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1 ltc1558-3.3/ltc1558-5 backup battery controller with programmable output n complete battery backup system in an so-8, 16-pin gn or so package n generates adjustable backup voltage 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 on-chip power-on reset n pushbutton reset input n reset assertion guaranteed at v cc = 1v n short-circuit protection n thermal limiting features descriptio n u the ltc ? 1558 is a backup battery controller that provides all the functions necessary to implement a backup power supply using a single nicd cell. it includes a 1.2v boost converter, an intelligent 2-stage battery charger, auto- matic backup switching and a microprocessor reset gen- erator. the boost converter uses a synchronous switching architecture to achieve a typical efficiency of 70%, ensur- ing 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. the ltc1558 also provides a user pro- grammable trickle charge current to compensate for self discharge losses in the backup cell. the ltc1558s automatic backup switching architecture 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 ltc1558 is available in an so-8, 16-lead gn or so package. applicatio n s u n notebook computers n palmtop computers/pdas n portable instruments n battery-powered systems typical applicatio n u , ltc and lt are registered trademarks of linear technology corporation. load current (ma) 0 0 backup time (minutes) 50 150 200 250 350 400 450 1558 ta02 100 300 10 25 30 5 15 20 v cc = 3.3v v bak = 3.78v nicd cell capacity = 110mahrs backup time vs 3.3v output load current c1 1 m f 1.2v nicd backup **battery main battery 4.5v to 10v r1 14k r2 100k load current 3a at normal mode 30ma at backup mode ltc1558-3.3 l1 22 m h* r4 221k 1% r3 220k r5 100k 1% 8 7 6 5 2 1 reset s1 q1 si4431dy 1558 ta01 3 4 v cc v bak backup reset gnd sw ctl fb + sumida cd54-22 m h sanyo cadnica n-110aa consult ltc1435 data sheet for circuit application information c in 100 m f 16v 2 * ** ? v cc 3.3v system m p c2 0.1 m f + ltc1435 ? synchronous buck regulator +
2 ltc1558-3.3/ltc1558-5 absolute m axi m u m ratings w ww u (note 1) terminal voltages v cc .......................................................................................... 6v v bak , backup ..................................................... 12v sw ...................................................................... 14v all other pins .................................. C 0.3v to v cc + 0.3v input currents (sw) ........................................... 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 package/order i n for m atio n w u u electrical characteristics v bat = 1.2v, t a = 0 c to 70 c unless otherwise noted. consult factory for industrial and military grade parts. symbol parameter conditions min typ max units battery backup switching v cc operating voltage range ltc1558-3.3 l 2.90 3.465 v ltc1558-5 l 4.40 5.250 v v bat backup battery cell voltage l 1.0 1.2 1.5 v v ref internal reference voltage l 1.247 1.272 1.297 v i vcc quiescent supply current (note 2) l 155 250 m a i bat peak inductor current (backup mode) 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) backup request trip point voltage at v fb relative to v ref l C 10.5 C 7.5 C 5.5 % v bst(on) boost converter assertion trip point voltage at v fb relative to v ref l C 10.5 C 7.5 C 5.5 % v bak(off) backup deassertion trip point voltage at v fb relative to v ref l C9 C6 C4 % v bst(off) boost converter deassertion trip point voltage at v fb relative to v ref l C 10.5 C 7.5 C 5.5 % v lobat low v bat detect (note 3) l 0.95 1 1.05 v order part number ltc1558cgn-3.3 LTC1558CGN-5 ltc1558cs-3.3 ltc1558cs-5 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 fb nc v bak v bak v cc backup reset reset nc lobat t jmax = 125 c, q ja = 110 c/ w (gn) t jmax = 125 c, q ja = 110 c/ w (s) order part number s8 part marking ltc1558cs8-3.3 ltc1558cs8-5 155833 15585 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 fb v bak v cc backup reset
3 ltc1558-3.3/ltc1558-5 electrical characteristics v bat = 1.2v, t a = 0 c to 70 c unless otherwise noted. symbol parameter conditions min typ max units v uvlo(on) v cc uvlo trip voltage (note 4) ltc1558-3.3 l 2.90 3.00 3.10 v ltc1558-5 l 4.40 4.55 4.70 v v uvlo(off) v cc uvlo recovery trip voltage (note 4) ltc1558-3.3 l 3.00 3.10 3.20 v ltc1558-5 l 4.55 4.70 4.85 v v lobat v bat uvlo trip voltage (note 5) l 0.85 0.9 0.95 v backup battery charger i chgf battery charge current fast recharge l 11 16 21 ma i chgt programmable trickle charge current range 0.05 2 ma 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 8 10 12 a/a v ctl(clamp) trickle charge clamp voltage i chgt = 1ma l 0.45 0.5 0.55 v pushbutton reset v ctl ctl input threshold 250 mv t ctl ctl input low time (debounce time) 20 ms reset timer t hreset pushbutton duration for hard reset 1.10 1.8 3.4 s 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 internal v cc monitor comparator t plh v uvlo(on) comparator propagation d v cc = C (9% v cc + 300mv), v od = 300mv 9 m s delay (rising) 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 feedback pin i fb fb pin bias current 110 na 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 pushbutton reset. note 3: only applies to 16-pin version. note 4: thresholds will track each other and are guaranteed not 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 drawn from the nicd battery during backup. note 7: the ltc1558 switches automatically between the low and high operating current levels. see applications information for more details.
4 ltc1558-3.3/ltc1558-5 typical perfor m a n ce characteristics uw nicd terminal voltage (v) 1.0 0 output power (mw) 25 50 75 100 125 150 1.1 1.2 1.3 1.4 1558 g01 v cc = 5v (ltc1558-5) v bak = 6v output power vs battery voltage output voltage, v bak (v) 2 switching frequency (khz) 50 75 10 1558 g03 25 0 4 6 8 125 100 v batt = 1.2v v cc = 3.3v (ltc1558-3.3) i pk = 330ma boost converter switching frequency nicd cell capacity (mahr) 0 0 backup time (hours) 0.5 1.0 1.5 2.0 2.5 3.0 125 250 375 500 1558 g02 v batt = 1.2v v bak = 6v p out = 100mw backup time vs battery capacity normalized fast recharge current vs temperature trickle charge multiplier factor boost converter switching duty cycle output voltage, v bak (v) 2 duty cycle (%) 40 60 10 1558 g04 20 0 4 6 8 100 80 v batt = 1.2v v cc = 3.3v (ltc1558-3.3) i pk = 330ma nicd battery trickle current (ma) 0.05 7.5 trickle charge factor (ma/ma) 9.5 10.0 10.5 0.1 1 2 1558 g05 9.0 8.5 8.0 v batt = 1.2v temperature ( c) 0 0.950 current ratio (ma/ma) 0.960 0.970 0.980 0.990 25 50 1558 g06 75 1.000 0.955 0.965 0.975 0.985 0.995 1.005 fast recharge time (assume fully exhausted nicd battery) battery capacity (mahr) 64 0 time (hours) 10 20 30 40 60 128 256 1558 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 1558 g08 56 5 4.7v v cc = 5v (ltc1558-5) reset output voltage vs supply voltage supply voltage (v) 0 0 reset voltage (v) 0.5 1.0 1.5 2.0 3.5 1 234 3v 1558 g09 2.5 3.0 3.10v v cc = 3.3v (ltc1558-3.3)
5 ltc1558-3.3/ltc1558-5 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 so-8. ctl (pins 3/5): control. this pin provides three functions. in backup mode this pin enters a high impedance state and monitors the backup battery cell voltage (v bat ). if v bat drops below 0.9v, the ltc1558 enters into uvlo. during trickle charge mode, an external resistor r ext sets the trickle charge current. in all modes, pulling the ctl pin below 250mv will generate either a soft or hard reset pulse. see the applications information section for more information. fb (pins 4/7): output voltage feedback. this pin is fed to the ltc1558s internal comparators. the boost converters output voltage is set with an external resistor divider connected from v bak to fb. the ltc1558 enters backup mode when fb drops 7.5% below the internal reference voltage (v ref ). during backup, the boost converter runs whenever fb drops below this (v ref C 7.5%) threshold. the ltc1558 exits backup mode when fb rises above (v ref C 6%). 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 when the ltc1558 comes out of uvlo. the hard reset stops the internal boost converter if it is running. this pin is held low whenever the ltc1558 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 if the ctl pin is pulled low for less than two seconds (soft reset). unlike hard reset, soft reset does not affect the ltc1558s current operating mode. backup (pins 6/13): backup active. this is an open-drain output that pulls low unless the ltc1558 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 input. a 12v zener diode is connected inter- nally to this pin to act as a voltage clamp. see the applications information 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 ltc1558 monitors v cc .if v cc drops below the rated output voltage by greater than 9%, the ltc1558 enters uvlo mode and reset is as- serted. the ltc1558 will only exit from uvlo if v cc rises to greater than C 6% of the rated output voltage. see the applications information section for more details. v bak (pins 8/15, 16): backup supply output. the ltc1558s boost converter provides regulated output voltage to the system through v bak during backup mode. 16-pin gn and so package 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 ltc1558 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 ltc1558-3.3/ltc1558-5 pi n fu n ctio n s uuu lobat (pin 9): low-battery detector output. this is an open-drain output that pulls low when the backup cell drops below 1v. it gives early warning to the system controller that the backup cell is getting weak. this pin is disabled when the ltc1558 is in trickle charge mode. reset (pin 12): system reset, active high. this is a ttl- compatible output driver. it can be used to connect to systems that require active high logic. the reset output will go high whenever reset is pulled low. if reset is externally pulled low, reset will go high. v bat backup reset v cc v bak 1558 sw02 200ms rated battery terminal voltage rated v cc voltage ?% 1 2 3 4 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 fb reset n1 p1 v bak v cc /v bak ctl sw + + uvlo detector reset backup lobat 1558 bd block diagra m w + r1 1558 sw01 v bat main battery c in multiple power outputs r2 1.2v nicd sw ltc1558 reset v bak q ext v cc backup to system control fb v in for more detailed application schematics please refer to the typical applications section main system regulator simplified ltc1558 connections in a battery backup system cold power boot-up (main battery replaced/turned on)
7 ltc1558-3.3/ltc1558-5 switchi n g wavefor m s uw cold power boot-up description 1. the v bat voltage increases and turns on the q ext body diode. v bak follows v bat by one body diode drop. 2. v bak increases above the system regulators minimum input voltage. the system regulator wakes up and starts ramping up the system power supply. reset remains asserted from v cc = 1v. 3. the ltc1558s internal bandgap wakes up. the ltc1558s internal boost converter does not turn on as reset remains asserted. once v fb is greater than (v ref C 6%), backup is deasserted after the t phl delay time. q ext turns on and v bak = v bat . 4. reset is asserted for a further 200ms after v cc exceeds C 6% of its rated value. backup mode description 1. trigger into backup mode. the main battery fails and v fb drops 7.5% below the ltc1558s internal v ref . the backup pin is asserted after a t rise delay time and the ltc1558s boost converter is turned on. 2. backup mode. the ltc1558s boost converter charges and discharges the inductor with 165ma peak current. if v fb doesnt recover above (v ref C 7.5%) (due to a heavy load), the boost converter increases peak charg- ing current to 330ma. when v fb rises above (v ref C 7.5%), the boost converter stops but 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 external mosfets body diode to conduct and v fb is pulled higher than (v ref C 6%). backup deasserts and the boost converter finishes its last cycle. 4. trigger into uvlo. during backup, the 1.2v nicd cell grows weak and its terminal voltage falls. the lobat pin is asserted to give an early warning when the cell voltage drops below 1v. reset is asserted when the cell voltage drops below 0.9v and the ltc1558 enters uvlo mode. backup mode (main battery discharged) inductor current reset backup v fb v nicd lobat 1558 sw03 t rise t rise 7.5% 1.2v 7.5% 7.5% 1v 0.9v ?% boost converter output t fall t rise t rise 4 3 2 1
8 ltc1558-3.3/ltc1558-5 applicatio n s i n for m atio n wu u u overview the ltc1558 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 system design flexibility. the ltc1558 allows the use of a low cost rechargeable nicd cell for backup, eliminating the need for expensive, replaceable 4.5v lithium backup cells. the ltc1558 includes an onboard boost converter de- signed to generate an adjustable voltage (3v to 10v) from a single 1.2v nicd cell. this voltage is connected to the systems dc/dc converter input, enabling the system to continue operation when the main battery 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 externally adjustable trickle charge circuit maintains the cell charge after the fast charge cycle has completed, minimizing drain from the main battery during standby. included in the ltc1558 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 ltc1558 also performs v cc supervisory functions during normal system operations. an ltc1558-3.3 moni- tors a 3.3v supply voltage at its v cc pin whereas an ltc1558-5 monitors a 5v supply at its v cc pin. in both cases, the ltc1558 derives power for the majority of the internal circuitry (except for the boost converter) from the v cc pin. table 1 shows the signal conditions for the ltc1558s various operating modes. note that v cc in table 1 refers to the rated v cc voltage, 3.3v or 5v. boost converter operation the ltc1558 uses an onboard synchronous boost con- verter 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 by the external divider connected to the fb pin, supports the main system regulator during figure 1. typical ltc1558 connection + boost converter to system regulator input ltc1588 r1 fb main battery c in r2 1558 f01 backup logic v ref v bak backup backup. it can supply 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 ltc1558 to accurately measure the charge removed from the backup cell by counting the charge pulses. the ltc1558 enters backup mode when the main battery voltage drops. as shown in figure 1, the main battery voltage is scaled down by an external resistor divider and fed to the ltc1558s backup comparators. these com- pare the scaled voltage with an internal trimmed v ref (1.272v), switching the ltc1558 into backup mode when v fb drops 7.5% below v ref . upon entering backup mode, the backup pin is asserted and the internal boost converter turns on. the backup signal is used to turn off the external p-channel mosfet, isolating the main bat- tery from the ltc1558 and the system regulators input. the ltc1558s boost converter will charge the input capacitor c in of the system regulator until v fb rises above (v ref C 7.5%). table 1 operating modes conditions uvlo reset 1v < v cc < v cc (rated value) C 9% or v bat < 0.9v pushbutton reset v ctl < 250mv uvlo reset recovery v cc > v cc (rated value) C 6% backup mode activation v fb < (v ref C 7.5%) backup mode exit v fb > (v ref C 6%) boost converter activation v fb < (v ref C 7.5%) boost converter deactivation v fb > (v ref C 7.5%)
9 ltc1558-3.3/ltc1558-5 once v fb rises above (v ref C 7.5%) , the ltc1558s boost converter deactivates and the freshly charged input capacitor supplies power to the system regulator. the cycle repeats again when the input capacitors charge is drained away and v fb again drops below (v ref C 7.5%) . the backup pin remains asserted until the main battery is restored. this ensures that the ltc1558 does not switch in and out of backup mode unnecessarily. the ltc1558s boost converter minimizes output ripple under light load conditions by reducing the charge trans- ferred for the first two consecutive switch cycles. when v fb falls below (v ref C 7.5%), the boost operation starts by connecting the sw pin to ground through an internal 0.5 w n-channel mosfet (n1 in the block diagram). the current through the external 22 m h inductor rises linearly through this switch. light current mode 165ma (peak) 330ma (peak) heavy current mode 1558 f02 figure 2. inductor current during switching 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 (p1 in the block diagram). the inductor current discharges through p1, charging up the capacitor connected exter- nally to v bak (c in 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 ltc1558 looks at the fb pin voltage. if v fb has increased above the (v ref C 7.5%) threshold, the boost converter shuts off both switches and waits for v fb to drop below (v ref C 7.5%) again. if v fb is still less than (v ref C 7.5%) after the first boost cycle, the ltc1558 immediately reconnects sw to ground, repeating the boost cycle. if after two consecutive pulses, v fb is still not above the boost threshold (v ref C 7.5%) , the ltc1558 decides that the load is not so light after all, applicatio n s i n for m atio n wu u u 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 fb exceeds the (v ref C 7.5%) boost threshold, the ltc1558 stops the boost converter and resets the internal two pulse counter. the next time v fb falls below (v ref C 7.5%) , the boost converter restarts in low current mode for at least two boost cycles. moderate or changing loads will cause the ltc1558 to shift between the two peak inductor current limits, keeping the output in tight regulation. near its maximum load capability, the ltc1558 will stay in 330ma high current mode and the output voltage v bak will hover around the user pro- grammed value. v bak capacitor esr the type of output capacitor and the user programmed v bak value will affect the ltc1558s output ripple and efficiency. in most applications, the main v bak capacitor is primarily determined by the requirements of the main power supply. such a capacitor will generally meet the requirements of the ltc1558. in unusual circumstances or circuits where the main system regulators input ca- pacitor is located some distance away from the ltc1558, a local output capacitor may be necessary. 1 boost cycle v bak esr ripple discharge period t disch charge period t ch 1588 f03 figure 3. v bak ripple the maximum ripple on the v bak pin is equal to 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
10 ltc1558-3.3/ltc1558-5 proportional to the difference between v bak (3v to 10v) and the battery cell voltage, v bat (1.2v). assuming esr = 0.2 w , i ind(peak) = 330ma, v bak = 6v, v ripple(p-p) = (i ind(peak) )(r esr(cap) ) = (330ma)(0.2 w ) = 66mv since v bak must be scaled down to v fb , the external resistor ratio = 6v/1.272v = 4.717 therefore the noise amplitude seen by the fb compara- tors is: = 66mv/4.717 = 14mv the discharge time period, t disch = (l ? i ind(peak) )/(v bak C v bat ) = (22 m h ? 330ma)/(6v C 1.2v) = 1.5 m s for lowest v bak = 3v and maximum i ind(peak) = 445ma, v ripple(p-p) = 89mv rb resistor ratio = 2.358 noise amplitude = 37.7mv t disch = 5 m s the internal v fb comparators are designed to have a slow response time to filter away this ripple. the (v ref C 6%) fb comparator has a 6 m s rising edge delay and 2 m s falling edge delay. the (v ref C 7.5%) fb comparator has a similar 6 m s rising time delay but a much longer falling time delay of 20 m s. this enables the comparator to control the booster properly, and avoids turning off the boost converter prematurely due to false triggering by the esr ripple. exit from backup when a new battery is inserted into the system, the higher main battery voltage turns on the external p-channel mosfets body diode and raises v bak (and v fb ) to a higher voltage. the ltc1558 detects the return of the main applicatio n s i n for m atio n wu u u battery by watching for v fb to exceed (v ref C 6%) . the ltc1558 then stops its internal boost converter and begins to recharge the nicd cell. backup is deasserted to signal to the system controller to restore system loading and resume normal operations. at the same time, the external p-channel mosfet is driven by the backup signal. the p-channel mosfet turns on and allows the main battery to bypass its body diode and drive the system regulator directly. since the user can replace the main battery anytime during the ltc1558s backup operations, the backup signal may be deasserted while the boost converter is switching. to prevent the potential problem of residual energy in the inductor, the ltc1558 will only stop the boost converter after it has completed the current boost cycle. uvlo lockout under excessive backup load very heavy loads (above the ltc1558s maximum power output) will pull the boost converters output below the boost threshold. under these conditions, the ltc1558s boost converter will continue to supply 330ma current pulses to the system regulator while charge on the v bak capacitor (c in ) drains away. the system regulator will not maintain its output regulation and the system v cc will drop. when v cc drops below C 9% of the rated voltage for more than 9 m s, the ltc1558s v cc supervisory circuit activates uvlo mode, shutting off the boost converter and asserting the reset pins. the 9 m s delay prevents the ltc1558 from being fooled by brief transients or noise spikes on its v cc pin. upon receipt of the reset signals, the host system should shut down in a orderly manner. the ltc1558s v cc supervisory circuit will remain alive until v cc is less than 1v to ensure valid reset pin signals. 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 ltc1558 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 pins. since the ctl pin can also be connected to an external pushbutton reset, the ltc1558 includes
11 ltc1558-3.3/ltc1558-5 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 pushbutton 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 ltc1558 will treat this as a hard reset after 2 seconds. an optional lobat output, available in the 16-pin gn or so package, can be used to signal the system when the cell voltage falls below 1v, giving an early warning that the backup cell is heavily discharged. the lobat output is disabled when the ltc1558 is in trickle charge mode because the ctl pin is pulled to 0.5v by the ltc1558. fault protection and thermal limit the ltc1558s 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 case, the nicd cell is assumed to be damaged and the ltc1558s 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 ltc1558 will enter uvlo either when v cc drops below (v cc(rated voltage) C 9%) or after the ltc1558 detects ctl lower than 0.25v for 2 seconds, in which case hard reset occurs. the discharging time can also get abnormally long if a serious overload condition occurs during switching. the timer will shut off the p-channel pass transistor after 10 m s, protecting the boost converter. the ltc1558 will end up in uvlo as v cc drops below (v cc(rated voltage) C 9%). in addition, the ltc1558 is protected for safe area opera- tion with an internal thermal shutdown circuit. if the device is overloaded for a long period of time, the thermal shutdown circuit forces the ltc1558 into uvlo. the threshold temperature for thermal shutdown is typically 155 c. applicatio n s i n for m atio n wu u u the ltc1558s 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 ltc1558 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 estimate battery charge by counting switch pulses. the gas gauge counts up from zero as charge is removed from the backup cell in backup mode. it takes roughly 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 = 5v, the gas gauge divider will increment by one count every 7.5 m s while the boost converter is running. full count is reached after approximately 2.2 hours, equivalent to about 512mahr of charge. upon entering recharge mode (after the main battery is restored) the ltc1558 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 replace about 160% of the charge previously removed from the backup cell. when the gas gauge counter reaches zero, the ltc1558 reduces the charging current at the sw pin to the user- programmed trickle charge current level. under some circumstances, the ltc1558 can exit the backup mode with invalid gas gauge contents. this can occur under three possible conditions: a) the backup cell was completely exhausted during a backup cycle and the ltc1558 entered uvlo. b) the backup cell was replaced while the main supply was disabled. c) a backup cycle was terminated prematurely by a hard reset or an output overload.
12 ltc1558-3.3/ltc1558-5 in these cases, the ltc1558 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 of charge 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 will be wasted. however, the ltc1558s 15ma fast charge current should not be 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 ltc1558 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 ex- ample, a small 60mahr button cell can back up the system for 20 minutes at an output power of 100mw. note that at lower programmed v bak values, the boost converter effi- ciency improves and allows more backup time from the same cell compared to a higher v bak value. once it reaches full recharge, a cell bigger than 512mahr is likely to overrun the gas gauge counter before it runs out of charge during an extended backup cycle. the ltc1558 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 comes out of backup. this ensures that the backup cell is always replenished with at least a 1mahr charge every time the ltc1558 enters backup mode. applicatio n s i n for m atio n wu u u battery backup cell trickle charge when the gas gauge counter reaches zero, the ltc1558 terminates fast recharge and reduces the recharge current to the user-programmed trickle current level. the ltc1558 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 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 ltc1558 trickle charges only after the completion of the fast re- charge 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 approximately 150 m a. r ext v cc 47 m f i 10i 1.2v nicd cell sw ctl 0.5v 1558 f04 11 1 ltc1558 + + + figure 4. trickle current charger undervoltage lockout the ltc1558 includes an undervoltage lockout (uvlo) system that ensures that the system will shutdown grace- fully if the backup cell is exhausted or overloaded. as described in the previous section, the ltc1558 will
13 ltc1558-3.3/ltc1558-5 terminate backup operation and remain off until the main power supply returns. it then runs a fast recharge cycle to recharge the backup cell. an onboard low-battery com- parator in the 16-pin gn or so package provides an early warning signal when the backup cell drops below 1v. the uvlo circuit also trips if the ltc1558s v cc supervi- sory circuit detects that v cc drops below C 9% of the rated v cc voltage due to overload or output short-circuit condi- tions. once the uvlo circuit trips, the ltc1558 asserts the reset pins until the v cc voltage drops below 1v. it will then remain off until v cc rises to within (v cc C 6%) of the rated output voltage. during power-up from uvlo, the ltc1558 asserts the reset pins until the (v cc C 6%) threshold. once v cc exceeds (v cc C 6%), the reset pins remain asserted for another 200ms (hard reset) before being released to inform the system to start operating. reset operation the ltc1558 includes an onboard pushbutton reset switch controller. if the ctl pin is pulled to ground (< 250mv) by a pushbutton or an open-drain output, the ltc1558 gen- erates a pulse at the resetpins after the trailing edge of applicatio n s i n for m atio n wu u u the ctl signal. a short (less than 2s) low going signal at ctl will generate a soft reset (100 m s) pulse at the reset pins. a low ctl signal for more than 2s will generate a hard reset pulse at its resetpins. during hard reset, the ltc1558 will disable 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 pushbutton 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 ltc1558 has a ttl-compatible input, shdn, that shuts down the whole chip, asserts the reset pins and places the ctl, v bak and sw pins into high impedance states. the shdn pin has an internal pull-up that ensures the chip will not shut down if the pin is left floating. the shdn pin typically draws 8 m a when pulled low at v cc = 5v. the chip consumes less than 50 m a during shutdown while v cc is still alive. 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 shut off completely. note that the backup cell slowly discharges through r ext in this mode. inductor selection the ltc1558 is designed to operate with a recommended inductor value of 22 m h ( 20%) with < 0.2 w dc resistance. using inductor values higher than 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 2 lists the recom- mended surface mount inductor part numbers. ctl reset a 0v 0v 0v 20ms debounce b > 0.25v t ctl < 20ms 20ms < t ctl < 2s > 0.25v ?oft?pushbutton reset at ctl a. ctl < 0.25v for less than 20ms b. ctl > 0.25v for more than 20ms ?ard?pushbutton 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 1558 f05 reset ctl reset 200ms 2s t ctl > 2s 20ms 20ms figure 5. pushbutton resets
14 ltc1558-3.3/ltc1558-5 table 2. recommended inductors part typ inductor manufacturer number value dcr ( w ) sumida cd54-220 22 m h 20% 0.18 sumida cdrh73/74 22 m h 20% 0.2/0.11 capacitor selection the ltc1558 requires a minimum v bak capacitor of 44 m f to ensure that the boost converter can regulate the output at 20ma load. the capacitors esr should be small (< 0.2 w ) to minimize voltage spikes that might incorrectly trigger the ltc1558s internal fb comparators. note that the ltc1558 can usually share the output capacitor with the system regulator. thus its ratings like v max , i ripple(rms) , etc., will all have to meet the system regulators specifica- tions as well. battery selection a primary application for the ltc1558 is a bridging supply, only providing backup current while the main system battery is being replaced. in these applications, the ltc1558 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. the ltc1558 can work with standard or memory backup specific nicd cells. memory backup cells can operate at higher temperatures and have lower self discharge rates. the ltc1558s 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 3. applicatio n s i n for m atio n wu u u table 3. button/cylindrical nicd 1.2v cells part capacity manufacturer number (mahr) r series ( 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 p-11aa 110 0.08 (standard) 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 ltc1558s boost converter output power drops significantly when the nicd cells internal resistance increases at the end of its charge. this is because the inductor charging time will increase due to a larger r/l time constant, decreasing the switching frequency. it is advisable, especially for batteries with high internal resistance, to include a 47 m f bypass capacitor across the battery to ensure that the boost converter can deliver the maximum output power regardless of the nicd internal resistance.
15 ltc1558-3.3/ltc1558-5 typical applicatio n s u ltc1558-3.3 low main battery voltage (4.5v to 10v) application + + 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 c3 4.7 m f 16v d1 cmdsh-3 1558 ta03 d2 mbrs140t3 r5 20k 1% sumida cdrh125-10 irc lr2d1d-01-rq33-f sumida cd54-220 * ** ? r1 35.7k 1% c5 1000pf q2 n-channel si4412dy q1 n-channel si4412dy sfb extv cc 11 7 8 12 15 14 13 c2 1 m f 16 510 1 2 3 6 4 9 c6 100pf c osc 68pf r c 10k c ss 0.1 m f c c 330pf c1 100pf c c2 51pf + c in 22 m f 35v 2 + c in 100 m f 10v 2 v out 3.3v 3a ctl c11 47 m f 6.3v backup battery 1.2v nicd main battery 4.5v to 10v q11 p-channel si4431dy r14 14k sw ltc1558-3.3 l11 ? 22 m h gnd fb r11 221k 1% r12 100k 1% 7 1 8 5 6 3 reset pushbutton 2 4 v bak v cc reset backup + r13 100k c12 1 m f reset backup + typical low voltage application the maximum main battery voltage is less than the maxi- mum v bak pin voltage (12v). this configuration has the lowest number of external components. the ltc1435s minimum input voltage is 3.5v. the v bak voltage, set by r11 and r12, is programmed to 3.8v. therefore, the main batterys lowest voltage should be 3.8v + 1 body diode drop = 4.5v. this will enable a fresh main battery to turn on the external p-channel mosfet and power up the system out of uvlo during cold power boot or out of backup mode when the ltc1558 is power- ing up the system. a 100k pull-up resistor enables the open-drain backup pin to turn the external p-channel mosfet off when v bak is higher than v cc .
16 ltc1558-3.3/ltc1558-5 typical applicatio n s u ltc1558-5 medium main battery voltage (7v to 18v) application + + 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 c3 4.7 m f 16v d1 cmdsh-3 1558 ta04 d2 mbrs140t3 r6 11k 1% sumida cdrh125-10 irc lr2d1d-01-rq33-f sumida cd54-220 * ** ? r1 35.7k 1% c5 1000pf q2 n-channel si4412dy q1 n-channel si4412dy sfb extv cc 11 7 8 12 15 14 13 c2 1 m f 16 510 1 2 3 6 4 9 c6 100pf c osc 68pf r c 10k c ss 0.1 m f c c 330pf c1 100pf c c2 51pf + c in 22 m f 35v 2 + c out 100 m f 10v 2 v out 5v 3a ctl c11 47 m f 6.3v backup battery 1.2v nicd main battery 7v to 18v q11 p-channel si4431dy r14 14k sw ltc1558-5 l11 ? 22 m h gnd fb r11 422k 1% r12 100k 1% 7 1 8 5 6 3 reset pushbutton 2 4 v bak v cc reset backup + r13 100k c12 1 m f d11 1n5818 reset backup + typical medium voltage application the maximum main battery voltage is more than the maximum v bak pin voltage (12v). this configuration is needed for most notebook computers that have 3-cell or 4-cell series connected lithium battery packs. the schottky diode d11 (1n5818) prevents the main batterys high terminal voltage from overstressing the ltc1558s v bak pin during nonbackup conditions. an internal zener inside the ltc1558 will clamp v bak to 12v when the 1n5818s reverse bias leakage current increases at high temperature. a 100k pull-up resistor enables the ltc1558s open-drain backup pin to turn the external p-channel mosfet off during backup mode, even when v bak is higher than v cc . the main battery pack should have an internal control to shut itself down once its energy is used up. this prevents the lithium cells from deep discharge damage. once the main battery shuts down, the fb voltage drops and the ltc1558 switches to backup mode.
17 ltc1558-3.3/ltc1558-5 typical applicatio n s u ltc1558-5 high main battery voltage (48v) application pgate v in v cc p-drive v cc c t i th sense cap shutdown 2 rgnd ngate pgnd sgnd shutdown 1 sense + 1 2 3 4 5 6 7 8 16 15 14 13 12 11 10 9 ltc1149-5 c2 0.068 m f c1 0.047 m f d1 1n4148 r11 422k 1% r12 100k 1% r16 100k z11 12v q12 2n3906 d2 1n4148 c c 3300pf r15 100k main battery 48v q11 p-channel mtd2955e r c 1k c4 470pf c3 3.3 m f c5 1000pf q2 n-channel irfz34 d3 mbr380 c6 0.1 m f l1* 68 m h r sense ** 0.04 w c out 220 m f 10v os-con 1558 ta05 v out 5v 2.5a *hurricane lab hl-ki168m **irc lr2512-01-ro40-5 ? sumida cd54-220 q1 p-channel mtd2955e shutdown r4 100 w r3 100 w + + c in 100 m f 100v + ctl c11 47 m f 6.3v backup battery 1.2v nicd r14 14k sw ltc1558-5 l11 ? 22 m h 7 1 8 5 6 3 reset pushbutton d11 mbr170 2 4 v bak v cc reset backup fb gnd + c12 1 m f reset backup + typical high voltage application the maximum main battery voltage is 48v. the schottky diode d11 (mbr170) prevents the main batterys high terminal voltage from overstressing the ltc1558s v bak pin during nonbackup conditions. an internal zener inside the ltc1558 will clamp v bak to 12v when the mbr170s reverse bias leakage current increases at high temperature. as shown above, the design must ensure that v bat does not force the external p-channel mosfets v gs above its maximum rating (15v for the mtd2955e) shown during nonbackup mode. during nonbackup mode, the ltc1558s open-drain backup pin is low. the external 12v zener and 2n3906 conduct and the mtd2955es v gs is clamped at approxi- mately 12v. during backup, the backup pin floats and the 2n3906s base voltage is pushed nearer to v bak . the mtd2955e is effectively turned off, isolating the main battery from v bak during backup. the main battery pack should have an internal control to shut itself down once its energy is used up. this prevents it from deep discharge damage.
18 ltc1558-3.3/ltc1558-5 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 ltc1558-3.3/ltc1558-5 package descriptio n u dimensions in inches (millimeters) unless otherwise noted. 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 * ** s8 package 8-lead plastic small outline (narrow 0.150) (ltc dwg # 05-08-1610) 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 * ** s package 16-lead plastic small outline (narrow 0.150) (ltc dwg # 05-08-1610) 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 ltc1558-3.3/ltc1558-5 1558f lt/tp 0298 4k ? printed in usa ? linear technology corporation 1998 linear technology corporation 1630 mccarthy blvd., milpitas, ca 95035-7417 l (408) 432-1900 fax: (408) 434-0507 l telex: 499-3977 l www.linear-tech.com related parts part number description comments ltc690/ltc691 microprocessor supervisory circuits microprocessor power supply monitor and backup with ltc694/ltc695 power fail comparator lt ? 1020 micropower linear regulator includes low-battery and dropout detectors lt1120 micropower linear regulator so-8 package, includes low-battery detector ltc1149 high efficiency synchronous step-down v in up to 48v, burst mode tm operation switching regulator ltc1235 microprocessor supervisory circuit includes pushbutton reset and power fail comparator ltc1435 high efficiency, low noise synchronous ultrahigh efficiency, burst mode operation step-down switching regulator ltc1479 powerpath tm controller for dual battery systems complete power management controller for battery notebook computers and other portable equipment lt1521 micropower low dropout regulator 300ma, sot-223 package burst mode and powerpath are trademarks of linear technology corporation.

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Price & Availability of LTC1558CGN-5

	To Download LTC1558CGN-5 Datasheet File
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