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Электронный компонент: IN1232

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IN1232
1
M
ICRO
M
ONITOR
C
HIP

DESCRIPTION
The IN1232 MicroMonitor Chip monitors three vital conditions for a microprocessor: power supply,
software execution, and external override. First, a precision temperature-compensated reference and
comparator cir-
cuit monitors the status of V
CC
.
When an out-of-tolerance condition occurs, an internal power fail
signal is generated which forces reset to the active state. When V
CC
returns to an in-tolerance
condition, the reset signals are kept in the active state for a minimum of 250 ms to allow the power
supply and processor to stabilize.
The second function the IN1232 performs is pushbutton reset control. The IN1232 debounces the
pushbutton input and guarantees an active reset pulse width of 250 ms minimum. The third function is
a watchdog timer. The IN1232 has an internal timer that forces the reset signals to the active state if
the strobe input is not driven low prior to time-out. The watchdog timer function can be set to operate
on time-out settings of approximately 150 ms, 600 ms, and 1.2 seconds.

FEATURES
Halts and restarts an out-of-control
microprocessor
Holds microprocessor in check during
power transients
Automatically restarts microprocessor
after power failure
Monitors pushbutton for external override
Accurate 5% or 10% microprocessor
power supply monitoring
Eliminates the need for discrete
components
Dip-8
SO-14
PIN DESCRIPTION
PBRST Pushbutton
Reset
Input
TD Time
Delay
Set
TOL
Selects 5% or 10% V
CC
Detect
GND Ground
RST
Reset Output (Active High)
RST
Reset Output (Active Low, open
drain)
ST Strobe
Input
V
CC
+5 Volt Power
NC No
Connections

IN1232
2

ABSOLUTE MAXIMUM RATINGS*
Voltage on V
CC
Pin Relative to Ground -0.5V to +7.0V
Voltage on I/O Relative to Ground
-0.5V to V
CC
+ 0.5V
Operating Temperature
0
o
C to 70
o
C
Operating Temperature (Industrial
Version)
-40
o
C to +85
o
C
Storage Temperature
-55
o
C to +125
o
C
Soldering Temperature
260
o
C for 10 seconds
* This is a stress rating only and functional operation of the device at these or any other
conditions above those indicated in the operation sections of this specification is not implied.
Exposure to absolute maximum rating conditions for extended periods of time may affect
reliability.
RECOMMENDED DC OPERATING CONDITIONS
(0
o
C to 70
o
C)
PARAMETER SYMBOL
MIN
TYP
MAX
UNITS
NOTES
Supply Voltage
V
CC
4.5
5.0
5.5 V 1
ST and PBRST Input High
Level
V
IH
2.0
V
CC
+0.3 V
1
ST and PBRST Input Low
Level
V
IL
-0.3
+0.8
V 1
DC ELECTRICAL CHARACTERISTICS
(0 C to 70
C; V
CC = 4.5 to 5.5V)
PARAMETER SYMBOL
MIN
TYP
MAX
UNITS
NOTES
Input Leakage
I
IL
-1.0
+1.0
A
3
Output Current @ 2.4V
I
OH
-8
-10
mA
5
Output Current @ 0.4V
I
OL
8 10 mA
Low Level @ RST
V
OL
0.4
V 1
Output Voltage @ -500
A V
OH
V
CC
-0.5V V
CC
-0.1V
V 1,7
Operating Current
I
CC
0.5 2.0
mA
2
V
CC
Trip Point (TOL = GND) V
CCTP
4.50 4.62 4.74
V 1
V
CC
Trip Point (TOL = V
CC
)
V
CCTP
4.25 4.37 4.49
V 1
CAPACITANCE
(
t
A
= 25
o
C)
PARAMETER SYMBOL
MIN
TYP
MAX
UNITS
NOTES
Input Capacitance
C
IN
5 pF
Output Capacitance
C
OUT
7 pF
AC ELECTRICAL CHARACTERISTICS (0
o
C to 70
o
C; V
CC = 5V + 10%)
PARAMETER SYMBOL
MIN
TYP
MAX
UNITS
NOTES
PBRST = V
IL
t
PB
20
ms
RESET Active Time
t
RST
250
610 1000
ms
ST Pulse Width
t
ST
20
ns
6,
8
V
CC
Fail Detect to RST and
RST
t
RPD
100 175
s
V
CC
Slew Rate 4.75V to
4.25V
t
F
300
s
V
CC
Detect to RST and RST
Transition
t
RPU
250
610 1000
ms
4
V
CC
Slew Rate 4.25V to
4.75V
t
R
0 5
s
PBRST Stable Low to RST
and RST
t
PDLY
20 ms
NOTES:
1. All voltages referenced to ground.
2. Measured with outputs open.
3. PBRST is internally pulled up to V
CC
with an internal impedance of 10K typical.
4. t
R
= 5
s.
IN1232
3
5. RST is an open drain output.
6. Must not exceed t
TD
minimum. See Table 1.
7. RST remains within 0.5V of V
CC
on power-down until V
CC
drops below 2.0V. RST remains
within 0.5V of GND on power-down until V
CC
drops below 2.0V.
8. Watchdog can not be disabled. It must be strobed to avoid resets.



OPERATION - POWER MONITOR
The IN1232 detects out-of-tolerance power supply conditions and warns a processor-based system
of impending power failure. When V
CC
falls below a preset level as defined by TOL (Pin 3), the V
CC
comparator outputs the signals RST (Pin 5) and RST (Pin 6). When TOL is connected to ground, the
RST and RST signals become active as V
CC
falls below 4.75 volts. When TOL is connected to V
CC
, the
RST and RST signals become active as V
CC
falls below 4.5 volts. The RST and RST are excellent
control signals for a microprocessor, as processing is stopped at the last possible moments of
valid V
CC
. On power-up, RST and RST are kept active
for a minimum of 250 ms to allow the power
supply and processor to stabilize.
OPERATION - PUSHBUTTON RESET
The IN1232 provides an input pin for direct connection to a pushbutton (Figure 2). The pushbutton
reset input requires an active low signal. Internally, this input is de-bounced and timed such that RST
and RST signals of at least 250 ms minimum are generated. The 250 ms delay starts as the
pushbutton reset input is released from low level.
OPERATION - WATCHDOG TIMER
A watchdog timer function forces RST and RST signals to the active state when the ST input is not
stimulated for a predetermined time period. The time period is set by the TD input to be typically 150
ms with TD connected to ground, 600 ms with TD left unconnected, and 1.2 sec-
onds with TD connected to V
CC
.
The watchdog timer
starts timing out from the set time period as soon
as RST and RST are inactive. If a high-to-low transition occurs on the ST input pin prior to time-out,
the watchdog timer is reset and begins to time-out again. If the watchdog timer is allowed to time-out,
then the RST and RST signals are driven to the active state for 250 ms minimum. The ST input can be
derived from microprocessor address signals, data signals, and/or control signals. When the
microprocessor is functioning normally, these signals would, as a matter of routine, cause the watch-
dog to be reset prior to time-out. To guarantee that the watchdog timer does not time-out, a high-to-
low transition must occur at or less than the minimum shown in Table 1. A typical circuit example is
shown in Figure 3.
MICROMONITOR BLOCK DIAGRAM
IN1232
4
PUSHBUTTON RESET
WATCHDOG TIMER
TIMING DIAGRAM: PUSHBUTTON RESET
TIMING DIAGRAM: STROBE INPUT
WATCHDOG TIMEOUTS
TIME-OUT
TD PIN
MIN
TYP
MAX
GND
62.5 ms
150 ms
250 ms
Float
250 ms
600 ms
1000 ms
V
CC
500 ms
1200 ms
2000 ms
TIMING DIAGRAM: POWER DOWN
IN1232
5
TIMING DIAGRAM: POWER UP