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FEATURES
Halts and restarts an out-of-control
microprocessor
Holds microprocessor in check during power
transients
Automatically restarts microprocessor after
power failure
Monitors pushbutton for external override
Accurate 5%, 10% or 20% resets for 3.3V
systems and 5% or 10% resets for 5.0V
systems
Eliminates the need for discrete components
3.3V 20% tolerance for use with 3.0V
systems
Pin-compatible with the MAXIM
MAX705/MAX706 in 8-pin DIP, 8-pin SOIC,
and -SOP
8-pin DIP, 8-pin SOIC and 8-pin -SOP
packages
Industrial temperature range -40C to +85C
PIN ASSIGNMENT
DS1705 and DS1706_R/S/T
(*DS1706L and DS1706P)
PIN DESCRIPTION
PBRST - Pushbutton Reset Input
VCC - Power Supply
GND - Ground
IN - Input
NMI - Non-maskable Interrupt
ST - Strobe Input
RST - Active Low Reset Output
*RST - Active High Reset Output
(DS1706P and DS1706L only)
WDS - Watchdog Status Output
DESCRIPTION
The DS1705/DS1706 3.3- or 5.0-Volt MicroMonitor monitors three vital conditions for a microprocessor:
power supply, software execution, and external override. A precision temperature compensated reference
and comparator circuit monitor the status of VCC at the device and at an upstream point for maximum
protection. When the sense input detects an out-of-tolerance condition, a non-maskable interrupt is
generated. As the voltage at the device degrades, an internal power fail signal is generated which forces
DS1705/DS1706
3.3V and 5.0V MicroMonito
r
19-5212; Rev 4/10
www.maxim-ic.com
8-Pin
-SOP (118-mil)
See Mech. Drawings Section on website
RST(*RST)
WDS
PBRST
VCC
ST
NMI
IN
GND
1
2
3
4
8
7
6
5
8-Pin DIP (300 -mil)
PBRST
VCC
GND
IN
WDS
RST
ST
NMI
1
2
3
4
8
7
6
5
8-Pin SOIC (150-mil)
1
2
3
4
8
7
6
5
PBRST
VCC
GND
IN
WDS
RST(*RST)
ST
NMI
DS1705/DS1706
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the reset to an active state. When VCC returns to an in-tolerance condition, the reset signal is kept in the
active state for a minimum of 130 ms to allow the power supply and processor to stabilize.
The second function the DS1705/DS1706 performs is pushbutton reset control. The DS1705/DS1706
debounces the pushbutton input and guarantees an active reset pulse width of 130 ms minimum.
The third function is a watchdog timer. The DS1705/DS1706 has an internal timer that forces the WDS
output signal to the active state if the strobe input is not driven low prior to time-out.
OPERATION
Power Monitor
The DS1705/DS1706 detects out-of-tolerance power supply conditions and warns a processor-based
system of impending power failure. When VCC falls below the minimum VCC tolerance, a comparator
outputs the RST (or RST) signal. RST (or RST) is an excellent control signal for a microprocessor, as
processing is stopped at the last possible moment of valid VCC. On power-up, RST (or RST) are kept
active for a minimum of 130 ms to allow the power supply and processor to stabilize.
Pushbutton Reset
The DS1705/DS1706 provides an input pin for direct connection to a pushbutton reset (see Figure 2). The
pushbutton reset input requires an active low signal. Internally, this input is debounced and timed such
that a RST (or RST) signal of at least 130 ms minimum will be generated. The 130 ms delay commences
as the pushbutton reset input is released from the low level. The pushbutton can be initiated by connecting
the WDS or NMI outputs to the PBRST input as shown in Figure 3.
Non-Maskable Interrupt
The DS1705/DS1706 generates a non-maskable interrupt ( NMI ) for early warning of a power failure. A
precision comparator monitors the voltage level at the IN pin relative to an on-chip reference generated
by an internal band gap. The IN pin is a high impedance input allowing for a user-defined sense point. An
external resistor voltage divider network (Figure 5) is used to interface with high voltage signals. This
sense point may be derived from a regulated supply or from a higher DC voltage level closer to the main
system power input. Since the IN trip point VTP is 1.25 volts, the proper values for R1 and R2 can be
determined by the equation as shown in Figure 5. Proper operation of the DS1705/DS1706 requires that
the voltage at the IN pin be limited to VCC. Therefore, the maximum allowable voltage at the supply being
monitored (VMAX) can also be derived as shown in Figure 5. A simple approach to solving the equation is
to select a value for R2 high enough to keep power consumption low, and solve for R1. The flexibility of
the IN input pin allows for detection of power loss at the earliest point in a power supply system,
maximizing the amount of time for system shutdown between NMI and RST (or RST).
When the supply being monitored decays to the voltage sense point, the DS1705/DS1706 pulses the NMI
output to the active state for a minimum 200 s. The NMI power-fail detection circuitry also has built-in
hysteresis of 100 V. The supply must be below the voltage sense point for approximately 5 s before a
low NMI will be generated. In this way, power supply noise is removed from the monitoring function,
preventing false interrupts. During a power-up, any detected IN pin levels below VTP by the comparator
are disabled from generating an interrupt until VCC rises to VCCTP. As a result, any potential NMI pulse
will not be initiated until VCC reaches VCCTP.
Connecting NMI to PBRST would allow non-maskable interrupt to generate an automatic reset when an
out-of-tolerance condition occurred in a monitored supply. An example is shown in Figure 3.
DS1705/DS1706
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Watchdog Timer
The watchdog timer function forces WDS signals active when the ST input is not clocked within the 1
second time-out period. Time-out of the watchdog starts when RST (or RST) becomes inactive. If a high-
to-low transition occurs on the ST input pin prior to time-out, the watchdog timer is reset and begins to
time out again. If the watchdog timer is allowed to time out, the WDS signal is driven active (low) for a
minimum of 130 ms. The ST input can be derived from many microprocessor outputs. The typical signals
used are the microprocessors address signals, data signals, or control signals. When the microprocessor
functions normally, these signals would, as a matter of routine, cause the watchdog to be reset prior to
time-out. To guarantee that the watchdog timer does not time out, a high-to-low transition must occur at
or less than the minimum watchdog time-out of 1 second. A typical circuit example is shown in Figure 6.
MICROMONITOR BLOCK DIAGRAM Figure 1
40k
180k
PUSH-BUTTON RESET Figure 2
DS1705/DS1706
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PUSH-BUTTON RESET CONTROLLED BY NMI AND WDS Figure 3
TIMING DIAGRAM: PUSHBUTTON RESET Figure 4
NON-MASKABLE INTERRUPT CIRCUIT EXAMPLE Figure 5
V
SENSE = R2
R2 R1 X 1.25 VMAX =
TP
SENSE
V
V X VCC
Example: VSENSE = 4.50V at the trip point
V
CC = 3.3V
10 kΩ = R2
Therefore:
25.1
50.4 X 3.3 = 11.88V maximum
4.5 =
10
k
10k R1
X 1.25 R1 = 26 kΩ
DS1705/DS1706
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WATCHDOG TIMER Figure 6
TIMING DIAGRAM: STROBE INPUT Figure 7
TIMING DIAGRAM: NON-MASKABLE INTERRUPT Figure 8
DS1705/DS1706
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TIMING DIAGRAM: POWER-DOWN Figure 9
DS1705/DS1706
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TIMING DIAGRAM: POWER-UP Figure 10
DS1705/DS1706
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ABSOLUTE MAXIMUM RATINGS
Voltage Range on VCC Pin Relative to Ground -0.5V to +7.0V
Voltage Range on I/O Relative to Ground* -0.5V to (VCC + 0.5V)
Operating Temperature Range -40C to +85C
Storage Temperature Range -55C to +125C
Lead Temperature (soldering, 10s) +260C
Soldering Temperature (reflow)
Lead(Pb)-free +260C
Containing lead(Pb) +240C
This is a stress rating only and functional operation of the device at these or any other conditions above those indicated in the operation
sections of this specification is not implied. Exposure to absolute maximum rating conditions for extended periods of time may affect
reliability.
*The voltage input on IN, ST, and
PBRST
can be exceeded if the input current is less than 10 mA.
RECOMMENDED DC OPERATING CONDITIONS (TA = -40C to +85C)
PARAMETER SYMBOL MIN TYP MAX UNITS NOTES
Supply Voltage VCC 1.2 5.5 V 1
ST and PBRST Input High Level VIH 2.0
VCC-0.5
V
CC+0.3 V 1, 3
1, 4
ST and PBRST Input Low Level VIL -0.03 +0.5 V 1
DC ELECTRICAL CHARACTERISTICS (VCC = 1.2V to 5.5V, TA = -40C to +85C.)
PARAMETER SYMBOL MIN TYP MAX UNITS NOTES
VCC Trip Point DS1705/DS1706L VCCTP 4.50 4.65 4.75 V 1
VCC Trip Point DS1706 VCCTP 4.25 4.40 4.50 V 1
VCC Trip Point DS1706T VCCTP 3.00 3.08 3.15 V 1
VCC Trip Point DS1706S VCCTP 2.85 2.93 3.00 V 1
VCC Trip Point DS1706P or R VCCTP 2.55 2.63 2.70 V 1
Input Leakage IIL -1.0 +1.0
A 2
Output Current @ 2.4V IOH 350
A 3
Output Current @ 0.4V IOL 10 mA 3
Output Voltage @ -500 A VOH V
CC-0.3 VCC-0.1 V 3
Operating Current
@ VCC < 5.5V
ICC 60
A 5
Operating Current
@ VCC < 3.6V
ICC 50
A 5
IN Input Trip Point VTP 1.20 1.25 1.30 V 1
CAPACITANCE (TA = +25C)
PARAMETER SYMBOL MIN TYP MAX UNITS NOTES
Input Capacitance CIN 5 pF
Output Capacitance COUT 7 pF
DS1705/DS1706
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AC ELECTRICAL CHARACTERISTICS (VCC = 1.2V to 5.5V, TA = -40C to +85C.)
PARAMETER SYMBOL MIN TYP MAX UNITS NOTES
PBRST = VIL tPB 150 ns
Reset Active Time tRST 130 205 285 ms
ST Pulse Width tST 10 ns 6
VCC Detect to RST and RST tRPD 5 8
s 9
VCC Slew Rate tF 20 s
VCC Detect to RST and RST tRPU 130 205 285 ms 7
VCC Slew Rate tR 0 ns
PBRST Stable Low to RST and RST tPDLY 250 ns
Watchdog Timeout tTD 1.0 1.6 2.2 s 8
VIN Detect to NMI tIPD 5 8
s 9
NOTES:
1. All voltages are referenced to ground.
2. PBRST is internally pulled up to VCC with an internal impedance of 40 ktypical and the ST input is
internally pulled up to VCC with an internal impedance of 180 ktypical.
3. VCC ≥ 2.4V.
4. VCC < 2.4V.
5. Measured with outputs open and all inputs at VCC or ground.
6. Must not exceed tTD minimum.
7. tR = 5 s.
8. Minimum watchdog time-out tested at 2.7V for the 3.3V devices and 4.5V for the 5.0V devices.
9. Noise immunity pulses < 2 s will not cause a reset.
DS1705/DS1706
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PART MARKING CODES
cccccc
cccccc
###xx
8-pin DIP
(300 MIL)
8-pin SOIC
(150 MIL)
8-pin µSOP
(118 MIL)
DS170AB
yywwrv
###xx
DS170AB
yywwrv
###xx
170AB
ywwrv
BRAND CODES
CODE DESCRIPTION VALUES
AB Device type and tolerance 5_, 6_, 6L, 6P, 6R, 6S, 6T (where’_’ is a blank)
yww or yyww Date Code. Identifies the year and work
week the device was assembled.
y, the last digit of the year.
yy, the last two digits of the year.
ww, the work week (values 01 through 52).
rv Die Revision A letter followed by a number (eg. B1)
###xx Lot Code Three numbers followed by 2 letters
cccccc Country of Assembly Abbreviation of country name.
DS1705/DS1706
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ORDERING INFORMATION
PART TEMP RANGE PIN-PACKAGE VERSION
DS1705EPA -40°C to +85°C 8-pin PDIP (300 mils) 5V-5% MONITOR, /RST, /WDS
DS1705ESA -40°C to +85°C 8-pin SO (150 mils) 5V-5% MONITOR, /RST, /WDS
DS1705EUA -40°C to +85°C 8-pin µSOP (118 mils) 5V-5% MONITOR, /RST, /WDS
DS1706EPA -40°C to +85°C 8-pin PDIP (300 mils) 5V-10% MONITOR, /RST, /WDS
DS1706ESA -40°C to +85°C 8-pin SO (150 mils) 5V-10% MONITOR, /RST, /WDS
DS1706EUA -40°C to +85°C 8-pin µSOP (118 mils) 5V-10% MONITOR, /RST, /WDS
DS1706LEPA -40°C to +85°C 8-pin PDIP (300 mils) 5V-5% MONITOR, RST, /WDS
DS1706LESA -40°C to +85°C 8-pin SO (150 mils) 5V-5% MONITOR, RST, /WDS
DS1706LEUA -40°C to +85°C 8-pin µSOP (118 mils) 5V-5% MONITOR, RST, /WDS
DS1706PEPA -40°C to +85°C 8-pin PDIP (300 mils) 3.3V-20% MONITOR, RST, /WDS
DS1706PESA -40°C to +85°C 8-pin SO (150 mils) 3.3V-20% MONITOR, RST, /WDS
DS1706PEUA -40°C to +85°C 8-pin µSOP (118 mils) 3.3V-20% MONITOR, RST, /WDS
DS1706REPA -40°C to +85°C 8-pin PDIP (300 mils) 3.3V-20% MONITOR, /RST, /WDS
DS1706RESA -40°C to +85°C 8-pin SO (150 mils) 3.3V-20% MONITOR, /RST, /WDS
DS1706REUA -40°C to +85°C 8-pin µSOP (118 mils) 3.3V-20% MONITOR, /RST, /WDS
DS1706SEPA -40°C to +85°C 8-pin PDIP (300 mils) 3.3V-10% MONITOR, /RST, /WDS
DS1706SESA -40°C to +85°C 8-pin SO (150 mils) 3.3V-10% MONITOR, /RST, /WDS
DS1706SEUA -40°C to +85°C 8-pin µSOP (118 mils) 3.3V-10% MONITOR, /RST, /WDS
DS1706TEPA -40°C to +85°C 8-pin PDIP (300 mils) 3.3V-5% MONITOR, /RST, /WDS
DS1706TESA -40°C to +85°C 8-pin SO (150 mils) 3.3V-5% MONITOR, /RST, /WDS
DS1706TEUA -40°C to +85°C 8-pin µSOP (118 mils) 3.3V-5% MONITOR, /RST, /WDS
Note: Devices are also available in a lead(Pb)-free/RoHS-compliant package. Specify lead-free by adding a plus (+) to the part number
when ordering.
E = -40°C to +85°C temperature range
A = 8-lead device
P = Plastic DIP (300 mils)
S = SO (150 mils)
U = µSOP (118 mils)
PACKAGE INFORMATION
For the latest package outline information and land patterns, go to www.maxim-ic.com/packages. Note that a “+”, “#”, or “-”
in the package code indicates RoHS status only. Package drawings may show a different suffix character, but the drawing
pertains to the package regardless of RoHS status.
PACKAGE TYPE PACKAGE CODE DOCUMENT NO.
8 PDIP P8-2 21-0043
8 SO S8-2 21-0041
8 SOP U8-1 21-0036
DS1705/DS1706
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Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim
reserves the right to change the circuitry and specifications without notice at any time.
Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600
© 2010 Maxim Integrated Products
Maxim is a registered trademark of Maxim Integrated Products, Inc. The Dallas logo is a registered trademark of Maxim Integrated Products, Inc.
REVISION HISTORY
REVISION
DATE DESCRIPTION PAGES
CHANGED
4/10 Added the lead temperature and updated the soldering
temperature in the Absolute Maximum Ratings; corrected Note 9. 8, 9