reset Active Time vs Temperature
V
CC
= 5V
4.36
4.35
4.34
4.33
4.32
–50 –25
125
50
25
75
0
TEMPERATURE (˚C)
100
125
552
–50 –25
50
25
75
0
TEMPERATURE (˚C)
100
125
LTC1232 • TPC01
LTC1232 • TPC02
LTC1232 • TPC03
RST Output Voltage vs Supply Voltage
T
A
= 25°C
EXTERNAL PULL-UP = 10µA
3
2
1
0
100
125
0
1
3
4
2
SUPPLY VOLTAGE (V)
LTC1232 • TPC05
5
LTC1232 • TPC04
U
U
U
5
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