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PS8703 09/23/03
Product Features
Precision supply-voltage monitor
- 4.63V (PI4S705, PI4S813L, PI4S707)
- 4.38V (PI4S706, PI4S706H, PI4S708)
- 3.08V (PI4S706T, PI4S706TH, PI4S708T)
- 2.93V (PI4S706S, PI4S706SH, PI4S708S)
- 2.63V (PI4S706R, PI4S706P, PI4S708R)
200ms reset pulse width
Debounced TTL/CMOS-compatible manual-
reset input
Independent watchdog timer with 1.6sec time-out
(PI4S705, 706x, 706xH, and 813L ONLY )
Reset output signal:
- Active-low only (PI4S705, 706, 706T, 706S, 706R)
- Active-high only (PI4S813L, 706H, 706TH, 706SH,
706P)
- Active-high and active-low (PI4S707, 708, 708T,
708S, 708R)
Voltage monitor for power-fail or low battery warning
Guaranteed RESET/RESET valid at V
CC
= 1.2V
Description
The PI4S70xxx/PI4S813L family microprocessor (P)
supervisory circuits are targeted to improve reliability and
accuracy of power-supply circuitry in P systems. These devices
reduce the complexity and number of components required to
monitor power-supply and battery functions.
The main functions are:
1. Asserting reset output during power-p, power-down and
brownout conditions for P systems.
2. Detecting power failure or low-battery conditions with a
1.25V threshold detector.
3. Generating an independent watchdog output that goes low if
the watchdog input has not been toggled within 1.6 seconds.
4. Asserting reset output with an active-low manual-reset input
Applications
Computers
Controllers
Intelligent Instruments
Automotive Systems
Printers
Critical Microprocessor Power Monitoring
Low Cost P Supervisor Circuts
PI4S705, PI4S706x,PI4S707,
PI4S708x, PI4S813L
Product Pin Configuration
1
2
3
4
8
7
6
5
MR
V
CC
GND
PFI
WDO
RESET
WDI
PFO
1
2
3
4
8
7
6
5
MR
V
CC
GND
PFI
WDO
RESET
WDI
PFO
1
2
3
4
8
7
6
5
MR
V
CC
GND
PFI
RESET
RESET
NC
PFO
PI74S705
PI74S706
PI74S706T
PI74S706S
PI74S706R
PI74S813L
PI4S706H
PI4S706TH
PI4S706SH
PI4S706P
PI74S707
PI74S708
PI74S708T
PI74S708S
PI74S708R
Top View
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PS8703 09/23/03
PI4S705, PI4S706x, PI4S707, PI4S708x, PI4S813L
P Supervisor Circuts
Pin Name Type
Description
MR
Input
Manual-Reset: triggers a reset pulse when pulled below 0.8V, active low. It has an internal 250A
pull-up current and can be driven from a TTL or CMOS logic line as well as shorted to ground with a
switch.
V
CC
Power
Power Supply
GND
Ground
Ground Reference for all signals
PFI
Input
Power-Fail Voltage Monitor Input: When PFI is less than 1.25V, PFO goes low. Connect PFI to GND
or Vcc when not used.
PFO
Output
Power-Fail Output: it gets low and sinks current when PFI is less than 1.25V; otherwise PFO stays
high.
WDI
Input
Watchdog Input: If WDI remains high or low for 1.6sec, the internal watchdog timer runs out and
WDO goes low. Floating WDI or connecting WDI to a high-impedance three-state buffer disables the
watchdog feature. The internal watchdog timer clears whenever reset is asserted, WDI is three-stated,
or WDI sees a rising or falling edge.
NC
No Connect
RESET
Output
Reset Output pulses: low for 200ms when triggered, and stays low whenever Vcc is below the reset
threshold. It remains low for 200ms after V
CC
rises above the reset threshold or MR goes from low to
high. A watchdog timeout will not trigger RESET unless WDO is connected to MR.
WDO
Output
Watchdog Output: pulls low when the internal watchdog timer finishes its 1.6sec count and does not
go high again until the watchdog is cleared. WDO also goes low during low-line conditions. Whenever
Vcc is below the reset threshold, WDO stays low; however, unlike RESET, WDO does not have mini-
mum pulse width. As soon as V
CC
rises above the reset threshold, WDO goes high with no delay.
RESET
Output
The inverse of RESET: active high. Whenever RESET is high, RESET is low.
Pin Descriptiom
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PS8703 09/23/03
PI4S705, PI4S706x, PI4S707, PI4S708x, PI4S813L
P Supervisor Circuts
Block Diagram for PI4S707, PI4S708x
Block Diagram for PI7S705, PI4S706x, PI4S706xH, PI4S813L
Vcc
250uA
V
RST
1.25V
Watchdog
Transition Detector
Watchdog Timer
WDI
WDO
Timebase for Reset
& Watchdog
Reset Generator
MR
Vcc
PFI
RESET
(RESET)
PFO
*
Reset Generator
MR
Vcc
PFI
PFO
RESET
1.25V
V
RST
Vcc
250uA
RESET
*
*V
RST
= RESET Threshold Voltage
*V
RST
= RESET Threshold Voltage
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PS8703 09/23/03
PI4S705, PI4S706x, PI4S707, PI4S708x, PI4S813L
P Supervisor Circuts
Functional Description
The PI4S70xxx/813L family can assert reset output during power-up,
power-down and brownout conditions for uP system, detect power
failure or low-battery conditions with a 1.25V threshold detector and
have watchdog functions. Refer to Function Reference Table for their
individual features. For the typical application see Figure 4.
Reset Output
The supervisory circuits can assert reset for a microprocessor during
power-up, power-down and brownout to prevent code execution
errors.
On power-up, once V
CC
reaches about 1.2V, RESET is a guaranteed
logic low of 0.4V or less. As V
CC
rises, RESET stays low. When
V
CC
rises above the reset threshold, an internal timer releases
RESET after about 200ms. RESET pulses low whenever V
CC
drops below the reset threshold (brownout condition). If brownout
occurs in the middle of a previously initiated reset pulse, the pulse
continues for at least another 140ms.
On power-down, once V
CC
falls below the reset threshold, RESET
stays low and is guaranteed to be 0.4V or less until Vcc drops
below 1.2V.
The PI4S706xH, PI4S707, PI4S708x and PI4S813L active-high
RESET output is simply the complement of the RESET output,
and is guaranteed to be valid with V
CC
down to 1.2V. Some Ps,
such as Intel's 80C51, require an active-high reset pulse.
Watchdog Timer
The watchdog circuit monitors the P's activity. If the P does not
toggle the watchdog input (WDI) within 1.6sec and WDI is not in
high impedance, WDO goes low. As long as RESET is asserted or
the WDI input is in high impedance, the watchdog timer will stay
cleared and will not count. As soon as reset is released and WDI
is driven high or low, the timer will start counting. Pulses as short
as 50ns can be detected.
Typically, WDO will be connected to the non-maskable interrupt
input (NMI) of a P. When V
CC
drops below the reset threshold,
WDO will go low whether or not the watchdog timer has timed
out yet. Normally this would trigger an NMI interrupt, but RESET
goes low simultaneously, and thus overrides the NMI interrupt. If
WDI is left unconnected, WDO can be used as a low-line output.
Since floating WDI disables the internal timer, WDO goes low
only when V
CC
falls below the reset threshold, thus functioning
as a low-line output.
Manual Reset
The manual-reset input (MR) allows reset to be triggered by a push-
button switch. The switch is effectively debounced by the 140ms
minimum reset pulse width. MR is TTL/CMOS logic compatible,
so it can be driven by any external logic line.
Power-Fail Comparator
The power-fail comparator will send out a low signal once detects
a voltage lowered than 1.25V. It can be used for various purposes
because its output and non-inverting input are not internally
connected. The inverting input is internally connected to a 1.25V
reference.
Typical Application Circuit
DC Linear
Regulator
Vcc
Supervisory
PFI
Circuit
WDI
P
Vcc
RESET
I/O Line
NMI
Interrupt
IN
OUT
RESET
WDO
PFO
MR
P
Unregulated DC
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PS8703 09/23/03
PI4S705, PI4S706x, PI4S707, PI4S708x, PI4S813L
P Supervisor Circuts
Function Reference Table
Part No.
Reset
Threshold
Reset Active Low
or High
Nom. Reset
Time (ms),
t
RS
Nom. Watchdog
Time (sec), t
WD
Power Fail
Comp.
Manual Reset
Input
PI4S705
4.63V
LOW
200
1.6
1.25V detector
Yes
PI4S813L
4.63V
HIGH
200
1.6
1.25V detector
Yes
PI4S707
4.63V
LOW, HIGH
200
unavailable
1.25V detector
Yes
PI4S706
4.38V
LOW
200
1.6
1.25V detector
Yes
PI4S706H
4.38V
HIGH
200
1.6
1.25V detector
Yes
PI4S708
4.38V
LOW, HIGH
200
unavailable
1.25V detector
Yes
PI4S706T
3.08V
LOW
200
1.6
1.25V detector
Yes
PI4S706TH
3.08V
HIGH
200
1.6
1.25V detector
Yes
PI4S708T
3.08V
LOW, HIGH
200
unavailable
1.25V detector
Yes
PI4S706S
2.93V
LOW
200
1.6
1.25V detector
Yes
PI4S706SH
2.93V
HIGH
200
1.6
1.25V detector
Yes
PI4S708S
2.93V
LOW, HIGH
200
unavailable
1.25V detector
Yes
PI4S706R
2.63V
LOW
200
1.6
1.25V detector
Yes
PI4S706P
2.63V
HIGH
200
1.6
1.25V detector
Yes
PI4S708R
2.63V
LOW, HIGH
200
unavailable
1.25V detector
Yes
Symbol
Description
Test Conditions
Min
Typ
Max
Unit
V
CC
Supply Voltage for PI4S70xxx, 813L
1.2
5.5
V
V
IH1
MR Input High Voltage
V
CC
> 4.0V
2
2.4
V
CC
4.0V
0.7 x V
CC
V
IH2
WDI Input High Voltage
0.7 x V
CC
V
IL1
MR Input Low Voltage
V
CC
> 4.0V
0.8
V
CC
4.0V
0.2 x V
CC
V
IL2
WDI Input Low Voltage
0.3 x V
CC
T
A
Operating Temperature
0
70
C
DC Electrical Characteristics
(V
CC
=4.75V to 5.5V for PI4S705, PI4S813L, PI4S707 ; V
CC
= 4.5V to 5.5V for PI4S706, PI4S706H, PI4S708; V
CC
= 3.15V to
5.5V for PI4S706T, PI4S706TH, PI4S708T; V
CC
= 3.0V to 5.5V for PI4S706S, PI4S706SH, PI4S708S; V
CC
= 2.7V to 5.5V for
PI4S706R, PI4S706P, PI4S708R; T
A
= 0C to 70C; unless otherwise noted.)
Storage Temperature .....................................................-65
o
C to +150
o
C
Ambient Temperature with Power Applied .......................0
o
C to +70
o
C
Supply Voltage to Ground Potential (V
CC
to GND)....... -0.3V to +7.0V
DC Input Voltage (
All inputs except V
CC
and GND
) ........ -0.3V to V
CC
+0.3V
DC Output Current (All outputs) ...................................................20mA
Power Dissipation (W package) .................................................500mW
Absolute Maximum Ratings
Note:
Stresses greater than those listed under MAXIMUM
RATINGS may cause permanent damage to the de-
vice. This is a stress rating only and functional opera-
tion of the device at these or any other conditions
above those indicated in the operational sections
of this specification is not implied. Exposure to
absolute maximum rating conditions for extended
periods may affect reliability.
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