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1 of 12 091404 features converts cmos sram into nonvolatile memory unconditionally write-protects sram when v cc is out of tolerance automatically switches to battery backup supply when v cc power failure occurs flexible memory organization - mode 0: 4 banks with 1 sram each - mode 1: 2 banks with 2 srams each - mode 2: 1 bank with 4 srams each monitors voltage of a lithium cell and provides advanced warning of impending battery failure signals low-battery condition on active low battery warning output signal resets processor when power failure occurs and holds processor in reset during system power-up optional 5% or 10% power-fail detection 16-pin dip, 16-pin soic and 20-pin tssop packages industrial temperature range of -40c to +85c pin description v cci - +5v power supply input v cco - sram power supply output v bat - backup battery input a, b - address inputs cei1 - cei4 - chip enable inputs ceo1 - ceo4 - chip enable outputs tol - v cc tolerance select bw - battery warning output (open drain) rst - reset output (open drain) mode - mode input gnd - ground nc - no connection pin assignment ds1321 flexible nonvolatile controller with lithium battery monito r www.dalsemi.com 1 2 3 4 20 19 18 17 5 6 7 8 9 10 11 12 13 14 15 16 nc ds1321e 20-pin tssop v cci rst bw ceo1 ceo2 nc ceo3 ceo4 nc mode v cco v bat tol cei1 cei2 nc a /cei3 b/cei4 gnd 1 2 3 4 16 15 14 13 5 6 7 89 10 11 12 v cci rst bw ceo1 ceo2 ceo3 ceo4 mode v cco v bat tol cei1 cei2 a /cei3 b/cei4 gnd ds1321 16-pin dip (300-mil) 1 2 3 4 16 15 14 13 5 6 7 89 10 11 12 v cci rst bw ceo1 ceo2 ceo3 ceo4 mode v cco v bat tol cei1 cei2 a /cei3 b/cei4 gnd ds1321s 16-pin soic (150-mil)
ds1321 2 of 12 description the ds1321 flexible nonvolatile controller with lith ium battery monitor is a cmos circuit which solves the application problem of converting cm os srams into nonvolatile memory. incoming power is monitored for an out-of-t olerance condition. when such a condition is detected, chip enable outputs are inhibited to accomplish write protection and the ba ttery is switched on to supply the srams with uninterrupted power. special circuitry uses a low-l eakage cmos process which affords precise voltage detection at extremely low battery consumption. one ds1321 can support as many as four srams arranged in any of three memory configurations. in addition to battery-backup support, the ds1321 pe rforms the important function of monitoring the remaining capacity of the lithium battery and providing a warning before the battery reaches end-of-life. because the open-circuit voltage of a lithium backup battery remains relatively constant over the majority of its life, accurate battery monitoring requires loaded-battery voltage measurement. the ds1321 performs such measurement by periodically comparing th e voltage of the battery as it supports an internal resistive load with a carefully selected reference vo ltage. if the battery voltage falls below the reference voltage under such conditions, the battery will soon reach end-of-life. as a result, the battery warning pin is activated to signal the need for battery replacement. memory backup the ds1321 performs all the circuit functions required to provide battery-backup for as many as four srams. first, the device provides a switch to dir ect power from the battery or the system power supply (v cci ). whenever v cci is less than the v cctp trip point and v cci is less than the battery voltage v bat , the battery is switched in to provide backup power to the sram. this switch has voltage drop of less than 0.2 volts. second, the ds1321 handles power failure de tection and sram write-protection. v cci is constantly monitored, and when the supply goes out of toleranc e, a precision comparator detects power failure and inhibits the four chip enable outputs in order to write-protect the srams. this is accomplished by holding ceo1 through ceo4 to within 0.2 volts of v cco when v cci is out of tolerance. if any cei is active (low) at the time that power failure is detected, the corresponding ceo signal is kept low until the cei signal is brought high again. once the cei signal is brought high, the ceo signal is taken high and held high until after v cci has returned to its nominal voltage level. if the cei signal is not brought high by 1.5 s after power failure is detected, the corresponding ceo is forced high at that time. this specific scheme for delaying write protection for up to 1.5 s guarantees that any memory access in progress when power failure occurs will complete properly. power failure detection occurs in the range of 4.75 to 4.5 volts (5% tolerance) when the tol pin is wired to gnd or in the range of 4.5 to 4.25 volts (10% tolerance) when tol is connected to v cco .
ds1321 3 of 12 memory configurations the ds1321 can be configured via the mode pin for th ree different arrangements of the four attached srams. the state of the mode pin is latched at v cci = v cctp on power up. see figure 1 for details. memory configurations figure 1 mode = gnd (4 banks with 1 sram each): mode = v cco (2 banks with 2 sram each): mode floating (1 bank with 4 srams):
ds1321 4 of 12 battery voltage monitoring the ds1321 automatically performs periodic battery voltage monitoring at a factory-programmed time interval of 24 hours. such monitoring begins within t rec after v cci rises above v cctp and is suspended when power failure occurs. after each 24-hour period (t btcn ) has elapsed, the ds1321 connects v bat to an internal 1 m test resistor (r int ) for one second (t btpw ). during this one second, if v bat falls below the factory- programmed battery vo ltage trip point (v btp ), the battery warning output bw is asserted. while bw is active, battery testing will be performed with period t btcw to detect battery re moval and replacement. once asserted, bw remains active until the battery is physically removed and replaced by a fresh cell. the battery is still retested after each v cc power-up, however, even if bw was active on power-down. if the battery is found to be higher than v btp during such testing, bw is deasserted and regular 24-hour testing resumes. bw has an open-drain output driver. battery replacement following bw activation is normally done with v cci nominal so that sram data is not lost. during battery replacement, the minimum time duration between old battery detachment and new battery attachment (t bdba ) must be met or bw will not deactivate following attachment of the new battery. should bw not deactivate for this reason, the new battery can be detached for t bdba and then re- attached to clear bw . note: the ds1321 cannot constantly monitor an att ached battery because such monitoring would drastically reduce the life of the battery. as a resu lt, the ds1321 only tests the battery for one second out of every 24 hours and does not monitor the battery in any way between tests. if a good battery (one that has not been previously flagged with bw ) is removed between battery tests, the ds1321 may not immediately sense the removal and may not activate bw until the next scheduled battery test. if a battery is then reattached to the ds1321, the battery ma y not be tested until th e next scheduled test. note: battery monitoring is only a useful technique when testing can be done regularly over the entire life of a lithium battery. because the ds1321 onl y performs battery monitoring when v cc is nominal, systems which are powered-down for excessively long periods can completely drain their lithium cells without receiving any advanced warning. to prev ent such an occurrence, systems using the ds1321 battery monitoring feature should be powered-up periodi cally (at least once every few months) in order to perform battery testing. furthermore, anytime bw is activated on the first battery test after a power-up, data integrity should be checked via checksum or other technique. power monitoring the ds1321 automatically detects out -of-tolerance power supply conditi ons and warns a processor-based system of impending power failure. when v cci falls below the trip point level defined by the tol pin (v cctp ), the v cci comparator activates the reset signal rst . reset occurs in the range of 4.75 to 4.5 volts (5% tolerance) when the tol pin is connected to gnd or in the range of 4.5 to 4.25 volts (10% tolerance) when tol is connected to v cco . rst also serves as a power-on reset during power-up. after v cci exceeds v cctp , rst will be held active for 200 ms nominal (t rpu ). this reset period is sufficiently lo ng to prevent system operation during power-on transients and to allow t rec to expire. rst has an open-drain output driver.
ds1321 5 of 12 freshness seal mode when the battery is first attached to the ds1321 without v cc power applied, the device does not immediately provide battery-backup power on v cco . only after v cci exceeds v cctp will the ds1321 leave freshness seal mode. this mode allows a battery to be attached during manufacturing but not used until after the system has been activated for the first time. as a result, no battery energy is drained during storage and shipping. functional block diagram figure 2
ds1321 6 of 12 absolute maximum ratings* voltage on any pin relative to ground -0.5v to +7.0v 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 (-40c to +85c) parameter symbol min typ max units notes supply voltage tol=gnd v cci 4.75 5.0 5.5 v 1 supply voltage tol=v cco v cci 4.5 5.0 5.5 v 1 battery supply voltage v bat 2.0 3.0 6.0 v 1 logic 1 input v ih 2.0 v cci +0.3 v 1, 12 logic 0 input v il -0.3 +0.8 v 1, 12 dc electrical characteristics (-40c to +85c; v cci v cctp ) parameter symbol min typ max units notes operating current (ttl inputs) i cc1 1 1.5 ma 2 operating current (cmos inputs) i cc2 100 150 a 2, 5 ram supply voltage v cco v cc1 -0.2 v 1 ram supply current (v cco v cci -0.2v) i cco1 185 ma 3 supply current (v cco v cci -0.3v) i cco2 260 ma 4 v cc trip point (tol=gnd) v cctp 4.50 4.62 4.75 v 1 v cc trip point (tol=v cco ) v cctp 4.25 4.37 4.50 v 1 v bat trip point v btp 2.50 2.6 2.70 v 1 output current @ 2.2v i oh -1 ma 7, 10 output current @ 0.4v i ol 4 ma 7, 10 input leakage i il -1.0 +1.0 a output leakage i lo -1.0 +1.0 a battery monitoring test load r int 0.8 1.2 1.5 m ? dc electrical characteristics (-40c to +85c; v cci < v bat ; v cci < v cctp ) parameter symbol min typ max units notes battery current i bat 100 na 2 battery backup current i cco3 500 a 6 supply voltage v cco v bat -0.2 v 1 ceo output v ohl v bat -0.2 v 1, 8
ds1321 7 of 12 capacitance (t a =25c) parameter symbol min typ max units notes input capacitance ( cei *, tol, mode) c in 7 pf output capacitance ( ceo *, bw , rst ) c out 7 pf ac electrical characteristics (-40c to +85c; v cci v cctp ) parameter symbol min typ max units notes cei to ceo propagation delay t pd 12 20 ns ce pulse width t ce 1.5 s 11 v cc valid to end of write protection t rec 125 ms 9 v cc valid to cei inactive t pu 2 ms v cc valid to rst inactive t rpu 150 200 350 ms 10 v cc valid to bw valid t bpu 1 s 10 ac electrical characteristics (-40c to +85c; v cci < v cctp ) parameter symbol min typ max units notes v cc slew rate t f 150 s v cc fail detect to rst active t rpd 15 s 10 v cc slew rate t r 15 s ac electrical characteristics (-40c to +85c; v cci v cctp ) parameter symbol min typ max units notes battery test to bw active t bw 1 s 10 battery test cycle-normal t btcn 24 hr battery test cycle-warning t btcw 5 s battery test pulse width t btpw 1 s battery detach to battery attach t bdba 7 s battery attach to bw inactive t babw 1 s 10
ds1321 8 of 12 timing diagram: power-up note: if v bat > v cctp , v cco will begin to slew with v cci when v cci = v cctp .
ds1321 9 of 12 timing diagram: power-down notes: if v bat > v cctp , v cco will slew down with v cci until v cci = v cctp .
ds1321 10 of 12 timing diagram: battery warning detection note: t bw is measured from the expiration of the internal timer to the activation of the battery warning output bw . timing diagram: battery replacement
ds1321 11 of 12 notes: 1. all voltages referenced to ground. 2. measured with outputs open circuited. 3. i cco1 is the maximum average load which the ds1321 can supply to attached memories at v cco v cci -0.2v. 4. i cco2 is the maximum average load which the ds1321 can supply to attached memories at v cco v cci -0.3v. 5. all inputs within 0.3v of ground or v cci . 6. i cco3 is the maximum average load current which the ds1321 can supply to the memories in the battery backup mode at v cco v bat -0.2v. 7. measured with a load as shown in figure 1. 8. chip enable outputs ceo1 - ceo4 can only sustain leakage current in the battery backup mode. 9. ceo1 through ceo4 will be held high for a time equal to t rec after v cci crosses v cctp on power-up. 10. bw and rst are open drain outputs and, as such, cannot source current. external pullup resistors should be connected to these pins for proper operation. both bw and rst can sink 10 ma. 11. t ce maximum must be met to ensure data integrity on power down. 12. in battery backup mode, inputs must never be below ground or above v cco . 13. the ds1321 is recognized by underwriters laboratory (u.l. ? ) under file e99151. dc test conditions outputs open all voltages are referenced to ground ac test conditions output load: see below input pulse levels: 0 - 3.0v timing measurement reference levels input: 1.5v output: 1.5v input pulse rise and fall times: 5 ns output load figure 3 *including scope and jig capacitance
ds1321 12 of 12 data sheet revision summary the following represent the key differences betw een 03/26/96 and 06/12/97 version of the ds1321 data sheet. please review this summary carefully. 1. changed i cco1 from 200 to 185 ma max 2. changed i cco2 from 350 to 260 ma max 3. changed v btp from 2.55 - 2.65v to 2.50 - 2.70v changed r im from 1.0 typ to 1.2 m and 1.4 max to 1.5 m 5. changed t pd from 5 typ, 15 max to 12 typ, 20 max 6. changed t rpo units from ns to s 7. changed block diagram to show u.l. compliance the following represent the key differences betw een 06/12/97 and 09/29/97 version of the ds1321 data sheet. please review this summary carefully. 1. changed ac test conditions the following represent the key differences betw een 09/29/97 and 12/12/97 version of the ds1321 data sheet. please review this summary carefully. 1. removed preliminary from title bar. 2. specified which inputs and outputs are relevant for c in and c out specs. this is not a change, just a clarification.

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