TC32M
ECONOMONITOR™ – 3-PIN SYSTEM SUPERVISOR WITH POWER
SUPPLY MONITOR AND WATCHDOG
FEATURES
GENERAL DESCRIPTION
1
2
■ Incorporates the Functionality of the Industry
Standard TC1232 (Processor Monitor, Watchdog
and Manual Override RESET Controller) into a
Small, Lower Cost Package
■ Guards Against Unstable Processor Operation
Resulting from Power "Brown-Out"
■ Automatically Halts and Restarts an Out-of-
Control Microprocessor
■ Output can be Wire-ORed, or Hooked to Manual
RESET Push-button Switch
■ Space-Saving 3-Pin TO-92 or SOT-223 Package
APPLICATIONS
■ All Microprocessor-Based Systems
■ Battery Powered Computers and Controllers
■ Automotive Systems
■ Intelligent Instruments
■ Critical Processor Monitoring
■ Embedded Controllers
PIN CONFIGURATIONS
TO-92
DD
V
GND
RS
1
23
TC32MCZB
TC32MEZB
SOT-223
V
DD
TC32MCDB
TC32MEDB
1
V
GND
4
2
DD
3
RS
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 VDD is within
tolerance to ensure a stable system start-up. Microprocessor 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-ofcontrol processor is indicated and the TC32M issues a
processor reset as a result.
The output of the TC32M can be wire-ORed with a pushbutton 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 configuration.
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
3
4
5
6
FUNCTIONAL BLOCK DIAGRAM
V
REF1
WATCHDOG
TIMER
TELCOM SEMICONDUCTOR, INC.
∆V
DETECTOR
V
REF2
DELAY
TIMER
V
DD
TC32M
RS
GND
TYPICAL OPERATING CIRCUIT
R1, 10k
R2,10k
RS
TC32M
RESET
MICROCONTROLLER EXAMPLE
5V
MICRO-
CONTROLLER
PO.1
RESET
7
8
TC32M-2 9/26/96
5-3
TC32M
ECONOMONITOR™ – 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 (VDD + 0.3V)
Operating Temperature Range
TC32MC Package .................................0°C to +70°C
TC32ME Package ............................– 40°C to +85°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 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 operational sections of the specifications is not implied.
Exposure to Absolute Maximum Rating Conditions for extended periods
may affect device reliability.
Storage Temperature Range ................– 65°C to +150°C
Lead Temperature (Soldering, 10 sec) .................+300°C
RECOMMENDED OPERATING CONDITIONS, DC: T
Symbol Parameter Test Conditions Min Typ Max Unit
V
DD
V
IH
V
IL
ELECTRICAL CHARACTERISTICS, DC: V
Symbol Parameter Test Conditions Min Typ Max Unit
I
IL
I
OL
I
CC
V
STH
V
STL
V
RST
Supply Voltage 4.5 — 5.5 V
RS Input HIGH Level for PB 2.0 — — V
RS Input LOW Level for PB — — 0.3 V
= 4.5V to 5.5V; TA = – 40°C to 85°C, unless otherwise specified.
DD
RS Input Leakage – 1 — +1 µA
RS Output Current V
= 0.4V 2.0 10 — mA
OL
Operating Current Note 1 — 50 200 µA
RS Strobe HIGH Level Figure 1 (V
RS Strobe LOW Level Figure 1 2.00 — (V
RESET Threshold VDD Falling 4.25 — 4.50 V
(Note 2, Figure 3)
= – 40°C to +85°C, unless otherwise specified.
A
– 0.5) — — V
DD
– 1.5) V
DD
ELECTRICAL CHARACTERISTICS, CAPACITANCE: T
= 25°C, unless otherwise specified.
A
Symbol Parameter Test Conditions Min Typ Max Unit
C
IN
C
OUT
ELECTRICAL CHARACTERISTICS, AC: T
Input Capacitance — — 5 pF
Output Capacitance — — 7 pF
= – 40°C to +85°C, VDD = 5V ±10%, unless otherwise specified.
A
Symbol Parameter Test Conditions Min Typ Max Unit
t
RST
t
ST
t
TD
t
RPD
NOTES: 1. No output load.
2. All voltages referenced to ground.
RESET Active Time Figure 2 500 700 900 msec
RS STROBE Pulse Width Figure 1 500 — — nsec
Watchdog Timeout Period Figure 1 500 700 900 msec
VDD Detect to RS LOW Figure 3 — — 100 nsec
5-4
TELCOM SEMICONDUCTOR, INC.
RS
V
IL
V
IH
V
DD
V
RST
t
RST
t
RPD
ECONOMONITOR™ – 3-PIN SYSTEM SUPERVISOR
WITH POWER SUPPLY MONITOR AND WA TCHDOG
t
ST
RS
V
(MIN)
STH
V
(MAX)
STL
V
(MIN)
STL
t
TD
1
TC32M
2
3
Note: t
will keep the watchdog timer from forcing RS LOW.
(A
is the maximum elapsed time between strobes which
TD
STROBE
is defined as a high-to-low transition from V
Figure 1. Watchdog Strobe
PB CLOSED
RS
V
IL
Figure 2. RS Pulled Low by Push-button Reset
PB OPEN
t
RST
to V
)
STL
.
Figure 3. Power Up / Down Reset Timing
STH
4
5
V
IH
6
PIN DESCRIPTION
Pin No. Symbol Description
1 GND Ground.
2VDDThe +5V power supply input.
3 RS RESET/STROBE (Bidirectional). The open drain goes active if:
1. V
falls below 4.5V nominal.
4VDDThe +5V power supply input. (SOT-223 only).
TELCOM SEMICONDUCTOR, INC.
DD
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
.) The watchdog timer is reset when processor causes a voltage level ≤ V
DD
applied to RS.
STL
to be
7
8
5-5
TC32M
ECONOMONITOR™ – 3-PIN SYSTEM SUPERVISOR
WITH POWER SUPPLY MONITOR AND WATCHDOG
DETAILED DESCRIPTION
The TC32M provides three important functions to safeguard stable processor operation: precision processor monitor, watchdog sanity timer and external override reset
control.
Processor Monitor
The RS pin is immediately driven low any time VDD 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 VDD 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
Pulling the bottom resistor of this divider low results in an
internal voltage change (
strobe
) sufficient to reset the watchdog timer, but above the VIL 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 generated 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 routine. If the interruption persists, new reset pulses are generated 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
DD.
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. Typical 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
) on RS when the processor I/O
STL
line is low. The use of 10kΩ, ±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 negativegoing changes in VDD. Systems with an inordinate amount
of electrical noise on VDD (such as systems using relays),
may require a 0.01µF 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.
=
5-6
TC32M
R1, 10k
R2,10k
RS
RESET
MICROCONTROLLER EXAMPLE
CONTROLLER
PO.1
RESET
Figure 4. TC32M Hardware Connections (R1, R2 chosen to Meet V
5V
MICRO-
TC32M
R1, 10k
RS
5V
R2, 10k
RESET
MICRO-
PROCESSOR
DECODER
ADDRESS
RESET
MICROPROCESSOR EXAMPLE
, V
STL
)
STH
TELCOM SEMICONDUCTOR, INC.
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