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WS4508S 1000 ma , single li - ion battery charger descriptions the WS4508S is a complete constant - current / constant voltage linear charger for single cell lithium - ion batteries. no external sense resistor is needed, and no blocking diode is required due to the internal mosfet architecture. thermal feedback regulates the charge current to limit the die temperature during high power o peration or high ambient temper ature. the charge voltage is fixed at 4.2v, and the charge current can be programmed externally with a single resistor. the WS4508S automatically terminates the charge cycle when the charge current drops to 1/10 the programmed value after the final float voltage is reached. when the input supply (wall adapter or usb supply) is removed, the WS4508S automatically enters a low current state, dropping the batt ery drain current to less than 0.5 ua . the WS4508S can be put into shutdown mo de, reducing supply current to 45 u a (typ.) . the WS4508S is available in so p - 8l - ep package . standard product is pb - free. features ? programmable charge current up to 1000 ma ? over - temperature protection ? under voltage lockout protection ? automatic recharge threshold 4.05v (typ.) ? charge status output pin ? 2.9v trickle charge threshold ? soft - start limits inrush current applications ? wireless phone ? mp3/mp4 player ? bluetooth device so p - 8l - ep 1 2 3 4 5 6 7 8 temp prog gnd vcc bat stdbyb chgb ce expose pad gnd pin c onfiguration (top view) 1 2 3 4 5 6 7 8 w s 4 5 0 8 s y y w w ws 45 0 8 s = device code y y = year ww = week order i nformation devic e package shipping WS4508S - 8 /tr so p - 8l - ep 3000 /reel&tape 1 of 13 4008-318-123 sales@twtysemi.com http://www.twtysemi.com product specification 1 2 3 4 5 6 7 8 temp prog gnd vcc bat stdbyb chgb ce expose pad gnd 1 2 3 4 5 6 7 8 w s 4 5 0 8 s y y w w
pin d escription s block diagram m a 5 u a v a c 1 c 2 c 3 v c c 3 u a t o b a t 2 . 9 v p r o g g n d c a c h g b r 5 r 4 r 3 0 . 1 v 1 v r 1 r 2 s h d n b t a t d i e 1 6 5 c 1 x 1 0 0 0 x v c c b a t s t d b y b c 4 c 5 i n v c e t e m p 8 0 % v c c 4 5 % v c c r e f 1 . 2 v pin number pin name function 1 temp batery temperature sense pin. when the battery temperature is too high or too low, the charging current will be terminated. 2 prog charge c ur rent setting , c harge c urrent m onitor and s hutdown p in. the charging current is given by i bat = ( 1/r prog )*1000. the chip will be shutdown when prog pin floating 3 gnd ground 4 vcc power supply 5 bat charge current output. provides charge current to the ba ttery and regulates the final float voltage to 4.2v. 6 stdbyb charge co mplete status output. low level status for charge finished. in addition, stdbyb p in will be in a high impedance state . 7 chgb open - drain charge status output. when the battery is cha rging, the chgb pin is pulled low. when the charge cycle is completed or vcc is removed, the chgb is forced high impedance. 8 ce chip enable. active high. WS4508S 2 of 13 4008-318-123 sales@twtysemi.com http://www.twtysemi.com product specification m a 5 u a v a c 1 c 2 c 3 v c c 3 u a t o b a t 2 . 9 v p r o g g n d c a c h g b r 5 r 4 r 3 0 . 1 v 1 v r 1 r 2 s h d n b t a t d i e 1 6 5 c 1 x 1 0 0 0 x v c c b a t s t d b y b c 4 c 5 i n v c e t e m p 8 0 % v c c 4 5 % v c c r e f 1 . 2 v
typical applications 4 8 7 6 3 v c c c e c h g b s t d b y b g n d b a t n t c l i - l o n r 1 r 2 1 0 u f 1 0 u f v c c l e d 1 l e d 2 r 3 r 4 t e m p b a t r p r o g 1 2 5 w s 4 5 0 8 s f igure1. typical a pplications w/t led i ndicate circuit 4 8 7 6 3 v c c c e c h g b s t d b y b g n d b a t l i - l o n 1 0 u f 1 0 u f v c c r 3 r 4 t e m p b a t r p r o g u p 1 2 5 w s 4 5 0 8 s figure2. t ypical a pplications w/t m icroprocessor d etect circuit WS4508S 3 of 13 4008-318-123 sales@twtysemi.com http://www.twtysemi.com product specification 4 8 7 6 3 v c c c e c h g b s t d b y b g n d b a t n t c l i - l o n r 1 r 2 1 0 u f 1 0 u f v c c l e d 1 l e d 2 r 3 r 4 t e m p b a t r p r o g 1 2 5 w s 4 5 0 8 s 4 8 7 6 3 v c c c e c h g b s t d b y b g n d b a t l i - l o n 1 0 u f 1 0 u f v c c r 3 r 4 t e m p b a t r p r o g u p 1 2 5 w s 4 5 0 8 s
electronics characteristics ( vcc=5v, ta=25 o c , unless otherwise noted) symbol parameter condition mi n. typ. max. unit i splychrg charge mode supply current r prog = 10 k 170 2 40 2 000 u a i batchrg charge mode battery current r prog = 1 k 9 0 0 1000 1 1 0 0 ma r prog = 10 k 80 93 110 ma v progchrg prog pin voltage r prog = 10 k 0.93 1.00 1.07 v i spl ystby standby mode supply current charge terminated 140 500 ua i batstby standby mode battery current charge terminated 0 - 2.5 - 6 ua i splyasd shutdown mode supply current v cc WS4508S 4 of 13 4008-318-123 sales@twtysemi.com http://www.twtysemi.com product specification
symbol parameter condition min. typ. max. unit v temp_en battery temperature detect function threshold volta ge temp pin rising(vcc=5v) temp pin falling(vcc=5v) 0.18 0.29 0.2 0.32 v v v temp_h temp pin high threshold voltage temp pin rising(vcc=5v) temp pin falling(vcc=5v) 72 80 73.5 82 %vcc %vcc v temp_ l temp pin low threshold voltage temp pin rising(vcc=5v) t emp pin falling(vcc=5v) 43 48.5 45 50 %vcc %vcc absolute maximum ratings parameter symbol rating unit supply voltage vcc - 0.3~ 8 v prog voltage v prog - 0.3~vcc v bat voltage v bat - 0.3~ 8 v chgb voltage v chgb - 0.3~vcc v prog pin current i prog 10 00 ma junction temperature tj 150 o c operation temperature top - 45~85 o c storage temperature tsg - 65~125 o c lead temperature (soldering 10s) 260 o c WS4508S 5 of 13 4008-318-123 sales@twtysemi.com http://www.twtysemi.com product specification
typical characteristics (ta=25 o c, unless otherwise noted) 4.5 5.0 5.5 6.0 6.5 0.0 0.2 0.4 0.6 0.8 1.0 1.2 v bat =4.0v r prog =2k r prog =1k v prog (v) v cc (v) -25 0 25 50 75 100 0.90 0.92 0.94 0.96 0.98 1.00 1.02 1.04 1.06 v cc =5.0v v bat =4.0v r prog =1k v prog (v) temperature( o c) prog pin voltage vs. supply voltage prog pin voltage vs. temperature 0.0 0.2 0.4 0.6 0.8 1.0 1.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2 i bat (a) v prog (v) v cc =5.0v r prog =1k -50 -25 0 25 50 75 100 3.2 3.3 3.4 3.5 3.6 3.7 3.8 3.9 4.0 4.1 4.2 4.3 v cc =5v v bat =4.3v v prog =0v i prog (ua) temperature( o c) charge current vs. prog pin voltage prog p in pull - up c urrent vs . temperature 2.0 2.1 2.2 2.3 2.4 2.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 v cc =5.0v v bat =4.3v i prog (ua) v prog (v) 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 -2000 -1600 -1200 -800 -400 0 i prog (ua) v prog (v) v cc =5.0v v bat =4.3v prog p in pull - up c urrent vs. prog p in v oltage prog p in c lamp c urrent vs. prog p in v oltage WS4508S 6 of 13 4008-318-123 sales@twtysemi.com http://www.twtysemi.com product specification 4.5 5.0 5.5 6.0 6.5 0.0 0.2 0.4 0.6 0.8 1.0 1.2 v bat =4.0v r prog =2k r prog =1k v prog (v) v cc (v) -25 0 25 50 75 100 0.90 0.92 0.94 0.96 0.98 1.00 1.02 1.04 1.06 v cc =5.0v v bat =4.0v r prog =1k v prog (v) temperature( o c) 0.0 0.2 0.4 0.6 0.8 1.0 1.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2 i bat (a) v prog (v) v cc =5.0v r prog =1k -50 -25 0 25 50 75 100 3.2 3.3 3.4 3.5 3.6 3.7 3.8 3.9 4.0 4.1 4.2 4.3 v cc =5v v bat =4.3v v prog =0v i prog (ua) temperature( o c) 2.0 2.1 2.2 2.3 2.4 2.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 v cc =5.0v v bat =4.3v i prog (ua) v prog (v) 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 -2000 -1600 -1200 -800 -400 0 i prog (ua) v prog (v) v cc =5.0v v bat =4.3v
4.6 4.8 5.0 5.2 5.4 5.6 5.8 6.0 4.15 4.16 4.17 4.18 4.19 4.20 4.21 4.22 4.23 v float (v) v cc (v) r prog =2k -25 0 25 50 75 100 4.12 4.14 4.16 4.18 4.20 4.22 4.24 4.26 4.28 v cc =5.0v r prog =1k v float (v) temperature( o c) bat p in o utput f loat v oltage vs. supply v oltage bat p in o utput f loat v oltage vs. temperature 0.0 0.2 0.4 0.6 0.8 1.0 4.10 4.12 4.14 4.16 4.18 4.20 4.22 4.24 4.26 v cc =5v v float (v) i bat (a) 0 1 2 3 4 5 6 0 3 6 9 12 15 18 21 24 27 30 i chrg (ma) v chrg (v) v cc =5.0v v bat =4.0v r prog =1k bat pin output float voltage vs. charge curre nt chgb pin current vs. chgb pin voltage -25 0 25 50 75 100 0 5 10 15 20 25 i chrg (ma) temperature( o c) v cc =5.0v v bat =4.0v v chrg =1.0v r prog =1k -25 0 25 50 75 100 75 78 81 84 87 90 93 96 i trikl (ma) temperature( o c) v cc =5.0v v bat =2.5v r prog =1k chgb pin current vs. temperature trickle charge current vs. temperature WS4508S 7 of 13 4008-318-123 sales@twtysemi.com http://www.twtysemi.com product specification 4.6 4.8 5.0 5.2 5.4 5.6 5.8 6.0 4.15 4.16 4.17 4.18 4.19 4.20 4.21 4.22 4.23 v float (v) v cc (v) r prog =2k -25 0 25 50 75 100 4.12 4.14 4.16 4.18 4.20 4.22 4.24 4.26 4.28 v cc =5.0v r prog =1k v float (v) temperature( o c) 0.0 0.2 0.4 0.6 0.8 1.0 4.10 4.12 4.14 4.16 4.18 4.20 4.22 4.24 4.26 v cc =5v v float (v) i bat (a) 0 1 2 3 4 5 6 0 3 6 9 12 15 18 21 24 27 30 i chrg (ma) v chrg (v) v cc =5.0v v bat =4.0v r prog =1k -25 0 25 50 75 100 0 5 10 15 20 25 i chrg (ma) temperature( o c) v cc =5.0v v bat =4.0v v chrg =1.0v r prog =1k -25 0 25 50 75 100 75 78 81 84 87 90 93 96 i trikl (ma) temperature( o c) v cc =5.0v v bat =2.5v r prog =1k
4.5 5.0 5.5 6.0 6.5 50 60 70 80 90 100 i bat (ma) v cc (v) r prog =1k v bat =2.5v -25 0 25 50 75 100 2.80 2.82 2.84 2.86 2.88 2.90 2.92 2.94 2.96 2.98 3.00 v cc =5.0v r prog =1k v trikl (v) temperature( o c) trickle charge current vs. supply voltage trickle charge threshold vs. temperature 4.5 5.0 5.5 6.0 6.5 0 200 400 600 800 1000 1200 i bat (a) v cc (v) r prog =1k v bat =4v -25 0 25 50 75 100 4.00 4.02 4.04 4.06 4.08 4.10 4.12 4.14 4.16 v cc =5.0v r prog =1k v rechrg (v) temperature( o c) charge current vs. supply voltage recharge voltage threshold vs. temperature -25 0 25 50 75 100 125 150 175 200 200 400 600 800 1000 1200 i bat (ma) temperature( o c) v cc =5v v bat =4v r prog =1k 2.5 2.7 2.9 3.1 3.3 3.5 3.7 3.9 4.1 4.3 4.5 0 100 200 300 400 500 600 700 800 900 1000 1100 1200 v cc =5.0v r prog =1k i bat (ma) v bat (v) -40 o 25 o 85 o charge current vs. temperature fully charge period waveform WS4508S 8 of 13 4008-318-123 sales@twtysemi.com http://www.twtysemi.com product specification 4.5 5.0 5.5 6.0 6.5 50 60 70 80 90 100 i bat (ma) v cc (v) r prog =1k v bat =2.5v -25 0 25 50 75 100 2.80 2.82 2.84 2.86 2.88 2.90 2.92 2.94 2.96 2.98 3.00 v cc =5.0v r prog =1k v trikl (v) temperature( o c) 4.5 5.0 5.5 6.0 6.5 0 200 400 600 800 1000 1200 i bat (a) v cc (v) r prog =1k v bat =4v -25 0 25 50 75 100 4.00 4.02 4.04 4.06 4.08 4.10 4.12 4.14 4.16 v cc =5.0v r prog =1k v rechrg (v) temperature( o c) -25 0 25 50 75 100 125 150 175 200 200 400 600 800 1000 1200 i bat (ma) temperature( o c) v cc =5v v bat =4v r prog =1k 2.5 2.7 2.9 3.1 3.3 3.5 3.7 3.9 4.1 4.3 4.5 0 100 200 300 400 500 600 700 800 900 1000 1100 1200 v cc =5.0v r prog =1k i bat (ma) v bat (v) -40 o 25 o 85 o
operation info r mation s the WS4508S is a single cell lithium - ion batt ery charger using a constant - current / constant - voltage algo rithm. it can deliver up to 1 a of charge current (using a good thermal pcb layout) with a final float voltage accuracy of 1%. the WS4508S includes an internal p - channel power mosfet and thermal r egulation circuitry. no blocking diode or external current sense resistor is required; thus, the basic charger circuit requires only two external components. furthermore, the WS4508S is cap able of operating from a usb power source. normal c harge c ycle a c harge cycle begins when the voltage at the vcc pin rises above the uvlo threshold level and a 1% program resistor is connected from the prog pin to ground or when a battery is connected to the charger output. if the bat pin is less than 2.9v, the charger e nters trickle charge mode. in this mode, the WS4508S supplies approximately 1/10 the programmed charge current to bring the battery voltage up to a safe level for full current charging. when the bat pin voltage rises above 2.9v, the charger enters constant - current mode, where the programmed charge current is supplied to the battery. when the bat pin approaches the final f loat voltage, the WS4508S enters constant - voltage mode and the charge current begins to decrease. t he charge cycle ends w hen the prog volt age is less than 100mv . programming charge current the charge current is programmed using a single resistor from the prog pin to ground. the battery charge current of constant current mode is 1000 times the current out of the prog pin. the program resist or and the charge current of constant current are calculated using the following equations: 1000 r v 1 i prog chrg ? ? ? ? ? ? ? ? ? ? charge t ermination a charge cycle is terminated when th e charge current falls to 1/10 of the programmed value after the final float voltage i s reached. this condition is detected by using an internal, filtered comparator to monitor the prog pin. when the prog pin voltage fal ls below 100mv for longer than t term (typically 1ms), charging is terminated. the charge curren t is latched off and the ws 4508s enters standby mode, where the i nput supply current drops to 1 30u a. (note: c c /10 termination is disabled in trickle charging mode and thermal limiting modes ). when charging, transient loads on the bat pin can cause the prog pin to fall below 100mv for short periods of time before the dc char ge current has dropped to 1/10 of the programmed value. the 1ms filter time (t term ) on the termination comparator ensures that transient loads of this nature do not result in premature charge cycle termination. o nce the average c harge current drops below 1/10 of t he programmed value, the WS4508S terminates the charge cycle and ceases to provide any current through the bat pin , the chip will be put into standby mode . in this state, all loads on the bat pin must be supplied by the battery . t r i c k l e c h a r g e m o d e c h a r g e c u r r e n t : c c / 1 0 c h g b : p u l l d o w n s t d b y b : h i g h i m p e d a n c e c o n s t a n t - c u r r e n t m o d e c h a r g e c u r r e n t : c c c h g b : p u l l d o w n s t d b y b : h i g h i m p e d a n c e c o n s t a n t v o l t a g e m o d e c h a r g e c u r r e n t : d e c r e a s e c h g b : p u l l d o w n s t d b y b : h i g h i m p e d a n c e s t a n d b y m o d e c h a r g e c u r r e n t : 0 a i c c : 1 3 0 u a i b a t : - 2 . 5 u a c h g b : h i g h i m p e d a n c e s t d b y b : p u l l d o w n s h u t d o w n m o d e c h a r g e c u r r e n t : 0 a i c c : 5 0 u a i b a t : - 1 u a c h g b : h i g h i m p e d a n c e s t d b y b : h i g h i m p e d a n c e b a t < 2 . 9 v 4 . 2 < b a t < 2 . 9 v b a t > = 4 . 2 v p r o g < 1 0 0 m v p r o g f l o a t i n g o r u v l o p r o g r e c o m m e n d o r u v l o s t o p p o w e r o n b a t < 4 . 0 5 v figure3. state diagram of a typical charge cycle WS4508S 9 of 13 4008-318-123 sales@twtysemi.com http://www.twtysemi.com product specification 1000 r v 1 i prog chrg u ? ? 1 ? t r i c k l e c h a r g e m o d e c h a r g e c u r r e n t : c c / 1 0 c h g b : p u l l d o w n s t d b y b : h i g h i m p e d a n c e c o n s t a n t - c u r r e n t m o d e c h a r g e c u r r e n t : c c c h g b : p u l l d o w n s t d b y b : h i g h i m p e d a n c e c o n s t a n t v o l t a g e m o d e c h a r g e c u r r e n t : d e c r e a s e c h g b : p u l l d o w n s t d b y b : h i g h i m p e d a n c e s t a n d b y m o d e c h a r g e c u r r e n t : 0 a i c c : 1 3 0 u a i b a t : - 2 . 5 u a c h g b : h i g h i m p e d a n c e s t d b y b : p u l l d o w n s h u t d o w n m o d e c h a r g e c u r r e n t : 0 a i c c : 5 0 u a i b a t : - 1 u a c h g b : h i g h i m p e d a n c e s t d b y b : h i g h i m p e d a n c e b a t < 2 . 9 v 4 . 2 < b a t < 2 . 9 v b a t > = 4 . 2 v p r o g < 1 0 0 m v p r o g f l o a t i n g o r u v l o p r o g r e c o m m e n d o r u v l o s t o p p o w e r o n b a t < 4 . 0 5 v
the WS4508S constantly monitors the bat pin voltage in standby mode. if this voltage drops below the 4.05v recharge threshold (v rechrg ), another charge c ycle begins and current is once again supplied to the battery. the state diagram of a typi cal charge cycle is as figure3. charge s tatus i ndicator WS4508S has two open - drain status indicator output chgb and stdby b . chgb is pull - down when the bl4056 in a c harge cycle. in other status chgb is in high impedance. chgb and stdby b are all in high impedance when the battery out of the normal temperature. represent in failure state, when temp pin in typical connecting, and the charger with no battery: red led and green led all dont light. the battery temperature sense function is disabled by connecting temp pin to gnd. if batte ry is not connected to charger and the bat pin connects a 10f capacitor, the frequency of chgb flicker about 1 - 4 s. charger state red chgb green stdbyb c harging light dark battery in full state dark light uvlo, battery temperature is outside temp range, battery is not connected(use temp) dark dark bat pin is connected to 10uf and no battery mode (temp=gnd) green led bright red led flicke r and the frequency is 1~4s thermal limiting an internal thermal feedback loop reduces the programmed charge current if the die temperature attempts to rise above a preset value of approximately 165 . this feature protects the WS4508S from excessive temp erature and allows the user to push the limits of the power handling capability of a given circuit board without risk of damaging the WS4508S . the charge current can be set according to typical (not worst - case) ambient temperature with the assurance that t he charger will automatically reduce the current in worst - case conditions. battery temperature sensing to prevent the damage caused by the very high or very low temperature done to the battery pack, the WS4508S continuously senses the battery pack temper ature by measuring the voltage at temp pin determined by the voltage divider circuit and the batterys internal ntc thermistor as shown in figure 1. the WS4508S compares the voltage at temp pin (v temp ) against its internal v low and v high thresholds to dete rmine if charging is allowed. in WS4508S , v low is fixed at 45% v cc , while v high is fixed at 80% v cc . if v temp v high , it indicates that the battery temperature is too high or too low and the charge cycle is suspended. when the v temp is betwee n v low and v high , charg ing cycle resume s. the battery temperature sens ing function can be disabled by connecting the temp pin to gnd. selecting r1 and r2 the values of r1 and r2 in the application circuit (figure1) can be determined according to the assum ed temperature monitor range and thermistor s values. the follows is an example: assume temperature monitor range is t l t h , ( t l t h ) ; the thermistor in battery has negative temperature coefficient ( ntc ), r tl is thermistor s resistance at t l r th is the resistance at t h so r tl r th then a t temperature t l , the voltage at temp pin is: cc tl 2 1 tl 2 templ v r || r r r || r v ? ? ? at temperature t h , the voltage at temp pin is: cc th 2 1 th 2 temph v r || r r r || r v ? ? ? because v templ =v high =k 2 v cc (k 2 =0.8) v temph =v low =k 1 v cc (k 1 =0.45) then we can have: WS4508S 10 of 13 4008-318-123 sales@twtysemi.com http://www.twtysemi.com product specification cc tl 2 1 tl 2 templ v r || r r r || r v u cc th 2 1 th 2 temph v r || r r r || r v u
2 1 th tl 1 2 th tl 1 k )k r (r ) k (k r r r ? ? ? ? ? ) k k (k r ) k k (k r ) k (k r r r 2 1 2 th 2 1 1 tl 1 2 th tl 2 ? ? ? ? ? ? ? ? likewise, for positive temperature coefficient thermistor in battery, we have r th r tl and we can calculate: 2 1 tl th 1 2 tl th 1 k )k r (r ) k (k r r r ? ? ? ? ? ) k k (k r ) k k (k r ) k (k r r r 2 1 2 tl 2 1 1 th 1 2 tl th 2 ? ? ? ? ? ? ? ? we can conclude that temperature monitor range is indepe ndent of power supply voltage v cc and it only depends on r1, r2, r tl and r th : the values of r th and r tl can be found in relat ed battery handbook or deduced from testing data. in actual application, if only one terminal temperature is concerned (normally pro tecting overheating), there is no need to use r2 but r1. it becomes very simple to calculate r1 in this case. undervoltage lockout (uvlo) an internal undervoltage lockout circuit monitors the input voltage and keeps the charger in shutdown mode until v cc rises above the undervoltage lockout threshold. the uvlo circuit has a built - in hysteresis of 2 5 0mv. furthermore, to protect against reverse current in the power mosfet, the uvlo circuit keeps the charger in shutdown mode if v cc falls to within 5 0mv of the battery voltage. if the uvlo comparator is tripped, the charger will not come out of shutdown mode until v cc rises 1 2 0mv ab ove the battery voltage. manual shutdown at any point in the charge cycle, the WS4508S can be put into shutdown mode by removing r prog thus floating the prog pin. this reduces the battery drain current to less than 1u a and the supply current to less than 50 u a. a new charge cycle can be initiated by reconnecting the program resistor . the ce pin can also shutdown the charger when the ce pin voltage is less the 0.4v. to restart the charge cycle, the ce pin voltage must be larger than 1.2v. in manual shutdown, the ch g b pin and the stdbyb pin are in a high impedance state if the WS4508S is in manual shutdown mode or in the undervoltage lockout mode: either vcc is within 1 2 0mv of the bat pin voltage or insufficient voltage is applied to the vcc pin. automatic r e charge once the charge cycle is terminated, the WS4508S continuously monitors the voltage on the bat pin using a comparator with a 2ms filter time (t rechrg ). a charge cycle restarts when the battery voltage falls below 4.05v (typ.) (which corresponds to ap proximately 80% to 90% battery capacity). this ensures that the battery is kept at or near a fully charged condition and eliminates the need for period ic charge cycle initiations. chgb output enters a pull - down state during recharge cycles. 4 8 7 6 3 v c c c e c h g b s t d b y b g n d b a t l i - l o n 1 0 u f 1 0 u f v c c r 3 r 4 t e m p b a t r p r o g u p 1 2 5 w s 4 5 0 8 s figure4. manual shutdown mode application circuit WS4508S 11 of 13 4008-318-123 sales@twtysemi.com http://www.twtysemi.com product specification 2 1 th tl 1 2 th tl 1 k )k r (r ) k (k r r r u u ) k k (k r ) k k (k r ) k (k r r r 2 1 2 th 2 1 1 tl 1 2 th tl 2 u u u 2 1 tl th 1 2 tl th 1 k )k r (r ) k (k r r r u u ) k k (k r ) k k (k r ) k (k r r r 2 1 2 tl 2 1 1 th 1 2 tl th 2 u u u 4 8 7 6 3 v c c c e c h g b s t d b y b g n d b a t l i - l o n 1 0 u f 1 0 u f v c c r 3 r 4 t e m p b a t r p r o g u p 1 2 5 w s 4 5 0 8 s
application information s stability c onsiderations the constant - voltage mode feedback loop is stable without an output capacitor provided a battery is connected to the charger output. with no battery present, an output capacitor is recommended to reduce ripple voltage. when using high value, low esr ceramic capacitors, it is recommended to add a 1 ? resistor in series with the capacitor. no series resistor is needed if tantalum capacitors are used. in constant - current mode, the prog pin is in the feedback loop, not the battery. the constant - current mode stability is affected by the impedance at the prog pin. with no additional capacitance on the prog pin, the charger is stable with prog ram resistor values as high as 1 0 k ? . however, additional capacitance on this node reduces the maximum allowed program resistor thus it should be avoided. thermal l imi t an internal thermal feedback loop reduces the programmed charge current if the die temperature attempts to rise above a preset value of approximately 165 c. t his feature protects the WS4508S from excessive temperature and allows the user to push the limi ts of the power handling capability of a given circuit board with out risk of damaging the WS4508S . the charge current can be set according to typical (not worst - case) ambient temperature with the assurance that the charger will automatically reduce the cur rent in worst - case conditions. power d issipation the conditions that cause the WS4508S to reduce charge current through thermal feed - back can be approximated by considering the power dissipated in the ic. nearly all of this power dissipation is g enerated by the internal mosfet . this is calculated to be approximately: bat bat cc d i ) v (v p ? ? ? it is im portant to remember that WS4508S applications do not be designed for worst - case thermal conditions since the ic will automatically reduce power dissipat ion when the junction temperature reaches approximately 165 c (constant temperature mode) . vcc b ypass c apacitor many types of capacitors c an be used for input bypass , however, caution must be exercised when using multilayer ceramic capacitors. because of the self - resonant and high q characteristics of some types of ceramic capacitor s, a 1 0 uf c eramic capacitor is recommended for this bypass capacitor. d ue to a high voltage transient will be generated under some start - up conditions, such as connecting the ch arger input to a live power source. charge c urrent s oft - s tart the WS4508S includes a soft - start circuit to minimize the inrush current at the start of a charge cycle. when a charge cycle is initiated, the charge current ramps from zero to the full - scale current over a period of appro ximately 100u s. this has the effect of minimizing the transient current load on the power supply during start - up. WS4508S 12 of 13 4008-318-123 sales@twtysemi.com http://www.twtysemi.com product specification bat bat cc d i ) v (v p u
package outline dimensions sop - 8l - ep symbol dimensions in millimeters min. typ. max. a 1. 35 1.55 1. 70 a1 0.00 0.10 0.1 5 a2 1. 25 1.40 1. 65 a3 0. 50 0.60 0. 70 b 0. 38 0. 51 d 4.80 4.90 5.00 d1 3.10 3.30 3.50 e 5.80 6.00 6.20 e1 3.80 3.90 4.00 e2 2.20 2.40 2.60 e 1.17 1.27 1.37 l 0.45 0.60 0.80 l1 1.04ref l2 0. 25bsc r 0.07 0 o 8 o WS4508S 13 of 13 4008-318-123 sales@twtysemi.com http://www.twtysemi.com product specification

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