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Linear Charger for Single-Cell Li+ Battery ELECTRICAL CHARACTERISTICS (continued) (VIN=8V, VBATT= 4V, EN/OK= open, RSET=2.8k(2, RSTRT= GND, TA=0C to +85C, unless otherwise noted. Typical values are atTA=+25°C.) PARAMETER CONDITIONS MIN TYP MAX UNITS Maximum Voltage(VIN-VDRv BATT =3.5V 3.5 7 VBATT Restart Threshold (As a Percentage of Voltage-Loop Set RSTRT= GND 92952598 Point RSTRT Internal Resistance 100 CURRENT LOOP Internal Currenl-Sense Resistance IN to CS pin-to-pin resistance 50 105 200 RMS Charge Current 1.4 A Current-Sense Amplifier Gain, ISET Ics=500mA, VSET =1.4V 0.95 1 mA/A to IN Fast Charge Current-Sense Amplifier Gain, IsFT Ics=50mA, VISFT=0.14V 0.73 to lIN Prequal VBATT= 2V 1.30mAA Current-Loop Regulation Set Point RSET =2. ks, VBATT=3.V, closed-loop 450500 A pertormance Current-Loop Gain △VDRV△VSET dB CHG Trio Threshold (As a ILOAD falling, RSET=2.8kQ2 15 Percentage of Full Load Current) % ILOAD rising, RSET=2.8kQ2 17 TIMER FUNCTION Timer Source /Sink Current VCT=0.9V A Timer Accuracy CCT= 100nF for 2 hours, 54 minutes nominal 10 10 % CHG Output Low Current VCHG A CHG Output High Leakage VCHG-12V A CHG BII∩ K Rate Fault state(50% duty cycle), CT= 100nF 1.5 ELECTRICAL CHARACTERISTICS (VIN= BV, VBATT=4V, EN/OK= open, RSET=2.8KQ2, RSTRT= GND, TA=-40'C to +85C, unless otherwise noted. PARAMETER CONDITIONS MIN MAX UNITS Supply vollage range 4.5 12 Input OK Trip Point, IN Rising 100 Input OK Trip Point, IN Falling 85 (VIN-VBATT VIN Input OK Trip Point, IN Rising 4.0 VIN Input OK Trip Point, IN Falling 3.9 4.4 V EN/OK Sink Current(When Input 100 A Power Not OK) VIN=3.9V, VBATT =4V, VEN/OK=0.8V EN/OK Source Current(When Input Power OK) VEN/OK= 2V 5 A EN/OK Logic Input High 4.5V≤VN≤12V 2 V EN/OK Lagic Input LOW 4.5V≤V|N≤12V 06 V Linear Charger for Single- Cell Li+ Battery GO ELECTRICAL CHARACTERISTICS (continued) O (VIN=BV, VBATT=4V, EN/OK=open, RSET =2.8kS2, RSTRT= GND, TA=-40C to +85"C, unless otherwise noted PARAMETER CONDITIONS MIN MAX UNITS Done, RSTRT= GND, VBATT=4. 1V for 100 MAX1898EUB42 and 4.0V for maX1898EUB41 BATT Input Current Done, RSTRT= open, VBATT=4.1V for MAX1898EUB42 and 4. 0V for maX1898EUB41 A EN/OK-GND 10 N 10 VIN= VBATT= 4V(IN+Ics) IN, CS Input Current VIN=12V, (IN+Ics), done, RSTRT= open 5 A VOLTAGE LOOP MAX1898EUB42 4.137 4.263 Voltage-Loop Set Point MAX 1898EUB41 4.038 4.162 MA×1898EUB42 2.394 2.646 VBATT Prequal Voltage Threshold Timers running MA×1898EUB41 2.337 2.583 DRV Sink Current VDRV= VIN -1V, VBATT =3.5V 3.5 mA Maximum Voltage(VIN-VDRV) VBATT=3.5V VBAII Restart Threshold (As a Percentage of Vollage-Loop Set RSTRT= GND oint) CURRENT LOOP nternal Current-Sense Resistance IN to CS pin-to-pin resistance 200 RMS Charge Current 1.4 A Current-Sense Amplifier Gain, ISET ICs=500mA, VSET=1.4V 0.93 1.07 mA/A to lIN Fast Charge Current-Sense Amplifier Gain, IsET Ics=50mA, VISET=0.14V 0.6 1.50 to lIN Prequal VBATT=2V mA/A Current-Loop Regulation Set Point RSET=2.8kQ, VBATT =3.5v, closed-looo 440 560 m performance CHG Trip Threshold(As a ILOAD falling, RSET =2.8kQ2 Percentage of Full Load Current % ILOAD rising, RSET =2.8kQ2 Timer Accuracy CCT= 100nF for 2 hours, 54 minutes nominal +13 CHG Output Low Current VCHG= 1V 35 G Output High Leakage VCHG= 12V CHG Blink Rate Fault state(50% duty cycle), cT= 100nF 2 Hz Note 1: Specifications to-40C are guaranteed by design and not production tested Linear Charger for Single- Cell Li+ Battery Typical Operating Characteristics (VIN= 5V, VBATT 4V, EN/OK= open, RSET =2.8kQ2, RSTRT= GND, TA=+25C, unless otherwise noted.) NORMALIZED TIMER PERIOD NORMALIZED BATT REGULATION PRECHARGE CURRENT VS TEMPERATURE VOLTAGE VS, TEMPERATURE VS INPUT VOLTAGE 102 NORMALIZED T0+25°C NORMIALIZED T0+25°0 ISET-2.8kQ CHARGING CURRENT SET FOR 500mA 098 ⊙1.000 c0.96 0998 工出 45 0.90 0996 40 5678 TEMPERATURE ( C) 上MPHA|UHE(°C) VIN (V) NORMALIZED BATTERY CURRENT vs。 BATTERY VOLTAGE VOLTAGE-LOOP GAIN 40 GAIN 08 10 妥04 0 50 1001000 BATTERY VOLTAGE(V) FREQUENCY ( kHz) AX Linear Charger for Single Cell Li+ Battery Pin Description 9-s PIN NAME FUNCTION N Sense Input Detects power source; positive side of internal current-sense resistor 2 CHG Open-Drain LED Driver. See Table 1 for CHG output states Logic-Level Enable Input and Input Power OK Output. Hold low to disable charger. Float for normal EN/OK operation, drive with an open-drain device to utilize both pin functions, or connect through 10kQ2 for logic controlled ON/OFF. See the EN/OK (EN Input, OK Output)section for details ISET serves two functions. It provides an analog output proportional to the actual charge current Output current from IsET is 1 mA per amp of battery charging current. The charging current is set by connecting a resistor from IsET to ground. See the Current-Limit Mode section 5 CT Safety Charge Timer Control Connect timer capacitor to program satety time-out interval; 100nF for approximately three hours. Connect to GNd to disable the timer function Automatic-Restart Control Pin. When tied tO GND, a new charging cycle starts if the cell drops 200mV below RSTRT the battery regulation threshold. The restart threshold may be lowered by connecting a resistor from RSTRT to ground. See the Reinitiating a Charging Cycle section. Automatic restart is disabled when RSTRT is unconnected or when CT is grounded(timer disabled BATT Battery Sense Input Positive terminal of single Li+ cell GND Ground DRV External Transistor Driver. This pin drives the gate/base of an external PMOS/ PNP pass transistor 10 CS Current-Sense Input. Negative side of internal current-sense resistor. Connect to source/emitter of PMOS/PNP pass transistor Detailed Description The prequalification cycle ends with the cell reaching The MAX1898 forms a complete charger for 1-cell Li+ 2.5V batteries. It includes precision voltage control (+0.75% Li+ cells can be damaged when fast-charged from a to optimize both cell performance and cycle life. completely dead state. A fully discharged cell may indi Factory-set 42V(MAX1898EUB42) and 4.1V ate an abnormal cell condition. As a built-in satety tea (MAX 1898EUB41) versions charge all common Li+ ture, the MAX1898 prequalifies the cell with 10 percent chemistries. Externally selectable charge current is or the user-programmed fast-charge current at the start sensed internally, eliminating the need for a current of a charge cycle. When the cell voltage rises to 2.5V, sense resistor. The charger also supplies outputs that the MaX1898 begins fast-charging indicate charge status(CHG), the presence of input power(EN/OK), and charge-current magnitude(ISET) Current-Limit ode Other features include a shutdown control input The MAX1898 regulates charging current by linearly (EN/OK), selectable threshold for charge-cycle restart controlling an external PMOS or PNP transistor. The without cycling input power(RSTRT), and a selectable maximum charging current is programmed by an exter- charge termination safety timer. See Figure 1 na rset resistor connected from iset to gnd, select the rsET value based on the tollowing formula The MAX 1898 initiates fast charge when any of these conditions are met (see figure 6 1400 An external power source is connected and the ce voltage is above 2.5V I=ASTCHG RSET The cell voltace falls to the restart threshold. 4.0V in where the max1898EUB42 or 3.9V for the maX1898EUB41 ASTCHG is in amps and rSet is in ohms The IC is reset by driving the en/Ok pin low and The isET pin may also be used to monitor the actual then high again charging current at any time. The output current from L Linear Charger for Single-Cell Li+ Battery 0.1uF L上 4.5VT012V 5mA CHG CHARGING FOR CCT= 100nF 20mQ CS 4709 0.1gF (2.8kg2「DF ICHARGF <20% DR∨ EOOmA CHARGF CURRENT 260mV ISET(FALLING 305mV ISET(RISING) PREQUAL LOGIC 25 69.275K DONE SHUTDOWN VL REG ESTART 34.637K9 BATT N EN,OK UVLO 厂ONF SHUTDOW SHUTDOWN RSIRI igure 1. Functional Diagram Linear Charger for Single Cell Li+ Battery Reinitiating a Charging Cycle 9-s 42 14 The MAX1898 can be configured so that a charging BATTEFY VOLTAGE cycle automatically restarts when the cell voltage drops 1.2 200mv below the battery regulation voltage(connect RSTRT to GND). The restart threshold can also be low 1.0己 ered by connecting an external resistor between RSTRT S 3.8 HAMP HOURS and GND. If automatic charging restart is not desired, BATTERY CURRENT this feature may be disabled by floating the rstrt pin 36 06 With restart disabled, charging can only be reinitiated by pulling EN/OK low, or by removing and reapplying the input power source 34 POWER DISSIPATION EN/OK (EN Input, OK Output) 32 The EN/OK pin serves two functions. It primarily serves as 3060c0120150180 a logic input(active high) to enable the charger. In addi TIME MINUTES tion to ON/OFF control, EN/OK also indicates when input power is connected. When input power is applied to IN Figure 2. Li+ Charging Profile VIN >VBATT and VIN>4.25 V)EN/OK pulls high(to 3V) with a 100kQ2 internal pullup resistance. Consequently, the ISET pin is 1mA per amp of charging current. The EN/ OK may be output to a logic input, to indicate ac output voltage at ISET is proportional to charging cur- adapter presence, but at the same time may be driven by rent as follows open-drain logic to turn the charger on and OFF. An open-drain logic-low input will over-ride the internal pullup HG X R resistor and turn off the charger (see Figure 3 ). When the 1000 open drain goes high impedance, EN/OK will go high if The voltage at ISET is nominally 1. 4V at the selected fast-charge current, and falls with charging current as POWER OI the cell becomes fully charged. See Figure 2 for typical Li+ charging profile PEN-DRAN CHG Status Output LOGIC CHG is an open-drain output that monitors the cell's charging status. CHG has a 5mA current limit so an EN/OK LED can be connected directly from iN to CHG for a MAX1898 visible indication. Alternatively, a pullup resistor(typi- cally 100kQ2)to a logic supply provides a logic-level output. Table 1 outlines the status of CHG for various GND charger states Figure 3. Driving EN/OK with Open-Drain Logic lo Relain ON/OFF Contro/ with Power OK Indication Table 1. CHG Output States CONDITION CHG No battery or no charger input High impedance (LED off) The cell voltage is less than 2.5v and charge current is regulated to 10% of the selected fast charge current (prequalification state) Low impedance(LED on) Cell voltage is greater than 2.5v (fast-charge state . ow impedance(LED on Charge cycle complete-charge current is less then 20% of the selected fast charge current or satety timer expires (3 hours for CCT= 100nF High impedance(LED ott) Charge cycle fault-the cell voltage is less than 2. 5V and the prequalification timer(45min for CcT Blinking, LED on 50% duty 100nF)has expired factor. 1. 5Hz Linear Charger for Single Cell Li+ Battery power is present at IN. If there is no(or insufficient) voltage at IN, EN, OK will remain low and the charger 5V T0 1 will remain oft Battery Drain Current CS The MaX1898 uses advanced CMos circuitry to com- pletely monitor battery state, while drawing minimal current from the cell itself. When the input voltage is less than the battery, battery drain is typically 3HA. When input power is BATT present and charging is complete(the charge timer 川AX expires), battery drain is then typically 40HA. This current MAX1898 may be reduced to 4HA by disabling the restart feature CcT, 100nF CAPACITOR ETS CHARGE TIME Applications Information TO 3hr INPUT POWER The MAX1898 basic application circuit is shown in OK OUTPUT OR EN/OK ENABLE INPUT UTPUT VOLTAG- PROPOFTIONAl Figure 4 ⊥rco TO CHARGE CURRENT RSET SETS 100nF 5∨T012 Figure 5. Application Circuit with PNP Pass Transistor CcnF]=34.33xtcHGhours BATT where CHARGE LEL Li+ CELL MAX1898 tCHG nominal charge time limit in hours CcT 100nF CAPACITOR The maximum charge timer is intended as a safety timer SETS CHARGE TIME It is normally not intended to be part of the charge-con- INPUT POWEF trol loop. When charging a Li+ cell at a 1C rate, normal OK OUTPLT OF ENABLE INPUT OUTPUT VOLTAGE charge time is approximately 1.5 hours, but this may PRCPORTIONA RSTRT GND TO CHANGE CURRENT have wide variations that depend on temperature and cell type. In most cases, 3 hours is recommended for the RSET SETS CHARGE maximum charge time limit when fast-charging at 1C SO that normal-charging is never interrupted by the charge timer. Consult the battery manufacturer for details on rec Figure 4. Basic Application Circuit ommended timer settings The charge safety timer may als pletely An LEd can be added as a charge-state indicator. A abled by connecting CT to ground. Note: If the charge timer is disabled, both the restart function and prequali 10uF bypass capacitor must be added to the BATT pin fication fault indication are also disabled. Only the indi A Schottky diode should be added between the exter- cation(blinking LED) is disabled, the prequalification nal transistor drain/collector and batt, to avoid battery function itself is not modified discharge in the event of an input source short circuit Figure 5 shows a charger circuit using an external PNP Controlling Automatic Restart pass transistor The mAX 1898 features automatic restart that resumes charging when the cell voltage drops to a predetermined Selecting Maximum Charge Time level. In most timed chargers, once charging times out, The maximum charge time can be set with an external subsequent loading of the battery can discharge the bat- capacitor connected from CT to GND. Select the timing tery and charging will not resume unless the charger is capacItor using restarted by an outside signal By automatically resuming charging when the battery voltage drops, the MAX1898 ensures that the cell does not remain partially charged Linear Charger for Single Cell Li+ Battery ASYNCHRONOUS FROM 9-s VIN <4.5V0 VBAT 2 5V SHUTDOWN VBATT> VIN CHARGER= CFr LED=O PREQUALIFICATION IMEOUT/4 10% CHARGE CURRENT LED=ON VBAII>VIN ----. VBATT <2.5V LED ELINKING AT 15HZ Ehr tIMer startS RSTRT= GND AND VBATT <4.0V (MAX1898EUB42 FAST CHARGE -, VBATT <3.9V(MAX1898CUB41) 100% CHARGEF CURR-NT TIMEoUT 3hr I CHARGE>22% ICHARGE< 20% TOP OFF TIMEOUT_3hr (CHARGE COMPLETE LED= OFF DOTTED LINE INDICATES THE STATES THAT RE NOT AVALABLE WHEN CT=O(TIMER DISABLED) Figure 6. Charger State Diagram after use when charger power is available. The restart resistor using the following equations feature can be configured in the following ways For MaX1898EUB42 Floating the RStRT pin disables restart. Once the battery is charged and the charge timer expires 69.275k(2 charging can only be started by cycling input power to IN, or by toggling EN/OK. When the restart func ly6-1 RSTRT(kQ2]= 37.301kg2 tion is disabled, battery drain after charge comple 1.4V tion is reduced to 4HA. With the restart function enabled, battery drain current after charge comple for Vrstrt values between 3V and 4V tion is 40HA For ma×1898EUB41 ground the rstri pin to enable the default restart threshold of 4v for the maX1898EUB42 and 3. 9V for 66822k9 the MAX1898EUB41 Once the battery is charged RSTRT KS2 37.30g and the charge timer expires, charging restarts when RSTAT the cell voltage drops to the restart-threshold voltage If desired, lower the restart-threshold voltage by con- for VRSTRT values between 3V and 3.9V necting a resistor from RSiRI to GND. Select the Note that if CT is grounded (charge timer disabled), the able 2 External transistors restart function is also disabled EXTERNAL RESISTANCE OLTAGE LIMIT POWER PACKAGE COMMENTS TRANSISTORS RATING DISSIPATION (W) PMOS sOme SOT223 Fairchild NDt454P PNP 15 SOT223 Zetex FzT968 0. 17V, VCE(sat) hFE= 300min PNP hFE= 160min, 1W 0.32V, VCE(sat) SOT89 FC×717 ating suitable for 0.5A charge or less 10

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