ds1814/ds1819 5 volt and 3.3 volt economonitor ds1814/ds1819 product preview 061198 1/8 features ? halts and restarts an outofcontrol microprocessor ? holds microprocessor in check during power tran- sients ? automatically restarts microprocessor after power failure ? monitors pushbutton for external override ? accurate 5%, 10% or 20% (3 volt only) microproces- sor power monitoring ? eliminates the need for discrete components ? 20% tolerance for use with 3.0 volt systems ? pin and function compatible with the max823/24/25 products ? low cost sot235 package ? industrial temperature 40 c to +85 c device rst rst pbrst wd ds181xa ds181xb ds181xc x x x x x x x x x x = `4' for 5 volt devices x = `9' for 3 volt devices pin assignment 45 2 sot235 package see mech. drawing 31 pin description ds181xa 1 rst active low reset output 2 gnd ground 3 pbrst pushbutton reset input 4st strobe input 5 vcc power supply ds181xb 1 rst active low reset output 2 gnd ground 3 rst active high reset output 4st strobe input 5 vcc power supply ds181xc 1 rst active low reset output 2 gnd ground 3 rst active high reset output 4 pbrst pushbutton reset input 5 vcc power supply description the ds1814 5 volt economonitor and the ds1819 3.3 volt economonitor monitors three vital conditions for a microprocessor: power supply, software execution, and external override. first, a precision temperature compensated reference and comparator circuit moni- tors the status of v cc . when an outoftolerance condition occurs, an internal power fail signal is gener- ated which forces the reset(s) to an active state. when v cc returns to an intolerance condition, the reset sig- nal is kept in the active state for a minimum of 140 ms to allow the power supply and processor to stabilize. the ds1814/ds1819 `a' and `c' perform pushbutton reset control. they debounce the pushbutton input and generate an active reset pulse width of 140 ms mini- mum. the ds1814/9 `a' and `b' versions perform a watchdog function. the watchdog is an internal timer that forces the reset signals to the active state if the strobe input does not change state every 1.12 seconds. the watchdog timer function can be disabled by leaving the watchdog strobe input unconnected.
ds1814/ds1819 061198 2/8 operation power monitor the ds1814 detects outoftolerance power supply conditions and warns a processorbased system of impending power failure. when v cc falls below a pre- set level, a comparator outputs the signal rst (or rst). rst (or rst) are excellent control signals for a micro- processor, as processing is stopped at the last possible moment of valid v cc . on powerup, rst (or rst) are kept active for a minimum of 140 ms to allow the power supply and processor to stabilize. pushbutton reset the ds1814 `a' and `c' 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 140 ms minimum will be generated. the 140 ms delay commences as the push- button reset input is released from the low level (see figure 3). watchdog timer the ds1814/ds1819 `a' and `b' versions watchdog timer function forces rst (and rst) signal(s) active when the st input is not clocked within the 1.12 second watchdog timeout period. timeout of the watchdog starts when rst (and rst) become(s) inactive. if a transition occurs on the st input pin prior to timeout, the watchdog timer is reset and begins to timeout again. if the watchdog timer is allowed to time out, then the reset output(s) will go active for 140 ms. the watch- dog can be disabled by floating (or tristating) the st input. the st input can be derived from many microprocessor outputs. the most typical signals used are the micro- processor data i/o signals and control signals. when the microprocessor functions normally, these signals would, as a matter of routine, cause the watchdog to be reset prior to timeout. to guarantee that the watchdog timer does not timeout , a transition must occur at or less than 1.12 seconds. a typical circuit example is shown in figure 4. the ds1814/19 watchdog function can be disabled at any time by tristarting the strobe input. a sample circuit to disable the watchdog is shown in figure 6. economonitor block diagram figure 1 level sense digital timeout *st *pbrst v cc v cc tolerance bias and debounce comparator delay + v cc v cc rst *rst t.c. reference *notes: st available on `a' and `b' versions pbrst available on `a' and `c' versions rst available on `b' and `c' versions
ds1814/ds1819 061198 3/8 pushbutton reset figure 2 gnd pbrst v cc DS1814C rst rst supply voltage timing diagram: pushbutton reset figure 3 rst pbrst rst v ih t rst v il t pdly t pb v oh v ol watchdog timer figure 4 gnd rst st v cc ds1814a pbrst z80 m p rst decoder address bus mreq supply voltage
ds1814/ds1819 061198 4/8 timing diagram: strobe input figure 5 indeterminate strobe invalid strobe min. max. valid strobe st t td rst watchdog disable circuit figure 6 st output tristate timing diagrampower down figure 7 v cctp t rpd v cc v oh v ol rst rst (b and c versions only) v cctp (max) v cctp (min) rst slews with v cc
ds1814/ds1819 061198 5/8 timing diagram: powerup figure 8 rst (b and c version only) rst rst v oh v ol t rpu v cctp(max) v cctp v cctp(min) v cc rst valid to 0 volts v cc figure 9 rst input 100k w output valid conditions the rst output uses a pushpull output which can maintain a valid output down to 1.0 volts v cc . to sink current below 1.0 volts a resistor can be connected form rst to ground (see figure 9.) this arrangement will maintain a valid value on rst during both powerup and down but will draw current when rst is in the high state. a value of about 100k w should be adequate in most situations. the output with a resistor pulldown can maintain a valid reset down to v cc equal to 0v.
ds1814/ds1819 061198 6/8 absolute maximum ratings* voltage on v cc pin relative to ground 0.5v to +7.0v voltage on i/o relative to ground 0.5v to v cc + 0.5v operating temperature 40 c to +85 c storage temperature 55 c to +125 c soldering temperature 260 c 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. recommended dc operating conditions (40 c to +85 c) parameter symbol min typ max units notes supply voltage v cc 1.0 5.5 v 1 st and pbrst input high level v ih 0.8 v cc v 1 st and pbrst input low level v il 0.3 v cc v 1 dc electrical characteristics (40 c to +85 c; v cc =1.2v to 5.5v) parameter symbol min typ max units notes v cc trip point ds18145 v cctp 4.50 4.75 v 1 v cc trip point ds181410 v cctp 4.25 4.50 v 1 v cc trip point ds18195 v cctp 3.00 3.15 v 1 v cc trip point ds181910 v cctp 2.85 3.00 v 1 v cc trip point ds181920 v cctp 2.55 2.70 v 1 reset trip point hysteresis (ds1814) v rh 10 mv reset trip point hysteresis (ds1819) v rh 5 mv output current @ 2.4v i oh 350 m a 3 output current @ 0.4v i ol 3.2 6 ma 3 output voltage @ 30 m a v oh v cc *.8 v cc *.9 v 3 operating current ds1814 i cc 10 15 m a 4 operating current ds1819 i cc 8 12 m a 5 st input current st = v cc , time averaged 120 160 m a 6 st input current st = gnd, time averaged 20 15 m a 6
ds1814/ds1819 061198 7/8 ac electrical characteristics (40 c to +85 c; v cc =1.2v to 5.5v) parameter symbol min typ max units notes pbrst = v il t pb 1 m s 7 reset active time t rst 140 200 280 ms st pulse width t st 50 ns 8 watchdog timeout t td 1.12 1.60 2.40 s v cc detect to rst and rst t rpd 30 40 m s 9 v cc slew rate (rising edge) 12.5 v/ m s v cc detect to rst and rst t rpu 140 200 280 ms pbrst stable low to rst and rst t pdly 500 ns capacitance (t a =25 c) parameter symbol min typ max units notes input capacitance c in 5 pf output capacitance c out 7 pf notes: 1. all voltages are referenced to ground. 2. pbrst is internally pulled up to v cc with an internal impedance of 50k w typical. 3. measured with v cc 2.7v. 4. measured with outputs open, v cc 5.5 volts, and all inputs at v cc or ground, except the st input at <10khz duty cyclesquare wave or st input open. 5. measured with outputs open, v cc 3.6 volts, and all inputs at v cc or ground, except the st input at <10khz duty cyclesquare wave or st input open. 6. the st input current is defined as the average input current when st is driven high or low. this input must be driven high or low by an output that can source or sink at least 200 m a when active. 7. noise immunity pulses <100 ns at pushbutton input will not cause a reset. 8. must not exceed t td minimum. 9. noise immunity pulses <2 m s at v cctp minimum will not cause a reset and v cctp v cc =100 mv.
ds1814/ds1819 061198 8/8 part marking codes sot235 package 12 3 a b c d aao, abo and aco represents the device type. 14a ds1814a 14b ds1814b 14c DS1814C 19a ds1819a 19b ds1819b 19d ds1819c ado represents the device tolerance. a5% b 10% c 20%
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