Document Outline
- Return to Contents
- List of Figures
- 1. Watchdog Strobe
- 2. RS Pulled Low by Push-button Reset
- 3. Power Up / Down Reset Timing
- 4. TC32M Hardware Connections
- Features
- Applications
- Pin Configurations
- Functional Block Diagram
- General Description
- Ordering Information
- Typical Operating Circuit
- Absolute Maximum Ratings*
- Recommended Operating Conditions, DC
- Electrical Characteristics, DC
- Electrical Characteristics, Capacitance
- Electrical Characteristics, AC
- Pin Description
- Detailed Description
- Processor Monitor
- Watchdog Timer
- Resistor Value Selection
- External Override Reset Control
- Supply Monitor Noise Sensitivity
5-3
TELCOM SEMICONDUCTOR, INC.
7
6
5
4
3
1
2
8
ECONOMONITORTM 3-PIN SYSTEM SUPERVISOR WITH POWER
SUPPLY MONITOR AND WATCHDOG
V
DD
V
REF2
V
REF1
TC32M
WATCHDOG
TIMER
RS
GND
V
DETECTOR
DELAY
TIMER
TC32M
FEATURES
s
Incorporates the Functionality of the Industry
Standard TC1232 (Processor Monitor, Watchdog
and Manual Override RESET Controller) into a
Small, Lower Cost Package
s
Guards Against Unstable Processor Operation
Resulting from Power "Brown-Out"
s
Automatically Halts and Restarts an Out-of-
Control Microprocessor
s
Output can be Wire-ORed, or Hooked to Manual
RESET Push-button Switch
s
Space-Saving 3-Pin TO-92 or SOT-223 Package
APPLICATIONS
s
All Microprocessor-Based Systems
s
Battery Powered Computers and Controllers
s
Automotive Systems
s
Intelligent Instruments
s
Critical Processor Monitoring
s
Embedded Controllers
ORDERING INFORMATION
Temperature
Part No.
Package
Range
TC32MCDB
SOT-223
0
C to +70
C
TC32MCZB
TO-92
0
C to +70
C
TC32MEDB
SOT-223
40
C to +85
C
TC32MEZB
TO-92
40
C to +85
C
PIN CONFIGURATIONS
1
1
2
4
3
2 3
GND
GND
TC32MCDB
TC32MEDB
TC32MCZB
TC32MEZB
V
DD
VDD
VDD
RS
RS
FUNCTIONAL BLOCK DIAGRAM
TO-92
SOT-223
TYPICAL OPERATING CIRCUIT
TC32M-2 9/26/96
5V
RESET
PO.1
RESET
MICRO-
CONTROLLER
R2,10k
MICROCONTROLLER EXAMPLE
RS
TC32M
R1, 10k
GENERAL DESCRIPTION
The TC32M is a fully-integrated processor supervisor in
a 3-pin package. It provides three important functions to
safeguard processor sanity: precision power on/off RESET
control, watchdog timer and external RESET override.
On power-up, the TC32M holds the processor in the
reset state for a minimum of 500msec after V
DD
is within
tolerance to ensure a stable system start-up. Microproces-
sor sanity is monitored by the on-board watchdog circuit.
The microprocessor must provide a high-to-low level shift
(through an external resistor divider) on the RS pin of the
TC32M. Should the processor fail to supply this signal within
the specified timeout period (typically 700msec), an out-of-
control processor is indicated and the TC32M issues a
processor reset as a result.
The output of the TC32M can be wire-ORed with a push-
button switch (or electronic signal) to override the TC32M
and unconditionally reset the processor. When connected to
a push-button switch, the TC32M provides contact debounce.
The TC32M is packaged in a space-saving TO-92
or SOT-223 package. It provides all of the functionality of the
industry standard TC1232 in a smaller, lower cost configu-
ration.
5-4
TELCOM SEMICONDUCTOR, INC.
TC32M
ECONOMONITORTM 3-PIN SYSTEM SUPERVISOR
WITH POWER SUPPLY MONITOR AND WATCHDOG
ABSOLUTE MAXIMUM RATINGS *
Supply Voltage ........................................................ +6.0V
Input Voltage, Any Pin ........ (GND 0.3V) to (V
DD
+ 0.3V)
Operating Temperature Range
TC32MC Package ................................. 0
C to +70
C
TC32ME Package ............................ 40
C to +85
C
Storage Temperature Range ................ 65
C to +150
C
Lead Temperature (Soldering, 10 sec) ................. +300
C
* Static-sensitive device. Unused devices must be stored in conductive
material. Protect devices from static discharge and static fields. Stresses
above those listed under Absolute Maximum Ratings may cause perma-
nent 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 operational sections of the specifications is not implied.
Exposure to Absolute Maximum Rating Conditions for extended periods
may affect device reliability.
ELECTRICAL CHARACTERISTICS, DC:
V
DD
= 4.5V to 5.5V; T
A
= 40
C to 85
C, unless otherwise specified.
Symbol
Parameter
Test Conditions
Min
Typ
Max
Unit
I
IL
RS Input Leakage
1
--
+1
A
I
OL
RS Output Current
V
OL
= 0.4V
2.0
10
--
mA
I
CC
Operating Current
Note 1
--
50
200
A
V
STH
RS Strobe HIGH Level
Figure 1
(V
DD
0.5)
--
--
V
V
STL
RS Strobe LOW Level
Figure 1
2.00
--
(V
DD
1.5)
V
V
RST
RESET Threshold
V
DD
Falling
4.25
--
4.50
V
(Note 2, Figure 3)
RECOMMENDED OPERATING CONDITIONS, DC:
T
A
= 40
C to +85
C, unless otherwise specified.
Symbol
Parameter
Test Conditions
Min
Typ
Max
Unit
V
DD
Supply Voltage
4.5
--
5.5
V
V
IH
RS
Input HIGH Level for PB
2.0
--
--
V
V
IL
RS Input LOW Level for PB
--
--
0.3
V
ELECTRICAL CHARACTERISTICS, AC:
T
A
= 40
C to +85
C, V
DD
= 5V
10%, unless otherwise specified.
Symbol
Parameter
Test Conditions
Min
Typ
Max
Unit
t
RST
RESET Active Time
Figure 2
500
700
900
msec
t
ST
RS STROBE Pulse Width
Figure 1
500
--
--
nsec
t
TD
Watchdog Timeout Period
Figure 1
500
700
900
msec
t
RPD
V
DD
Detect to RS LOW
Figure 3
--
--
100
nsec
NOTES: 1. No output load.
2. All voltages referenced to ground.
ELECTRICAL CHARACTERISTICS, CAPACITANCE:
T
A
= 25
C, unless otherwise specified.
Symbol
Parameter
Test Conditions
Min
Typ
Max
Unit
C
IN
Input Capacitance
--
--
5
pF
C
OUT
Output Capacitance
--
--
7
pF
5-5
TELCOM SEMICONDUCTOR, INC.
7
6
5
4
3
1
2
8
TC32M
RS
V
IL
V
IH
V
DD
V
RST
t
RST
t
RPD
Figure 3. Power Up / Down Reset Timing
Figure 1. Watchdog Strobe
Figure 2. RS Pulled Low by Push-button Reset
PB CLOSED
PB OPEN
RS
V
IH
t
RST
V
IL
V
STL
(MAX)
t
ST
t
TD
RS
Note: t
TD
is the maximum elapsed time between strobes which
will keep the watchdog timer from forcing RS LOW.
(A
STROBE is defined as a high-to-low transition from V
STH
to V
STL
)
.
V
STH
(MIN)
V
STL
(MIN)
Pin No.
Symbol
Description
1
GND
Ground.
2
V
DD
The +5V power supply input.
3
RS
RESET/STROBE (Bidirectional). The open drain goes active if:
1. V
DD
falls below 4.5V nominal.
2. If pulled low by an external electronic signal or switch closure.
3. If the watchdog is not strobed within the minimum watchdog timeout period.
4. During power-up and power-down.
In the input mode, RS connects to a voltage level shift network (typically a resistor divider
to V
DD
.) The watchdog timer is reset when processor causes a voltage level
V
STL
to be
applied to RS.
4
V
DD
The +5V power supply input. (SOT-223 only).
PIN DESCRIPTION
ECONOMONITORTM 3-PIN SYSTEM SUPERVISOR
WITH POWER SUPPLY MONITOR AND WATCHDOG
5-6
TELCOM SEMICONDUCTOR, INC.
so the time between toggles is less than one watchdog
timeout period. The strobe signal can be derived from
microprocessor address, data and/or control signals. Typi-
cal circuit examples are shown in Figure 4.
Resistor Value Selection
The values of R1 and R2 must be chosen to ensure a
valid low strobe level (V
STL
) on RS when the processor I/O
line is low. The use of 10k
,
5% tolerance resistors are
recommended. These values result in a nominal strobe level
of 2.5 on RS (min/max of 2.13V / 3.08V, assuming V
DD
=
5.0V
10%). Other resistor values can be used, so long as
the additive tolerances of the power supply and resistor
values result in a strobe that falls within V
STH
and V
STL
under
all additive tolerance conditions.
External Override Reset Control
A built-in debounce circuit allows a push-button switch
(PB) or other electronic signal to be wire-ORed to this pin as
an external RESET override control. The external
RESET is required to be an active low signal. Internally, this
input is timed to provide a minimum RESET pulse width of
500msec. Reference Figure 2.
Supply Monitor Noise Sensitivity
The TC32M is optimized for fast response to negative-
going changes in V
DD
. Systems with an inordinate amount
of electrical noise on V
DD
(such as systems using relays),
may require a 0.01
F bypass capacitor to reduce detection
sensitivity. This capacitor should be installed as close to the
TC32M as possible to keep the capacitor lead length short.
DETAILED DESCRIPTION
The TC32M provides three important functions to safe-
guard stable processor operation: precision processor moni-
tor, watchdog sanity timer and external override reset
control.
Processor Monitor
The RS pin is immediately driven low any time V
DD
is
below the nominal threshold voltage. As a result, this pin is
LOW when power is initially applied, holding the processor
in its reset state. RS remains low for a minimum of 500msec
after V
DD
is within tolerance to allow the power supply and
processor to stabilize.
Watchdog Timer
The processor drives the RS pin with an input/output
(I/O) line in series with an resistor voltage divider to V
DD.
Pulling the bottom resistor of this divider low results in an
internal voltage change (
strobe) sufficient to reset the watch-
dog timer, but above the V
IL
input threshold of the processor
RESET pin. The processor must continuously apply strobes
in this manner within a set period to verify proper software
execution. A momentary reset (500msec minimum) is gen-
erated by the TC32M if a hardware or software failure keeps
RS from being strobed within the watchdog timeout period.
This action typically initiates the processor's power-up rou-
tine. If the interruption persists, new reset pulses are gener-
ated each timeout period until RS is strobed. This timeout
period is typically 700msec.
The software routine that drives the RS strobe must be
in a section of the program that executes frequently enough
5V
5V
RESET
PO.1
RESET
MICRO-
CONTROLLER
MICRO-
PROCESSOR
R2,10k
MICROCONTROLLER EXAMPLE
RESET
DECODER
ADDRESS
RESET
R1, 10k
MICROPROCESSOR EXAMPLE
RS
TC32M
RS
TC32M
R1, 10k
R2, 10k
Figure 4. TC32M Hardware Connections (R1, R2 chosen to Meet V
STH
, V
STL
)
TC32M
ECONOMONITORTM 3-PIN SYSTEM SUPERVISOR
WITH POWER SUPPLY MONITOR AND WATCHDOG
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