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1 for more information www.linear.com/ltc2956 typical a pplica t ion fea t ures descrip t ion wake-up timer with pushbutton control the lt c ? 2956 is a micropower, wide input voltage range, configurable wake-up timer with pushbutton control. it periodically wakes up and turns on a connected system to perform tasks like monitoring temperature or capturing images. after completing the task, the ltc2956 turns the system off to conserve power. the wake-up timer period can be adjusted from 250 ms to 39 days using configuration resistors. the system awake time can be controlled by the input pulse at the sleep pin or adjusted by the capacitor at the onmax pin. the ltc2956 operates over a wide supply input range from 1.5v to 36 v. the low 800 na quiescent current suits bat - tery powered applications. the pushbutton input allows the user to shutdown, turn on or reset the wake-up timer. with the timer in shutdown, the quiescent current drops to 300 na. the ltc2956 also provides three status outputs to indicate mode transitions and pushbutton events. tw o versions are available for applications requiring either positive or negative enable polarities. a pplica t ions n 1.5v to 36v supply input range n adjustable wake-up period: 250ms to 39 days n adjustable maximum awake time n 0.8a quiescent current n 0.3a shutdown current n pushbutton input with debouncing n low leakage en output allows dc/dc converter control (ltc2956-1) n high voltage en output drives external p-channel mosfet (ltc2956-2) n 25kv esd hbm on pb input n 12-lead 3mm 3mm qfn and msop packages n heartbeat timers n periodic wake-up control n portable and battery-powered equipment n intervalometers n data acquisition l, lt , lt c , lt m , linear technology and the linear logo are registered trademarks and powerpath and thinsot are trademarks of linear technology corporation. all other trademarks are the property of their respective owners. 2956 ta01a pbout sleep offalert onalert turning off turned on pb gnd onmax v bat en v in range v out v in lt3060 shdn ltc2956-1 long v main 1.5nf p 100k 10k 1f 10k 10k 280k 9.76k period 100k t long = 1s, t onmax = 20ms, t period = 250ms + pb sleep en 2956 ta01b t sleep t awake t period short press starts cycling timer long press stops cycling timer p shuts off power timer periodically enables power ltc 2956 2956f
2 for more information www.linear.com/ltc2956 a bsolu t e maxi m u m r a t ings v in ( note 3) ................................................ C0. 3 v to 40 v input voltages : pb ........................................................... C 40 v to 40 v sleep ...................................................... C 0.3 v to 6v long , p eriod , range, onmax ............ 0. 3 v to 3.6 v output voltages : onalert , p bout , offalert ................... C 0.3 v to 6v en / en .................................................... C 0.3 v to 40 v operating temperature range : ltc 2956 c ................................................ 0 c to 70 c ltc 2 956 i ............................................. C 40 c to 85 c storage temperature range : qfn p ackage ..................................... C 65 c to 150 c msop p ackage .................................. C6 5 c to 150 c lead temperature ( soldering , 10 sec ): msop p ackage ................................................. 300 c (note 1) o r d er i n f or m a t ion lead free finish tape and reel part marking* package description temperature range ltc2956cud-1#pbf ltc2956cud-1#trpbf lgnh 12-lead (3mm 3mm) plastic qfn 0c to 70c ltc2956cud-2#pbf ltc2956cud-2#trpbf lgtc 12-lead (3mm 3mm) plastic qfn 0c to 70c ltc2956iud-1#pbf ltc2956iud-1#trpbf lgnh 12-lead (3mm 3mm) plastic qfn C40c to 85c ltc2956iud-2#pbf ltc2956iud-2#trpbf lgtc 12-lead (3mm 3mm) plastic qfn C40c to 85c ltc2956cms-1#pbf ltc2956cms-1#trpbf 29561 12-lead plastic msop 0c to 70c ltc2956cms-2#pbf ltc2956cms-2#trpbf 29562 12-lead plastic msop 0c to 70c ltc2956ims-1#pbf ltc2956ims-1#trpbf 29561 12-lead plastic msop C40c to 85c ltc2956ims-2#pbf ltc2956ims-2#trpbf 29562 12-lead plastic msop C40c to 85c consult lt c marketing for parts specified with wider operating temperature ranges. *the temperature grade is identified by a label on the shipping container. consult lt c marketing for information on nonstandard lead based finish parts. for more information on lead free part marking, go to: http://www.linear.com/leadfree/ for more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/ 12 11 10 4 5 6 top view 13 gnd ud package 12-lead (3mm 3mm) plastic qfn 7 8 9 3 2 1 onalert onmax long *en/ en pb gnd sleep offalert pbout range period v in t jmax = 125c, ja = ~68c/w exposed pad ( pin 13) is gnd, pcb connection op tional *pin 9 is en for ltc2956-1 and is en for ltc2956-2 1 2 3 4 5 6 onmax long range period v in gnd 12 11 10 9 8 7 onalert sleep offalert pbout *en/en pb top view ms package 12-lead plastic msop t jmax = 125c, ja = 135c/w *pin 8 is en for ltc2956-1 and is en for ltc2956-2 p in c on f igura t ion ltc 2956 2956f
3 for more information www.linear.com/ltc2956 e lec t rical c harac t eris t ics the l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at t a = 25c. v in = 3.3v, r com = 100k unless otherwise noted. (note 2) symbol parameter conditions min typ max units v in supply voltage range l 1.5 36 v i in v in supply current awake state, pb hi sleep state, pb hi off state, pb hi l l l 3 0.8 0.3 10 3 1 a a a v uvl v in undervoltage lockout v in rising l 1.08 1.24 1.4 v v uvl(hyst) v in undervoltage lockout hysteresis 100 mv wake-up timer t period period accuracy r period = 100k l 237 250 263 ms r period period-setting resistor range l 32.4 324 k timing (refer to timing diagram) t sleep_min minimum sleep duration l 76 128 180 ms t awake_min minimum awake time l 4 8 12 ms t onmax maximum awake time sleep = 0v, c onmax = 3900pf l 32 52 72 ms t db pb debounce time pb goes low en goes high l 19 32 45 ms t pd(sleep) sleep propagation delay sleep en transitions l 2 4 ms t pbout_first width of first pbout pulse after entering awake state l 76 128 180 ms t long long power down time r long = 9.76k, r com = 100k r long = open, r com = 100k l l 76 9.83 128 16.4 180 22.9 ms s t off offalert pulse width pb = 2v l 0.6 1 1.4 s input pins: pb, onmax, sleep v pb(min,max) pb voltage range l C36 36 v i pb pb input current pb = 0v pb = C36v l C1 C4 C8 C400 a a v pb(th) pb input threshold pb falling l 0.5 0.9 1.5 v v pb(hyst) pb input hysteresis 0.7 v v pb(oc) pb open circuit voltage i pb = 0a, C1a l 1.5 v r pb pb pull-up resistance l 0.45 0.9 1.35 m v sleep(th) sleep input threshold voltage sleep falling l 0.7 1 1.3 v v sleep(hyst) sleep input hysteresis 80 mv i sleep sleep leakage current sleep = 1v l 0 100 na v onmax(th) onmax input threshold voltage onmax rising l 0.6 1 1.5 v i onmax onmax pull-up current onmax = 0v l C1.1 C2 C2.8 a ltc 2956 2956f
4 for more information www.linear.com/ltc2956 symbol parameter conditions min typ max units output pins: en/en, pbout, onalert, offalert, period, range, long v en(voh) en voltage output high (ltc2956-1) i en = 0a, C1a l 1.5 v v en(voh) en voltage output high (ltc2956-2) i = 0a, C1a l v in C 1.5 v in v r en/en en/en pull-up resistance l 0.45 0.9 1.35 m v ol output low voltage (en/ en) output low voltage ( onalert , pbout) output low voltage ( offalert ) i = 1ma i = 3ma i = 6ma l l l 0.4 0.4 0.4 v v v i oh input leakage current (range, long) input leakage current (pbout, onalert, offalert) v = 1.5v v = 5v l l 100 100 na na v period period open circuit voltage i = C1a l 0.3 0.4 0.5 v e lec t rical c harac t eris t ics the l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at t a = 25c. v in = 3.3v, r com = 100k unless otherwise noted. (note 2) note 1: stresses beyond those listed under absolute maximum ratings may cause permanent damage to the device. exposure to any absolute maximum rating condition for extended periods may affect device reliability and lifetime. note 2: all currents into device pins are positive; all currents out of device pins are negative; all voltages are referenced to gnd unless otherwise noted. note 3: a substrate diode limits the v in pin to a minimum of C0.3v with respect to gnd. this pin may go below C0.3v with current limited to less than 50ma. timing diagram pb pbout sleep t pbout_first t db en offalert onalert t period t off 2956 ec td t long t pd(sleep) t pd(sleep) t awake_min t sleep_min t sleep_min t onmax t db ltc 2956 2956f
5 for more information www.linear.com/ltc2956 typical p er f or m ance c harac t eris t ics wake-up period vs period resistance wake-up period vs temperature maximum awake time vs c onmax maximum awake time vs temperature en output high voltage vs supply voltage en output high voltage vs temperature supply current vs temperature supply current vs supply voltage undervoltage lockout vs temperature temperature (c) ?50 i vin (a) 2.00 1.75 1.25 1.50 1.00 0.50 0.75 0.25 0 0?25 50 2956 g01 100 25 75 sleep state off state r period (k) 0 t period (seconds) 100 200 50 150 300 2956 g04 400 250 350 4.0 3.0 2.0 1.0 3.5 2.5 1.5 0.5 0 nrange = 4 r com = 100k r range = 17.4k temperature (c) ?50 t onmax (ms) 70 65 55 60 50 40 45 35 30 0?25 50 2956 g07 100 25 75 c onmax = 3.9nf v in (v) 1 v en(voh) (v) 4.0 3.5 3.0 2.0 2.5 1.5 1.0 32 5 2956 g08 7 4 6 temperature (c) ?50 v en(voh) (v) 4.0 3.8 3.4 3.6 3.2 3.0 0?25 50 2956 g09 100 25 75 v in = 7v temperature (c) ?50 256 254 250 252 248 246 244 0?25 50 2956 g05 100 25 75 t period (ms) nrange = 1 r period = 100k c onmax (nf) t onmax (ms) 2956 g06 10000 1000 100 10 1 100 1000 10 v in (v) 0 i vin (a) 1.4 1.2 0.8 1.0 0.6 0.4 10 20 5 15 30 2956 g02 40 25 35 t a = 85c t a = 25c t a = ?40c sleep state temperature (c) ?50 v uvl (v) 1.30 1.28 1.24 1.26 1.22 1.20 0?25 50 2956 g03 100 25 75 ltc 2956 2956f
6 for more information www.linear.com/ltc2956 typical p er f or m ance c harac t eris t ics pb input current vs pb voltage pb voltage vs external pb resistance to ground onalert output low voltage vs current en/en output low voltage vs temperature en/en output low voltage vs current pb debounce time vs temperature temperature (c) ?50 v en/en(vol) (v) 0.4 0.3 0.1 0.2 0 0?25 50 2956 g10 100 25 75 i en = 1ma pb voltage (v) ?40 i pb (a) ?200 ?160 ?120 ?80 ?40 0 40 0 ?20 2956 g13 40 20 external pb resistance to ground (k) 0 pb voltage (mv) 300 250 200 150 100 50 0 10 30 2956 g14 50 20 40 t a = 85c t a = ?40c t a = 25c i offalert (ma) 0 v vol (v) 0.4 0.3 0.1 0.2 0 642 10 2956 g15 16 8 12 14 t a = 85c t a = ?40c t a = 25c v in = 3.3v i en/en (ma) 0.0 v en/en(vol) (v) 0.4 0.3 0.1 0.2 0 1.00.5 2.0 2956 g11 3.0 1.5 2.5 t a = 85c t a = ?40c t a = 25c v in = 3.3v temperature (c) ?50 t db (ms) 50 40 45 35 25 20 30 0?25 50 2956 g12 100 25 75 ltc 2956 2956f
7 for more information www.linear.com/ltc2956 p in func t ions en: enable output ( ltc2956-1). en is an active high output to control the turn-on/off of a load. connect this pin to the run or shutdown pin of a voltage regulator. the ltc2956-1 pulls en high through an internal 900 k resis - tor and schottky diode to a 3.3 v regulated supply when the pushbutton is pressed or when the wakeup period is reached. en pulls low during the sleep state. this pin may be left open if unused. en: inverted enable output (ltc2956-2). en is an active low output to control the turn-on/off of the system power. it may drive a voltage regulators active low enable input, or it may drive the gate of a p-channel mosfet directly. in the sleep state, the ltc2956-2 pulls this pin to v in through an internal 900 k resistor. the ltc2956-2 pulls en to gnd when the pushbutton is pressed or when the wake-up timer period is reached. this pin may be left open if unused. exposed pad ( qfn only): exposed pad. leave open or connect to device ground. gnd: device ground. long: long power down time selection input. connect a resistor from the long pin to gnd. together with the 100k resistor between the range and long pin, this adjusts the t long power down time (t long can be adjusted from 128ms to 16.4 s). if sleep is pulled high or pb is pulled low longer than t long , the part goes into shutdown mode. see applications information for details. offalert : off alert open drain output. the ltc2956 pulls this pin low for 1 second (t off ) whenever the part goes from run mode to shutdown mode. this pin can be connected to the interrupt input of the system ( with a pull-up resistor to the system supply) to alert the system before shutdown. it can also be used to drive an external led to give a visual indication. this pin may be left open if unused. onalert : on alert open drain output. the ltc2956 pulls this pin low whenever the part goes from shutdown mode to run mode. the pin stays low while the en pin is high and it can be used as an input to the system to request for initial boot up routine. this pin may be left open if unused. onmax: maximum awake timer capacitor input. connect a capacitor from this pin to gnd adjust the maximum allowed awake time (t onmax ) at 13.3 ms/nf. if this pin is left floating, the minimum awake time is limited to 8ms. tie this pin to gnd if unused. pb: pushbutton input. this is an active low input with a 900k pull-up to an internal 3.3 v regulated supply. con - nect one terminal of the pushbutton switch to this pin and connect the other terminal of a pushbutton switch to gnd. the pin may be left open if unused. pbout: debounced pushbutton open drain output. this pin follows the debounced pb input. this pin may be left open if unused. period: wake-up timer adjust input. connect a resistor from the period pin to gnd to adjust the wake-up timer period. see the application section for resistor selection information. range: wake-up timer range selection input. connect a resistor from the range pin to gnd and a 100 k resistor between the range and long pin to choose the wake- up timer period range setting. see application section for information about the resistor selection. sleep: sleep input. the sleep input is active during run mode. in the awake state, a falling edge at the sleep input will pull en low (en high) and put the system into the sleep state. if the sleep input goes high during the sleep state, the ltc2956 re-enters the awake state and pulls en high (en low) to turn on the system. holding sleep high for more than t long will force the system into the shutdown mode. if unused, tie sleep to gnd, and use the onmax pin to control the awake time. v in : power supply input (1.5v to 36v). ltc 2956 2956f
8 for more information www.linear.com/ltc2956 b lock diagra m + ? en (ltc2956-1) 900k m5 m1 m4 v cc v cc logic cmp1 900k 0.9v v cc i period period en (ltc2956-2) 900k r period m3 m2 v in pbout m6 onalert m7 offalert onmax m8 onmax timer 32ms debounce regulator f = 2khz ? 400k r period osc1 f = 1khz clk programmable divider 1, 4, ?2 22 osc2 + ? 0.4v pb + ? cmp2 1v sleep v in amp s3 s1 v cc long r long s2 v cc range r range gnd r com 2956 bd ltc 2956 2956f
9 for more information www.linear.com/ltc2956 o pera t ion figure 1. functional state diagram 2956 f01 awake state: en = 1 t period restart run mode from off state: onalert = 0 en = 1 power-on t sleep_min = true and (t period = true or pb = low or sleep = high) pb = high and t awake_min = true and (sleep = true or t onmax = true) t sleep_min = true and pb = low (pb = low for t long) or (t onmax = false and sleep = high for t long ) v long < v cc /2 v long > v cc /2 sleep state: en = 0 onalert = 1 offalert = 1 off state: en = 0 offalert = 1 onalert = 1 shutdown mode t off = true shutting off state: en = 1 offalert = 0 ltc 2956 2956f
10 for more information www.linear.com/ltc2956 o pera t ion o verview the ltc2956 is a micropower, highly configurable wake- up timer with pushbutton control. it controls power to a con - nected system to allow that system to perform a periodic task. after completing the task, the ltc2956 turns the system off to conserve power. figure 1 shows a simpli - fied state diagram of the ltc2956. the ltc2956 has two modes of operation: run mode and shutdown mode. in run mode, the ltc2956 cycles between the awake state and the sleep state with a period of t period . during the awake state the en pin is pulled high to turn the system on, and the t onmax timer runs. the ltc2956 exits the awake state when a falling edge is detected on the sleep pin or if the t onmax timer expires. the ltc2956 ignores any sleep pin transitions for t awake_ min ( typically 8 ms) after entering the awake state to ensure that the minimum on time is met. in the sleep state, the en output stays low, and the connected system turns off. the ltc2956 returns to the awake state if the t period time is reached, if the pushbutton (connected to the pb pin) is pressed, or if a logic high is detected on the sleep pin. the minimum duration for the sleep state is t sleep_min ( typically 128 ms), and any input or t period transitions during this time are ignored in order to allow the system supply to sufficiently discharge. shutdown mode is a very low power mode with the timer disabled, entered through a long press of the pushbutton or a long high pulse at the sleep input. this is useful for products that are shipped with their batteries installed. a short press on the pushbutton brings the ltc2956 back into run mode. the ltc2956 can be configured to start in either run or shutdown mode at power-up via the long pin (see the applications information section). shutdown mode consists of the shutting off state and the off state. the shutting off state occurs first during the transition from run mode to shutdown mode, and allows time for the system to perform any shutdown tasks before the en pin goes low in the off state. this state is indicated by the offalert pin pulling low and lasts for t off (typically 1 s). once the t off timer completes, the ltc2956 transitions to the off state , the en pin is pulled low and all timers are disabled, and the quiescent current drops to about 0.3a. when the ltc2956 returns to the run mode from the shutdown mode, it first enters the from off state to allow the connected system to run initialization tasks. this is indicated by the onalert pin pulling low. the en pin is pulled high to turn the connected system on. the ltc2956 turns the connected system on and off via the en pin. the ltc2956-1's active high en pin can be connected to the system supply run pin while the ltc2956-2's active low en pin can directly control the system supply through a p-channel mosfet. the wake-up timer period can be adjusted from 250 ms to 39 days via resistors at the period and range pins. the timing of the long pushbutton press and sleep pulse can be adjusted via resistors connected to the long pin. to minimize the quiescent current, the range, long, and period pins are biased only when the ltc2956 performs a configuration cycle. timer configuration is performed once every 6 6 seconds while the part is operating in run mode, and it is also performed following power- up and whenever the ltc2956 exits the shutdown mode. during configuration, the ltc2956 biases and reads the voltages at the range and long pins that are defined by external configuration resistors. see configuration section for more details. operations with sleep tied low (passive system) the ltc2956 is designed to control the power of both active and passive systems. with a passive system where the sleep pin is not managed by a microcontroller, the sleep pin can be tied low and a capacitor connected to the onmax pin determines the awake time. the minimum t onmax must be longer than the maximum expected time the system takes to complete its routine tasks. ltc 2956 2956f
11 for more information www.linear.com/ltc2956 o pera t ion figure 2 shows the timing waveform of a passive system application using a ltc2956-1. when the t period time is reached, the ltc2956 enters the awake state and pulls the en output high to turn on the system. the t period timer restarts and the t onmax timer starts running. once the t onmax timer expires, the ltc2956 re- enters the sleep state and pulls the en output low. the t period timer continues to run until the next period is reached. note that the t period timer is a digital counter inside the ltc2956, but it is illustrated as a simple ramp in all the figures in this data sheet. the t onmax timer counts using both the analog ramp on the onmax pin as well as an internal digital counter. it is also represented as a simple ramp in all the figures in this data sheet. the ltc2956 ignores the t onmax timer during the first 8 ms (t awake_ min ) after the en output is pulled high which limits the minimum t awake time to t awake_min (8ms typical). operations with sleep toggling (active system) with an active system, i.e. microprocessor based, the system can toggle the sleep pin to terminate the awake state immediately after it has completed a routine/periodic task. the ltc2956 will pull the en output low to turn off the system and enter the sleep state. this keeps the awake time to a minimum and helps minimize the drain on the system battery. figure 3 shows the timing waveform for an active sys - tem application . when the t period time is reached, the ltc2956-1 enters the awake state and pulls the en output high to turn on the system. the t period timer resets, and the t onmax timer start running. when the system has completed its periodic task, the ltc2956 is commanded to re-enter the sleep state by pulling the sleep pin low. the ltc2956 ignores both the sleep pin and t onmax timer during the t awake_min interval (8 ms typical) just after en goes high in order to guarantee that the system has stabilized. if the system completes its task before t awake_min is reached, it can toggle sleep continuously until the ltc2956 responds by pulling en low ( figure 4). if the system only toggles the sleep pin during t awake_min , the ltc2956 will not respond to the sleep pins falling edge(s) and remains in the awake state until the t onmax timer expires. if sleep is held low during the entire awake state pe - riod, the t onmax timer will timeout (figure 2) forcing the figure 2. operation with sleep tied low (passive system) tonmax en ov state t period timer sleep 2956 f02 sleep awake sleep awake t period t onmax t awake_min ignored t awake_min ignored ltc 2956 2956f
12 for more information www.linear.com/ltc2956 o pera t ion ltc2956-1 back into the sleep state. this t onmax watchdog timer feature is particularly useful in applications where an active systems software/firmware might encounter a stuck state or infinite loop thus preventing the system from excessively discharging the battery. power up the ltc2956 can be configured to power up automatically in either run or shutdown mode. this is done through the resistive divider setting at long pin. if the voltage on the long pin is configured to be greater than v cc /2 (see table 2), the ltc2956 enters the run mode ( see figure 5). if the voltage on the long pin is configured to be less than v cc /2, the ltc2956 enters the shutdown mode. in shutdown mode, a press of the push button is needed to transition the wake-up timer to the awake state and start the t period timer ( figure 6). t configuration is the system configuration time. it can last between 0.1 s to 1s. figure 3. operation with sleep toggling (active system) figure 4. toggling sleep continuously to enter sleep state tonmax en state t period timer sleep 2956 f03 sleep awake sleep awake t period t onmax t awake_min t awake_min ignored ignored tonmax en state t period timer sleep 2956 f04 sleep awake sleep awake t period t onmax t awake_min t awake_min ignored ignored ltc 2956 2956f
13 for more information www.linear.com/ltc2956 figure 5. wake-up timer goes into run mode after power-up (v long > v cc /2) figure 6. using the pb to start the wake-up timer o pera t ion v in tonmax en pb pbout onalert state t period timer sleep 2956 f05 sleep awake/from off off stop sleep awake sleep awake t period t period t period t sleep_min t configuration v in tonmax en pb pbout onalert state t period timer sleep 2956 f06 sleep awake/from off off stop sleep awake awake t period t period t db t configuration ltc 2956 2956f
14 for more information www.linear.com/ltc2956 o pera t ion the onalert open drain output is pulled low on the first awake state after exiting shutdown mode or when first powered up with v long > v cc /2 selected. this output can be used to notify an active system to perform a power-up initialization routine. shutting off with a long pb press the ltc2956 can be put into the low power shutdown mode by holding the push button pb input low for a du - ration longer than t long . the t long can be adjusted with the resistive divider at the long pin. figure 7 shows the timing during a long press. after the t long timeout, the part enters the shutting off state, and the offalert pin is pulled low. this state persists for t off (typically 1 s) thus allowing an active system to perform power down tasks before the enable output is pulled low. if the push button input is held low for a duration shorter than t long , the ltc2956 pulls en high but does not enter the shutting off state. once pb is released, the ltc2956 pulls the en output low if the sleep pin has pulsed once or if t onmax has timed out. this short press can be used to override the timer for early wake-up or it can be used with the pbout output to drive the software menu. pressing the pushbutton will always restart the t period timer. this is useful for manual synchronization of the wakeup time with an external event. when the external event occurs, a short press will turn on the system and the next turn on will be t period later. figure 7. holding pb low to enter shutdown mode held in reset by pb tonmax tlong en pb pbout offalert state t period timer sleep 2956 f07 off stop 0v start sleep awake shutting off t long t off t awake_min t db stop restart ignored ltc 2956 2956f
15 for more information www.linear.com/ltc2956 o pera t ion shutting off with a long sleep pulse in an active system, the ltc2956 can also be placed into the low power shutdown mode by holding sleep high for a duration greater than t long (figure 8). the offalert pin is pulled low when t long times out and remains low during the shutting off state. unlike a long push button press event, however, the t onmax timer remains enabled while sleep is pulled high. if t onmax is adjusted to be less than t long , a long sleep pulse can never trigger a shutdown. if the sleep pulse width is shorter than t long , the ltc2956 pulls the en output high but does not enter the shutting off state. once sleep goes low ( or if t onmax times out first), the en output goes low and the device enters the sleep state. pulling sleep high during the sleep state during the sleep state, the system can prompt the ltc2956 to enter the awake state by pulling sleep pin high even if the t period time is not up. this is illustrated in figure 9. the ltc2956 automatically restarts the t period timer when it enters the awake state in response to the logic high on the sleep input. upon entering the sleep state, the ltc2956 ignores all inputs for t sleep_min . this allows time for the systems power supply to fully discharge before it is allowed to turn on again. if the system pulls sleep high during t sleep_ min , the ltc2956 will wait until t sleep_min expires before re- entering the awake state. prolonging awake time the ltc2956 restarts the t period timer on every rising edge of en. this allows the awake time, t awake to vary from cycle to cycle while the turn-on period stay constant. however, if t awake extends toward or beyond t period , the next awake state may be delayed due to the minimum sleep duration, t sleep_min (128 ms typically). this t sleep_min ensures that the system supply has sufficient time to discharge. refer to figure 10, the second awake time is longer, resulting in a longer t period due to t sleep_min . tonmax t onmax must be longer than t long to allow transition to shutdown mode tlong en offalert state t period timer sleep 2956 f08 off stop 0v sleep awake shutting off t awake_min stop restart ignored t off t long figure 8. holding sleep high to enter shutdown mode ltc 2956 2956f
16 for more information www.linear.com/ltc2956 o pera t ion push button debounce and pbout the pb input is debounced by an internal timer. this debounced signal is available at the pbout open drain output, and it can be used to interrupt the system for software purposes such as choosing an option from a menu. the initial pbout pulse in awake state typically has a width of at least t pbout,first (128 ms typical) which allows the system sufficient time to respond just after powering up ( see figure 11). subsequent pbout pulses have a width of at least t pd_db (32 ms typical). note that if the systems microcontroller toggles sleep during t pbout,first , the ltc2956 will enter the sleep state and release pbout high without waiting for t pbout_first to complete. figure 9. pulling the sleep input high to enter awake state figure 10. prolonged awake state tonmax en state t period timer sleep 2956 f09 sleep awake sleep awake restart t sleep_min t sleep_min t awake_min ignored ignored tonmax en sleep state t period timer 2956 f10 sleep stop sleep awake prolonged turn-on time normal turn-on time sleep awake awake t period t period t period delay due to t sleep_min t sleep_min t sleep_min ltc 2956 2956f
17 for more information www.linear.com/ltc2956 o pera t ion a pplica t ions i n f or m a t ion figure 11. pbout echoing debounced pb held in reset by pb held in reset by pb held in reset by pb ignored ignored tonmax tlong en pb pbout offalert state sleep 2956 f11 stop 0v start stop start stop start sleep sleep awake t long t awake_min 32ms >32ms >32ms 32ms 32ms 32ms 32ms ignored t pbout_first configuration configuring the ltc2956 wake- up timer is a 3-step process. the wake-up timer period is determined by the resistor to ground at the period pin and the resistive divider at the range pin. then the minimum time required for a long push button press that forces the wake-up timer into the shutdown mode is determined by another resistive divider at the long pin. finally, the maximum awake time (t onmax ) is set with a capacitor to gnd at the onmax pin. the ltc2956 biases and samples the voltages or current at these pins once every 66 s while in run mode. the part also samples these pins following power-up and when in from off state. step 1: set t period with resistors at the period and range pins the required resistance value at the period pin to set the wake-up timer period can be determined as follows: r period = 400 ? t period /nrange [k/s] nrange is the internal clock divider and can be adjusted through the resistive divider at the range pin as shown in table 1. it is advisable to select an nrange value that yields the largest allowable r period value. the ltc2956s oscillator can run with values of r period ranging from 32.4k to 324k. for example, if a t period of 3 s is desired, r period = 75k and nrange = 16 could be used, but r period = 300 k and nrange = 4 is a better choice. ltc 2956 2956f
18 for more information www.linear.com/ltc2956 a pplica t ions i n f or m a t ion table 1. range programming recommended t period nrange r range * [k] 0.25s to 0.8s 1 9.76 0.4s to 3.2s 4 17.4 1.6s to 12.8s 16 26.1 6.4s to 51.2s 64 35.7 25.6s to 3.4min 256 47.5 102s to 14min 1,024 61.9 6.8min to 55min 4,096 78.7 27min to 3.6hr 16,384 100 1.82hr to 15hr 65,536 127 7.28hr to 58hr 262,144 162 29hr to 233hr 1,048,576 210 233hr to 932hr 4,194,304 280 *r com = 100k step 2: set required pushbutton time for shutdown with the resistive divider at the long pin the resistive divider at the long pin sets the t long value and power up mode as shown in table 2: table 2. t long programming t long power up mode r long * [k] 0.128s shutdown 9.76 0.256s shutdown 17.4 0.512s shutdown 26.1 1.024s shutdown 35.7 2.048s shutdown 47.5 4.096s shutdown 61.9 8.192s shutdown 78.7 16.384s shutdown 100 0.128s run 127 0.256s run 162 0.512s run 210 1.024s run 280 2.048s run 383 4.096s run 576 8.192s run 1020 16.384s run open *r com = 100k step 3: set maximum awake time using capacitor at onmax pin the value of c onmax can be determined by the equation: c onmax = t onmax ? 75 [nf/s] for example, a t onmax of 133 ms requires a 10 nf capacitor. high voltage powerpath? switching the high voltage en open drain output of the ltc2956-2 is designed to switch on/off an external power p-channel mosfet. this allows a user to connect / disconnect a power supply ( or battery) to its load by toggling the pb pin. figure 12 shows the ltc2956-2 switching a 24 v battery application. r6 slows down the turning on of m1 so as to limit the inrush current when needed to charge up the capacitor at v out . r5 is optional C it helps to speed up the turning off of m1 and also to keep m1 off when the input voltage rise time is fast. pb pin in a noisy environment the rugged pb pin is designed to operate in noisy en- vironments. t ransients below ground and above v in will not damage the pb pin. additionally, the pb pin can withstand esd hbm strikes of up to 25 kv. however, if the pushbutton switch is located physically far from the figure 12. switching 24v battery stack with external p-channel mosfet 2956 f12 pbout sleep offalert onalert pb period onmax gnd 12v lead-acid batteries m1 r5* 100k r6 100k d1 12v r period c1 100nf c out en v in range ltc2956-2 long v out c onmax 100k r long r range *r5 is optional + + + ltc 2956 2956f
19 for more information www.linear.com/ltc2956 ltc2956 pb pin, the parasitic capacitance and parasitic series inductance of the connecting cable or pcb trace can cause erratic behavior. the parasitic capacitance can couple external noise onto the pb input; placing a 0.1f capacitor at the pin lessens the impact of this coupling. the parasitic series inductance may cause unpredictable ringing at the pb pin; placing a 5.1 k resistor from the pb pin to the pushbutton switch reduces this ringing. figure 13 shows an example of this rc network at the pb pin. external pull-up resistor on pb pin an internal 900 k pull-up resistor on the pb pin makes an external pull-up resistor unnecessary. leakage current on the pb board trace, however, will affect the open circuit voltage on the pb pin. if the leakage is too large (>2a), the pb voltage may fall close to the threshold window. to mitigate the effect of board leakage, a 10 k pull-up resistor to v in can be used (see figure 14). a pplica t ions i n f or m a t ion enhancing v in ruggedness and reverse battery protection placing a 1 k resistor and a 10 nf capacitor at the v in pin can be used to enhance ruggedness in some applications (see figure 15). the peak operating current of the ltc2956 is less than 10a , creating an insignificant 10mv drop across the 1 k resistor. the 10 nf bypass capacitor in combination with the 1 k series resistor can protect against high voltage input transients that momentarily exceed the 40 v absolute maximum voltage rating of the v in pin. these can occur during hot-plugging into a battery or ac adapter. this r-c filter can also protect against transients that may appear on the pcb ground during large esd strikes at the pb pin. a 1 k resistor in series with the v in pin also allows the ltc2956 to withstand reverse-input voltages up to C40v. the ltc2956s v in pin is internally clamped to one diode voltage below ground and can tolerate up to 50 ma of reverse current. in applications where a battery could be inserted backwards, this resistor will limit the reverse current to a safe level thus allowing internal clamping to protect the pin. figures 16 a and 16 b shows some additional simple re - verse batter y protection circuits that use a single mosfet. figure 16 a illustrates a high-side pmos in the power path while figure 16 b shows a low-side nmos in the ground path. in each circuit, the mosfet body diode is orientated in the direction of normal current flow. when the battery is installed incorrectly, the nmos/pmos gate is low/high, thus preventing the circuit from turning on. when the battery is properly installed, the nmos/pmos fet gate voltage is taken high/low, and its channel shorts out the diode. figure 13. noisy pb trace figure 14. external pull-up resistor on pb pin for board leakage greater than 2a figure 15. enhancing v in ruggedness 2956 f13 v in pb v in ltc2956-1 gnd c5 0.1f trace capacitance trace inductance noise parasitics r8 5.1k 2956 f13 v in v in pb ltc2956-1/ ltc2956-2 gnd v cc >2a external board leakage current r8 10k 900k 0.9v 2956 f15 pb gnd r7 1k c1 10nf v in ltc2956-1 to load ltc 2956 2956f
20 for more information www.linear.com/ltc2956 a pplica t ions i n f or m a t ion interface with switching regulators the ltc2956-1 en pin can be connected directly to most switching regulator shutdown inputs. the en pin high level output voltage (v en (v oh )) is typically 3.3 v when v in > 3.5 v, and v en (v oh ) = v in C 0.1 v if v in <3.0 v. with a minimum v in of 1.5 v, v en(oh) is still higher than most shutdown thresholds. figure 17 shows one such ap- plication. the ltc3528 regulator is a boost converter with a shutdown high threshold of 0.88v (maximum). if a higher v en (v oh ) is required, an external pull-up resistor can be connected from the en pin to any higher voltage (<36 v). the en pin is designed to be able to sink at least 1 ma of current during turn-off, so this external pull-up resistor value must be selected to source less than 1 ma with en at 0 v. the ltc2956-1 en pin can also be connected to switching regulators with a run/ss pin. run/ss typically has a dual function of a shutdown threshold and soft - start. switching regulators optimized for figure 16a. pmos reverse battery protection figure 16b. nmos reverse battery protection 2956 f16a pb gnd r20 10k c1 100nf v in ltc2956 load + 2956 f16b pb gnd r20 10k c1 100nf v in ltc2956 load + 2956 f17 pbout en sleep offalert onalert pb period onmax gnd 499k 287k r period 4.7f 4.7h v in range ltc2956-1 long 22f 22pf v out 3.3v, 0.4a v in 1.5v to 3.2v c onmax 100k r long r range v in shdn pgood v out sw ltc3528 gnd fb figure 17. 2-cell with 3.3v output ltc 2956 2956f
21 for more information www.linear.com/ltc2956 a pplica t ions i n f or m a t ion figure 19. recommended layout for the v in bypass capacitor figure 18. enabling a micropower dc/dc converter pbout sleep offalert onalert pb period onmax gnd r period c in v in en range ltc2956-1 long v in 5.5v to 25v c onmax 100k r long r range v in lt8610 tr/ss en/uv intv cc 0.22f 5v at 2.5a 243k 1m 10pf l1 2.2h 47f 1f 10nf rt pg 18.2k sync bst sw bias fb gnd pgnd p 2956 f18 12 11 10 4 5 6 13 7 8 9 3 2 1 1 2 3 4 5 6 v in v in c vin gnd gnd 12 11 10 9 8 7 ltc2956ms ltc2956ud 2956 f19 c vin micro-power applications may require an external pull-up resistor and capacitor to create a soft-start ramp. the en pins integrated 900 k pull-up resistance and an external capacitor can be used for this purpose. figure 18 shows the ltc2956-1 en pin connected to an lt8610 step-down regulators en/uv pin. layout considerations figure 19 shows example pcb layouts for the qfn and ms packages with external components. position the bypass capacitor close to the ltc2956 on the same side of the pcb, and keep the traces short in order to give the best protection against pb pin esd transients. ltc 2956 2956f
22 for more information www.linear.com/ltc2956 typical a pplica t ions micropower led beacon 2956 ta02 pbout sleep offalert onalert pb period onmax gnd r period 250k c1 2.2f en v in range ltc2956-1 long 4.7f led1 2.2f c onmax 10nf cpo en1 en2 i led v in c2 + c2 ? 2.2f c1 + c1 ? ltc3216 gnd i set1 r com 100k r long 35.7k t long = 1s, t onmax = 133ms, t period = 10s 20k i set2 6.65k r range 26.1k + micropower overtemperature detector 2956 ta03 pbout sleep offalert onalert pb period onmax gnd t alert r period 100k c1 100nf en v in range ltc2956-2 long 100nf 470pf q1 mmbt 3904 m1 c onmax 10nf v ref vtl vth d + d ? ut v ptat v cc ltc2996 gnd r com 100k r long 35.7k t long = 1s, t onmax = 133ms, t sleep = 4s 20.5k r5 100k r6 100k 9.76k 147 k ot d1 bas116 r range 26.1k yellow led1 fault at 125c + ltc 2956 2956f
23 for more information www.linear.com/ltc2956 typical a pplica t ions 2956 ta04 pbout sleep offalert onalert pb period onmax gnd 25v m1 r sense 45m r7 1k ov = 29.4v uvh = 25.1v uvl = 24.6v 100k r period 88.7k c1 10nf c t 82nf c out 100f z1* env in range ltc2956-1 long m2 1a load out c onmax 82nf uvl shdn in gndsw ov uvh source status gate sense ltc4231 gnd r com 100k r long 383k r range 100k t long = 2s, t onmax = 1s, t period = 1 hour ltc2956 forced into off mode if ltc4231 fails to power-up within 1s of en rising-edge + 845 1.21m 5.9k 34.8k timer d1 bas116 micropower, reverse battery protected pushbutton controller and sleep timer with hot-swap controller micropower time-lapse photography intervalometer 2956 ta05 pbout sleep offalert onalert pb period onmax gnd r period 100k c1 100nf lithium cell shutter en v in range ltc2956-1 long c onmax 10nf r com 100k r long 35.7k t long = 1s, t onmax = 133ms 9.76k 26.1k 47.5k 78.7k 127k 210k r4[1:12] 17.4k 35.7k 61.9k 100k 162k 280k + t period 0.25s 1s 4s 16s 64s 256s 17 minutes 1 hour, 8 minutes 4 hours, 33 minutes 18 hours, 12 minutes 3 days, 49 minutes 12 days, 3 hours ltc 2956 2956f
24 for more information www.linear.com/ltc2956 p ackage descrip t ion please refer to http://www .linear.com/designtools/packaging/ for the most recent package drawings. 3.00 0.10 (4 sides) recommended solder pad pitch and dimensions 1.65 0.05 (4 sides) note: 1. drawing conforms to jedec package outline mo-220 variation (weed-1) 2. drawing not to scale 3. all dimensions are in millimeters 4. dimensions of exposed pad on bottom of package do not include mold flash. mold flash, if present, shall not exceed 0.15mm on any side 5. exposed pad shall be solder plated 6. shaded area is only a reference for pin 1 location on the top and bottom of package pin 1 top mark (note 6) 0.40 0.10 bottom view?exposed pad 1.65 0.10 (4-sides) 0.75 0.05 r = 0.115 typ 0.25 0.05 1 pin 1 notch r = 0.20 typ or 0.25 45 chamfer 11 12 2 0.50 bsc 0.200 ref 2.10 0.05 3.50 0.05 0.70 0.05 0.00 ? 0.05 (ud12) qfn 0709 rev ? 0.25 0.05 0.50 bsc package outline ud package 12-lead plastic qfn (3mm 3mm) (reference ltc dwg # 05-08-1855 rev ?) ltc 2956 2956f
25 for more information www.linear.com/ltc2956 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 representa- tion that the interconnection of its circuits as described herein will not infringe on existing patent rights. p ackage descrip t ion please refer to http://www .linear.com/designtools/packaging/ for the most recent package drawings. msop (ms12) 0213 rev a 0.53 0.152 (.021 .006) seating plane 0.18 (.007) 1.10 (.043) max 0.22 ?0.38 (.009 ? .015) typ 0.86 (.034) ref 0.650 (.0256) bsc 12 11 10 9 8 7 note: 1. dimensions in millimeter/(inch) 2. drawing not to scale 3. dimension does not include mold flash, protrusions or gate burrs. mold flash, protrusions or gate burrs shall not exceed 0.152mm (.006") per side 4. dimension does not include interlead flash or protrusions. interlead flash or protrusions shall not exceed 0.152mm (.006") per side 5. lead coplanarity (bottom of leads after forming) shall be 0.102mm (.004") max 0.254 (.010) 0 ? 6 typ detail ?a? detail ?a? gauge plane 5.10 (.201) min 3.20 ? 3.45 (.126 ? .136) 0.889 0.127 (.035 .005) recommended solder pad layout 0.42 0.038 (.0165 .0015) typ 0.65 (.0256) bsc 4.039 0.102 (.159 .004) (note 3) 0.1016 0.0508 (.004 .002) 1 2 3 4 5 6 3.00 0.102 (.118 .004) (note 4) 0.406 0.076 (.016 .003) ref 4.90 0.152 (.193 .006) ms package 12-lead plastic msop (reference ltc dwg # 05-08-1668 rev a) ltc 2956 2956f
26 for more information www.linear.com/ltc2956 ? linear technology corporation 2015 lt 0215 ? printed in usa linear technology corporation 1630 mccarthy blvd., milpitas, ca 95035-7417 (408) 432-1900 fax : (408) 434-0507 www.linear.com/ltc2956 r ela t e d p ar t s typical a pplica t ion part number description comments ltc2900 adjustable quad supply monitor adjustable reset, 10-lead msop and 3mm 3mm dfn packages ltc2904/ltc2905 pin-adjustable dual supply monitors adjustable reset and tolerance, 8-lead sot-23 and 3mm 2mm dfn packages ltc2909 precision triple/dual input uv, ov and negative voltage monitor 6.5v shunt regulator for high voltage operation ltc2910 octal positive/negative voltage monitor eight adjustable inputs (0.5v) ltc2914 quad uv/ov positive/negative voltage monitor adjustable uv and ov trip values ltc2950/ltc2951 pushbutton on/off controllers high voltage, low power pushbutton controllers with power-down fault detect kill timer ltc2952 pushbutton powerpath controller with supervisor automatic low loss switchover between dc sources ltc2953 pushbutton controller with voltage monitoring adjustable supply monitor with 200ms reset ltc2954 pushbutton on/off controller with p interrupt adjustable turn on/off timers ltc2955 pushbutton on/off controller with automatic turn-on 1.2a supply current ltc4411 2.6a low loss ideal diode in thinsot? no external mosfet, automatic switching between dc sources ltc4412hv powerpath controller in thinsot efficient diode-oring, automatic switching between dc sources, 3v to 36v ltc4055 usb power controller and li-ion charger automatic switchover, charges 1-cell li-ion batteries ltc4352 ideal diode controller with monitoring controls n-channel mosfet, 0v to 18v operation low i q timer with 10% duty cycle 2956 ta06 pbout sleep offalert onalert pb onmax gnd 113k 100nf t period = 280ms, 10% duty cycle env in v in period ltc2956-1 range long 9.76k 100k t onmax = 29ms, t period = 280ms 2.2nf ltc 2956 2956f

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