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1 ltc1559-3.3/ltc1559-5 backup battery controller with fixed output n complete battery backup system in an so-8, 16-pin gn or so package n generates fixed backup voltage (3.07v/4.63v) from a single 1.2v nicd button cell n automatic main supply to backup switching n minimum 100mw output power n automatic fast recharge of nicd battery n programmable nicd trickle charge current n smart nicd charger minimizes recharge time and maximizes system efficiency after backup n onboard power-up and push-button reset generator n performs v cc supervisory functions n reset assertion guaranteed at v cc = 1v n short-circuit protection n thermal limiting features descriptio n u the ltc ? 1559 is a backup battery controller that provides all the functions necessary to implement a backup 3.3v or 5v power supply using a single nicd cell. it includes a 1.2v to 3.07v/4.63v boost converter, an intelligent 2-stage battery charger, automatic backup switching and a micro- processor reset generator. the boost converter uses a synchronous switching architecture to achieve a typical efficiency of 70%, ensuring maximum backup lifetime from a small nicd cell. the on-chip nicd charger uses an internal gas gauge to minimize fast recharge time and prevent overcharging of the backup cell, thereby improving system efficiency and extending the life of the backup cell. the ltc1559 also provides a user programmable trickle charge current to compensate for self-discharge losses in the backup cell. the ltc1559s automatic backup switching scheme requires minimum intervention from the host system and provides feedback to the host to minimize system loading in the backup state. its internal v cc fault detector and reset generator eliminate the need for a separate microproces- sor supervisory chip in most applications. the ltc1559 is available in an so-8, 16-pin gn or so package. applicatio n s u n notebook computers n palmtop computers/pdas n portable instruments n battery-powered systems , ltc and lt are registered trademarks of linear technology corporation. typical applicatio n u ctl c1 1 m f **backup battery 1.2v nicd main battery 4.5v to 28v r1 68k sw ltc1559-3.3 *l1 22 m h gnd ps 7 1 8 5 6 3 s1 reset 1559 ta01 2 4 v bak v cc reset backup + c3 100 f 10v v out 3.3v at normal mode 3a v bak 33ma (3.07v) at backup mode >33ma (3.3v) at normal mode c2 1 f system p r2 100k q1 p-mosfet si9424dy * sumida cd54-22 h ** panasonic p-11aah ? consult ltc1435 data sheet for application circuit information ? ltc1435 synchronous buck regulator + + backup time vs v bak output load current v bak load current (ma) 0 backup time (minutes) 800 700 600 500 400 300 200 100 0 15 25 1559 ta02 510 20 30 35 v bak = 3.07v nicd cell = p-11aah (110ma hrs)
2 ltc1559-3.3/ltc1559-5 absolute m axi m u m ratings w ww u (note 1) terminal voltages v cc ........................................................................ 6v v bak .................................................................... 12v sw ...................................................................... 14v all other pins .............................. C 0.3v to v cc + 0.3v sw input currents ............................................. 500ma v bak output current ................... short-circuit protected operating ambient temperature range ....... 0 c to 70 c junction temperature .......................................... 125 c storage temperature range .................. C 65 c to 150 c lead temperature (soldering, 10 sec)................... 300 c order part number order part number s8 part marking ltc1559cs8-3.3 ltc1559cs8-5 electrical characteristics v bat = 1.2v, t a = 0 c to 70 c unless otherwise noted. ltc1559cgn-3.3 LTC1559CGN-5 ltc1559cs-3.3 ltc1559cs-5 consult factory for industrial and military grade parts. t jmax = 125 c, q ja = 130 c/ w 1 2 3 4 8 7 6 5 top view s8 package 8-lead plastic so sw gnd ctl ps v bak v cc backup reset t jmax = 125 c, q ja = 110 c/ w (gn) t jmax = 125 c, q ja = 110 c/ w (s) top view s package 16-lead plastic so gn package 16-lead plastic ssop 1 2 3 4 5 6 7 8 16 15 14 13 12 11 10 9 sw sw pgnd gnd ctl shdn ps nc v bak v bak v cc backup reset reset nc lobat package/order i n for m atio n w u u symbol parameter conditions min typ max units battery backup switching v cc operating voltage range ltc1559-3.3 l 2.900 3.5 v ltc1559-5 l 4.400 5.5 v v bat backup battery cell voltage l 1.0 1.2 1.5 v i vcc quiescent supply current (note 2) l 155 250 m a i bat peak inductor current (backup) boost converter in low current mode (note 7) l 80 165 225 ma boost converter in high current mode (note 7) l 225 330 445 ma i bat(shdn) battery standby current v cc = 0v l 0.1 15 m a i vcc(shdn) supply current during shutdown (note 3) l 50 m a v bak(on) v cc backup request/booster assertion ltc1559-3.3 l 3.011 3.070 3.127 v trip point (note 4) ltc1559-5 l 4.475 4.625 4.775 v v bak(off) v cc backup deassertion trip point ltc1559-3.3 l 3.061 3.119 3.176 v (note 4) ltc1559-5 l 4.550 4.700 4.850 v v lobat1 low v bat detect (note 3) l 0.95 1.00 1.05 v v uvlo(on) v cc uvlo trip voltage (note 4) ltc1559-3.3 l 2.904 3.003 3.102 v ltc1559-5 l 4.400 4.550 4.700 v v uvlo(off) v cc uvlo trip voltage (note 4) ltc1559-3.3 l 3.061 3.119 3.176 v ltc1559-5 l 4.550 4.700 4.850 v 155933 15595
3 ltc1559-3.3/ltc1559-5 electrical characteristics v bat = 1.2v, t a = 0 c to 70 c unless otherwise noted. symbol parameter conditions min typ max units uvlo reset monitor v lobat2 v bat uvlo trip voltage (note 5) l 0.85 0.9 0.95 v backup battery charger i chgf battery charge current during fast recharge l 11 16 21 ma i chgt user-programmable trickle charge l 0.05 2 ma current range q rech fast recharge factor (note 6) 1.35 1.6 1.85 c/c q trk nominal trickle charge multiplier factor i chgt = 1ma l 8 10 12 a/a v ctl(clamp) ctl clamp voltage in trickle mode i chgt = 1ma l 0.45 0.5 0.55 v push-button reset v ctl ctl input threshold 250 mv t ctl ctl input low time (debounce time) 20 26 ms reset timer t hreset push-button duration for hard reset 1.10 1.8 3.4 sec t rst reset pulse width v ctl low for < t hreset (soft reset) l 50 80 150 m s v ctl low for > t hreset (hard reset) l 115 185 345 ms v rst1 reset output voltage v cc = 1v, i sink = 10 m a l 5 200 mv v rst reset output voltage v cc = 4.25v, i sink = 1.6ma l 0.1 0.4 v i sc reset output current output source current v cc = 3.3v 10 ma output source current v cc = 5v 20 ma short-circuit current output sink current v cc = 3.3v 20 ma output sink current v cc = 5v 40 ma ps comparator v hyst comparator threshold hysteresis t a = 25 c90mv internal v cc monitor comparator tr uvlo, comparator propagation delay (rising) 7.5 m s shutdown pin (note 3) v shdn shdn input threshold logic low, v il l 0.8 v logic high, v ih l 2v i shdn shdn pin bias current v cc = 5v, v shdn = 0v l 815 m a the l denotes specifications which apply over the full operating temperature range. note 1: absolute maximum ratings are those values beyond which the life of a device may be impaired. note 2: quiescent current is measured during push-button reset. note 3: only applies to 16-pin version. note 4: although the v bak(on) , v bak(off) , v uvlo(on) and v uvlo(off) threshold voltages have a specification tolerance, they are guaranteed by design and tested in production never to overlap. note 5: low cell voltage reset is only triggered when 0.25v < v ctl < 0.9v for at least 20 m s while in backup mode. note 6: fast recharge factor is defined as the ratio of charge replenished to the nicd battery during fast recharge to the charge withdrawn from the nicd battery during backup. note 7: the ltc1559 switches automatically between the low and high operating current levels. see applications information for more details.
4 ltc1559-3.3/ltc1559-5 typical perfor m a n ce characteristics uw nicd terminal voltage (v) 1.0 output power (mw) 140 120 100 80 60 40 20 0 1.1 1.2 1.3 1.4 1559 g01 i pk = 330ma c l = 200 f output power vs battery voltage boost converter switching frequency backup time vs battery capacity normalized fast recharge current vs temperature trickle charge multiplier factor boost converter switching duty cycle temperature ( c) 0 0.950 current ratio (ma/ma) 0.960 0.970 0.980 0.990 25 50 1559 g06 75 1.000 0.955 0.965 0.975 0.985 0.995 1.005 fast recharge time (assume nicd battery fully exhausted) battery capacity (ma hr) 64 0 time (hours) 10 20 30 40 60 128 256 1559 g07 512 50 reset output voltage vs supply voltage supply voltage (v) 0 0 reset voltage (v) 1 2 3 4 6 1 234 4.55v 1559 g08 56 5 4.7v ltc1559-5 reset output voltage vs supply voltage output voltage, v bak (v) 2 duty cycle (%) 40 60 10 1559 g04 20 0 4 6 8 100 80 ltc1559-3.3 v bat = 1.2v i pk = 330ma nicd cell capacity (ma hr) 50 backup time (hours) 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0 125 250 375 500 1559 g02 v bat = 1.2v p out = 100mw output voltage, v bak (v) 2 switching frequency (khz) 50 75 10 1559 g03 25 0 4 6 8 125 100 ltc1559-3.3 v bat = 1.2v i pk = 330ma nicd battery trickle current (ma) 10.5 10.4 10.3 10.2 10.1 10.0 9.9 9.8 9.7 9.6 9.5 trickle charge factor (ma/ma) 1559 g05 0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 supply voltage (v) 0 reset voltage (v) 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0 1 234 3v 1559 g09 ltc1559-3.3 3.12v
5 ltc1559-3.3/ltc1559-5 pi n fu n ctio n s uuu pin numbers are shown first for the so-8 package then the gn16 and s16 packages sw (pins 1/1, 2): boost converter switching node. con- nect a 22 m h inductor from sw to the positive terminal of the backup cell. in backup mode, this node is alternately switched between ground and v bak , generating the backup output voltage. in fast or trickle charge mode, an internal regulator outputs a constant dc current from this pin through the 22 m h inductor and into the nicd battery. during power-up or undervoltage lockout (uvlo), the sw pin enters a high impedance state. gnd (pins 2/4): system ground. the low power internal circuitry returns to this pin in the 16-pin packages. gnd and pgnd are bonded together to this pin in the 8-pin package. ctl (pins 3/5): control. this pin provides three functions. in backup mode this pin is a high impedance input and monitors the backup battery cell voltage (v bat ). if v bat drops below 0.9v, the ltc1559 enters uvlo. during trickle charge mode, an external resistor r ext sets the trickle charge current. in all modes, pulling the ctl pin below 250mv generates either a soft or hard reset pulse. see the applications information section for more information. ps (pins 4/7): power supply sense. this pin senses the presence of the main supply and triggers the ltc1559 to terminate backup mode. during backup, v cc is driven externally by the ltc1559s boost converts output (v bak ). when ps > v cc during backup, the ltc1559 pulls down the backup pin, reconnecting the system regulator out- put to the system v cc . the ps pin is needed in applications that use a p-channel mosfet (driven by the backup signal) to isolate the system regulator during backup. if not needed, ps can be disabled by tying it to ground. reset (pins 5/11): system reset, active low. this is an open-drain output. this pin provides a low going reset signal to the system processor. a 200ms pulse is gener- ated if the ctl pin is pulled low for more than two seconds (hard reset) or if the ltc1559 comes out of uvlo. this hard reset stops the internal boost converter if it is running. this pin is held low if the ltc1559 is in uvlo and is guaranteed to be valid when v cc is greater than or equal to 1v. reset also provides a low going 100 m s signal whenever the ctl pin is pulled low for less than two seconds (soft reset). unlike hard reset, soft reset does not affect the ltc1559s current operating mode. backup (pins 6/13): system backup signal. this is a ttl-compatible output driver that pulls low unless the ltc1559 is in backup mode. backup signals the system controller that the system is in backup mode so that it can reduce system loading. backup can also be used to drive the gate of a p-channel mosfet in series with the main system regulators output. see the applications informa- tion section for more details. v cc (pins 7/14): power supply input. all internal circuits except the boost converter are powered from this pin. a 0.1 m f bypass capacitor is required from v cc to ground. the uvlo detector inside the ltc1559 monitors v cc . if v cc drops below the rated output voltage by 9%, the ltc1559 enters uvlo mode and reset is asserted. the ltc1559-3.3 exits uvlo if v cc rises to greater than C 5.5% of the rated output voltage. the ltc1559-5 exits uvlo if v cc rises to greater than C6 % of the rated output voltage. see the applications information section for more details. v bak (pins 8/15, 16): backup supply output. the ltc1559s boost converter provides the regulated output voltage to the system through v bak during backup mode. 16-pin gn and so packages pgnd (pin 3): power ground. the internal driver circuitry returns to this pin. pgnd should be connected to a low impedance ground plane in close proximity to the nicd battery cell. shdn (pin 6): chip shutdown. a ttl-compatible active low voltage at shdn puts the ltc1559 into low power shutdown mode. in shutdown, all internal circuits power down and are held in a reset state. the sw, ctl and v bak pins enter into high impedance states. in shutdown mode, supply current drops to below 50 m a and current drawn from the backup cell drops to below 15 m a.
6 ltc1559-3.3/ltc1559-5 lobat (pin 9): low backup battery detector output. this is an open-drain output with an internal weak pull-up. it is asserted if the nicd cell terminal voltage drops below 1.0v. this pin is pulled high if the ltc1559 is in trickle charge mode. pi n fu n ctio n s uuu 1559 sw01 v bat main battery c out backup system v cc 1.2v nicd sw 22 h ltc1559 reset ps q ext v bak v cc backup to system control v in for more detailed circuit application schematics, please refer to the typical applications section main system regulator v out v bat backup reset v cc ps 1559 sw02 200ms rated battery terminal voltage rated v cc voltage 5.5% (ltc1559-3.3) 6% (ltc1559-5) 1 2 3 4 cold power boot-up (main battery replaced/turned on) simplified ltc1559 connections in a battery backup system switchi n g wavefor m s uw + level sense and debounce thermal limit shutdown logic bandgap v ref = 1.272v charger reset generator boost/backup logic gas gauge v ref v ref v cc shdn ps reset n1 p1 v bak v cc /v bak ctl sw + + uvlo detector reset backup lobat 1559 bd block diagra m w reset (pin 12): system reset, active high. this is a ttl- compatible output driver. it can connect to systems that require active high logic. the reset output will go high if reset is pulled low.
7 ltc1559-3.3/ltc1559-5 switchi n g wavefor m s uw cold power boot-up description 1. system regulator starts to ramp up the output (ps) once the v bat voltage increases beyond the minimum input value. 2. v cc starts to increase once ps is high enough to turn on q ext s body diode. reset is asserted when v cc is less than or equal to 1v. 3. the ltc1559s internal bandgap wakes up. q ext turns on and v cc = ps. the ltc1559s internal boost con- verter does not turn on as reset remains asserted. 4. reset is asserted for a further 200ms after v cc reaches C 5.5% of its rated v cc value for the ltc1559-3.3 and C 6% of its rated v cc value for the ltc1559-5. backup mode (main battery discharged) ltc1559-3.3 inductor current reset backup v cc v nicd lobat 1559 sw03 t r t r ?% 1.2v ?% ?% 1v 0.9v 5.5% boost converter output t f t r t r (4) (3) (2) (1) ? ? backup mode description 1. trigger into backup mode. main battery fails and v cc drops 7% below the rated value. the backup pin is asserted after a t r delay time and the boost converter is turned on. 2. backup mode. the ltc1559s boost converter charges and discharges the inductor with 165ma peak current. if v cc doesnt increase above v cc (rated value) C 7% (due to a heavy load), the boost converter increases peak charging current to 330ma. if v cc rises above v cc (rated value) C 7%, the boost converter stops and the backup pin remains asserted. 3. recovery from backup mode. while the boost con- verter is running, the main battery is restored. this causes the system regulator to increase ps above v cc . when ps > v cc or v cc > v cc (rated value) C 5.5%, the backup pin deasserts and the boost converter finishes its last cycle. 4. trigger into uvlo. during backup, the 1.2v nicd cell is discharged and its terminal voltage falls. the lobat pin is asserted to give an early warning if the cell voltage drops below 1v. reset is asserted when the cell voltage drops below 0.9v and the ltc1559 enters uvlo mode.
8 ltc1559-3.3/ltc1559-5 applicatio n s i n for m atio n wu u u overview the ltc1559 is a versatile backup battery control system designed to provide all the functions necessary to imple- ment a complete, highly integrated backup system within a single chip. it allows the system to maintain its rated supply voltage during backup, offering maximum sys- tem design flexibility. the ltc1559 allows the use of a low cost rechargeable nicd cell for backup, eliminating the need for expensive, replaceable 4.5v lithium backup cells. the ltc1559 includes an onboard boost converter designed to generate a fixed voltage (3.07v for 3.3v parts and 4.625v for 5v parts) from a single 1.2v nicd cell. when connected to the system dc/dc converters output, the ltc1559 enables the system connected to the v cc rail to continue operation when the main power supply fails. a smart recharging circuit uses an accumulating gas gauge to measure the charge extracted from the backup battery during a backup cycle. this measured charge is then replaced in a fast recharge cycle, without wasting excess power or overcharging the backup cell. an exter- nally adjustable trickle charge circuit maintains the cell charge after the fast charge cycle has completed, minimiz- ing drain from the main battery during standby. included in the ltc1559 is a complete backup circuit that monitors the main system power and automatically switches in the backup circuit as the primary power supply falls away (due to a weak or disconnected main battery). the ltc1559 also performs v cc supervisory functions during normal system operations. an ltc1559-3.3 monitors a 3.3v supply voltage at its v cc pin while an ltc1559-5 monitors a 5v supply at its v cc pin. in both cases, the ltc1559 derives power for the majority of the internal circuitry (except for the boost converter) from its v cc pin. table 1 shows the signal conditions for the various operating modes of the ltc1559-3.3. table 2 shows the signal conditions for the various operating modes of the ltc1559-5. table 1. ltc1559-3.3 operating modes operating modes conditions uvlo reset 1v < v cc < v cc (rated value) C 9% or v bat < 0.9v push-button reset v ctl < 250mv uvlo reset recovery v cc > v cc (rated value) C 5.5% backup mode activation v cc < v cc (rated value) C 7% backup mode exit v cc > v cc (rated value) C 5.5% or ps > v cc boost converter activation v cc < v cc (rated value) C 7% boost converter deactivation v cc > v cc (rated value) C 7% table 2. ltc1559-5 operating modes operating modes conditions uvlo reset 1v < v cc < v cc (rated value) C 9% or v bat < 0.9v push-button reset v ctl < 250mv uvlo reset recovery v cc > v cc (rated value) C 6% backup mode activation v cc < v cc (rated value) C 7.5% backup mode exit v cc > v cc (rated value) C 6% or ps > v cc boost converter activation v cc < v cc (rated value) C 7.5% boost converter deactivation v cc > v cc (rated value) C 7.5% boost converter operation the ltc1559 uses an onboard boost converter with a fixed peak current architecture that provides a simple and flexible system solution while eliminating the need for conventional frequency compensation. the boost converters output, set to 93% (ltc1559-3.3) or 92.5% (ltc1559-5) of the rated v cc , supports the system v cc during backup. it supplies a minimum backup power of 100mw. the boost converter operates in a modified pulse-skipping mode; each switch cycle transfers a known amount of charge from the backup cell to the regulated output. this prevents uncontrolled discharge of the backup cell and allows the ltc1559 to accurately measure the charge removed from the backup cell by counting the charge pulses. the ltc1559 enters backup mode when the main battery voltage drops and causes v cc , the system regulators output, to fall. as shown in figure 1, v cc is scaled down by an internal resistor divider and fed to the ltc1559s backup comparators. these compare the scaled voltage
9 ltc1559-3.3/ltc1559-5 applicatio n s i n for m atio n wu u u ferred for the first two consecutive switch cycles. if v cc falls below v cc (rated value) C 7% (ltc1559-3.3) , the boost operation starts by connecting the sw pin internally to ground through an internal 0.5 w n-channel mosfet (n1 in the block diagram). the current through the exter- nal 22 m h inductor rises linearly through this switch. when the switch current reaches an internally preset level of 165ma, the boost converter connects the sw pin to the v bak pin through an internal 2 w p-channel mosfet. the inductor current discharges through the p-channel (p1 in the block diagram) and charges up the systems v cc capacitor (c out of the system regulator, figure 1). the inductor current falls at a rate proportional to the differ- ence between the backup cell voltage and the output voltage v bak . when the inductor current reaches zero, indicating all of its energy has been transferred to the output capacitor, the ltc1559 monitors the v cc voltage. if v cc has increased above the v cc (rated value) C 7% (ltc1559-3.3) threshold, the boost converter shuts off both switches and waits for v cc to drop below v cc (rated value) C 7% (ltc1559-3.3) again. with an internal trimmed v ref (1.272v), switching the ltc1559 into backup mode if v cc drops 7% (ltc1559-3.3) or 7.5% (ltc1559-5) below its rated value. upon entering backup mode, the backup pin is asserted and the internal boost converter turns on. the backup signal turns off the external p-channel mosfet (if used), isolating the system regulator from the ltc1559. the boost converter charges the v cc capacitor, c out , of the system regulator until v cc rises above v cc (rated value) C 7% (ltc1559-3.3) or v cc (rated value) C 7.5% (ltc1559-5). once v cc rises above v cc (rated value) C 7% (ltc1559- 3.3) , the boost converter deactivates and the freshly charged v cc capacitor c out supplies power to the system. the cycle repeats again when the v cc capacitors charge is drained away and v cc again drops below v cc (rated value) C 7% (ltc1559-3.3) . the backup pin remains asserted until the main battery is restored. this ensures that the ltc1559 does not switch in and out of backup mode unnecessarily. the ltc1559s boost converter minimizes output ripple under light load conditions by reducing the charge trans- figure 1. typical ltc1559 connection + boost converter system regulator ltc1559 r1 ps v cc r2 1559 f01 backup logic v ref backup system v cc v bak c out light current mode 165ma (peak) 330ma (peak) heavy current mode 1559 f02 figure 2. inductor current during switching figure 3. v bak ripple 1 boost cycle v bak esr ripple discharge period t disch charge period t ch 1559 f03
10 ltc1559-3.3/ltc1559-5 if v cc is still less than v cc (rated value) C 7% (ltc1559- 3.3) after the first boost cycle, the ltc1559 immediately reconnects sw to ground, repeating the boost cycle. if after two consecutive pulses, v cc is still not above the boost threshold v cc (rated value) C 7% (ltc1559-3.3) , the ltc1559 decides that the load is not so light after all, and doubles the internal inductor charging current limit to 330ma for subsequent cycles. this is high current mode. by doubling the peak inductor current, each boost cycle effectively carries four times more energy compared to low current mode (e = 1/2 ? li 2 ), doubling the available output power. when v cc exceeds the v cc (rated value) C 7% (ltc1559-3.3) boost threshold, the ltc1559 stops the boost converter and resets the internal 2-pulse counter. the next time v cc falls below v cc (rated value) C 7% (ltc1559-3.3) , the boost converter restarts in low current mode for at least two boost cycles. moderate or changing loads cause the ltc1559 to shift between the two peak inductor current limits, keeping the output in tight regula- tion. near its maximum load capability, the ltc1559 will stay in 330ma high current mode and the output voltage v bak will hover around v cc (rated value) C 7% (ltc1559-3.3) . v cc capacitor esr the type of output capacitor and the rated v cc value will affect the ltc1559s output ripple and efficiency. in most applications, the v cc capacitor is primarily determined by the requirements of the main power supply. such a capacitor will generally meet the requirements of the ltc1559. in unusual circumstances or circuits where the main system v cc capacitor is located some distance away from the ltc1559, a local output capacitor may be necessary. the ripple on the v cc pin is equal to the capacitor esr voltage drop due to the boost converters output current pulses. the ripple frequency and output duty cycle is proportional to the inductor discharge time. given a fixed inductor value (22 m h) and a known peak current limit, the boosters discharge time in each boost cycle is propor- tional to the difference between v bak (93% of the rated v cc for the ltc1559-3.3 and 92.5% of the rated v cc for the ltc1559-5) and the battery cell voltage, v bat (1.2v). applicatio n s i n for m atio n wu u u assuming esr = 0.2 w , i ind(peak) = 330ma, v cc = 5v, v ripple(p-p) = (i ind(peak) )(r esr(cap) ) = (330ma)(0.2 w ) = 66mv since v cc must be scaled down internally, the external resistor ratio: = 5v/1.272v = 3.931 therefore the ripple seen by the v cc comparators is: = 66mv/3.931 = 16.79mv the discharge time period, t disch = (l ? i ind(peak) )/(v bak C v bat ) = (22 m h ? 330ma)/(4.625 C 1.2v) = 2.12 m s for v cc = 3.3v and i ind(peak) = 330ma, v ripple(p-p) = 66mv rb resistor ratio = 3.3/1.272 = 2.594 ripple voltage = 25.4mv t disch = 3.9 m s the internal v cc comparators are designed to have a slow response time to filter away this ripple. the v cc (rated value) C 5.5% (ltc1559-3.3) and v cc (rated value) C 9% comparators have a 6 m s rising edge delay and 2 m s falling edge delay. the v cc (rated value) C 7% (ltc1559-3.3) comparator has a similar 6 m s rising time delay but a much longer falling time delay of 20 m s. this enables the com- parator to control the boost converter properly, and avoids turning off the boost converter prematurely due to false triggering by the esr ripple. exit from backup when a main battery is inserted into the system, the ltc1559 follows a specific sequence to exit backup mode and return control to the main supply. the sequence depends on the type of main power supply used. in systems where the main supplys output impedance is
11 ltc1559-3.3/ltc1559-5 applicatio n s i n for m atio n wu u u to the load while charge on the v cc capacitor drains away. if v cc drops below v cc (rated voltage) C 9% for more than 7.5 m s, the ltc1559s v cc supervisory circuit activates uvlo mode, shutting off the boost converter and assert- ing the reset pins. the 7.5 m s delay prevents the ltc1559 from being fooled by brief transients or noise spikes on its v cc pin. upon receipt of the reset signal, the host system should shut down in an orderly manner. the ltc1559s v cc supervisory circuit will remain alive until v cc is less than 1v to ensure a valid reset pin signal. backup cell voltage monitoring as the boost converter removes charge from the backup nicd cell, the cells terminal voltage falls. permanent damage to the nicd cell can occur if it is discharged to below 0.9v. to prevent this, the ltc1559 monitors the cells terminal voltage through the ctl pin during backup. if the ctl pin drops below 0.9v for more than 20 m s, the uvlo circuit shuts down the boost converter and asserts the reset and reset pins. since the ctl pin can also be connected to an external push-button reset, the ltc1559 includes internal logic to ensure that the low cell voltage reset is triggered only if the ctl pin is between 0.9v and 0.25v. this will prevent a push-button reset (which pulls ctl below 250mv) from being mistaken as a low cell voltage condition. unusual situations where the nicd cell voltage drops drastically below 0.25v will also trigger uvlo, since the ltc1559 will treat this as a hard reset after two seconds. an optional lobat output, available in the 16-pin gn or so package, can be used to signal the system if the cell voltage falls below 1v, giving an early warning that the backup cell is heavily discharged. the lobat pin is disabled if the ltc1559 is in trickle charge mode, because the ctl pin is regulated to 0.5v by the ltc1559. fault protection and thermal limit the ltc1559s boost converter incorporates two internal timers that turn off the switch transistors if the inductor charge or discharge time gets abnormally long. the inductor charge time may get abnormally long if the nicd cell voltage drops below 0.25v without triggering the 0.25v < v bat < 0.9v low cell voltage comparator. in this high when inactive (typically a boost regulator with an output catch diode), the ltc1559 detects the return of the main supply by watching for v cc to exceed v cc (rated value) C 5.5% (ltc1559-3.3). the ltc1559 then shuts down its internal boost converter and begins to recharge the nicd cell. in such applications, the ps pin is not used and can be tied to ground. no external p-channel mosfet is required to isolate the main supply from the system v cc during backup. in systems where the main supplys output impedance is low when inactive (typically buck regulators), the main supply must be disconnected from the system v cc during backup to prevent the inactive supply from loading the ltc1559. this is typically accomplished using an external p-channel mosfet as shown in figure 1. when the main supply is restored, the p-channel mosfets body diode forward-biases. this allows current to flow into the sys- tem v cc , but the forward drop across this diode may prevent v cc from reaching the v cc (rated value) C 5.5% (ltc1559-3.3) threshold that deactivates the ltc1559s backup mode. in such systems, the ps pin should connect directly to the output of the main system supply. when the system regulators voltage rises about 2.5% above the backup v cc , the ps comparator triggers and causes the ltc1559 to deassert the backup pin signal. this signals the system controller to restore sys- tem loading and resume normal operation. at the same time, the external p-mosfet is driven by the backup signal. the p-channel mosfet turns on and allows the main regulator to bypass its body diode and drive the system v cc directly. since the user can replace the main battery anytime during the ltc1559s backup operation, the backup signal may be deasserted while the boost converter is switching. to prevent the potential problem of residual energy in the inductor, the ltc1559 will only stop the boost converter after it completes the current boost converter cycle. uvlo under excessive backup load very heavy loads (above the ltc1559s maximum power output) will pull the boost converters output below the boost threshold. under these conditions, the ltc1559s boost converter continues to supply 330ma current pulses
12 ltc1559-3.3/ltc1559-5 case, the nicd cell is assumed to be damaged and the ltc1559s priority is shutting down the system grace- fully. in this case, the timer will shut off the n-channel switch transistor after a maximum charging time (14 m s). the boost converter continues switching but delivers reduced output power, causing v cc to drop. the ltc1559 enters uvlo if v cc drops below v cc (rated value) C 9% or if the ltc1559 detects that ctl is lower than 0.25v for two seconds, in which case hard reset occurs. the discharge time can also get abnormally long if a serious overload condition occurs during switching. the timer shuts off the p-channel pass transistor after 10 m s, protecting the boost converter. the ltc1559 enters uvlo as v cc drops below v cc (rated value) C 9%. in addition, the ltc1559 has safe area operation protec- tion with an internal thermal shutdown circuit. if the device is overloaded for a long period of time, the thermal shutdown circuit forces the ltc1559 into uvlo. the threshold temperature for thermal shutdown is typically 155 c. the ltc1559s boost converter is designed so that no current drains from the battery to the load during output short circuit or v cc = 0v conditions. this assures that the system can be powered down for a long period of time. this eliminates the risk of finding a nonfunctioning backup system upon power-up. backup cell fast recharge the ltc1559 includes an onboard gas gauge circuit, consisting of a 23-bit divider and a 9-bit up/down counter. the gas gauge logic assumes that the boost converter uses a 22 m h inductor, allowing it to accurately measure battery charge by counting pulses. the gas gauge counts up from zero as charge is removed from the backup cell in backup mode. it takes 8.4 million 165ma boost pulses (low current mode) to increment the up/down counter by one count. in high current mode, the 330ma pulses skip the first two bits of the divider because each 330ma pulse carries four times as much energy as a 165ma pulse. at maximum load and v cc = 4.625v (ltc1559-5), the gas gauge counter will increment by one count every 7.5 m s while the boost converter is running. full count is reached applicatio n s i n for m atio n wu u u after approximately 2.2 hours, equivalent to about 512mahr of charge. upon entering recharge mode (after the main battery is restored) the ltc1559 connects a 16ma fast recharge current source from v cc to the sw pin. at the same time, an internal free running oscillator counts down the gas gauge counter at a rate designed to typically replace 160% of the charge previously removed from the backup cell. when the gas gauge counter reaches zero, the ltc1559 reduces the charging current at the sw pin to the user- programmed trickle charge current level. under some circumstances, the ltc1559 can exit backup mode with invalid gas gauge contents. this occurs under three possible conditions: 1. the backup cell was completely exhausted during a backup cycle and the ltc1559 entered uvlo. 2. the backup cell was replaced while the main supply was disabled. 3. a backup cycle was terminated prematurely by a hard reset or an output overload. in these cases, the ltc1559 assumes that the backup cell is exhausted and presets the gas gauge counter to a default capacity of 128mahr. it then initiates a recharge cycle. setting the gas gauge to this default value results in a fast recharge cycle long enough to replenish 1.6 times 128mahr into the backup cell (13.9 hours). if the backup cell is actually exhausted, it will be fully recharged. if the battery is partially or fully charged, or is significantly smaller than 128mahr capacity, the extra charging time is wasted. however, the ltc1559s 16ma fast charge cur- rent is not high enough to damage the cell. once the full- count recharge has been completed, the backup cell is assumed to be fully charged and subsequent backup/ recharge cycles resume normally. although the ltc1559 will not fully recharge backup cells larger than 128mahr capacity upon power-up, it can still be used with such cells. such a cell will be fully replenished by the subsequent trickle charge cycle. under most con- ditions, even a partially charged large cell will still be capable of supporting several hours of backup. for
13 ltc1559-3.3/ltc1559-5 applicatio n s i n for m atio n wu u u example, a small 60mahr saft cell can back up the system for 20 minutes at an output power of 100mw. note that at v cc = 3.07v (ltc1559-3.3), the boost converter efficiency improves and allows more backup time from the same cell compared to v cc = 4.625v (ltc1559-5). once it reaches full recharge, a cell bigger than 512mahr will overrun the gas gauge counter before it runs out of charge during an extended backup cycle. the ltc1559 gas gauge counter will not roll over if this occurs; it will stay at full count until the backup cycle ends and then partially recharge the cell with a full count cycle as above. very short backup cycles (< 32s) may not extract enough charge from the backup cell to increment the gas gauge counter at all. to ensure that the backup cell is not slowly nibbled away, the gas gauge counter is always incremented by 1mahr each time the controller exits backup. this ensures that the backup cell is replenished with at least a 1mahr charge every time the ltc1559 enters backup mode. battery backup cell trickle charge when the gas gauge counter reaches zero, the ltc1559 terminates fast recharge and reduces the recharge current to the user-programmed trickle current level. the ltc1559 provides a trickle current that the user can program from 50 m a to 2ma. the trickle current is set by an external resistor from the positive terminal of the backup cell to the figure 4. trickle current charger r ext v cc 1 m f i 10i 1.2v nicd cell sw ctl 0.5v 1559 f04 11 1 ltc1559 + + + ctl pin. in trickle charge mode, ctl is regulated to 0.5v, resulting in a ctl pin current of (v bat C 0.5)/r ext . this current is internally multiplied to feed back ten times the r ext current into the backup battery. since the ltc1559 trickle charges only after the completion of the fast recharge cycle, the backup cell voltage should be very close to 1.2v. this simplifies the calculation of the r ext resistor value. for example, a 47k resistor from v bat to ctl sets the trickle charge current to 150 m a. undervoltage lockout the ltc1559 includes an undervoltage lockout (uvlo) circuit that shuts the system down gracefully if the backup cell is exhausted or overloaded. as described in the previous section, the ltc1559 terminates backup opera- tion and remains off until the main power supply returns. it then runs a fast recharge cycle to recharge the backup cell. an onboard low-battery comparator in the 16-pin gn or so package provides an early warning signal if the backup cell drops below 1v. the uvlo circuit trips if the ltc1559s v cc supervisory circuit detects that v cc drops below C 9% of the rated v cc voltage due to overload or output short-circuit conditions. once the uvlo circuit trips, the ltc1559 asserts the reset and reset pins until the v cc voltage drops below 1v. it then remains off until v cc rises to within C 5.5% of the rated output voltage (ltc1559-3.3). during power-up from uvlo, the ltc1559 asserts the reset and reset pins until the v cc (rated value) C 5.5% (ltc1559-3.3) threshold. once v cc exceeds v cc (rated value) C 5.5% (ltc1559-3.3), the reset and reset pins remain asserted for another 200ms (hard reset) before being released to inform the system to start operating. reset operation the ltc1559 includes an onboard push-button reset switch controller. if the ctl pin is pulled to ground (< 250mv) by a push-button or an open-drain output, the ltc1559 generates a pulse at the reset and reset pins after the trailing edge of the ctl signal. a short (less than two seconds) low going signal at ctl generates a soft reset (100 m s) pulse at the reset pins. a low ctl signal for more than two seconds generates a hard reset pulse at the reset and reset pins. during hard reset, the
14 ltc1559-3.3/ltc1559-5 applicatio n s i n for m atio n wu u u shut off completely. note that the backup cell slowly discharges through r ext in this mode. inductor selection the ltc1559 is designed to operate with a recommended inductor value of 22 m h ( 20%) with < 0.2 w dc resistance. using inductor values above 22 m h will deliver more output power but will cause the gas gauge counter to count inaccurately and under-recharge the backup cell. at the same time, the n-channel transistor timer will limit the peak current if the charging time becomes overextended due to the higher inductor value. using inductor values lower than 22 m h will degrade the boost converters maxi- mum output power and cause the gas gauge counter to overcharge the backup cell. table 3 lists a few recom- mended surface mount inductor part numbers. table 3. recommended inductors part typ inductor dcr manufacturer number value ( w ) sumida cd54-220 22 m h 20% 0.18 sumida cdrh73/74 22 m h 20% 0.2/0.11 capacitor selection the ltc1559 requires a v cc capacitor of 100 m f to ensure that boost converter can regulate the output under maxi- mum load conditions. the capacitors esr should be small (<0.2 w ) to minimize voltage spikes that might incorrectly trigger the ltc1559s internal v cc compara- tors. note that the ltc1559 can usually share the output capacitor with the system regulator. however, a 1 m f is recommended directly at the ltc1559s v cc pin. the v cc capacitors ratings like v max , i ripple(rms) all must meet the system regulators specifications as well. battery selection a primary application for the ltc1559 is a bridging supply, only providing backup current while the main system battery is being replaced. in these applications, the ltc1559 works well with nicd button cells or small cylindrical cells, reducing system costs and board space. it is optimized for use with up to 512mahr battery capacities. figure 5. push-button resets ctl reset (a) 0v 0v 0v 20ms debounce (b) > 0.25v t ctl < 20ms 20ms < t ctl < 2s > 0.25v ?oft?push-button reset at ctl (a) ctl < 0.25v for less than 20ms (b) ctl > 0.25v for more than 20ms ?ard?push-button reset at ctl ctl < 0.25v for more than 2s 20ms debounce at falling and rising reset edge 100 m s 100 m s ctl 1559 f05 reset ctl reset 200ms 2s t ctl > 2s 20ms 20ms ltc1559 disables the boost converter if it is in backup mode. all signals at the ctl pin are debounced for 20ms to prevent multiple resets, allowing the ctl pin to be connected directly to a push-button to ground. the reset pin is an open-drain output that requires an external pull-up resistor. the reset pin is a ttl compat- ible cmos output. shutdown the 16-pin ltc1559 has a ttl compatible input, shdn that shuts down the whole chip, asserts the reset and reset pins and places the ctl, v bak and sw pins into high impedance states. the shdn pin has an internal pull- up of 8 m a that ensures the chip will not shut down if the pin is left floating. the chip consumes less than 50 m a during shutdown. although there is no shdn pin for the so-8 package, the user can shut down the part by pulling ctl to ground. the chip enters hard reset leaving only the bandgap and comparators alive. the charger and the boost converter
15 ltc1559-3.3/ltc1559-5 the ltc1559 works with standard or memory backup specific nicd cells. memory backup cells can operate at higher temperatures and have lower self-discharge rates. the ltc1559s trickle charger is designed to accommo- date both memory backup cells (with low self-discharge) and standard cells (with higher self-discharge). some recommended manufacturers and part numbers are listed in table 4. the internal resistance of the backup cell increases power dissipation as the boost converter draws current from it during switching, degrading efficiency. due to the fixed inductor peak current architecture, the ltc1559s boost converter output power drops significantly when the nicd cells internal resistance increases at the end of its charge. the inductor charging time increases due to a larger r/l time constant, decreasing the switching frequency. it is advisable, especially for batteries with high internal resis- tance, to include a 1 m f or larger bypass capacitor across the battery to ensure that the boost converter can deliver the maximum output power regardless of the nicd inter- nal resistance. applicatio n s i n for m atio n wu u u table 4. button/cylindrical nicd 1.2v cells manufacturer part capacity r series (type) number (mahr) ( w ) saft gb60 60 1.1 (memory backup) gb170 170 0.4 gb280 280 0.4 saft vb10e 100 0.038 (standard) vb22e 220 0.022 vb30e 300 0.017 vb60e 600 0.014 sanyo n-50aaa 55 0.055 (standard) n-110aa 120 0.03 n-120ta 130 0.034 n-150n 170 0.027 n-200aaa 220 0.021 n-270aa 305 0.015 n-500a 500 0.09 panasonic (standard) p-11aa 110 0.08
16 ltc1559-3.3/ltc1559-5 typical applicatio n u ltc1559-3.3 backup system with an ltc1435 main system regulator (ltc1435 output sense at the drain of q11) description the ps pin connects to q11s drain and allows the ltc1559 to detect the restoration of the main battery during backup mode. once the ltc1435s output is greater than v out + bg sense sense + intv cc boost sw c osc sgnd pgnd run/ss i th v osense v in ltc1435 tg c4 0.1 m f r sense ** 0.033 w l1* 10 m h *sumida cdrh125-10 **irc lr2010-01-r033-f ? sumida cd54-220 c3 4.7 m f 16v d1 cmdsh-3 1559 ta03 d2 mbrs140t3 r5 20k 1% r1 35.7k 1% c5 1000pf c6 100pf q2 n-channel si4412dy q1 n-channel si4412dy sfb extv cc 11 7 8 12 15 14 13 c in 22 f 35v 2 16 5 10 1 2 3 6 4 9 c osc 68pf r c 10k c ss 0.1 m f c c 330pf c1 100pf c c2 51pf + c2 0.1 f backup output 3.3v main output 3.3v ctl c11 1 m f 6.3v backup battery 1.2v nicd main battery 4.5 to 28v q11 p-channel si9424y r14 14k sw ltc1559-3.3 l11 ? 22 m h gnd ps 7 1 8 5 6 3 reset push-button 2 4 v bak v cc reset backup + r15 100k c12 1 m f reset backup + + c out 100 m f 10v 2 + c15 100 m f 10v during backup mode, the ltc1559 deasserts its backup pin and returns control back to the ltc1435. q11 turns on and allows the ltc1435 to charge c15. please refer to the applications information section for more details.
17 ltc1559-3.3/ltc1559-5 package descriptio n u dimensions in inches (millimeters) unless otherwise noted. 1 2 3 4 0.150 ?0.157** (3.810 ?3.988) 8 7 6 5 0.189 ?0.197* (4.801 ?5.004) 0.228 ?0.244 (5.791 ?6.197) 0.016 ?0.050 0.406 ?1.270 0.010 ?0.020 (0.254 ?0.508) 45 0 ?8 typ 0.008 ?0.010 (0.203 ?0.254) so8 0996 0.053 ?0.069 (1.346 ?1.752) 0.014 ?0.019 (0.355 ?0.483) 0.004 ?0.010 (0.101 ?0.254) 0.050 (1.270) typ dimension does not include mold flash. mold flash shall not exceed 0.006" (0.152mm) per side dimension does not include interlead flash. interlead flash shall not exceed 0.010" (0.254mm) per side * ** s8 package 8-lead plastic small outline (narrow 0.150) (ltc dwg # 05-08-1610)
18 ltc1559-3.3/ltc1559-5 package descriptio n u dimensions in inches (millimeters) unless otherwise noted. gn package 16-lead plastic ssop (narrow 0.150) (ltc dwg # 05-08-1641) gn16 (ssop) 1197 * dimension does not include mold flash. mold flash shall not exceed 0.006" (0.152mm) per side ** dimension does not include interlead flash. interlead flash shall not exceed 0.010" (0.254mm) per side 12 3 4 5 6 7 8 0.229 ?0.244 (5.817 ?6.198) 0.150 ?0.157** (3.810 ?3.988) 16 15 14 13 0.189 ?0.196* (4.801 ?4.978) 12 11 10 9 0.016 ?0.050 (0.406 ?1.270) 0.015 0.004 (0.38 0.10) 45 0 ?8 typ 0.007 ?0.0098 (0.178 ?0.249) 0.053 ?0.068 (1.351 ?1.727) 0.008 ?0.012 (0.203 ?0.305) 0.004 ?0.0098 (0.102 ?0.249) 0.025 (0.635) bsc
19 ltc1559-3.3/ltc1559-5 package descriptio n u dimensions in inches (millimeters) unless otherwise noted. s package 16-lead plastic small outline (narrow 0.150) (ltc dwg # 05-08-1610) 0.016 ?0.050 0.406 ?1.270 0.010 ?0.020 (0.254 ?0.508) 45 0 ?8 typ 0.008 ?0.010 (0.203 ?0.254) 1 2 3 4 5 6 7 8 0.150 ?0.157** (3.810 ?3.988) 16 15 14 13 0.386 ?0.394* (9.804 ?10.008) 0.228 ?0.244 (5.791 ?6.197) 12 11 10 9 s16 0695 0.053 ?0.069 (1.346 ?1.752) 0.014 ?0.019 (0.355 ?0.483) 0.004 ?0.010 (0.101 ?0.254) 0.050 (1.270) typ dimension does not include mold flash. mold flash shall not exceed 0.006" (0.152mm) per side dimension does not include interlead flash. interlead flash shall not exceed 0.010" (0.254mm) per side * ** information furnished by linear technology corporation is believed to be accurate and reliable. however, no responsibility is assumed for its use. linear technology corporation makes no represen- tation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
20 ltc1559-3.3/ltc1559-5 ? linear technology corporation 1998 ltc1559-3.3 backup system with an ltc1435 main system regulator (ltc1435 output sense at the source of q11, ltc1559s ps pin is grounded) 1559f lt/tp 1098 4k ? printed in usa part number description comments ltc690/ltc691 microprocessor supervisory circuits microprocessor power supply monitor and backup with power fail ltc694/ltc695 comparator ltc699 microprocessor supervisory circuits microprocessor power supply monitor and backup ltc1232 microprocessor supervisory circuits include push-button reset ltc1235 microprocessor supervisory circuits include push-button reset and power fail comparator ltc1149 high efficiency synchronous step-down v in up to 48v, burst mode tm operation switching regulator ltc1435 high efficiency, low noise synchronous ultrahigh efficiency, burst mode operation step-down switching regulator ltc1479 powerpath tm controller for dual complete power management controller for battery battery systems notebook computers and other portable equipment ltc1558 battery backup controller with similar to ltc1559 except that it backs up the main system regulators programmable output input, allowing backup of multiple output voltages powerpath and burst mode are trademarks of linear technology corporation. related parts description with its sense pin at the source of q11, the ltc1435 can raise v out above v cc (rated voltage) C 5.5% once the main typical applicatio n u + bg sense sense + intv cc boost sw c osc sgnd pgnd run/ss i th v osense v in ltc1435 tg c4 0.1 m f r sense ** 0.033 w l1* 10 m h *sumida cdrh125-10 **irc lr2010-01-r033-f ? sumida cd54-220 c3 4.7 m f 16v d1 cmdsh-3 1559 ta04 d2 mbrs140t3 r5 20k 1% r1 35.7k 1% c5 1000pf c6 100pf q2 n-ch si4412dy q1 n-channel si4412dy sfb extv cc 11 7 8 12 15 14 13 c in 22 f 35v 2 16 5 10 1 2 3 6 4 9 c osc 68pf r c 10k c ss 0.1 m f c c 330pf c1 100pf c c2 51pf + c2 0.1 m f v out 3.3v ctl c11 1 m f 6.3v backup battery 1.2v nicd main battery 4.5 to 28v q11 p-channel si9424dy r14 14k sw ltc1559-3.3 l11 ? 22 m h gnd ps 7 1 8 5 6 3 reset push-button 2 4 v bak v cc reset backup + r15 100k c12 1 m f reset backup + c out 100 m f 10v 2 + linear technology corporation 1630 mccarthy blvd., milpitas, ca 95035-7417 (408) 432-1900 l fax: (408) 434-0507 l www.linear-tech.com battery is restored. thus, the ltc1559 does not use the ps pin to sense the ltc1435s output during backup mode. the ps pin is grounded in this case. please refer to the applications information section for more details.

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