1 tc70 tc71 micromaster ? C system supervisor with power supply monitor, watchdog and battery backup micromaster ? C system supervisor with power supply monitor, watchdog and battery backup v cc v cco v batt tc70/71 cei
(tc70) d v
detector watchdog
timer wdd
(tc70) ceo
(tc70) tdo
(tc71) v ref1 v ref2 v ref3 pf
(tc71) tdi
(tc71) rs battery
back-up
control delay
timer gnd pin configurations (dip and soic) 1 8 27 3 6 4 5 tc70 1 8 27 3 6 4 5 tc71 ceo v cco gnd cei v cc v cco gnd tdi v cc wdd v batt rs tdo pf v batt rs ordering information part no. package temp. range t c70coa 8-pin soic 0 c to +70 c tc70cpa 8-pin plastic dip 0 c to +70 c tc70eoa 8-pin soic C 40 c to +85 c tc70epa 8-pin plastic dip C 40 c to +85 c t c71coa 8-pin soic 0 c to +70 c tc71cpa 8-pin plastic dip 0 c to +70 c tc71eoa 8-pin soic C 40 c to +85 c tc71epa 8-pin plastic dip C 40 c to +85 c functional block diagram tc70/71 features n maximum functional integration: precision power supply monitor, watchdog timer, external reset override, threshold detector and battery backup controller in an 8-pin package n generates power-on reset and guards against unstable processor operation resulting from power "brownout" n automatically halts and restarts an out-of- control microprocessor n output can be wire-ored, or hooked to manual reset push-button switch n watchdog disable pin for easier prototyping (tc70) n voltage monitor for power fail or low battery warning (tc71) n available in 8-pin plastic dip or 8-pin soic packages n cost effective typical applications n all microprocessor-based systems n test equipment n instrumentation n set-top boxes general description the tc70/71 is a fully-integrated power supply monitor, watchdog and battery backup circuit in a space-saving 8-pin package. when power is initially applied, the tc70/71 holds the processor in its reset state for a minimum of 500msec after v cc is in tolerance to ensure stable system start-up. after start-up, processor sanity is monitored by the on-board watchdog circuit. the processor must provide periodic high- to-low level transitions to the tc70/71 to verify proper execution. should the processor fail to supply this signal within the specified timeout period, an out-of-control proces- sor is indicated and the tc70/71 issues a momentary processor reset as a result. the tc70 also features a watchdog disable pin to facilitate system test and debug. the output of the tc70/71 can be wire-ored to a push- button switch (or electronic signal) to reset the processor. when connected to a push-button switch, the tc70/71 provides contact debounce. the integrated battery backup circuit on-board the tc70/ 71 converts cmos ram into nonvolatile memory by first write-protecting, then switching the v cc line of the ram over to an external battery. the tc71 incorporates an additional 1.3v threshold detector for power fail warning, low battery detection or to monitor power supply voltages other than +5v. telcom semiconductor reserves the right to make changes in the circuitry and specifications of its devices. tc70/71-1 12/3/96
2 micromaster ? C system supervisor with power supply monitor, watchdog and battery backup tc70 tc71 *this is a stress rating only and functional operation of the device at these or any other conditions above those indicated in the operational sections of the specifications is not implied. exposure to absolute maximum rating conditions for extended periods may affect device reliability. absolute maximum ratings* voltage (any pin) with respect to ground ................................ gnd C 0.3 to v cc + 0.3v operating temperature range ............... C 40 c to +85 c storage temperature range ................ C 65 c to +150 c lead temperature (soldering, 10 sec) ................. +300 c electrical characteristics: recommended dc operations : t a = t min to t max, unless otherwise specified. symbol parameter test conditions min typ max unit v cc supply voltage note 1 4.5 5.0 5.5 v v ih input high level cei, wdd (note 1) 2.5 v rs (note 1) 2.2 v il input low level cei, wdd, rs (note 1) 0.8 v electrical characteristics: dc : t a = t min to t max , v cc = 4.5v to 5.5v, unless otherwise specified. symbol parameter test conditions min typ max unit i cc1 operating current notes 2, 3 5 6.5 ma i cc2 operating current in v cc = 0; v batt = 2.8v; (note 3) 0.01 0.20 m a battery backup mode i ih input leakage cei 4 7 m a i il input leakage cei 1 m a i ih input leakage rs 1 m a i stby battery standby current 5.5v > v cc > v batt + 0.2v C 1.0 0.02 m a i stby battery standby current 5.5v > v cc > v batt + 0.2v C 0.1 0.02 m a t a = 25 c electrical characteristics: dc : power supply monitor, ext. reset and watchdog: t a = t min to t max , v cc = 4.5v to 5.5v, unless otherwise specified. symbol parameter test conditions min typ max unit i ol output current 0.4v v ol = 0.4v 2 5 ma (rs, tdo, ceo, pf pins) i oh output current 2.4v v oh = 2.4v 2 3 ma (tdo, ceo, pf pins) wdd i wdd input current wdd = gnd C 120 m a wdd = v cc 25 v sth rs strobe (high) level figure 3 (note 1) v dd C 0.5 v v stl rs strobe (low) level figure 3 (note 1) 2.2 v dd C 1.8 v v cctrip v cc trip point (note 1) 0 c t a 70 c 4.25 4.49 C 40 c t a 85 c 4.20 4.49 electrical characteristics: dc : battery backup and threshold detector: t a = t min to t max , v cc = 4.5v to 5.5v, unless otherwise specified. symbol parameter test conditions min typ max unit v out1 v cco output voltage i out = 1ma v cc C 0.3 v cc C 0.1 v i out = 50ma v cc C 0.5 v cc C 0.20 v out2 v out in battery backup mode i out = 250 m a, v cc < v batt C 0.2, v batt = 2.8v v batt C 0.1 v batt C 0.02 v
3 tc70 tc71 micromaster ? C system supervisor with power supply monitor, watchdog and battery backup electrical characteristics: (cont.) dc : battery backup and threshold detector: t a = t min to t max , v cc = 4.5v to 5.5v, unless otherwise specified. symbol parameter test conditions min typ max unit i out2 v cco output current in v cco = v batt C 0.3v 500 m a battery backup mode v batt = 2.8v v sw battery switchover threshold v batt C 0.01 v (v cc falling) v hyst battery switchover hysteresis 20 mv voh ceo ceo output voltage in v cc < v batt C 0.2, v batt = 2.8v v batt C 0.2 v battery backup mode i oh = 10 m a v tdi threshold detector trip voltage 1.2 1.4 v i tdi threshold detector input current t a = 25 c C25 +25 na v tdi (hyst) threshold detector hysteresis 10 mv electrical characteristics: ac : power supply monitor, ext. reset and watchdog: t a = t min to t max , v cc = 4.5v to 5.5v, unless otherwise specified. symbol parameter test conditions min typ max unit t pbh pb hold time figure 4 (note 4) 20 msec t rst reset active time figure 6 500 900 msec t st rs strobe pulsewidth figure 3 500 nsec t td watchdog timeout period figure 3 500 700 900 msec t rpd v cc detect to rs low figure 6 100 nsec electrical characteristics: ac : battery backup and threshold detector: t a = t min to t max , v cc = 4.5v to 5.5v, unless otherwise specified. symbol parameter test conditions min typ max unit t pd ce propagational delay figure 7 50 nsec electrical characteristics: ac : t a = t min to t max . symbol parameter test conditions min typ max unit t f v cc fall time from figure 5 (note 1) 10 m sec 4.25v to 3.0v t r v cc rise time from figure 5 (note 1) 0 m sec 3.0v to 4.25v notes: 1. all voltages referenced to ground. 2. no output load. 3 measured with v cco and ceo open. 4. the rs output must be held low for a minimum of 20msec to guarantee a reset.
4 micromaster ? C system supervisor with power supply monitor, watchdog and battery backup tc70 tc71 strobed within the watchdog timeout period. this action typically initiates the processor's power-up routine. if the interruption persists, new reset pulses are generated each timeout period until rs is strobed. the timeout period is typically 700msec. it is often difficult to debug a system while the watchdog is continuously generating reset pulses. for example, the watchdog must be disabled when the system is operated with an in-circuit emulator (ice). the watchdog disable input (tc70) is provided for system debugging, (or if the watchdog timer on-board the processor is to be used). grounding wdd disables the watchdog (all other functions remain intact). for normal watchdog operation, wdd can be tied to v dd . the software routine that drives the rs strobe must be in a section of the program that executes frequently enough so the time between toggles is less than one watchdog timeout period. the strobe signal can be derived from microprocessor address, data and/or control signals. typi- cal circuit examples are shown in figure 1. pin description pin no pin no (tc70) (tc71) symbol description 11 v cco v cc output. the higher of v cc or v batt is internally switched to this output. connect to v cc if v batt and v cco are not used. 22 v cc v cc input. +5v power supply. 3 3 gnd gnd input. ground. 4 C cei chip enable input. chip enable to static ram or other device to be battery backed-up. connect to ground if v cco is not used. C 4 tdi threshold detector input. when the voltage on threshold detector input (tdi) is less than 1.3v, threshold detector output (tdo) goes low. 5 C ceo chip enable output. this line goes low only when cei is low and v cc is above the reset threshold. C 5 tdo threshold detector output. tdo goes low when tdi is less than 1.3v and v cc is greater than v batt . (the threshold detector is turned off when v cc is less than v batt . 6 C wdd watchdog disable input. grounding this line disables the watchdog timer (no reset pulses are generated after the watchdog timer times out). this input is provided to facilitate system debug. this input is internally pulled-up and can be left open, or tied to v cc for normal watchdog operation. C 6 pf power fail output. this line goes low when v cc is below 4.5v nominal. it is used to write-protect the external device to be battery backed. 7 7 rs reset/store (bidirectional). an open drain with pull-up (in output mode) that goes active if: 1. v cc falls below 4.5v nominal 2. if pulled low by an external electronic signal or switch closure 3. if the watchdog is not strobed within the minimum watchdog timeout period 4. during power-up and power down in the input mode, rs is a negative edge triggered input that resets the watchdog timer when pulled to ground through a 10k w , 5% tolerance resistor. 88v batt backup battery input. connect to ground if battery backup is not used. detailed description precision power supply monitor the rs pin is immediately driven low any time v cc is below 4.5v nominal. the processor is held in its reset state during power-up and power-down. rs remains low for a minimum of 500msec after v cc is within tolerance to allow the power supply and processor to stabilize. watchdog timer the processor drives the rs pin with an input/output (i/o) line in series with a voltage divider to v dd . pulling the bottom of this divider low results in an internal voltage change (strobe) sufficient to reset the watchdog timer, but above the v il input threshold of the processor reset input. the processor must continuously apply strobes in this manner within a set period to verify proper software execu- tion. a momentary reset (500msec minimum) is generated if a hardware or software failure keeps rs from being
5 tc70 tc71 micromaster ? C system supervisor with power supply monitor, watchdog and battery backup figure 1. tc70 typical application v cc ce wdd vcco ceo tc70 address
decoder address
cmos
ram
i/o
reset reset processor +5v +3v l i
battery r2
13k
r1
10k +5v v batt v cc gnd cei rs data corruption during power up and power down. the battery switchover circuit compares v cc to the v batt input and connects vcco to whichever is higher. switchover (v sw ) occurs when v cc is 10mv below v batt as v cc falls, and when v cc is 10mv more than v batt as v cc rises. the battery switchover comparator has 20mv of hysteresis to prevent switch chattering if v cc falls very slowly. integrated battery backup (tc71) the tc71 differs from the tc70 in that it has a power fail (pf) output instead of a gated chip enable (cei, ceo). pf must be externally gated with the decode for the cmos ram or other device to be battery-backed. (many cmos rams have both ce and ce enables. in this case, the pf output can be connected directly to the ce input of the ram). pf is high as long as v cc is greater than 4.5v nominal. when v cc falls below 4.5v nominal, pf is driven low. battery switchover for the tc71 is otherwise identical to that of the tc70. supply monitor noise sensitivity the tc70/71 is optimized for fast response to negative- going changes in v dd . systems with an inordinate amount of electrical noise on v dd (such as systems using relays), may require a 0.1 m f bypass capacitor to reduce detection sensitivity. this capacitor should be installed as close to the tc70/71 as possible to keep the capacitor lead length short. typical applications figure 1 shows a full feature implementation of the tc70; figure 2 shows the tc71. resistors r1 and r2 of figure 2 set the trip point voltage for the early power fail warning circuit using the tc71 threshold detector. resistor value selection the values of r1 and r2 must be chosen to ensure a valid low strobe level (v stl ) on rs when the processor i/o line is low. the use of 10k w and 13k w , 5% tolerance resistors are recommended. these values result in a nomi- nal strobe level of 2.83v on rs (min/max of 2.43v/3.24v, assuming v dd = 5.0v 10%). other resistor values can be used, so long as the additive tolerances of the power supply and resistor values result in a strobe that falls within v sth and v stl under all additive tolerance conditions. external override reset control a built-in debounce circuit allows a pushbutton switch (or other electronic reset signal) to be wire-ored to rs as an external reset override (figure 4). the external reset signal is required to be an active low signal of at least 20msec in duration. internally, this input is timed to provide a minimum reset pulse width output of 500msec. threshold detector the tc71 issues a low-true output on the tdo pin any time the tdi pin is less than 1.3v and v cc is greater than v batt . the voltage to be monitored is connected to the tdi input through a simple resistor divider. the threshold detec- tor can be used to generate an early power fail warning if the unregulated dc input to the +5v regulator is available for monitoring. integrated battery backup (tc70) the ceo line (tc70) drives the ce input of a cmos ram or other device to be battery-backed. ceo follows cei as long as v cc is greater than 4.5v nominal. if v cc falls below 4.5v nominal, ceo is driven to the potential of vcco thus write protecting the ram and preventing accidental
6 micromaster ? C system supervisor with power supply monitor, watchdog and battery backup tc70 tc71 figure 4. rs override reset figure 3. watchdog strobe figure 2. tc71 typical application v cc ce wdd vcco pf tc71 tc55rp
regulator filter cap address
nmi
cmos
ram
i/o
reset reset processor 3v l i r4 r3 v batt v cc v cc v cc tdi gnd ce tdo ac i n rs address
decoder rectifier r4
13k r3
10k v stl (max) t st t td rs note: t td is the maximum elapsed time between strobes which
will keep the watchdog timer from forcing rs low.
(a strobe is defined as a high-to-low transition from v sth to v stl ) . v sth (min) v stl (min) pb closed pb open
rs v ih t rst
v il t pbh
7 tc70 tc71 micromaster ? C system supervisor with power supply monitor, watchdog and battery backup figure 5. power up/down slew rate figure 6. power up/down reset timing figure 7. battery backup (power-up) figure 8. battery backup (power-down) 3.0v 4.25v v cc t r t f rs v ol v oh v cc 4.25v t rst t rpd
t pd t r
v ih v cc v batt- 0.2v v ih
cei ceo 4.25v 3.0v
t f t pd v il v batt-0.2v v cc cei 4.25v 3.0v ceo
8 micromaster ? C system supervisor with power supply monitor, watchdog and battery backup tc70 tc71 package dimensions dimensions: inches (mm) .050 (1.27) typ. 8 max. pin 1 .244 (6.20)
.228 (5.79) .157 (3.99)
.150 (3.81) .197 (5.00)
.189 (4.80) .018 (0.46)
.014 (0.36) .010 (0.25)
.004 (0.10) .069 (1.75)
.053 (1.35) .010 (0.25)
.007 (0.18) .050 (1.27)
.016 (0.40) 8-pin soic 8-pin plastic dip 3 min. pin 1 .260 (6.60)
.240 (6.10) .045 (1.14)
.030 (0.76) .070 (1.78)
.045 (1.14) .400 (10.16)
.348 (8.84) .200 (5.08)
.140 (3.56) .150 (3.81)
.115 (2.92) .110 (2.79)
.090 (2.29) .022 (0.56)
.015 (0.38) .040 (1.02)
.020 (0.51) .015 (0.38)
.008 (0.20) .310 (7.87)
.290 (7.37) .400 (10.16)
.310 (7.87)
9 tc70 tc71 micromaster ? C system supervisor with power supply monitor, watchdog and battery backup printed in the u.s.a. sales offices telcom semiconductor 1300 terra bella avenue p.o. box 7267 mountain view, ca 94039-7267 tel: 415-968-9241 fax: 415-967-1590 e-mail: liter@c2smtp.telcom-semi.com telcom semiconductor austin product center 9101 burnet rd. suite 214 austin, tx 78758 tel: 512-873-7100 fax: 512-873-8236 telcom semiconductor h.k. ltd. 10 sam chuk street, ground floor san po kong, kowloon hong kong tel: 852-2324-0122 fax: 852-2354-9957
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