ASM706 P/ R/ S/ T/ J
ASM708 R/ S/ T/ J
April 2005
rev 1.5
3/3.3/4.0 V µP Supervisor Circuits
Features
•
Precision power supply monitor
•2.63V threshold (ASM706P/R, ASM708R)
•2.93V threshold (ASM706S, ASM708S)
•3.08V threshold (ASM706T, ASM708T)
•New 4.00V threshold (ASM706J, ASM708J)
•
•
Debounced manual reset input
Auxiliary voltage monitor comparator
•1.25V threshold
•Battery monitor / auxiliary supply monitor
•
•
•
Watchdog timer (ASM706P/R/S/T/J)
•Watchdog can be disabled by floating WDI
200ms reset time delay
Three reset signal options
•Active HIGH: ASM706P
•Active LOW: ASM706R/S/T/J
•Active HIGH and LOW outputs: ASM708R/S/T/J
•
•
DIP, SO and MicroSO packages
Guaranteed RESET assertion to V
CC
= 1.1V
General Description
The ASM706P/R/S/T/J and ASM708R/S/T/J are cost effective
CMOS supervisor circuits that monitor power-supply, battery
voltage level and
µP/µC
operation.
The family offers several functional options. Each device
generates a reset signal during power-up, power-down and
brownout conditions. A reset is generated when the supply
drops
below
2.63V
(ASM706P/R,
ASM708R),
2.93V
(ASM706S, ASM708S), 3.08V (ASM706T, ASM708T) or 4.00V
(ASM706J, ASM708J). In addition, the ASM706P/R/S/T/J
feature a 1.6 second watchdog timer. The watchdog timer
output will trigger a reset if connected to MR. Floating the WDI
input pin disables the watchdog timer.
The ASM708R/S/T/J have both active-HIGH and active-LOW
reset outputs but no watchdog function. The ASM706P has the
same pin-out and functions as the ASM706R but has an active-
HIGH reset output.
A versatile power-fail circuit, useful in checking battery levels
and non-5V supplies, has a 1.25V threshold. All devices have a
manual reset input. All devices are available in 8-pin DIP, SO
and the compact MicroSO packages. The MicroSO package
requires 50% less PC board area than the conventional SO
package.
Applications
•
•
•
•
•
•
•
•
Computers and embedded controllers
CTI applications
Automotive systems
Portable/Battery-operated systems
Intelligent instruments
Wireless communication systems
PDAs and hand-held equipment
Safety systems
Typical Operating Circuit
Unregulated DC
+3.3V Regulator
V
CC
V
CC
PFI
ASM706 R/S/T
ASM708 R/S/T
(ASM706 P)
µP
R
1
RESET
(RESET)
WDI
WDO
PFO
RESET
(RESET)
I/O LINE
NMI
INTERRUPT
R
2
MR
Alliance Semiconductor
2575 Augustine Drive . Santa Clara, CA 95054 . Tel: 408.855.4900 . Fax: 408.855.4999 . www.alsc.com
Notice: The information in this document is subject to change without notice
April 2005
rev 1.5
ASM706 P/ R/ S/ T/ J
ASM708 R/ S/ T/ J
Block Diagrams
Transition
Detector
V
CC
Timebase
20kΩ
20kΩ
RESET
Generator
WDI
Watchdog
Timer
WDO
V
CC
RESET
MR
RESET
(RESET) ASM706P
MR
RESET
Generator
RESET
V
CC
+
+
-
2.63V (ASM706P/R)
2.93V (ASM706S)
3.08V (ASM706T)
4.00V (ASM706J)
V
CC
+
+
-
2.63V (ASM708R)
2.93V (ASM708S)
3.08V (ASM708T)
4.00V (ASM708J)
PFI
+
-
PFI
PFO
+
-
PFO
1.25V
1.25V
ASM706P/R/S/T/J
GND
ASM708R/S/T/J
GND
Pin Configuration
MicroSO
ASM706R/S/T/J
2
7 RESET
6
5
WDI
PFO
2
7
6
5
PFO
PFI
GND
RESET
2
ASM708R/S/T/J
DIP/SO
ASM708R/S/T/J
ASM706P
V
CC
2
7 RESET
6
5
NC
PFO
V
CC
2
7 RESET V
CC
6
5
WDI
PFO
ASM706P
MR
1
MR
WDO
MR
WDO
ASM706R/S/T/J
8 RESET
1
8
1
8
(RESET)
RESET
(ASM706P)
WDO
1
8
WDI
RESET
1
8
7
6
5
NC
PFO
PFI
GND
GND 3
PFI
4
GND 3
PFI
4
GND 3
PFI
4
MR 3
V
CC
4
MR 3
V
CC
4
3/3.3/4.0 V µP Supervisor Circuits
Notice: The information in this document is subject to change without notice
2 of 18
April 2005
rev 1.5
ASM706 P/ R/ S/ T/ J
ASM708 R/ S/ T/ J
Pin Description
Pin Number
ASM706P
DIP/
SO
MicroSO
ASM706R/S/T/J
DIP/
SO
MicroSO
ASM708R/S/T/J
DIP/
SO
MicroSO
Manual reset input. The active LOW input triggers
a reset pulse. It is pulled HIGH by a 20kΩ pull-up
resistor. It is compatible with TTL/CMOS signals
when V
CC
= 5V. It can be shorted to ground
through a mechanical switch. Leave floating or
connect to V
CC
if the function is not used.
2
3
4
4
5
6
2
3
4
4
5
6
2
3
4
4
5
6
V
CC
GND
PFI
Monitored power supply input.
Ground.
Power-fail input voltage monitor. With PFI less
than 1.25V, PFO goes LOW. Connect PFI to
Ground when not in use.
Power-fail output. The output is active LOW and
sinks current when PFI is less than 1.25V. If not
used, leave the pin unconnected.
Watchdog input. WDI controls the internal watch-
dog timer. A HIGH or LOW signal for 1.6sec at
WDI allows the internal timer to run-out, setting
WDO low. A rising or falling edge must occur at
WDI within 1.6 seconds or WDO goes LOW. The
watchdog function is disabled by floating WDI. The
internal watchdog timer clears when: Reset is
asserted; WDI is three-stated; or WDI sees a rising
or falling edge.
Not Connected
Active LOW reset output. Pulses LOW for 200ms
when triggered, and stays LOW whenever V
CC
is
-
-
7
1
7
1
RESET
below the reset threshold. RESET remains LOW
for 200ms after V
CC
rises above the reset thresh-
old or MR goes from HIGH to LOW. A watchdog
timeout will not trigger RESET unless WDO is con-
nected to MR.
Name
Function
1
3
1
3
1
3
MR
5
7
5
7
5
7
PFO
6
8
6
8
-
-
WDI
-
-
-
-
6
8
NC
3/3.3/4.0 V µP Supervisor Circuits
Notice: The information in this document is subject to change without notice
3 of 18
April 2005
rev 1.5
Pin Number
ASM706P
DIP/
SO
MicroSO
ASM706R/S/T/J
DIP/
SO
MicroSO
ASM708R/S/T/J
DIP/
SO
MicroSO
Name
ASM706 P/ R/ S/ T/ J
ASM708 R/ S/ T/ J
Function
8
2
8
2
-
-
WDO
Watchdog output. WDO goes LOW when the 1.6
second interval watchdog timer times-out and
does not go HIGH until a transition occurs at WDI.
In addition, when V
CC
falls below the reset thresh-
old, WDO goes LOW. Unlike RESET, WDO does
not have a minimum pulse width and as soon as
V
CC
exceeds the reset threshold, WDO becomes
HIGH with no delay.
Active HIGH reset output. The inverse of RESET.
7
1
-
-
8
2
RESET
3/3.3/4.0 V µP Supervisor Circuits
Notice: The information in this document is subject to change without notice
4 of 18
ASM706 P/ R/ S/ T/ J
ASM708 R/ S/ T/ J
April 2005
rev 1.5
Detailed Descriptions
A
proper
reset
input
enables
a
microprocessor/
microcontroller to start in a known state. ASM706 P/ R/ S/ T/
J and ASM708 R/ S/ T/ J assert reset to prevent code
execution errors during power-up, power-down and brown-
out conditions.
RESET/RESET Operation
The RESET/RESET signals are designed to start or return a
µP/µC
to a known state.
With V
CC
above 1.2V, RESET and RESET are guaranteed to
be asserted. During a power-up sequence, the reset outputs
remain asserted until the supply rises above the threshold
level. The resets are deasserted approximately 200ms after
crossing the threshold.
In a brownout situation where V
CC
falls below the threshold
level, the reset outputs are asserted. If a brownout occurs
during an already initiated reset period, the reset period will
extend for an additional reset period of 200ms.
The ASM708 devices have dual reset outputs, one active
LOW and one active HIGH. The ASM706P has a single
active HIGH reset and the ASM706/R/S/T/J devices have an
active LOW reset output.
Alliance
Part #
ASM706P
ASM706R
ASM706S
ASM706T
ASM706J
ASM708R
ASM708S
ASM708T
ASM708J
RESET
Polarity
HIGH
LOW
LOW
LOW
LOW
HIGH & LOW
HIGH & LOW
HIGH & LOW
HIGH & LOW
Watchdog
Timer
YES
YES
YES
YES
YES
NO
NO
NO
NO
Manual Reset (MR)
The active-LOW manual reset input is pulled high by an
internal 20kΩ pull-up resistor and can be driven low by
CMOS/TTL logic or a mechanical switch to ground. An
external debounce circuit is unnecessary since the 140ms
minimum reset time will debounce mechanical push button
switches. The minimum MR input pulse width is 0.5µs with a
3V V
CC
input and 0.15µs with a 5V V
CC
input. If not used, tie
MR to V
CC
or leave floating.
Figure 1: WDI Three-state operation
By connecting the watchdog output (WDO) and MR, a
watchdog timeout forces a RESET to be generated.
Watchdog Timer
A watchdog timer available on the ASM706P/R/S/T/J
monitors
µP/µC
activity. An output line on the processor is
used to toggle the WDI line. If the line is not toggled within 1.6
seconds on the Watchdog Input (WDI), the internal timer puts
the Watchdog Output (WDO) into a LOW state. WDO will
remain LOW until a toggle is detected at WDI.
The watchdog function is disabled, meaning it is cleared and
not counting, if WDI is floated or connected to a three-stated
circuit. The watchdog timer is also disabled if RESET is
asserted. When RESET becomes inactive and the WDI input
sees a high or low transition as short as 100ns (V
CC
= 2.7V)/
50ns (V
CC
= 4.5V), the watchdog timer will begin a 1.6
Threshold
2.63V
2.63V
2.93V
3.08V
4.00V
2.63V
2.93V
3.08V
4.00V
3/3.3/4.0 V µP Supervisor Circuits
Notice: The information in this document is subject to change without notice
5 of 18
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