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may 2008 rev 1 1/38 38 L6924U usb compatible battery charger system with integrated power switch for li-ion/li-polymer features fully integrated solution, with power mosfet, reverse blocking diode, sense resistor, and thermal protection charges single-cell li-ion batteries from selectable ac adapter or usb input programmable charge current up to 1 a in ac adapter mode programmable charging current in usb mode for both high power and low power inputs 4.2 v output voltage with 1 % accuracy linear or quasi-pulse operating mode closed loop thermal control programmable end-of-charge current programmable charge timer (ntc) or (ptc) thermistor interface for battery temperature monitoring and protection status outputs to drive leds or to interface with a host processor small vfqfpn 16-leads package (3 mm x 3 mm) applications pdas, gps and mp3 players usb powered devices cellular phones digital still cameras standalone chargers wireless appliances vfqfpn16 table 1. device summary order codes package packaging L6924U vfqfpn16 tu b e L6924U013tr tape and reel www.st.com
contents L6924U 2/38 contents 1 device description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 2 pin description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 2.1 pin description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 3 maximum ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 3.1 absolute maximum ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 3.2 thermal data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 4 electrical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 5 block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 6 operation description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 6.1 linear mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 6.2 quasi-pulse mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 7 applications information: charging process . . . . . . . . . . . . . . . . . . . . 17 7.1 charging process flow chart . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 7.2 pre-charge phase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 7.3 ac or usb mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 7.4 fast charge phase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 7.5 end-of-charge current . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 7.6 recharge flow chart . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 7.7 recharge threshold . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 7.8 maximum charging time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
L6924U contents 3/38 8 application information: m onitoring and protection . . . . . . . . . . . . . . 23 8.1 ntc thermistor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 8.2 battery absence detection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 8.3 status pins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 8.4 shutdown . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 9 additional applications information . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 9.1 selecting input capacitor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 9.1.1 selecting output capacitor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 9.2 layout guidelines and demonstration board . . . . . . . . . . . . . . . . . . . . . . . 30 10 application idea: dual input management with ac priority . . . . . . . . 33 11 package mechanical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 12 revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
device description L6924U 4/38 1 device description the L6924U is a fully monolithic battery charger that safely charges single-cell li-ion/polymer battery from either usb power source or ac adapter. in usb mode, the L6924U supports both low power and high power mode. alternatively the device can charge from ac wall adapter. the ideal solution for space-limited portable products is produced in bcd6 technology and integrates the power mosfet, reverse blocking diode, sense resistor and thermal protection into a compact vfqfpn16 package. when an external voltage regulated adapter or usb port is used, the L6924U works in linear mode, and charges the battery in a constant current constant voltage (cc/cv) profile. moreover, when a current-limited adapter is used, the device can operate in quasi-pulse mode, dramatically reducing the power dissipation. regardless of the charging app roach, a closed loop thermal control avoids device overheating. the device has an operating input voltage ranging from 2.5 v to 12 v and it allows the user to program many parameters, such as fast-charge current, end-of- charge current threshold, and charge timer. the L6924U offers two open collector outputs for diagnostic purposes, which can be used to either drive two external leds or communicate with a host microcontroller. finally, the L6924U also provides other features like gas gauge function, check for battery presence, and monitoring and protecting the battery from unsafe thermal conditions. figure 2. basis application schematic figure 1. minimum size application board
L6924U pin description 5/38 2 pin description figure 3. pin connection (top view) 2.1 pin description table 2. pin functions pin i/o name pin description 1 i v in input pin of the power stage. 2 i v insns supply voltage pin of the signal circuitry. the operating input voltage range is from 2.5 v and 12 v, and the start-up threshold is 4 v. 3-4 o st 2 -st 1 open-collector status pins. 5 i t prg maximum charging time program pin. it must be connected with a capacit or to gnd to fix the maximum charging time, see chapter 7.8: maximum charging time on page 22 . 6 - gnd ground pin. 7 i sd shutdown pin. when connected to gnd enables the device; when floating disables the device. 8 i th temperature monitor pin. it must be connected to a resistor divider including an ntc or ptc resistor. the charge process is disabled if the battery temperature (sensed through the ntc or ptc) is out of the programmable temperature window see chapter 8.1: ntc thermistor on page 24 .
pin description L6924U 6/38 pin i/o name pin description 9 i isel switch from high power usb (i usb up to 500 ma) and low power usb (i usb/5 ) in usb mode. a low level sets the L6924U in low power mode and a high level sets the L6924U in high power mode. when the ac mode is selected, the isel pin must be connected to ground or left floating. 10 i v osns output voltage sense pin. it senses the battery voltage to control the voltage regulation loop. 11 o v out output pin. (connected to the battery) 12 o v ref external reference voltage pin. (r eference voltage is 1.8 v 2 %) 13 i/o i end charge termination pin. a resistor connected from this pin to gnd fixes the charge termination current threshold i endth : if i chg < i endth , the charge process ends. the voltage across the resistor is proportional to the current delivered to the battery (gas gauge function). 14 i mode select pin between ac adapter and usb port. a high level sets the L6924U in usb mode while a low level sets the L6924U in the ac adapter mode. when the ac adapter input is selected, the isel pin status does not affect the current set. 15 i i usb charge current program pin in usb mode: a resistor connected from this pin to ground fixes th e fast charge current value (i usb up to 500 ma) with an accuracy of 7 %. the usb high power/low power mode is selected with the isel pin. 16 i i ac charge current program pin in ac mode: a resistor connected from this pin to gnd fixes the fast charge current value (i ac up to 1 a) with an accuracy of 7 %. table 2. pin functions (continued)
L6924U maximum ratings 7/38 3 maximum ratings stressing the device above the rating listed in the ?absolute maximum ratings? table may cause permanent damage to the device. these are stress ratings only and operation of the device at these or any other conditions above those indicated in the operating sections of this specification is not imp lied. exposure to absolute ma ximum rating conditions for extended periods may affect device reliability. refer also to the st microelectronics sure program and other relevant quality documents. 3.1 absolute maximum ratings 3.2 thermal data table 3. absolute maximum ratings symbol parameter value unit v in input voltage -0.3 to 16 v v insns , sd input voltage -0.3 to v in v v out , v osns output voltage -0.3 to 5 v isel, mode input voltage -0.3 to 6 v st1, st2 output voltage -0.3 to v in v output current 30 ma v ref , th, i end , i ac , i usb , t prg , gnd -0.3 to 4 v all pins maximum withstanding volt age range test condition: cdfaec-q100-002- ?human body model? acceptance criteria: ?normal performance? 2 kv table 4. thermal data symbol parameter value unit r thja thermal resistance junction to ambient (1) 1. device mounted on demonstration board 75 c/w t stg storage temperature range ?55 to 150 c t j junction temperature range ?40 to 125 c p tot power dissipation at t = 70 c 0.67 w
electrical characteristics L6924U 8/38 4 electrical characteristics table 5. electrical characteristics (t j = 25 c, v in = 5 v, unless otherwise specified) symbol parameter test condition min typ max unit v in (1) operating input voltage 2.5 12 v start up threshold 4.1 v i in (1) supply current charging mode (r prg = 24 k ? )1.82.5ma shutdown mode (r prg = 24 k ? )6080a i sink current flowing from v out shutdown mode (r prg = 24 k ? )500na stand by mode (r prg = 24 k ? ) (v in = 2.5 v < v battery ) 500 na v out (1) battery regulated voltage 4.16 4.2 4.24 v i ac charge current with ac adapter input mode at gnd, r prg = 24 k ? 450 490 525 ma mode at gnd, r prg = 12 k ? 905 975 1045 ma i usb charge current with usb input mode at high, isel at high, r prg-usb = 24 k ? 450 490 525 ma mode at high, isel at low, r prg-usb = 2 4 k ? 86 96 105 i pre_ac pre-charge current with ac input mode at gnd, r ac = 24 k ? 41 49 56 ma i pre_usb pre-charge current with usb input (high power mode) mode at high, isel at high r usb = 24 k ? 41 49 56 ma pre-charge current with usb input (low power mode) mode at high, isel at low r usb = 24 k ? 7.6 9.6 11.4 ma v preth pre-charge voltage threshold 2.9 3.0 3.1 v i endth termination current r end = 3.3 k ? 12 16 20 ma t maxch (2) maximum charging time c tprg = 10 nf r[i prg ] = 24 k ? 3hours t maxch (2) maximum charging time accuracy c tprg = 5.6n f r prg = 24 k ? 10 % sd th shutdown threshold high 2 v shutdown threshold low 0.4 v st1,2 output status sink current status on 10 ma mode th mode threshold high 1.3 v mode threshold low 0.4 v isel th isel threshold high 1.3 v isel threshold low 0.4 v
L6924U electrical characteristics 9/38 symbol parameter test condition min typ max unit r ds(on) power mosfet resistance (3) charge current = 500 ma 280 380 m ? th ntc pin hot threshold voltage 10 12.5 15 %v ref ntc pin cold threshold voltage 40 50 60 %v ref 1. t j from -40 c to 125 c 2. guaranteed by design 3. device working in quasi pulse mode table 5. electrical characteristics (continued) (t j = 25 c, v in = 5 v, unless otherwise specified)
block diagram L6924U 10/38 5 block diagram figure 4. block diagram osc bg analog pre. ntc/ptc manag. vdd vdd vdd vosns vref 4.2v vref logic sd vin vins st1 st2 tprg th vpre vref vdd logic body control logic vbg iac iusb power mos mos driver charge control ca-va-ta reg uvlo thermal control gnd logic iend logic vout logic logic i fault i detect gas gauge isel mode
L6924U operation description 11/38 6 operation description the L6924U is a fully integrated battery charger that allows a very compact battery management system for space limited applications. it integrates in a small package, all the power elements: power mosfet, reverse blocking diode and the sense resistor. it normally works as a linear charger when powered from an external voltage regulated adapter or usb port. however, thanks to its very low minimum input voltage (down to 2.5 v) the L6924U can also work as a quasi-pulse charger when powered from a current limited adapter. to work in this condition, it is enough to set the device?s charging current higher than the adapter one ( chapter 6.2: quasi-pulse mode on page 14 ). the advantage of the linear charging approach is that the device has a direct control of the charging current and so the designer needn?t to rely on power source. however, the advantage of the quasi-pulse approach is that the power dissipated inside the portable equipment is dramatically reduced. with regard to the charging approach, the L6924U charges the battery in three phases: pre-charge constant current: in this phase (active when the battery is deeply discharged) the battery is charged with a low current (internally set to 10 % of the fast- charge current). fast-charge constant current: in this phase the device charges the battery with the maximum current (i ac for ac adapter mode, i usb for usb mode). constant voltage: when the battery voltage is close to the selected output voltage, the device starts to reduce the current, until the charge termination is done. the full flexibility is provided by: programmable fast-charging current (i ac or i usb ) ( chapter 7.4 on page 19 ). programmable end of charge current threshold (i endth ) ( chapter 7.5 on page 20 ). programmable end of charge timer (t maxch ) ( chapter 7.8 on page 22 ). if a ptc or ntc resistor is used, the device can monitor the battery temperature in order to protect the battery from operating in unsafe thermal conditions. beside the good thermal behavior guaranteed by low thermal resistance of the package, additional safety is provided by the built-in temperature control loop. the ic monitors continuously its junction temperature. when the temperature reaches approximately 120 c, the thermal control loop starts working, and reduces the charging current, in order to keep the ic junction temperature at 120 c. two open collector outputs are available for diagnostic purpose (status pins st1 and st2). they can be also used to drive external leds or to interface with a microcontroller. the voltage across the resistor connected between i end and gnd gives information about the actual charging current (working as a gas gauge), and it can be easily fed into a microcontroller adc. battery disconnection control is provided thanks to the differentiated sensing and forcing output pins. a small current is sunk and forced through v out . if v osns doesn?t detect the battery, the ic goes into a standby mode. figure 5 on page 12 shown the real charging profile of a li-ion battery, with a fast charge current of 450 ma (r 1 or r 2 = 26 k ? ).
operation description L6924U 12/38 figure 5. li-ion charging profile 6.1 linear mode when operating in linear mode, the device works in a way similar to a linear regulator with a constant current limit protection. it charges the battery in three phases: pre-charging current ("pre-charge" phase). constant current ("fast-charge" phase). constant voltage ("voltage regulation" phase). v adp is the output voltage of the upstream ac-dc adapter that is, in turn, the input voltage of the L6924U. if the battery voltage is lower than the default pre-charge voltage (v preth ), the pre-charge phase takes place. the battery is pre-charged with a low current , internally set to 10 % of the fast charge current. when the battery voltage goes higher than v preth , the battery is charged with the fast charge current (i usb or i ac according to the selection of the mode pin). finally, when the battery voltage is close to the regulated output voltage (4.2 v), the voltage regulation phase takes place and the charging current is reduced. the charging process ends when the charging current reaches the programmed value (i endth ) or when the charging timer expires. figure 6 shows the different phases. 0.000 0.050 0.100 0.150 0.200 0.250 0.300 0.350 0.400 0.450 0.500 0 200 400 600 800 1000 1200 charging time (sec) ichg (a) 0.000 0.500 1.000 1.500 2.000 2.500 3.000 3.500 4.000 4.500 vbatt (v) ichg vbatt
L6924U operation description 13/38 figure 6. typical charge curves in linear mode the worst case in power dissipation occurs when the device starts the fast-charge phase. in fact, the battery voltage is at its minimum value. in this case, there is the maximum difference between the adapter voltage and battery voltage, and the charge current is at its maximum value. the power dissipated is given by the following formula: equation 1 the higher the adapter voltage is, the higher the power dissipated is. the maximum power dissipated depends on the thermal impedance of the device mounted on board. end charge voltage-regulation phase power dissipation pre-charge phase fast-charge phase i preth i chg v oprgth battery voltage charge current adapter voltage v adp v preth chg bat adp dis i v v p ? = ) (
operation description L6924U 14/38 6.2 quasi-pulse mode the quasi-pulse mode can be used when the system can rely on the current limit of the upstream adapter to charge the battery. in this case, the fast charge current must be set higher than the current limit of the adapter. in this mode, the L6924U charges the battery with the same three phases as in linear mode, but the power dissipation is greatly reduced as shown in figure 7 . figure 7. typical charge curves in quasi pulse mode the big difference is due to the fact that the charge current is higher than the current limit of the adapter. during the fast-charge phase, the output voltage of the adapter drops and goes down to the battery voltage plus the voltage drop across the power mosfet of the charger, as shown in the following equation: equation 2 adapter voltage charge current power dissipation battery voltage end charge voltage regulation phase pre-charge phase fast-charge phase i lim ilim x rdson i preth i chg v preth v oprgth v adp mos bat adp in v v v v ? + = =
L6924U operation description 15/38 where ? v mos is given by: equation 3 where, i lim = current limit of the wall adapter, and r ds(on) = resistance of the power mosfet. the difference between the programmed charge current and the adapter limit should be high enough to minimize the r ds(on) value (and the power dissipation). this makes the control loop completely unbalanced and the power element is fully turned on. figure 8 shows the r ds(on) values for different output voltage and charging currents for an adapter current limit of 500 ma. figure 8. r ds(on) curves vs charging current and output voltage i r v lim on ds mos = ? ) (
operation description L6924U 16/38 neglecting the voltage drop across the charger ( ? v mos ) when the device operates in this condition, its input voltage is equal to the battery one, and so a very low operating input voltage (down to 2.5 v) is required. the power dissipated by the device during this phase is: equation 4 when the battery voltage approaches the final value, the charger gets back the control of the current, reducing it. due to this, the upstream adapter exits the current limit condition and its output goes up to the regulated voltage v adp . this is the worst case in power dissipation: equation 5 in conclusion, the advantage of the linear char ging approach is that the designer has the direct control of the charge current, and consequently the application can be very simple. the drawback is the high power dissipation. the advantage of the quasi-pulse charging method is that the power dissipated is dramatically reduced. the drawback is that a dedicated upstream adapter is required. 2 ) ( lim on ds ch i r p = lim bat adp dis i v v p ? = ) (
L6924U applications information: charging process 17/38 7 applications information: charging process 7.1 charging process flow chart figure 9. charging process flow chart
applications information: charging process L6924U 18/38 7.2 pre-charge phase the L6924U allows pre-charging the battery with a low current when the battery is deeply discharged. the battery is considered deeply discharged when its voltage is lower than a threshold (v preth ), internally set to 3 v. during pre-charge phase, the current (i prech ) has a default value equal to 10 % of the fast- charge current. a safety timer is also present. if the battery voltage does not rise over v preth within this time, a fault is given ( chapter 7.8: maximum charging time on page 22 ). if at the beginning of the charge process, the battery voltage is higher than the v preth , the pre-charge phase is skipped. 7.3 ac or usb mode the L6924U can charge batteries from both ac adapter and usb inputs. the choice of the power supply is done by driving the mode pin. a low level sets the L6924U in ac mode. the fast charge current is determined by the resistor connected to the i ac pin ( chapter 7.4: fast charge phase ), regardless the resistor connected to i usb . the same way, a high level at the mode pin sets the L6924U in usb mode. the fast charge current is determined by the resistor connected to the i usb pin ( chapter 7.4: fast charge phase ), regardless the resi stor connected to i ac . figure 10. mode pin selection i ac r ac L6924U mode ac adapter mode r usb i ac r ac L6924U mode usb mode r usb i usb v in i usb sets the fast charge current sets the fast charge current i ac r ac L6924U mode ac adapter mode r usb i ac r ac L6924U mode usb mode r usb i usb v in i usb sets the fast charge current sets the fast charge current
L6924U applications information: charging process 19/38 7.4 fast charge phase when the battery voltage reaches the pre-charge voltage threshold (v preth ), the L6924U enters the fast-charge phase. in this phase the device charges the battery wi th a constant current, whose value can be set by external resistors connected to i ac pin (ac adapter mode selected) or to i usb pin (usb mode) with an accuracy of 7 %. in ac adapter mode (mode pin low), the resistor r ac can be calculated as: equation 6 where v bg is the internal reference equal to 1.23 v, whereas k prg is a constant equal to 9500. figure 11. i ac pin connection in usb mode (mode pin high), the resistor r usb can be selected as: equation 7 where v bg and k prg have the same meaning and value above mentioned. the charge current in usb mode depends on r usb as well as the state of the isel pin. when this pin is high, the ?high-power? usb mode is selected and the charge current is determined by the equation 7. the charge current in usb mode should be set in accordance with the typical usb current capability (up to 500 ma). if isel is low, the ?low-power? usb mode is selected and the charge current is a fifth of the high-power usb mode charge current (up to 100 ma) during low power usb mode operation, since the charge current is reduced by one fifth, the maximum charging time is proportionally increased ( section 7.8: maximum charging time ). prg ac bg ac k i v r ? ? ? ? ? ? ? ? ? = prg usb bg usb k i v r ? ? ? ? ? ? ? ? ? =
applications information: charging process L6924U 20/38 figure 12. i usb pin connection regardless of the operation mode (ac adapter or usb), during the fast-charge phase the battery voltage increases until it reaches the programmed output voltage (4.2 v). a safety timer is also present. if the fa st-charge phase does not finish within the programmed time (see chapter 7.8: maximum charging time on page 22 ), a fault is given. 7.5 end-of-charge current when the charge voltage approaches the battery regulated voltage (internally set to 4.2 v), the voltage regulation phase takes place. the ch arge current starts to decrease until it goes below a programmable termination current, i endth . this current can be selected by an external resistor connected between the i end pin and gnd figure 13 , whose value can be calculated as: equation 8 figure 13. i end pin connection where k end is 1050; and v min is 50 mv. when the charge current goes below i endth , after a deglitch time, the status pins notify the end of charge and the charge process ends. this de-glitch time is expressed as: equation 9 where t maxch is the maximum charging time. ( chapter 7.8 on page 22 ) ? ? ? ? ? ? ? ? = endth end min end i k v r e 220 maxch deglitch t t =
L6924U applications information: charging process 21/38 i end pin is also used to monitor the charge current, because the current injected in r end is proportional to the charge current. the voltage across r end can be used by a microcontroller to check the charge status like a gas gauge. 7.6 recharge flow chart figure 14. recharge flow chart 7.7 recharge threshold when, from an end-of-charge condition, the battery voltage goes below the recharging threshold (v rch ), the device goes back in charging state. the value of the recharge threshold is 4.05 v.
applications information: charging process L6924U 22/38 7.8 maximum charging time to avoid the charging of a dead battery for a long time, the L6924U has the possibility can be set a maximum charging time starting from the beginning of the fast-charge phase. this timer can be set with a capacitor, connected between the t prg pin and gnd. the c tprg is the external capacitor (in nf) and is given by the following formula: equation 10 note: the maximum recommended c tprg value must be less than 50 nf. figure 15. t prg pin connection where, r prg = resistor which sets the current (r usb or r ac ) v ref = 1.8 v, k t = 279 x 10 5 , v bg = 1.23 v, and t maxch is the charging time given in seconds. if the battery does not reach the end-of-charge condition before the time expires, a fault is issued. also during the pre-charge phase th ere is a safety timer, given by: equation 11 if this timer expires and the batt ery voltage is still lower than v preth , a fault signal is generated, and the charge process finishes. note: when the device is charged in low power usb mode, in order to take into account the reduced charge current, the maximum charging time is proportionally increased (five times the maximum charging time calculated with r usb ) 9 10 ? ? ? ? ? ? ? ? ? ? ? ? = ref prg bg t maxch tprg v r v k t c e maxch maxprech t t = 8 1
L6924U application information: monitoring and protection 23/38 8 application information: monitoring and protection the L6924U uses a vfqfpn 3 mm x 3 mm 16-pin package with an exposed pad that allows the user to have a compact application and good thermal behavior at the same time. the L6924U has a low thermal resistance because of the exposed pad (approximately 75 c/w, depending on the board characteristi cs). moreover, a built-in thermal protection feature prevents the L6924U from having thermal issues typically present in a linear charger. thermal control is implemented with a ther mal loop that reduces the charge current automatically when the junction temperature reaches approximately 120 c. this avoids further temperature rise and keeps the junction temperature constant. this simplifies the thermal design of the application as well as protects the device a gainst over-temperature damage. the figure above shows how the thermal loop ac ts (with the dotted lines), when the junction temperature reaches 120 c. figure 16. power dissipation both linear and quasi pulse mode with thermal loop
application information: monitoring and protection L6924U 24/38 8.1 ntc thermistor the device allows designers to monitor the battery temperature by measuring the voltage across an ntc or ptc resistor. li-ion batteries have a narrow range of operating temperature, usually from 0 c to 50 c. this window is programmable by an external divider which is comprised of an ntc th ermistor connected to gnd and a resistor connected to v ref . when the voltage on the th pi n exceeds the minimum or maximum voltage threshold (internal window comparator), the device stops the charge process, and indicates a fault condition through the status pin. when the voltage (and thus, the temperature), returns to the window range, the device re- starts the charging process. moreover, there is a hysteresis for both the upper and lower thresholds, as shown in figure 18 . note: t bat = ok when the battery temperature between 0 c and 50 c figure 17. battery temperature control flow chart figure 18. voltage window with hysteresis on th v mi nth v maxth v mi nth_hys v maxth_hys 900mv 780mv 225mv 248mv voltage variation on th pin charge disable charge enable
L6924U application information: monitoring and protection 25/38 when the th pin voltage rises and exceeds the v minth = 50 % of v ref (900 mv typ), the L6924U stops the charge, and indicates a fault by the status pins. the device re-starts to charge the battery, only when the voltage at the th pin goes under v minth_hys = 780 mv (typ). for what concerns the high temperature limi t, when the th pin voltage falls under the v maxth = 12.5 % of v ref (225 mv typ.), the L6924U stops the charge until the th pin voltage rises at the v maxth_hys = 248 mv (typ.). when the battery is at the low temperature limit, the th pin voltage is 900 mv. the correct resistance ratio to set the lo w temperature limit at 0 c can be found with the following formula: equation 12 where rup is the pull-up resistor, v ref is equal to 1.8 v, and r ntc0c is the value of the ntc at 0 c. since at the low temperature limit v minth = 900 mv: equation 13 it follows that: equation 14 similarly, when the battery is at the high temperature limit, the th pin voltage is 225 mv. the correct resistance ratio to set the high temperat ure limit at 50 c can be found with the following formula: equation 15 figure 19. pin connection c ntc up c ntc ref minth r r r v v + = 0 0 c ntc up c ntc r r r + = 0 0 8 . 1 9 . 0 up c ntc r r = 0 c ntc up c ntc ref maxth r r r v v + = 50 50
application information: monitoring and protection L6924U 26/38 where r ntc50c is the value of the ntc at 50 c. considering v maxth = 225 mv it follows that: equation 16 consequently: equation 17 based on equations 14 and 17, it derives that: equation 18 the temperature hysteresis can be estimated by the formula: equation 19 where v th is the pin voltage threshold on the rising edge, v th_hys is the pin voltage threshold on the falling edge, and ntc t (- %/c) is the negative temperature coefficient of the ntc at temperature (t) expressed in % resistance change per c. for ntc t values, see the characteristics of the ntc manufacturers (e.g. the 2322615 series by vishay). at the low temperature, the hysteresis is approximately: equation 20 obviously at the high temperature hysteresis is: equation 21 c ntc up c ntc r r r + = 50 50 8 . 1 225 . 0 7 50 up c ntc r r = 7 50 0 = c ntc c ntc r r t th hys th th hys ntc v v v t ? = _ c ntc mv mv mv t c hys ? = 0 900 780 900 0 c ntc mv mv mv t c hys ? = 50 225 248 225 50
L6924U application information: monitoring and protection 27/38 considering typical values for ntc 0c and ntc 50c , the hysteresis is: equation 22 and: equation 23 if a ptc connected to gnd is used, the selection is the same as above, the only difference is when the battery temperature increases, the voltage on the th pin increases, and vice versa. for applications that do not need a monitor of the battery temperature, the ntc can be replaced with a simple resistor whose va lue is one half of the pull-up resistor r up . in this case, the voltage at the th pin is always inside the voltage window, and the charge is always enabled. 8.2 battery absence detection this feature provides a battery absent detection scheme to detect the removal or the insertion of the battery. if the battery is removed, the charge current falls below the i endth . at the end of de-glitch time, a detection current i detect , equal to 1 ma, is sunk from the output for a time of t detect . the device checks the voltage at the output. if it is below the v preth , a current equal to i detect is injected in the output capacitor for a t detect , and it is checked to see if the voltage on the output goes higher than v rch (4.05 v). if the battery voltage changes from v preth to v rch and vice versa in a t detect time, it means that no battery is connected to the charger. the t detect is expressed by: equation 24 c mv mv mv t c hys o 5 . 2 051 . 0 900 780 900 0 ? ? = c mv mv mv t c hys o 5 . 2 039 . 0 225 248 225 50 ? ? ? = 3 10 54 = maxch detect t t
application information: monitoring and protection L6924U 28/38 figure 20. battery absence detection flow chart battery absent detect low absent v bat > v preth fast charge detect high absent v bat > v rch pre charge no yes yes no detect low absent = a i sink is sunk for a t det from the battery detect high absent = a i inj is injected for a t det in the battery t det = 100ms (typ.) i sink = i inj = 1ma (typ.)
L6924U application information: monitoring and protection 29/38 8.3 status pins to indicate various charger status conditions , there are two open-colle ctor output pins, st1 and st2. these status pins can be used eith er to drive status leds , connected with an external power source, by a resistor, or to communicate to a host processor. 8.4 shutdown the L6924U has a shutdown pin; when the pin is connected to gnd, the device is operating. when the pin is left floating, the device enters the shutdown mode, the consumption from the input is dramatically reduced to 60 a (typ.). in this condition, v ref is turned off. figure 21. st1 and st2 connection with leds or microcontroller table 6. status leds indications charge condition description st1 st2 charge in progress when the device is in pre-charge or fast- charge status on off charge done when the charging current goes below the i endth off on stand by mode when the input voltage goes under v bat + 50 mv off off bad battery temperature when the voltage on the th pin is out of the programmable window, in accordance with the ntc or ptc thermistor on on battery absent when the battery pack is removed on on over time when t maxch or t maxprech expires on on
additional applications information L6924U 30/38 9 additional applications information 9.1 selecting input capacitor in most applications, a 1 f ceramic capacitor, placed close to the v in and v insn pins can be used to filter the high frequency noise. 9.1.1 selecting output capacitor typically, a 4.7 f ceramic capacitor placed close to the v out and v outsn pin is enough to keep voltage control loop stable . this ensures proper operation of battery absent detection in removable battery pack applications. 9.2 layout guidelines and demonstration board the thermal loop keeps the device at a constant temperature of approx imately 120 c which in turn, reduces i chg . however, in order to maximize the cu rrent capability, it is important to ensure a good thermal path. therefore, the ex posed pad must be properly soldered to the board and connected to the other layer through thermal vias. the recommended copper thickness of the layers is 70 m or more. the exposed pad must be electrically connected to gnd. figure 22 shows the thermal image of the board with the power dissipation of 1 w. in this instance, the temperature of the case is 89 c, but the junction temperature of the device is given by the following formula: equation 25 where the r thja of the device mounted on board is 75 c/w, the power dissipated is 1 w, and the ambient temperature is 25 c. in this case the junction temperature is: equation 26 amb diss a thj j t p r t + = ? c t j o 100 25 1 75 = + =
L6924U additional applications information 31/38 the v osns pin can be used as a remote sense; so , it should be connected as closely as possible to the battery. the demonstration board layout and schematic are shown in figure 24 and figure 25 . figure 22. thermal image of the demonstration board figure 23. demonstration board layout, top side figure 24. demonstration board layout, bottom side
additional applications information L6924U 32/38 figure 25. demonstration board schematic table 7. demonstration board components description name value description r1 24 k ? ac mode fast-charge current resistor. used to set the charging current in ac mode. r2 24 k ? usb mode fast-charge current resistor. us ed to set the charging current in usb mode. r3 3.3 k ? end of charge current resistor. used to set the termination current and, as a ?gas gauge? when measuring the voltage across on it. r4 1 k ? pull up resistor. connected between vref and th pin. r5 1 k ? pull up resistor. to be used wh en the st1 is connected with a led. r6 1 k ? pull up resistor. to be used wh en the st2 is connected with a led. rt1 470 ? if a ntc is not used, a half value of r4 must be mounted to keep the th voltage in the correct window. c1 1 f input capacitor. c2 4.7 f output capacitor. c3 10 nf t max capacitor. used to set t he maximum charging time. c4 1 nf v ref filter capacitor. d1 green st1 led. d2 red st2 led. j1 st2 jumper. using to select the led or the external microcontroller. j2 st1 jumper. using to select the led or the external microcontroller. j3 sd jumper. if open, the device is in sd mode; when closed, the device starts to work. j4 low power/ high power usb mode selection jumper. j5 ac/usb mode selection jumper.
L6924U application idea: dual input management with ac priority 33/38 10 application idea: dual input management with ac priority in some applications both ac adapter and usb power source may be available. figure 1 shows a possible schematic which prov ides the possibility to manage two power sources (ac/usb) and gives the priority to ac a dapter in case both sources are available at the same time. for simplicity, only the relevant parts of l6924 u for this application have been indicated. if only the ac adapter is available, since the ga tes of q1 and q2 are connected to ac, both mosfets are off. the ac adapter voltage is provided to the pin v in through the diode d1. the voltage of the pin v in is: a correct choice of this di ode is important to limit v diode and keeping v in as close as possible to ac. in this condition the pin mode is low. this sets the L6924U in ac mode and the battery is charged with the current programmed by r ac . when only the usb power source is available, both q1 and q2 switch on and the pin v in is connected to usb. the pin mode is connected to the drains of q1 and q2 and is high. therefore usb mode for L6924U is selected and the battery is char ged with a current in accordance with the resistor connected to the pin i usb (r usb ). the voltage of the pin v in is given by: the voltage drop across the mosfets must be kept as low as possible to avoid reducing too much the voltage of the pin v in . when both sources are present, this circuit give s the priority to the ac adapter. in fact, for v ac 5 v, surely both q1 and q2 are off and v in is connected to the ac adapter through d1. the pin mode is kept low and L6924U is set to ac mode. the use of two p-channel mosfets connected as shown in figure 1 is particularly useful in this case because they remove any path between the two power sources. diode ac in v v v ? = ( ) ? + ? =
application idea: dual input mana gement with ac priority L6924U 34/38 figure 26. dual input management L6924U v in mode ac usb r g r m q1 q2 d1 i ac i usb r ac r usb v out li-ion battery L6924U v in mode ac usb r g r m q1 q2 d1 i ac i usb r ac r usb v out li-ion battery
L6924U package mechanical data 35/38 11 package mechanical data in order to meet environmental requirements, st offers these devices in ecopack ? packages. these packages have a lead-free second level interconnect . the category of second level interconnect is marked on the package and on the inner box label, in compliance with jedec standard jesd97. the maximum ratings related to soldering conditions are also marked on the inner box label. ecopack is an st trademark. ecopack specifications are available at: www.st.com.
package mechanical data L6924U 36/38 table 8. vfqfpn16 (3 mm x 3 mm) mechanical data dim. mm. inch min typ max min typ max a 0.800 0.900 1.000 0.031 0.035 0.039 a1 0.020 0.050 0.001 0.002 a2 0.650 1.000 0.025 0.039 a3 0.250 0.010 b 0.180 0.230 0.300 0.007 0.010 0.012 d 2.875 3.000 3.125 0.113 0.120 0.123 d2 0.250 0.700 1.250 0.009 0.027 0.050 e 2.875 3.000 3.125 0.113 0.118 0.123 e2 0.250 0.700 1.250 0.009 0.027 0.049 e 0.450 0.500 0.550 0.017 0.019 0.021 l 0.300 0.400 0.500 0.011 0.015 0.019 ddd 0.080 0.003 figure 27. package dimensions e a a1 e k e2 b r d2 k l a3 d this drawing is not to scale
L6924U revision history 37/38 12 revision history table 9. document revision history date revision changes 20-may-2008 1 first release
L6924U 38/38 please read carefully: information in this document is provided solely in connection with st products. stmicroelectronics nv and its subsidiaries (?st ?) reserve the right to make changes, corrections, modifications or improvements, to this document, and the products and services described he rein at any time, without notice. all st products are sold pursuant to st?s terms and conditions of sale. purchasers are solely responsible for the choice, selection and use of the st products and services described herein, and st as sumes no liability whatsoever relating to the choice, selection or use of the st products and services described herein. no license, express or implied, by estoppel or otherwise, to any intellectual property rights is granted under this document. i f any part of this document refers to any third party products or services it shall not be deemed a license grant by st for the use of such third party products or services, or any intellectual property contained therein or considered as a warranty covering the use in any manner whatsoev er of such third party products or services or any intellectual property contained therein. unless otherwise set forth in st?s terms and conditions of sale st disclaims any express or implied warranty with respect to the use and/or sale of st products including without limitation implied warranties of merchantability, fitness for a parti cular purpose (and their equivalents under the laws of any jurisdiction), or infringement of any patent, copyright or other intellectual property right. unless expressly approved in writing by an authorized st representative, st products are not recommended, authorized or warranted for use in milita ry, air craft, space, life saving, or life sustaining applications, nor in products or systems where failure or malfunction may result in personal injury, death, or severe property or environmental damage. st products which are not specified as "automotive grade" may only be used in automotive applications at user?s own risk. resale of st products with provisions different from the statements and/or technical features set forth in this document shall immediately void any warranty granted by st for the st product or service described herein and shall not create or extend in any manner whatsoev er, any liability of st. st and the st logo are trademarks or registered trademarks of st in various countries. information in this document supersedes and replaces all information previously supplied. the st logo is a registered trademark of stmicroelectronics. all other names are the property of their respective owners. ? 2008 stmicroelectronics - all rights reserved stmicroelectronics group of companies australia - belgium - brazil - canada - china - czech republic - finland - france - germany - hong kong - india - israel - ital y - japan - malaysia - malta - morocco - singapore - spain - sweden - switzerland - united kingdom - united states of america www.st.com

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