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DS1707/DS1708
3.3 and 5.0-Volt MicroMonitor
www.maxim-ic.com
FEATURES
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 20% tolerance compatible with 3.0V systems Pin compatible with the MAXIM MAX707/MAX708 in 8-pin DIP, 8-pin SOIC packages 8-pin DIP, 8-pin and m-SOP SOIC and 8-pin m-SOP packages available Industrial temperature range -40C to +85C
PIN ASSIGNMENT
PBRST VCC GND IN 1 2 3 4 8 7 6 5 RST RST NC NMI
8-Pin DIP (300-mil) PBRST VCC GND IN 1 2 3 4 8 7 6 5 RST RST NC NMI
8-Pin SOIC (150-mil) RST RST PBRST VCC 1 2 3 4 8 7 6 5 NC NMI IN GND
8-Pin m-SOP (118-mil) See Mech. Drawings Section on website
DS1707 and DS1708_R/S/T
PIN DESCRIPTION
PBRST
VCC GND IN
NMI
NC
RST
RST
- Pushbutton Reset Input - Power Supply - Ground - Input - Non-maskable Interrupt - No Connect - Active Low Reset Output - Active High Reset Output
DESCRIPTION
The DS1707/DS1708 3.3- or 5.0-Volt MicroMonitor monitors three vital conditions for a microprocessor: power supply, voltage sense, 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 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.
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The third function the DS1707/DS1708 performs is pushbutton reset control. The DS1707/DS1708 debounces the pushbutton input and guarantees an active reset pulse width of 130 ms minimum.
OPERATION Power Monitor
The DS1707/DS1708 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 and RST signals. RST and RST are excellent control signals for a microprocessor, as processing is stopped at the last possible moment of valid VCC. On power-up, RST and RST are kept active for a minimum of 130 ms to allow the power supply and processor to stabilize.
Pushbutton Reset
The DS1707/DS1708 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 RST and RST signals 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 NMI output to the PBRST input as shown in Figure 3.
Non-Maskable Interrupt
The DS1707/DS1708 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 DS1707/DS1708 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 shut-down between NMI and RST/ RST . When the supply being monitored decays to the voltage sense point, the DS1707/DS1708 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 the 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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MICROMONITOR BLOCK DIAGRAM Figure 1
40kW
PUSHBUTTON RESET Figure 2
PUSHBUTTON RESET CONTROLLED BY NMI Figure 3
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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:
4.50 =
R1 + 10k X 1.25 10k
R1 = 26 k
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TIMING DIAGRAM: NON-MASKABLE INTERRUPT Figure 6
TIMING DIAGRAM: POWER-DOWN Figure 7
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TIMING DIAGRAM: POWER UP Figure 8
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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 limits on IN and PBRST can be exceeded if the input current is less than 10 mA.
RECOMMENDED DC OPERATING CONDITIONS
PARAMETER Supply Voltage
PBRST Input High Level 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 DS1707 VCC Trip Point DS1708 VCC Trip Point DS1708T VCC Trip Point DS1708S VCC Trip Point DS1708R Input Leakage Output Current @ 2.4V Output Current @ 0.4V Output Voltage @ -500A 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 MIN TYP MAX 5 7 pF pF
(tA=25C)
UNITS NOTES
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AC ELECTRICAL CHARACTERISTICS
PARAMETER
PBRST = VIL
(-40C to +85C; VCC=1.2V to 5.5V)
MIN 150 130 20 130 0 250 5 8 205 285 205 5 285 8 TYP MAX UNITS ns ms ms ms ms ns ns ms 7 6 7 NOTES
SYMBOL tPB tRST tRPD tF tRPU tR tPDLY tIPD
Reset Active Time 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
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. 3. VCC 2.4V 4. VCC < 2.4V 5. Measured with outputs open and all inputs at VCC or ground. 6. tR = 5 ms 7. 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 7_, 8_, 8R, 8S, 8T (where'_' is a blank) Date Code. Identifies the year and y, the last digit of the year. yy, the last two digits of the year. work week the device was ww, the work week (values 01 through 52). assembled. 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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ORDERING INFORMATION
ORDERING PACKAGE OPERATING NUMBER TEMPERATURE DS1707EPA 8-pin DIP (300mil) -40C TO +85C DS1707ESA 8-pin SOIC (150 mil) -40C TO +85C DS1707EUA 8-pin SOP (118 mil) -40C TO +85C DS1708EPA 8-pin DIP (300mil) -40C TO +85C DS1708ESA 8-pin SOIC (150 mil) -40C TO +85C DS1708EUA 8-pin SOP (118 mil) -40C TO +85C DS1708REPA 8-pin DIP (300mil) -40C TO +85C DS1708RESA 8-pin SOIC (150 mil) -40C TO +85C DS1708REUA 8-pin SOP (118 mil) -40C TO +85C DS1708SEPA 8-pin DIP (300mil) -40C TO +85C DS1708SESA 8-pin SOIC (150 mil) -40C TO +85C DS1708SEUA 8-pin SOP (118 mil) -40C TO +85C DS1708TEPA 8-pin DIP (300mil) -40C TO +85C DS1708TESA 8-pin SOIC (150 mil) -40C TO +85C DS1708TEUA 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, RST 5V-5% MONITOR, /RST, RST 5V-5% MONITOR, /RST, RST 5V-10% MONITOR, /RST, RST 5V-10% MONITOR, /RST, RST 5V-10% MONITOR, /RST, RST 3.3V-20% MONITOR, /RST, RST 3.3V-20% MONITOR, /RST, RST 3.3V-20% MONITOR, /RST, RST 3.3V-10% MONITOR, /RST, RST 3.3V-10% MONITOR, /RST, RST 3.3V-10% MONITOR, /RST, RST 3.3V-5% MONITOR, /RST, RST 3.3V-5% MONITOR, /RST, RST 3.3V-5% MONITOR, /RST, RST
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