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DS1705/DS1706 3.3 and 5.0 Volt MicroMonitor
www.maxim-ici.com
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 m-SOP 8-pin DIP, 8-pin SOIC and 8-pin m-SOP packages Industrial temperature range -40C to +85C
PIN ASSIGNMENT
PBRST VCC GND IN 1 2 3 4 8 7 6 5 WDS RST ST NMI
8-Pin DIP (300 -mil) PBRST VCC GND IN 1 2 3 4 8 7 6 5 WDS RST(*RST) ST NMI
8-Pin SOIC (150-mil) RST(*RST) WDS PBRST VCC 1 2 3 4 8 7 6 5 ST NMI IN GND
8-Pin m-SOP (118-mil) See Mech. Drawings Section on website
DS1705 and DS1706_R/S/T (*DS1706L and DS1706P)
PIN DESCRIPTION
PBRST
VCC GND IN
NMI ST RST
*RST
WDS
- Pushbutton Reset Input - Power Supply - Ground - Input - Non-maskable Interrupt - Strobe Input - Active Low Reset Output - Active High Reset Output (DS1706P and DS1706L only) - 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
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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 ms. The NMI power-fail detection circuitry also has built-in hysteresis of 100 mV. The supply must be below the voltage sense point for approximately 5 ms 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.
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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 highto-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
40kW
180kW
PUSH-BUTTON RESET Figure 2
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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
VSENSE = Example:
R1+ R2 X 1.25 R2
VMAX =
VSENSE X VCC VTP
VSENSE = 4.50V at the trip point VCC = 3.3V 10 k = R2
4.50 X 3.3 = 11.88V maximum 1.25
Therefore:
4.5 =
R1 + 10k X 1.25 10k
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R1 = 26 k
DS1705/DS1706
WATCHDOG TIMER Figure 6
TIMING DIAGRAM: STROBE INPUT Figure 7
TIMING DIAGRAM: NON-MASKABLE INTERRUPT Figure 8
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TIMING DIAGRAM: POWER-DOWN Figure 9
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TIMING DIAGRAM: POWER-UP Figure 10
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ABSOLUTE MAXIMUM RATINGS*
Voltage on VCC Pin Relative to Ground Voltage on I/O Relative to Ground** Operating Temperature Storage Temperature Soldering Temperature * -0.5V to +7.0V -0.5V to VCC + 0.5V -40C to +85C -55C to +125C 260C for 10 seconds
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
PARAMETER Supply Voltage
ST and PBRST Input High Level ST and PBRST Input Low Level
(-40C to +85C)
MAX 5.5 VCC+0.3 +0.5 UNITS V V V NOTES 1 1, 3 1, 4 1
SYMBOL VCC VIH VIL
MIN 1.2 2.0 VCC-0.5 -0.03
TYP
DC ELECTRICAL CHARACTERISTICS
PARAMETER VCC Trip Point DS1705/DS1706L VCC Trip Point DS1706 VCC Trip Point DS1706T VCC Trip Point DS1706S VCC Trip Point DS1706P or R Input Leakage Output Current @ 2.4V Output Current @ 0.4V Output Voltage @ -500 mA Operating Current @ VCC < 5.5V Operating Current @ VCC < 3.6V IN Input Trip Point SYMBOL VCCTP VCCTP VCCTP VCCTP VCCTP IIL IOH IOL VOH ICC ICC VTP 1.20 10 MIN 4.50 4.25 3.00 2.85 2.55 -1.0
(-40C to +85C; VCC=1.2V to 5.5V)
TYP 4.65 4.40 3.08 2.93 2.63 350 MAX 4.75 4.50 3.15 3.00 2.70 +1.0 UNITS V V V V V mA mA mA VCC-0.1 60 50 1.25 1.30 V mA mA V NOTES 1 1 1 1 1 2 3 3 3 5 5 1
VCC-0.3
CAPACITANCE
PARAMETER Input Capacitance Output Capacitance SYMBOL CIN COUT
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(tA=258C)
MIN TYP MAX 5 7 UNITS pF pF NOTES
DS1705/DS1706
AC ELECTRICAL CHARACTERISTICS
PARAMETER
PBRST = VIL
(-40C to +85C; VCC=1.2V to 5.5V)
MIN 150 130 10 5 20 130 0 250 1.0 1.6 5 2.2 8 205 285 8 205 285 TYP MAX UNITS ns ms ns ms ms ms ns ns s ms 8 9 7 6 9 NOTES
SYMBOL tPB tRST tST tRPD tF tRPU tR tPDLY tTD tIPD
Reset Active Time
ST Pulse Width
VCC Detect to RST and RST VCC Slew Rate VCC Detect to RST and RST VCC Slew Rate
PBRST Stable Low to RST and RST
Watchdog Timeout VIN Detect to NMI
NOTES:
1. All voltages are referenced to ground. 2. PBRST is internally pulled up to VCC with an internal impedance of 40 kW typical and the ST input is internally pulled up to VCC with an internal impedance of 180 kW 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 ms. 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 ms at VCCTP minimum will not cause a reset.
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PART MARKING CODES
8-pin DIP (300 MIL)
DS170AB yywwrv ###xx
cccccc
8-pin SOIC (150 MIL)
DS170AB yywwrv ###xx
cccccc
8-pin SOP (118 MIL)
170AB ywwrv
###xx
Code AB yww or yyww rv ###xx cccccc
Brand Codes Description Values Device type and tolerance 5_, 6_, 6L, 6P, 6R, 6S, 6T (where'_' is a blank) Date Code. Identifies the y, the last digit of the year. year and work week the yy, the last two digits of the year. device was assembled. ww, the work week (values 01 through 52). Die Revision A letter followed by a number (eg. B1) Lot Code Three numbers followed by 2 letters Country of Assembly Abbreviation of country name.
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DS1705/DS1706
ORDERING INFORMATION
ORDERING PACKAGE OPERATING NUMBER TEMPERATURE DS1705EPA 8-pin DIP (300mil) -40C TO +85C DS1705ESA 8-pin SOIC (150 mil) -40C TO +85C DS1705EUA 8-pin SOP (118 mil) -40C TO +85C DS1706EPA 8-pin DIP (300mil) -40C TO +85C DS1706ESA 8-pin SOIC (150 mil) -40C TO +85C DS1706EUA 8-pin SOP (118 mil) -40C TO +85C DS1706LEPA 8-pin DIP (300mil) -40C TO +85C DS1706LESA 8-pin SOIC (150 mil) -40C TO +85C DS1706LEUA 8-pin SOP (118 mil) -40C TO +85C DS1706PEPA 8-pin DIP (300mil) -40C TO +85C DS1706PESA 8-pin SOIC (150 mil) -40C TO +85C DS1706PEUA 8-pin SOP (118 mil) -40C TO +85C DS1706REPA 8-pin DIP (300mil) -40C TO +85C DS1706RESA 8-pin SOIC (150 mil) -40C TO +85C DS1706REUA 8-pin SOP (118 mil) -40C TO +85C DS1706SEPA 8-pin DIP (300mil) -40C TO +85C DS1706SESA 8-pin SOIC (150 mil) -40C TO +85C DS1706SEUA 8-pin SOP (118 mil) -40C TO +85C DS1706TEPA 8-pin DIP (300mil) -40C TO +85C DS1706TESA 8-pin SOIC (150 mil) -40C TO +85C DS1706TEUA 8-pin SOP (118 mil) -40C TO +85C * Contact factory for availability of Pb-free versions. E = -40C to +85C temperature range A = 8 lead device P = Plastic DIP (300 mil) S = SOIC (150 mil) U = SOP (118 mil) VERSION 5V-5% MONITOR, /RST, /WDS 5V-5% MONITOR, /RST, /WDS 5V-5% MONITOR, /RST, /WDS 5V-10% MONITOR, /RST, /WDS 5V-10% MONITOR, /RST, /WDS 5V-10% MONITOR, /RST, /WDS 5V-5% MONITOR, RST, /WDS 5V-5% MONITOR, RST, /WDS 5V-5% MONITOR, RST, /WDS 3.3V-20% MONITOR, RST, /WDS 3.3V-20% MONITOR, RST, /WDS 3.3V-20% MONITOR, RST, /WDS 3.3V-20% MONITOR, /RST, /WDS 3.3V-20% MONITOR, /RST, /WDS 3.3V-20% MONITOR, /RST, /WDS 3.3V-10% MONITOR, /RST, /WDS 3.3V-10% MONITOR, /RST, /WDS 3.3V-10% MONITOR, /RST, /WDS 3.3V-5% MONITOR, /RST, /WDS 3.3V-5% MONITOR, /RST, /WDS 3.3V-5% MONITOR, /RST, /WDS
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