PI4S705, PI4S706x,PI4S707,
PI4S708x, PI4S813L
Low Cost µP Supervisor Circuts
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 (µP)
supervisory circuits are targeted to improve reliability and
accuracy of power-supply circuitry in µP 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-µp, power-down and
brownout conditions for µP 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
Product Pin Configuration
MR
1
2
3
4
8
7
6
5
WDO
RESET
WDI
PFO
MR
V
CC
GND
PFI
1
2
3
4
8
7
6
5
WDO
RESET
WDI
PFO
MR
V
CC
GND
PFI
1
2
3
4
8
7
6
5
PI74S707
PI74S708
PI74S708T
PI74S708S
PI74S708R
RESET
RESET
NC
PFO
V
CC
GND
PFI
PI74S705
PI74S706
PI74S706T
PI74S706S
PI74S706R
PI74S813L
PI4S706H
PI4S706TH
PI4S706SH
PI4S706P
Top View
1
PS8703
09/23/03
PI4S705, PI4S706x, PI4S707, PI4S708x, PI4S813L
µP Supervisor Circuts
Pin Descriptiom
Pin Name
MR
V
CC
GND
PFI
PFO
Type
Input
Power
Ground
Input
Output
Description
Manual-Reset:
triggers a reset pulse when pulled below 0.8V, active low. It has an internal 250μA
pull-up current and can be driven from a TTL or CMOS logic line as well as shorted to ground with a
switch.
Power Supply
Ground Reference
for all signals
Power-Fail Voltage Monitor Input:
When PFI is less than 1.25V, PFO goes low. Connect PFI to GND
or Vcc when not used.
Power-Fail Output:
it gets low and sinks current when PFI is less than 1.25V; otherwise PFO stays
high.
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.
No Connect
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.
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.
The inverse of RESET:
active high. Whenever RESET is high, RESET is low.
WDI
NC
RESET
Input
WDO
RESET
Output
Output
2
PS8703
09/23/03
PI4S705, PI4S706x, PI4S707, PI4S708x, PI4S813L
µP Supervisor Circuts
Block Diagram for PI7S705, PI4S706x, PI4S706xH, PI4S813L
WDI
Watchdog
Transition Detector
V cc
250uA
Watchdog Timer
WDO
Timebase for Reset
& Watchdog
Reset Generator
MR
Vcc
V
RST
RESET
(RESET)
*
PFI
1.25V
PFO
*V
RST
= RESET Threshold Voltage
Block Diagram for PI4S707, PI4S708x
Vcc
250uA
MR
Vcc
Reset Generator
RESET
RESET
*
V
RST
PFI
PFO
1.25V
*V
RST
= RESET Threshold Voltage
3
PS8703
09/23/03
PI4S705, PI4S706x, PI4S707, PI4S708x, PI4S813L
µP 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.
Watchdog Timer
The watchdog circuit monitors the µP’s activity. If the µP 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 µP. 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.
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 µPs,
such as Intel’s 80C51, require an active-high reset pulse.
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
Unregulated DC
IN
DC Linear
Regulator
OUT
µP
Vcc
Vcc
PFI
MR
RESET
I/O Line
NMI
Interrupt
RESET
µP Supervisory
Circuit
WDI
WDO
PFO
4
PS8703
09/23/03
PI4S705, PI4S706x, PI4S707, PI4S708x, PI4S813L
µP Supervisor Circuts
Function Reference Table
Part No.
PI4S705
PI4S813L
PI4S707
PI4S706
PI4S706H
PI4S708
PI4S706T
PI4S706TH
PI4S708T
PI4S706S
PI4S706SH
PI4S708S
PI4S706R
PI4S706P
PI4S708R
Reset
Threshold
4.63V
4.63V
4.63V
4.38V
4.38V
4.38V
3.08V
3.08V
3.08V
2.93V
2.93V
2.93V
2.63V
2.63V
2.63V
Reset Active Low
or High
LOW
HIGH
LOW, HIGH
LOW
HIGH
LOW, HIGH
LOW
HIGH
LOW, HIGH
LOW
HIGH
LOW, HIGH
LOW
HIGH
LOW, HIGH
Nom. Reset
Time (ms),
t
RS
200
200
200
200
200
200
200
200
200
200
200
200
200
200
200
Nom. Watchdog
Time (sec), t
WD
1.6
1.6
unavailable
1.6
1.6
unavailable
1.6
1.6
unavailable
1.6
1.6
unavailable
1.6
1.6
unavailable
Power Fail
Comp.
1.25V detector
1.25V detector
1.25V detector
1.25V detector
1.25V detector
1.25V detector
1.25V detector
1.25V detector
1.25V detector
1.25V detector
1.25V detector
1.25V detector
1.25V detector
1.25V detector
1.25V detector
Manual Reset
Input
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Absolute Maximum Ratings
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
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.
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
= 0ºC to 70°C; unless otherwise noted.)
Symbol
V
CC
V
IH1
V
IH2
V
IL1
V
IL2
T
A
Description
Supply Voltage for PI4S70xxx, 813L
MR Input High Voltage
WDI Input High Voltage
MR Input Low Voltage
WDI Input Low Voltage
Operating Temperature
0
V
CC
> 4.0V
V
CC
≤ 4.0V
V
CC
> 4.0V
V
CC
≤ 4.0V
Test Conditions
Min
1.2
2
0.7 x V
CC
0.7 x V
CC
0.8
0.2 x V
CC
0.3 x V
CC
70
ºC
2.4
V
Typ
Max
5.5
Unit
5
PS8703
09/23/03
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