Also included is a watchdog timer to stop and restart a
microprocessor that is "hung-up". Three watchdog time-
out periods are selectable: 150ms, 610ms and 1,200ms. If the
ST input is not strobed LOW before the time-out period
expires, a reset is issued.
Devices are available in 8-pin DIP, 8-pin SO and compact
8-pin MicroSO packages.
1999 IMP, Inc.
408-432-9100/www.impweb.com
1
Key Features
x
Pin compatible with the Dallas Semiconductor
DS1832
-- Over 40% lower supply current
x
3.3V supply monitor
x
Push-pull output
x
Selectable watchdog period
x
Debounce manual push-button reset input
x
Precision temperature-compensated voltage
reference and comparator
x
Power-up, power-down and brownout detection
x
250ms minimum reset time
x
Active LOW and HIGH reset signal
x
Selectable trip point tolerance: 10% or 20%
x
Low-cost 8-pin DIP/SO and 8-pin MicroSO
packages
x
Wide operating temperature 40
C to +85
C
Block Diagram
V
CC
RESET
PBRST
1
1832_02.eps
40k
9
TOL
IMP1832
3
V
CC
+
10%/20% Tolerance
Selection
Reference
V
CC
8
6
TD
Push Button
Debounce
2
Watchdog
Timebase Selection
GND
4
Reset &
Watchdog Timer
ST
7
Watchdog
Transition Detector
V
CC
RESET
5
IMP1
IMP1
832
832
P
OWER
M
ANAGEMENT
3.3V
3.3V
P P
P P
o
o
w
w
er Suppl
er Suppl
y
y
Monit
Monit
or and R
or and R
eset Cir
eset Cir
cuit
cuit
Select
Select
able T
able T
r
r
i
i
p
p
-P
-P
oint T
oint T
oler
oler
ance and
ance and
W
W
atc
atc
hdog P
hdog P
er
er
iod
iod
Push-Butt
Push-Butt
on R
on R
eset
eset
Push-Pull R
Push-Pull R
eset Outputs
eset Outputs
The IMP1832 microprocessor supervisor can halt and restart a "hung-
up" or "stalled" microprocessor, restart a microprocessor after a power
failure, and debounce a manual push-button microprocessor reset
switch. The IMP1832 features over 40% lower supply current than the
pin compatible Dallas Semiconductor DS1832.
Precision temperature compensated reference and comparator circuits
monitor the 3.3V, V
CC
input voltage. During power-up or when the V
CC
power supply falls outside selectable tolerance limits, both RESET and
RESET become active. When V
CC
rises above the threshold voltage, the
reset signals remain active for an additional 250ms minimum, allowing
the power supply and system microprocessor to stabilize. The trip point
tolerance signal, TOL, selects the trip level tolerance to be either 10- or
20-percent.
RESET and RESET outputs are push-pull.
A debounced manual reset input, PBRST, activates the reset outputs for
a minimum period of 250ms.
2
408-432-9100/www.impweb.com
1999 IMP, Inc.
Pin Configuration
IMP1
IMP1
832
832
Pin Descriptions
IMP1832
5
1832_01.eps
RESET
6 RESET
7 ST
8
4
3
2
1
V
CC
GND
TOL
TD
PBRST
Ordering Information
DIP/SO/MicroSO
r
e
b
m
u
N
t
r
a
P
e
g
a
k
c
a
P
e
r
u
t
a
r
e
p
m
e
T
g
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t
a
r
e
p
O
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a
R
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u
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a
M
(
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r
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C
)
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t
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p
p
A
2
3
8
1
P
M
I
P
I
D
-
8
0
4
C
5
8
o
t
C
0
2
V
3
.
3
S
2
3
8
1
P
M
I
O
S
-
8
0
4
C
5
8
o
t
C
0
2
V
3
.
3
A
M
E
S
2
3
8
1
P
M
I
O
S
o
r
c
i
M
-
8
0
4
C
5
8
o
t
C
0
2
V
3
.
3
s
p
e
.
1
0
t
_
2
3
8
1
Pin Number
8-Pin Package
Name
Function
1
PBRST
Debounced manual pushbutton reset input
2
TD
Watchdog time delay selection. (t
TD
= 150ms for TD = GND, t
TD
= 610ms for TD = Open,
and t
TD
=1200ms for TD = V
CC
)
3
TOL
Selects 10% (TOL connected to GND) or 20% (TOL connected to V
CC
) trip point tolerance
4
GND
Ground
5
RESET
Active HIGH reset output. RESET is active:
1. If V
CC
falls below the reset voltage trip point.
2. If PBRST is LOW.
3. If ST is not strobed LOW before the timeout period set by TD expires.
4. During power-up.
6
RESET
Active LOW reset output. (See RESET)
7
ST
Strobe Input
8
V
CC
5V power
1999 IMP, Inc.
408-432-9100/www.impweb.com
3
IMP1
IMP1
832
832
Absolute Maximum Ratings
Electrical Characteristics
Voltage on V
CC
. . . . . . . . . . . . . . . . . . . . . . . . 0.5V to 7V
Voltage on ST, TD . . . . . . . . . . . . . . . . . . . . . 0.5V to V
CC
+ 0.5V
Voltage on PBRST, RESET, RESET . . . . . . . . 0.5V to V
CC
+ 0.5V
Operating Temperature Range . . . . . . . . . . . 40
C to 85
C
Soldering Temperature . . . . . . . . . . . . . . . . . . 260
C for 10 seconds
Storage Temperature . . . . . . . . . . . . . . . . . . . 55
C to 125
C
Voltages measured with respect to ground.
These are stress ratings only and functional operation is not implied.
Parameter
Symbol
Conditions
Min
Typ
Max
Units
Supply Voltage (V
CC
)
V
CC
1.0
5.5
V
ST and PBRST Input High Level
V
IH
V
CC
2.7V
2
V
CC
+ 0.3V
V
ST and PBRST Input High Level
V
IH
V
CC
<
2.7V
V
CC
- 0.4V
V
ST and PBRST Input Low Level
V
IL
0.3
0.5
V
V
CC
Trip Point (TOL = GND)
V
CCTP
2.80
2.88
2.97
V
V
CC
Trip Point (TOL = V
CC
)
V
CCTP
2.47
2.55
2.64
V
Watchdog Time-Out Period
t
TD
TD = GND
62.5
150
250
ms
Watchdog Time-Out Period
t
TD
TD = V
CC
500
1200
2000
ms
Watchdog Time-Out Period
t
TD
TD floating
250
610
1000
ms
Output Voltage
V
OH
I = 500
A, V
CC
< 2.7V
V
CC
- 0.3V
V
CC
- 0.1V
V
Output Current
I
OH
Output = 2.4V, V
CC
2.7V
350
A
Output Current
I
OL
Output = 0.4V, V
CC
2.7V
10
mA
Input Leakage
I
IL
1.0
1.0
A
RESET Low Level
V
OL
0.4
V
Internal Pull-Up Resistor
PBRST pin
40
k
Operating Current
I
CC1
Outputs open. V
CC
3.6V
20
A
and all inputs at V
CC
or GND
Input Capacitance
C
IN
5
pF
Output Capacitance
C
OUT
7
pF
PBRST Manual Reset
t
PB
PBRST = V
IL
20
ms
Minimum Low Time
Reset Active Time
t
RST
250
610
1000
ms
ST Pulse Width
t
ST
Must not exceed t
RD
minimum.
20
ns
Watchdog cannot be disabled.
V
CC
Fail Detect to
t
RPD
Pulses < 2
s at V
CCTP
5
8
s
RESET or RESET
minimum will not cause reset.
V
CC
Slew Rate
t
F
20
s
PBRST Stable LOW to
t
PDLY
20
ms
RESET and RESET Active
V
CC
Detect to RESET or
t
RPU
t
rise
= 5
s
250
610
1000
ms
RESET Inactive
V
CC
Slew Rate
t
R
0
ns
Unless otherwise stated, 1.2V
V
CC
5.5V and over the operating temperature range of 40
C to +85
C . All voltages are referenced
to ground.
On power-down, once V
CC
falls below the reset threshold RESET
stays LOW and is guaranteed to be 0.4V or less until V
CC
drops
below 1.2V. The active HIGH reset signal is valid down to a V
CC
level of 1.2V also.
Manual Reset Operation
Push-button switch input, PBRST, allows the user to override the
internal trip point detection circuits and issue reset signals. The
pushbutton input is debounced and is pulled HIGH through an
internal 40k
resistor.
When PBRST is held LOW for the minimum time t
PB
, both resets
become active and remain active for a minimum time period of
250ms after PBRST returns HIGH.
The debounced input is guaranteed to recognize pulses greater
than 20ms. No external pull-up resistor is required, since PBRST
is pulled HIGH by an internal 40k
resistor.
The PBRST can be driven from a TTL or CMOS logic line or short-
ed to ground with a mechanical switch.
e
c
n
a
r
e
l
o
T
t
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e
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e
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r
e
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)
V
(
e
g
a
t
l
o
V
t
n
i
o
P
P
I
R
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i
M
l
a
n
i
m
o
N
x
a
M
V
=
L
O
T
C
C
%
0
2
7
4
.
2
5
5
.
2
4
6
.
2
D
N
G
=
L
O
T
%
0
1
0
8
.
2
8
8
.
2
7
9
.
2
s
p
e
.
2
0
t
2
3
8
1
4
408-432-9100/www.impweb.com
1999 IMP, Inc.
IMP1
IMP1
832
832
Application Information
Supply Voltage Monitor
The IMP1832 monitors the microprocessor or microcontroller
power supply and issues reset signals, both active HIGH and
active LOW, that halt processor operation whenever the power
supply voltage levels are outside a predetermined tolerance.
Tolerance levels are set with the TOL pin.
RESET and RESET signals are generated at the last moment of a
valid V
CC
signal. On power-up, both reset signals are active for a
minimum of 250ms after the supply has returned to intolerance
level. This allows the power supply and monitored processor to
stabilize before instruction execution is allowed to begin.
Trip Point Tolerance Selection
With TOL connected to V
CC
, RESET and RESET become active
whenever V
CC
falls below 2.64V. RESET and RESET become active
when V
CC
falls below 2.98V if TOL is connected to ground.
After V
CC
has risen above the trip point set by TOL, RESET and
RESET remain active for a minimum time period of 250ms.
Figure 1. Timing Diagram: Power Up
Figure 2. Timing Diagram: Power Down
1832_04.eps
V
CCTP(MAX)
V
CCTP
V
CCTP(MIN)
V
CC
RESET
RESET
t
R
t
RPU
V
OH
V
OL
Figure 3. Timing Diagram: Pushbutton Reset
V
IH
V
IL
V
OH
V
OL
RESET
RESET
PBRST
t
PDLY
t
PB
t
RST
1832_07.eps
Figure 4. Application Circuit: Pushbutton Reset
1832_05.eps
PBRST
Supply
Voltage
1
V
CC
TD
2
ST
TOL
IMP1832
P
3
4
RESET
GND
8
7
6
5
RESET
RESET
V
CCTP(MAX)
V
CCTP
V
CCTP(MIN)
V
CC
RESET
RESET
t
F
V
OH
V
OL
t
RPD
1832_03.eps
Watchdog Timer and ST Input
A watchdog timer stops and restarts a microprocessor that is
"hung-up". Through the time delay input, TD, three watchdog
time-out periods are selectable: 150ms, 610ms and 1,200ms. If the
strobe input, ST, is not strobed LOW prior to timeout, reset signals
become active. On power-up or after the supply voltage returns to
an in-tolerance condition, the reset signal remains active for
250ms minimum, allowing the power supply and system micro-
processor to stabilize.
ST Pulses as short as 20ns can be detected.
Figure 5. Timing Diagram: Strobe Input
RESET
ST
Valid
Strobe
Valid
Strobe
Invalid
Strobe
t
RST
t
ST
Note: ST is ignored whenever a reset is active.
t
TD
(Min)
t
TD
(Max)
1832_08.eps
1999 IMP, Inc.
408-432-9100/www.impweb.com
5
IMP1
IMP1
832
832
Application Information
Figure 6. Application Circuit: Watchdog Timer
A HIGH-to-LOW ST signal transition must be regularly issued
no later than the minimum time-out period defined by the state of
the TD signal. This guarantees the watchdog timer does not
time-out.
Timeouts periods of approximately 150ms, 610ms or 1,200ms are
selected through the TD pin.
1832_06.eps
PBRST
Supply
Voltage
1
V
CC
TD
2
ST
TOL
IMP1832
m
P
Decoder
3
4
RESET
GND
8
7
6
5
RESET
MREQ
Address
Bus
RESET
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n
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a
M
D
N
G
5
.
2
6
0
5
1
0
5
2
g
n
i
t
a
o
l
F
0
5
2
0
1
6
0
0
0
1
V
C
C
0
0
5
0
0
2
1
0
0
0
2
s
p
e
.
3
0
t
_
2
3
8
1
The watchdog timer can not be disabled. It must be strobed with
a high-to-low transition to avoid a watchdog timeout and reset.
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