DS1218 nonvolatile controller DS1218 021798 1/4 features ? converts cmos ram into nonvolatile memories ? unconditionally write protects when v cc is out of tolerance ? automatically switches to battery when power fail occurs ? space saving 8pin minidip/8pin 150 mil soic ? consumes less than 100 na of battery current pin assignment v cci v bat ceo cei v cc0 nc nc gnd 1 2 3 4 8 7 6 5 pin description v cci input +5 volt supply v cco ram power (v cc ) supply cei chip enable input nc no connection ceo chip enable output v bat + battery gnd ground description the DS1218 is a cmos circuit which solves the applica- tion problems of converting cmos ram into nonvolatile memory. incoming power is monitored for an out of tol- erance condition. when such a condition is detected, the chip enable output is inhibited to accomplish write protection and the battery is switched on to supply ram with uninterrupted power. special circuitry uses a low- leakage cmos process which affords precise voltage detection at extremely low battery consumption. the 8pin minidip package keeps pc board real estate re- quirements to a minimum. by combining the DS1218 nonvolatile controller chip with a full cmos memory and lithium batteries, ten years of nonvolatile ram operation can be achieved. operation the DS1218 nonvolatile controller performs the circuit functions required to battery back up a ram. first, a switch is provided to direct power from the battery or v cci supply depending on which is greater. this switch has a voltage drop of less than 0.2v. the second func- tion which the nonvolatile controller provides is power fail detection. the DS1218 constantly monitors the v cc supply. when v cci falls to 1.26 times the battery volt- age a precision comparator outputs a power fail detect signal to the chip enable logic. the third function of write protection is accomplished by holding the chip enable output signal to within 0.2v of the v cci or battery supply, when a power fail condition is detected. during nominal supply conditions, the chip enable out- put will follow chip enable input with a maximum propa- gation delay of 10 ns.
DS1218 021798 2/4 absolute maximum ratings* voltage on any pin relative to ground 0.5v to +7.0v operating temperature 0 c to 70 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 (0 c to 70 c) parameter symbol min typ max units notes supply v cci 4.5 5.0 5.5 v 1 logic 1 v ih 2.0 5.5 v 1 logic 0 v il 0.3 0.8 v 1 battery supply v bat 2.5 3.0 3.5 v 1 dc electrical characteristics (0 c to 70 c; v cci = 5v 10%) parameter symbol min typ max units notes active current i cci 2 5 ma 3 battery current i bat 100 na 3, 4 ram current (v cco1 v cci 0.3v) i cco 80 ma 5 ram current (v cco v cci 0.2v) i cco 70 ma input leakage i il 1.0 +1.0 m a ceo output @ 2.4v i oh 1.0 ma ceo output @ 0.4v i ol 4.0 ma v cc trip point v cctp 1.26xv bat capacitance (t a = 25 c) parameter symbol min typ max units notes input capacitance c in 5 pf output capacitance c out 7 pf ac electrical characteristics (0 c to 70 c; v cc = 5.0v 10%) parameter symbol min typ max units notes ce propagation delay t pd 4 10 ns 2 recovery at powerup t rec 0.2 2 ms v cc slew rate t f 500 m s ce pulse width t ce 1.5 m s 6, 7
DS1218 021798 3/4 timing diagram: power up ????????? ????????? ????????? cei v bat t pd don't care v cctp v bat 0.2 ceo v cci t rec t pd timing diagram: power down ??????????? ??????????? ??????????? cei v bat t f don't care v bat 0.2 4.5 v cctp t pd t pd ceo v cci t ce t ce
DS1218 021798 4/4 notes: 1. all voltages referenced to ground. 2. measured with a load as shown in figure 1. 3. outputs open. 4. drain from battery when v cc < v bat . 5. maximum amount of current which can be drawn through pin 1 of the controller. 6. t ce max must be met to ensure data integrity on power loss. 7. ceo can only sustain leakage current in the battery backup mode. output load figure 1 +5 volts 50 pf d.u.t. 1.1k 680 w
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