EVALUATION KIT AVAILABLE LE AVAILAB MAX1737 Stand-Alone Switch-Mode Lithium-Ion Battery-Charger Controller General Description Features The MAX1737 is a switch-mode lithium-ion (Li+) battery charger that charges one to four cells. It provides a regulated charging current and a regulated voltage with only a 0.8% total voltage error at the battery terminals. The external N-channel switch and synchronous rectifier provide high efficiency over a wide input voltage range. A built-in safety timer automatically terminates charging once the adjustable time limit has been reached. The MAX1737 regulates the voltage set point and charging current using two loops that work together to transition smoothly between voltage and current regulation. An additional control loop monitors the total current drawn from the input source to prevent overload of the input supply, allowing the use of a low-cost wall adapter. Stand-Alone Charger for Up to Four Li+ Cells The per-cell battery voltage regulation limit is set between +4.0V and +4.4V and can be set from one to four by pin strapping. Battery temperature is monitored by an external thermistor to prevent charging if the battery temperature is outside the acceptable range. The MAX1737 is available in a space-saving 28-pin QSOP package. Use the evaluation kit (MAX1737EVKIT) to help reduce design time. 90% Conversion Efficiency 0.8% Accurate Battery Regulation Voltage Low Dropout: 98% Duty Cycle Safely Precharges Near-Dead Cells Continuous Voltage and Temperature Monitoring <1A Shutdown Battery Current Input Voltage Up to +28V Safety Timer Prevents Overcharging Input Current Limiting Space-Saving 28-Pin QSOP 300kHz PWM Oscillator Reduces Noise Ordering Information PART TEMP RANGE PIN-PACKAGE MAX1737EEI -40C to +85C 28 QSOP Typical Operating Circuit Applications Notebook Computers Hand-Held Instruments Li+ Battery Packs Desktop Cradle Chargers INPUT SUPPLY DCIN VL Pin Configuration Functional Diagrams 28 DCIN ISETIN 2 27 CSSP ISETOUT 3 26 CSSN THM 4 25 DHI REF 5 24 LX GND 6 MAX1737 REF 22 VLO VADJ 8 21 DLO CCV 9 MAX1737 LX BST ISETIN VLO ISETOUT CELL DLO VADJ PGND CS 23 BST BATT 7 RS CCS BATT 20 PGND CCS 10 19 CS CCI 11 18 SHDN CELL 12 17 FULLCHG TIMER1 13 16 FASTCHG FAULT TIMER2 15 sheet. 14 Pin Configurations appear at end of data Functional Diagrams continued at end of data sheet. QSOP UCSP is a trademark of Maxim Integrated Products, Inc. SYSTEM LOAD DHI TOP VIEW VL 1 CSSP CSSN ON OFF CCV THM CCI FASTCHG TIMER1 FULLCHG TIMER2 FAULT Li+ BATTERY 1 TO 4 CELLS SHDN GND For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642, or visit Maxim's website at www.maximintegrated.com. 19-1626; Rev 4; 9/07 MAX1737 Stand-Alone Switch-Mode Lithium-Ion Battery-Charger Controller ABSOLUTE MAXIMUM RATINGS CSSP, CSSN, DCIN to GND ...................................-0.3V to +30V BST, DHI to GND....................................................-0.3V to +36V BST to LX..................................................................-0.3V to +6V DHI to LX ..........................................-0.3V to ((BST - LX) + 0.3V) LX to GND ...............................................-0.3V to (CSSN + 0.3V) FULLCHG, FASTCHG, FAULT to GND ..................-0.3V to +30V VL, VLO, SHDN, CELL, TIMER1, TIMER2, CCI, CCS, CCV, REF, ISETIN, ISETOUT, VADJ, THM to GND ........................................................-0.3V to +6V DLO to GND...............................................-0.3V to (VLO + 0.3V) BATT, CS to GND ...................................................-0.3V to +20V PGND to GND, CSSP to CSSN..............................-0.3V to +0.3V VL to VLO ..............................................................-0.3V to +0.3V VL Source Current...............................................................50mA Continuous Power Dissipation (TA = +70C) 28-Pin QSOP (derate 10.8mW/C above +70C)........860mW Operating Temperature Range ...........................-40C to +85C Junction Temperature ......................................................+150C Storage Temperature Range .............................-65C to +150C Lead Temperature (soldering, 10s) .................................+300C Stresses beyond those listed under "Absolute Maximum Ratings" may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability. ELECTRICAL CHARACTERISTICS (Circuit of Figure 1, VDCIN = VCSSN = VCSSP = +18V, SHDN = VL, CELL = GND, VBATT = VCS = +4.2V, VVADJ = VREF / 2, ISETIN = ISETOUT = REF, RTHM = 10k, TA = 0C to +85C, unless otherwise noted. Typical values are at TA = +25C.) PARAMETER CONDITIONS MIN TYP MAX UNITS SUPPLY AND REFERENCE 6 DCIN Input Voltage Range DCIN Quiescent Supply Current 5 6.0V < VDCIN < 28V 28 V 7 mA DCIN to BATT Undervoltage Threshold, DCIN Falling 0.05 0.155 V DCIN to BATT Undervoltage Threshold, DCIN Rising 0.19 0.40 V 5.70 V mV VL Output Voltage 6.0V < VDCIN < 28V VL Output Load Regulation IVL = 0 to 15mA REF Output Voltage 5.10 5.40 44 65 4.179 4.20 4.221 V REF Line Regulation 6V < VDCIN < 28V 2 6 mV REF Load Regulation IREF = 0 to 1mA 6 14 mV 330 kHz SWITCHING REGULATOR PWM Oscillator Frequency VBATT = 15V, CELL = VL 270 300 LX Maximum Duty Cycle In dropout fOSC / 4, VCCV = 2.4V, VBATT = 15V, CELL = VL 97 98 CSSN + CSSP Off-State Leakage VCSSN = VCSSP = VDCIN = 28V, SHDN = GND 2 DHI, DLO On-Resistance LX Leakage BATT, CS Input Current Absolute Voltage Accuracy Battery Regulation Voltage Adjustment Range 2 10 A 7 A LX = VDCIN = 28V, SHDN = GND 0.1 10 SHDN = GND, VBATT = 19V 0.1 5 CELL = SHDN = VL, VBATT = 17V 225 500 19 V 4.2 4.233 V/cell BATT, CS Input Voltage Range Battery Regulation Voltage (VBATTR) % 0 CELL = float, GND, VL, or REF (Note 1) 4.167 Not including VADJ resistor tolerances -0.8 +0.8 -1 +1 With 1% VADJ resistors VCCV = 2V VVADJ = GND 3.948 3.979 4.010 VVADJ = REF 4.386 4.421 4.453 A % V/cell Maxim Integrated MAX1737 Stand-Alone Switch-Mode Lithium-Ion Battery-Charger Controller ELECTRICAL CHARACTERISTICS (continued) (Circuit of Figure 1, VDCIN = VCSSN = VCSSP = +18V, SHDN = VL, CELL = GND, VBATT = VCS = +4.2V, VVADJ = VREF / 2, ISETIN = ISETOUT = REF, RTHM = 10k, TA = 0C to +85C, unless otherwise noted. Typical values are at TA = +25C.) PARAMETER CONDITIONS MIN TYP MAX UNITS 0.584 0.80 mS ERROR AMPLIFIERS CCV Amplifier Transconductance (Note 2) 4.15V < VBATT < 4.25V, VCCV = 2V 0.39 CCV Amplifier Maximum Output Current 3.5V < VBATT < 5V, VCCV = 2V 50 CS to BATT Current-Sense Voltage VISETOUT = VREF / 5 30 40 50 mV CS to BATT Full-Scale Current-Sense Voltage VBATT = 3V to 17V, CELL = GND or VL 185 200 215 mV CS to BATT Current-Sense Voltage When in Prequalification State VBATT < 2.4V per cell 5 10 15 mV 355 385 415 mV CS to BATT Hard Current-Limit Voltage A CSSP to CSSN Current-Sense Voltage 6V < VCSSP < 28V, VISETIN = VREF / 5, VCCS = 2V 10 20 30 mV CSSP to CSSN Full-Scale Current-Sense Voltage 6V < VCSSP < 28V, VCCS = 2V 90 105 115 mV CCI Amplifier Transconductance VCCI = 2V 0.6 1 1.4 mS 2 2.6 CCI Amplifier Output Current VCS - VBATT = 0, 400mV CCS Amplifier Transconductance ISET = REF, VCCS = 2V CCS Amplifier Output Current VCSSP - VCSSN = 0, 200mV 100 1.2 A 100 mS A CCI, CCS Clamp Voltage with Respect to CCV 25 200 mV CCV Clamp Voltage with Respect to CCI, CCS 25 200 mV STATE MACHINE THM Trip-Threshold Voltage THM low-temperature or high-temperature current 1.386 1.4 1.414 V THM Low-Temperature Current VTHM = 1.4V 46.2 49 51.5 A THM High-Temperature Current VTHM = 1.4V 344 353 362 A THM COLD Threshold Resistance (Note 3) Combines THM low-temperature current and THM rising threshold, VTRT/ITLTC 26.92 28.70 30.59 k THM HOT Threshold Resistance (Note 3) Combines THM high-temperature current and THM rising threshold, VTRT/ITHTC 3.819 3.964 4.115 k BATT Undervoltage Threshold (Note 4) 2.4 2.5 2.6 V/cell BATT Overvoltage Threshold (Note 5) 4.55 4.67 4.8 V/cell BATT Charge Current Full-Charge Termination Threshold CS-BATT (Note 6) 35 44 55 mV BATT Recharge Voltage Threshold (Note 7) 94 95 96 % of VBATTR TIMER1, TIMER2 Oscillation Frequency 2.1 2.33 2.6 kHz Prequalification Timer 6.25 7.5 8.75 min Fast-Charge Timer 81 90 100 min Full-Charge Timer 81 90 100 min Maxim Integrated 3 MAX1737 Stand-Alone Switch-Mode Lithium-Ion Battery-Charger Controller ELECTRICAL CHARACTERISTICS (continued) (Circuit of Figure 1, VDCIN = VCSSN = VCSSP = +18V, SHDN = VL, CELL = GND, VBATT = VCS = +4.2V, VVADJ = VREF / 2, ISETIN = ISETOUT = REF, RTHM = 10k, TA = 0C to +85C, unless otherwise noted. Typical values are at TA = +25C.) PARAMETER CONDITIONS Top-Off Timer Temperature Measurement Frequency 1nF on TIMER1 and TIMER2 MIN TYP MAX UNITS 40.5 45 49.8 min 0.98 1.12 1.32 Hz CONTROL INPUTS/OUTPUTS SHDN Input Voltage High 1.4 V SHDN Input Voltage Low (Note 8) VADJ, ISETIN, ISETOUT Input Voltage Range 0.6 V 0 VREF V VADJ, ISETIN, ISETOUT Input Bias Current VVADJ, VISETIN, VISETOUT = 0 or 4.2V -50 50 nA SHDN Input Bias Current SHDN = GND or VL -1 1 A -5 5 A ISETIN Adjustment Range VREF / 5 VREF V ISETOUT Adjustment Range VREF / 5 VREF V 300 mV CELL Input Bias Current 150 ISETOUT Voltage for ICHG = 0 CELL Input Voltage 0 0.5 For 2 cells 1.5 2.5 For 3 cells VREF - 0.3 For 4 cells VVL - 0.4 FASTCHG, FULLCHG, FAULT Output Low Voltage ISINK = 5mA FASTCHG, FULLCHG, FAULT Output High Leakage FASTCHG, FULLCHG, FAULT = 28V; SHDN = GND 4 220 For 1 cell VREF + 0.3 V VVL 0.5 V 1 A Maxim Integrated MAX1737 Stand-Alone Switch-Mode Lithium-Ion Battery-Charger Controller ELECTRICAL CHARACTERISTICS (Circuit of Figure 1, VDCIN = VCSSN = VCSSP = +18V, SHDN = VL, CELL = GND, VBATT = VCS = +4.2V, VVADJ = VREF / 2, ISETIN = ISETOUT = REF, RTHM = 10k, TA = -40C to +85C, unless otherwise noted.) (Note 9) PARAMETER CONDITIONS MIN MAX UNITS SUPPLY AND REFERENCE DCIN Input Voltage Range VL Output Voltage 6.0V < VDCIN < 28V REF Output Voltage REF Line Regulation 6 28 V 5.1 5.7 V 4.166 4.242 V 6 mV 260 340 kHz 7 0 19 V 4.158 4.242 V/cell 6V < VDCIN < 28V SWITCHING REGULATOR PWM Oscillator Frequency VBATT = 15V, CELL = VL DHI, DLO On-Resistance BATT, CS Input Voltage Range Battery Regulation Voltage (VBATTR) CELL = float, GND, VL, or REF Absolute Voltage Accuracy Not including VADJ resistor tolerances -1 1 % CS to BATT Current-Sense Voltage VISETOUT = VREF / 5 25 55 mV CS to BATT Full-Scale Current-Sense Voltage VBATT = 3V to 17V, CELL = GND or VL 180 220 mV CS to BATT Current-Sense Voltage When in Prequalification State VBATT < 2.4V per cell 3 17 mV ERROR AMPLIFIERS CS to BATT Hard Current-Limit Voltage 350 420 mV CSSP to CSSN Current-Sense Voltage 6V < VCSSP < 28V, VISETIN = VREF / 5, VCCS = 2V 5 35 mV CSSP to CSSN Full-Scale Current-Sense Voltage 6V < VCSSP < 28V, VCCS = 2V 85 115 mV STATE MACHINE THM Trip-Threshold Voltage THM low-temperature or high-temperature current 1.386 1.414 V THM Low-Temperature Current VTHM = 1.4V 46.2 51.5 A THM COLD Threshold Resistance (Note 3) Combines THM low-temperature current and THM rising threshold, VTRT/ITLTC 26.92 30.59 k BATT Undervoltage Threshold (Note 4) 2.4 2.6 V/cell BATT Overvoltage Threshold (Note 5) 4.55 4.8 V/cell 35 55 mV 0.93 1.37 Hz BATT Charge Current Full-Charge Termination Threshold, CS-BATT (Note 6) Temperature Measurement Frequency Maxim Integrated 1nF on TIMER1 and TIMER2 5 MAX1737 Stand-Alone Switch-Mode Lithium-Ion Battery-Charger Controller ELECTRICAL CHARACTERISTICS (continued) (Circuit of Figure 1, VDCIN = VCSSN = VCSSP = +18V, SHDN = VL, CELL = GND, VBATT = VCS = +4.2V, VVADJ = VREF / 2, ISETIN = ISETOUT = REF, RTHM = 10k, TA = -40C to +85C, unless otherwise noted.) (Note 9) PARAMETER CONDITIONS MIN TYP MAX UNITS CONTROL INPUTS/OUTPUTS SHDN Input Voltage High SHDN Input Voltage Low (Note 8) 1.4 V 0.6 V Note 1: Battery Regulation Voltage = Number of Cells x (3.979V + 0.10526 x VVADJ). Note 2: This transconductance is for one cell. Divide by number of cells to determine actual transconductance. Note 3: See Thermistor section. Note 4: Below this threshold, the charger reverts to prequalification mode and ICHG is reduced to about 5% of full scale. Note 5: Above this threshold, the charger returns to reset. Note 6: After full-charge state is complete and peak inductor current falls below this threshold, FULLCHG output switches high. Battery charging continues until top-off timeout occurs. Note 7: After charging is complete, when BATT voltage falls below this threshold, a new charging cycle is initiated. Note 8: In shutdown, charging ceases and battery drain current drops to 5 A ( max), but internal IC bias current remains on. Note 9: Specifications to -40C are guaranteed by design and not production tested. 6 Maxim Integrated MAX1737 Stand-Alone Switch-Mode Lithium-Ion Battery-Charger Controller Typical Operating Characteristics (Circuit of Figure 1, VDCIN = +18V, ISETIN = ISETOUT = REF, VVADJ = VREF / 2, TA = +25C, unless otherwise noted.) CHARGING CURRENT-SENSE VOLTAGE vs. ISETOUT VOLTAGE 2.5 2.0 1.5 1.0 0.5 150 125 100 75 50 25 80 60 40 20 0.5 1.0 1.5 2.0 0 0 2.5 CHARGING CURRENT (A) ISETOUT VOLTAGE (V) VOLTAGE LIMIT vs. VADJ VOLTAGE REFERENCE VOLTAGE vs. TEMPERATURE 4.40 4.30 4.25 4.20 4.15 4.10 EFFICIENCY vs. INPUT VOLTAGE 4.200 REFERENCE VOLTAGE (V) 4.35 4.05 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 ISETIN VOLTAGE (V) 4.205 MAX1737 toc04 4.45 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 100 4.195 90 EFFICIENCY (%) 0 MAX1737 toc03 100 0 0 VOLTAGE LIMIT (V) 175 4.190 4.185 MAX1737 toc06 3.0 200 INPUT CURRENT-SENSE VOLTAGE (mV) 3.5 120 MAX1737 toc05 BATTERY VOLTAGE (V) 4.0 225 INPUT CURRENT-SENSE VOLTAGE vs. ISETIN VOLTAGE MAX1737 toc02 R18 = 0.1 CHARGING CURRENT-SENSE VOLTAGE (mV) 4.5 MAX1737 toc01 BATTERY VOLTAGE vs. CHARGING CURRENT 80 70 60 4.180 CELL = FLOAT (2 CELLS) VBATT = 7V R18 = 0.1 (IBATT = 2A) 4.00 3.95 4.175 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 50 -40 VADJ VOLTAGE (V) 40 60 80 100 8 4.200 4.198 4.196 4.194 10 PREQUALIFICATION MODE 1 24 28 1000 TIMEOUT (MINUTES) 4.202 20 MAX1737 toc09 TOP-OFF MODE 4.204 16 FAST-CHARGE TIMEOUT vs. TIMER2 CAPACITANCE FULL-CHARGE MODE 100 12 INPUT VOLTAGE (V) 1000 TIMEOUT (MINUTES) REFERENCE VOLTAGE (V) 4.206 20 TIMEOUT vs. TIMER1 CAPACITANCE MAX1737 toc07 4.208 0 TEMPERATURE (C) REFERENCE LOAD REGULATION 4.210 -20 MAX1737 toc08 0 100 10 4.192 0.1 4.190 0 100 200 300 400 500 600 700 800 900 1000 REFERENCE CURRENT (A) Maxim Integrated 1 0.1 1 CAPACITANCE (nF) 10 0.1 1 10 CAPACITANCE (nF) 7 MAX1737 Stand-Alone Switch-Mode Lithium-Ion Battery-Charger Controller Pin Description 8 PIN NAME FUNCTION 1 VL 2 ISETIN 3 ISETOUT 4 THM Thermistor Input. Connect a thermistor from THM to GND to set a qualification temperature range. If unused, connect a 10k resistor from THM to ground. See Thermistor section. 5 REF 4.2V Reference Voltage Output. Bypass REF to GND with a 1F or larger ceramic capacitor. 6 GND Analog Ground 7 BATT Battery Voltage-Sense Input and Current-Sense Negative Input 8 VADJ Voltage Adjust. Use a voltage-divider to set the VADJ voltage between 0 and VREF to adjust the battery regulation voltage by 5%. See Setting the Voltage Limit section. 9 CCV Voltage Regulation Loop Compensation Point 10 CCS Input Source Current Regulation Compensation Point 11 CCI Battery-Current Regulation Loop Compensation Point 12 CELL 13 TIMER1 Timer 1 Adjustment. Connect a capacitor from TIMER1 to GND to set the prequalification, full-charge, and top-off times. See Timers section. 14 TIMER2 Timer 2 Adjustment. Connect a capacitor from TIMER2 to GND to set the fast-charge time. See Timers section. 15 FAULT Charge Fault Indicator. Open-drain output pulls low when charging terminates abnormally (Table 1). 16 FASTCHG Fast-Charge Indicator. Open-drain output pulls low when charging with constant current. 17 FULLCHG Full-Charge Indicator. Open-drain output pulls low when charging with constant voltage in full-charge state. 18 SHDN 19 CS 20 PGND 21 DLO Synchronous-Rectifier MOSFET Gate-Drive Output 22 VLO Synchronous-Rectifier MOSFET Gate-Drive Bias. Bypass VLO to PGND with a 0.1F capacitor. 23 BST High-Side MOSFET Gate Drive Bias. Connect a 0.1F or greater capacitor from BST and LX. 24 LX Power Inductor Switching Node. Connect LX to the high-side MOSFET source. 25 DHI High-Side MOSFET Gate-Drive Output 26 CSSN Source Current-Sense Negative Input. See Input Current Regulator section. 27 CSSP Source Current-Sense Positive Input. See Input Current Regulator section. 28 DCIN Power-Supply Input. DCIN is the input supply for the VL regulator. Bypass DCIN to GND with a 0.1F capacitor. Also used for the source undervoltage sensing. Chip Power Supply. Output of the 5.4V linear regulator from DCIN. Bypass VL to GND with a 2.2F or larger ceramic capacitor. Input Current Limit Adjust. Use a voltage-divider to set the voltage between 0 and VREF. See Input Current Regulator section. Battery Charging Current Adjust. Use a voltage-divider to set the voltage between 0 and VREF. See Charging Current Regulator section. Cell-Count Programming Input. See Table 2 Shutdown Input. Drive SHDN low to disable charging. Connect SHDN to VL for normal operation. Battery Current-Sense Positive Input. See Charging Current Regulator section. Power Ground Maxim Integrated MAX1737 Stand-Alone Switch-Mode Lithium-Ion Battery-Charger Controller Detailed Description The DC-DC converter uses an external dual N-channel MOSFET as a switch and a synchronous rectifier to convert the input voltage to the charging current or voltage. The typical application circuit is shown in Figure 1. Figure 2 shows a typical charging sequence and Figure 3 shows the block diagram. Charging current is set by the voltage at ISETOUT and the voltage across R18. The battery voltage is measured at the BATT pin. The battery regulation voltage is set to 4.2V per cell and can be adjusted 5% by changing the voltage at the VADJ pin. By limiting the adjust range, the voltage The MAX1737 includes all of the functions necessary to charge between one and four series Li+ battery cells. It includes a high-efficiency synchronous-rectified stepdown DC-DC converter that controls charging voltage and current. It also includes input source-current limiting, battery temperature monitoring, battery undervoltage precharging, battery fault indication, and a state machine with timers for charge termination. D1 D2 28 INPUT SUPPLY CSSP DCIN 27 C7 0.1F 1 C8 0.1F VL MAX1737 C2 0.1F C1 4.7F 18 CSSN 2 R8 3 C3 1F 8 12 R9 C4 0.1F 6 R1 10k 9 26 C9 0.1F + SHDN VLO 5 R12 ISETIN ISETOUT VADJ CELL GND CCV BST DHI LX DLO PGND + C19 22F SYSTEM LOAD 22 D3 REF C18 22F C11 0.1F 23 25 24 C10 0.1F L1 22H R18 C15 68F 21 20 THERMISTOR 1nF CS C5 47nF 19 0.1F 11 CCI C6 47nF BATT 10 7 0.1F CCS C13 1nF 13 Li+ BATTERY (1 TO 4 CELLS) TIMER1 THM 4 C14 1nF 14 16 FAST CHARGE FULL CHARGE 17 15 TIMER2 FASTCHG FULLCHG FAULT FAULT Figure 1. Typical Application Circuit Maxim Integrated 9 MAX1737 Stand-Alone Switch-Mode Lithium-Ion Battery-Charger Controller FASTCHARGE STATE BATTERY CURRENT FULLCHARGE STATE TOP-OFF STATE DONE CHARGE I = 1C BATTERY VOLTAGE FASTCHG OUTPUT OPENDRAIN LOW FULLCHG OUTPUT OPENDRAIN LOW BATTERY INSERTION OR SHDN HIGH TRANSITION TO VOLTAGE MODE (APPROX 85% CHARGE) TOP-OFF TIMER TIMES OUT, END OF ALL CHARGE FUNCTIONS FULL-CHARGE TIMER TIMES OUT OR BATTERY CURRENT DROPS TO C/10 (APPROX 95% CHARGE) Figure 2. Charge State and Indicator Output Timing for a Typical Charging Sequence accuracy is better than 1% while using 1% setting resistors. The MAX1737 includes a state machine that controls the charging algorithm. Figure 4 shows the state diagram. Table 1 lists the charging state conditions. When power is applied or SHDN is driven high, the part goes into the reset state where the timers are reset to zero to prepare for charging. From the reset state, it enters the prequalification state. In this state, 1/20 of the fastcharge current charges the battery, and the battery temperature and voltage are measured. If the voltage is above the undervoltage threshold and the temperature is within the limits, then it will enter the fast-charge state. If the battery voltage does not rise above the undervoltage threshold before the prequalification timer expires, the charging terminates and the FAULT output goes low. The prequalification time is set by the TIMER1 capacitor (CTIMER1). If the battery is outside the temperature limits, charging and the timer are suspended. Once the temperature is back within limits, charging and the timer resume. In the fast-charge state, the FASTCHG output goes low, and the batteries charge with a constant current (see the Charging Current Regulator section). If the battery voltage reaches the voltage limit before the fast timer expires, the part enters the full-charge state. If the fastcharge timer expires before the voltage limit is reached, charging terminates with a fault indication. The fast-charge time limit is set by the TIMER2 capaci- 10 tor (CTIMER2). If the battery temperature is outside the limits, charging pauses and the timers are suspended until the temperature returns to within the limits. In the full-charge state, the FULLCHG output goes low and the batteries charge at a constant voltage (see the Voltage Regulator section). When the charging current drops below 10% of the charging current limit, or if the full-charge timer expires, the state machine enters the top-off state. In the top-off state, the batteries continue to charge at a constant voltage until the top-off timer expires, at which time it enters the done state. In the done state, charging stops until the battery voltage drops below the recharge-voltage threshold. It then enters the reset state to start the charging process again. In the full-charge or the top-off state, if the battery temperature is outside the limits, charging pauses and the timers are suspended until the battery temperature returns to within limits. Voltage Regulator Li+ batteries require a high-accuracy voltage limit while charging. The MAX1737 uses a high-accuracy voltage regulator (0.8%) to limit the charging voltage. The battery regulation voltage is nominally set to 4.2V per cell and can be adjusted 5% by setting the voltage at the VADJ pin between reference voltage and ground. By limiting the adjust range of the regulation voltage, an overall voltage accuracy of better than 1% is maintained while using 1% resistors. CELL sets the cell count from one to four series cells (see Setting the Battery Regulation Voltage section). An internal error amplifier (GMV) maintains voltage regulation (Figure 3). The GMV amplifier is compensated at CCV. The component values shown in Figure 1 provide suitable performance for most applications. Individual compensation of the voltage regulation and current regulation loops allows for optimal compensation of each. Charging Current Regulator The charging current-limit regulator limits the charging current. The current is sensed by measuring the voltage across the current-sense resistor (R18, Figure 1) placed between the BATT and CS pins. The voltage on the ISETOUT pin also controls the charging current. Full-scale charging current is achieved by connecting ISETOUT to REF. In this case, the full-scale currentsense voltage is 200mV from CS to BATT. When choosing the charging current-sense resistor, note that the voltage drop across this resistor causes further power loss, reducing efficiency. However, adjusting ISETOUT to reduce the voltage across the Maxim Integrated MAX1737 Stand-Alone Switch-Mode Lithium-Ion Battery-Charger Controller SHDN 160ns SLOPE COMP STOP SAW BATT BATT CS REF/42 5x CSI MAX1737 CCI GMI 3R ISETOUT R R/9 SW+ PREQ GND GATE CONTROL SWGND CSSP PWMCOMP 10x CSS CSSN CSCCI LVC 3R GMS ISETIN CCS GND REF/2.6 EA+ DHI ON CS+ BST DHI PWMCMP LX ILIMIT DLO LOWILIM OSC EA- LO VLO DLO PGND CCV R R REF/2 GND REF/42 R R/2 R/2 R/2 160ns ONE CELL PWMOSC TWO CELL THREE FOUR REF GND R VADJ 9R GMV CCV CCS R GND Figure 3. PWM Controller Block Diagram current-sense resistor may degrade accuracy due to the input offset of the current-sense amplifier. The charging-current error amplifier (GMI) is compensated at CCI. A 47nF capacitor at CCI provides suitable performance for most applications. Maxim Integrated Input Current Regulator The total input current (from a wall cube or other DC source) is the sum of system supply current plus the battery-charging current. The input current regulator limits the source current by reducing charging current when input current exceeds the set input current limit. System current normally fluctuates as portions of the system are powered up or put to sleep. Without input 11 MAX1737 Stand-Alone Switch-Mode Lithium-Ion Battery-Charger Controller SHUTDOWN SHUTDOWN IS ENTERED FROM ALL STATES WHEN SHDN IS LOW. FASTCHG = HIGH FULLCHG = HIGH FAULT = HIGH VDCIN < BATT SHDN HIGH VBATT < UNDERVOLTAGE THRESHOLD VDCIN > VBATT RESET FASTCHG = HIGH FULLCHG = HIGH FAULT = HIGH PREQUAL FAULT PREQUAL TIMEOUT FASTCHG = LOW FULLCHG = HIGH FAULT = HIGH FASTCHG = HIGH FULLCHG = HIGH FAULT = LOW VBATT > 2.5V TEMP NOT OK TEMP OK FAST CHARGE FASTCHG = LOW FULLCHG = HIGH FAULT = HIGH ONCE PER SECOND TEMP OK ONCE PER SECOND TEMP QUAL TEMP OK VBATT < 0.95 x VBATTR VBATT = BATTERY REGULATION VOLTAGE (VBATTR) FULL CHARGE VBATT < 0.95 x VBATTR FASTCHG = HIGH FULLCHG = LOW FAULT = HIGH TEMP OK TEMP NOT OK FAST-CHARGE TIMEOUT TEMP NOT OK ICHARGE < IMIN OR FULL-CHARGE TIMEOUT TOP-OFF FASTCHG = HIGH FULLCHG = HIGH FAULT = HIGH TOP-OFF TIMEOUT DONE FASTCHG = HIGH FULLCHG = HIGH FAULT = HIGH Figure 4. State Diagram current regulation, the input source must be able to supply the maximum system current plus the maximum charger input current. By using the input current limiter, the current capability of the AC wall adapter may be lowered, reducing system cost. Input current is measured through an external sense resistor at CSSP and CSSN. The voltage at ISETIN also adjusts the input current limit. Full-scale input current is achieved when ISETIN is connected to REF, setting the full-scale current-sense voltage to 100mV. When choosing the input current-sense resistor, note that the voltage drop across this resistor adds to the power loss, reducing efficiency. Reducing the voltage 12 across the current-sense resistor may degrade input current limit accuracy due to the input offset of the input current-sense amplifier. The input current error amplifier (GMS) is compensated at CCS. A 47nF capacitor at CCS provides suitable performance for most applications. PWM Controller The PWM controller drives the external MOSFETs to control the charging current or voltage. The input to the PWM controller is the lowest of CCI, CCV, or CCS. An internal clamp limits the noncontrolling signals to within 200mV of the controlling signal to prevent delay when switching between regulation loops. Maxim Integrated MAX1737 Stand-Alone Switch-Mode Lithium-Ion Battery-Charger Controller Table 1. Charging State Conditions STATE ENTRY CONDITIONS STATE CONDITIONS Reset From initial power on or From done state if battery voltage < recharge voltage threshold or VDCIN - VBATT < 100mV or VBATT > battery overvoltage threshold Timers reset, charging current = 0, FASTCHG = high, FULLCHG = high, FAULT = high Prequalification From reset state if input power, reference, and internal bias are within limits Battery voltage undervoltage threshold, charging current = C/20, timeout = 7.5min typ (CTIMER1 = 1nF), FASTCHG = low, FULLCHG = high, FAULT = high Fast Charge (Constant Current) From prequalification state if battery voltage > undervoltage threshold Undervoltage threshold battery voltage battery regulation voltage, charging current = current limit, timeout = 90min typ (CTIMER2 = 1nF), FASTCHG = low, FULLCHG = high, FAULT = high Full Charge (Constant Voltage) From fast-charge state if battery voltage = battery regulation voltage Battery voltage = battery regulation voltage, charging current current limit, timeout = 90min typ (CTIMER1 = 1nF), FASTCHG = high, FULLCHG = low, FAULT = high Top-Off (Constant Voltage) From full-charge state if full-charge timer expires or charging current 10% of current limit Battery voltage = battery regulation voltage, charging current 10% of current limit, timeout = 45min typ (CTIMER1 = 1nF), FASTCHG = high, FULLCHG = high, FAULT = high Done From top-off state if top-off timer expires Recharge voltage threshold battery voltage battery regulation voltage, charging current = 0, FASTCHG = high, FULLCHG = high, FAULT = high Over/Under Temperature From fast-charge state or full-charge state if battery temperature is outside of limits Charge current = 0, timers suspended, FASTCHG = no change, FULLCHG = no change, FAULT = no change Fault From prequalification state if prequalification timer expires or From fast-charge state if fast-charge timer expires Charging current = 0, FASTCHG = high, FULLCHG = high, FAULT = low Maxim Integrated 13 MAX1737 Stand-Alone Switch-Mode Lithium-Ion Battery-Charger Controller The current-mode PWM controller uses the inductor current to regulate the output voltage or current, simplifying stabilization of the regulation loops. Separate compensation of the regulation circuits allows each to be optimally stabilized. Internal slope compensation is included, ensuring stable operation over a wide range of duty cycles. The controller drives an external N-channel MOSFET switch and a synchronous rectifier to step the input voltage down to the battery voltage. A bootstrap capacitor drives the high-side MOSFET gate to a voltage higher than the input source voltage. This capacitor (between BST and LX) is charged through a diode from VLO when the synchronous rectifier is on. The high-side MOSFET gate is driven from BST, supplying sufficient voltage to fully drive the MOSFET gate even when its source is near the input voltage. The synchronous rectifier is driven from DLO to behave like a diode, but with a smaller voltage drop for improved efficiency. A built-in dead time (50ns typ) between switch and synchronous rectifier turn-on and turn-off prevents crowbar currents (currents that flow from the input voltage to ground due to both the MOSFET switch and synchronous rectifier being on simultaneously). This dead time may allow the body diode of the synchronous rectifier to conduct. If this happens, the resulting forward voltage and diode recovery time will cause a small loss of efficiency and increased power dissipation in the synchronous rectifier. To prevent the body diode from conducting, place an optional Schottky rectifier in parallel with the drain and source of the synchronous rectifier. The internal current-sense circuit turns off the synchronous rectifier when the inductor current drops to zero. Timers The MAX1737 includes safety timers to terminate charging and to ensure that faulty batteries are not charged indefinitely. TIMER1 and TIMER2 set the timeout periods. TIMER1 controls the maximum prequalification time, maximum full-charge time, and the top-off time. TIMER2 controls the maximum fast-charge time. The timers are set by external capacitors. The typical times of 7.5 minutes for prequalification, 90 minutes for full charge, 45 minutes for top-off, and 90 minutes for fast charge are set by using a 1nF capacitor on TIMER1 and TIMER2 (Figure 1). The timers cannot be disabled. Charge Monitoring Outputs FASTCHG, FULLCHG, and FAULT are open-drain outputs that can be used as LED drivers. FASTCHG indicates the battery is being fast charged. FULLCHG indicates the charger has completed the fast-charge 14 cycle (approximately 85% charge) and is operating in voltage mode. The FASTCHG and FULLCHG outputs can be tied together to indicate charging (see Figure 2). FAULT indicates the charger has detected a charging fault and that charging has terminated. The charger can be brought out of the FAULT condition by removing and reapplying the input power, or by pulling SHDN low. Thermistor The intent of THM is to inhibit fast-charging the cell when it is too cold or too hot (+2.5C TOK +47.5C), using an external thermistor. THM time multiplexes two sense currents to test for both hot and cold qualification. The thermistor should be 10k at +25C and have a negative temperature coefficient (NTC); the THM pin expects 3.97k at +47.5C and 28.7k at +2.5C. Connect the thermistor between THM and GND. If no temperature qualification is desired, replace the thermistor with a 10k resistor. Thermistors by Philips/BCcomponents (2322-640-63103), Cornerstone Sensors (T101D103-CA), and Fenwal Electronics (140103LAG-RB1) work well. Shutdown When SHDN is pulled low, the MAX1737 enters the shutdown mode and charging is stopped. In shutdown, the internal resistive voltage-divider is removed from BATT to reduce the current drain on the battery to less than 1A. DHI and DLO are low. However, the internal linear regulator (VLO) and the reference (REF) remain on. The status outputs FASTCHG, FULLCHG, and FAULT are high impedance. When exiting shutdown mode, the MAX1737 goes back to the power-on reset state, which resets the timers and begins a new charge cycle. Source Undervoltage Shutdown (Dropout) If the voltage on DCIN drops within 100mV of the voltage on BATT, the charger resets. Table 2. Cell-Count Programming CELL CELL COUNT (N) GND 1 Float 2 REF 3 VL 4 Maxim Integrated MAX1737 Stand-Alone Switch-Mode Lithium-Ion Battery-Charger Controller Design Procedure Setting the Battery Regulation Voltage VADJ sets the per-cell voltage limit. To set the VADJ voltage, use a resistor-divider from REF to GND. A GND-to-VREF change at VADJ results in a 5% change in the battery limit voltage. Since the full VADJ range results in only a 10% change on the battery regulation voltage, the resistor-divider's accuracy need not be as high as the output voltage accuracy. Using 1% resistors for the voltage-dividers results in no more than 0.1% degradation in output voltage accuracy. VADJ is internally buffered so that high-value resistors can be used. Set VVADJ by choosing a value less than 100k for R8 and R9 (Figure 1) from VADJ to GND. The percell battery termination voltage is a function of the battery chemistry and construction; thus, consult the battery manufacturer to determine this voltage. Once the per-cell voltage limit battery regulation voltage is determined, the VADJ voltage is calculated by the equation: 9.5 x V BATTR - (9.0 x V VADJ = REF ) N where VBATTR is N x the cell voltage. CELL is the programming input for selecting cell count N. Table 2 shows how CELL is connected to charge one to four cells. Setting the Charging Current Limit Figure 1) between CSSP and CSSN. The full-scale source current is IFSS = 0.1V / R12. The input current limit (IIN) is therefore: V IIN = I FSS ISETIN VREF Set ISETIN to REF to get the full-scale current limit. Short CSSP and CSSN to DCIN if the input source current limit is not used. In choosing the current-sense resistor, note that the drop across this resistor causes further power loss, reducing efficiency. However, too low a resistor value may degrade input current limit accuracy. Inductor Selection The inductor value may be changed to achieve more or less ripple current. The higher the inductance, the lower the ripple current will be; however, as the physical size is kept the same, higher inductance typically will result in higher series resistance and lower saturation current. A good trade-off is to choose the inductor so that the ripple current is approximately 30% to 50% of the DC average charging current. The ratio of ripple current to DC charging current (LIR) can be used to calculate the optimal inductor value: L= VBATT (VDCIN(MAX) - VBATT ) VDCIN(MAX) x f x I CHG x LIR A resistor-divider from REF to GND sets the voltage at ISETOUT (V ISETOUT ). This voltage determines the charging current during the current-regulation fastcharge mode. The full-scale charging current (IFSI) is set by the current-sense resistor (R18, Figure 1) between CS and BATT. The full-scale current is IFSI = 0.2V / R18. where f is the switching frequency (300kHz). The charging current ICHG is therefore: The input capacitor absorbs the switching current from the charger input and prevents that current from circulating through the source, typically an AC wall cube. Thus, the input capacitor must be able to handle the input RMS current. Typically, at high charging currents, the converter will operate in continuous conduction (the inductor current does not go to 0). In this case, the RMS current of the input capacitor may be approximated by the equation: V I CHG = I FSI ISETOUT VREF In choosing the current-sense resistor, note that the drop across this resistor causes further power loss, reducing efficiency. However, too low a value may degrade the accuracy of the charging current. Setting the Input Current Limit A resistor-divider from REF to GND can set the voltage at ISETIN (VISETIN). This sets the maximum source current allowed at any time during charging. The source current (IFSS) is set by the current-sense resistor (R12, Maxim Integrated The peak inductor current is given by: LIR I PEAK = I CHG 1+ 2 Capacitor Selection I CIN I CHG D - D2 where I CIN = the input capacitor RMS current, D = PWM converter duty ratio (typically VBATT / VDCIN), and ICHG = battery charging current. 15 MAX1737 Stand-Alone Switch-Mode Lithium-Ion Battery-Charger Controller The maximum RMS input current occurs at 50% duty cycle, so the worst-case input ripple current is 0.5 x ICHG. If the input to output voltage ratio is such that the PWM controller will never work at 50% duty cycle, then the worst-case capacitor current will occur where the duty cycle is nearest 50%. The impedance of the input capacitor is critical to preventing AC currents from flowing back into the wall cube. This requirement varies depending on the wall cube's impedance and the requirements of any conducted or radiated EMI specifications that must be met. Aluminum electrolytic capacitors are generally the least costly, but are usually a poor choice for portable devices due to their large size and low equivalent series resistance (ESR). Tantalum capacitors are better in most cases, as are high-value ceramic capacitors. For equivalent size and voltage rating, tantalum capacitors will have higher capacitance and ESR than ceramic capacitors. This makes it more critical to consider RMS current and power dissipation when using tantalum capacitors. The output filter capacitor is used to absorb the inductor ripple current. The output capacitor impedance must be significantly less than that of the battery to ensure that it will absorb the ripple current. Both the capacitance and ESR rating of the capacitor are important for its effectiveness as a filter and to ensure stability of the PWM circuit. The minimum output capacitance for stability is: VBATT VREF 1+ VDCIN(MIN) COUT > VBATT x f x RCS where COUT is the total output capacitance, VREF is the reference voltage (4.2V), VBATT is the maximum battery voltage (typically 4.2V per cell), and VDCIN(MIN) is the minimum source input voltage. The maximum output capacitor ESR allowed for stability is: RESR < RCS x VBATT VREF where RESR is the output capacitor ESR and RCS is the current-sense resistor from CS to BATT. Setting the Timers The MAX1737 contains four timers: a prequalification timer, fast-charge timer, full-charge timer, and top-off timer. Connecting a capacitor from TIMER1 to GND and TIMER2 to GND sets the timer periods. The TIMER1 input controls the prequalification, full-charge, and top-off times, while TIMER2 controls fast-charge 16 timeout. The typical timeouts for a 1C charge rate are set to 7.5 minutes for the prequalification timer, 90 minutes for the fast-charge timer, 90 minutes for the fullcharge timer, and 45 minutes for the top-off timer by connecting a 1nF capacitor to TIMER1 and TIMER2. Each timer period is directly proportional to the capacitance at the corresponding pin. See the Typical Operating Characteristics. Compensation Each of the three regulation loops--the input current limit, the charging current limit, and the charging voltage limit--can be compensated separately using the CCS, CCI, and CCV pins, respectively. The charge-current loop error amp output is brought out at CCI. Likewise, the source-current error amplifier output is brought out at CCS; 47nF capacitors to ground at CCI and CCS compensate the current loops in most charger designs. Raising the value of these capacitors reduces the bandwidth of these loops. The voltage-regulating loop error amp output is brought out at CCV. Compensate this loop by connecting a capacitor in parallel with a series resistor-capacitor (RC) from CCV to GND. Recommended values are shown in Figure 1. Applications Information MOSFET Selection The MAX1737 uses a dual N-channel external power MOSFET switch to convert the input voltage to the charging current or voltage. The MOSFET must be selected to meet the efficiency and power-dissipation requirements of the charging circuit, as well as the temperature rise of the MOSFETs. The MOSFET characteristics that affect the power dissipation are the drain-source on-resistance (R DS(ON) ) and the gate charge. In general, these are inversely proportional. To determine the MOSFET power dissipation, the operating duty cycle must first be calculated. When the charger is operating at higher currents, the inductor current will be continuous (the inductor current will not drop to 0A) and, in this case, the high-side MOSFET duty cycle (D) can be approximated by the equation: D VBATT VDCIN and the synchronous-rectifier MOSFET duty cycle (D) will be 1 - D or: V -V D DCIN BATT VDCIN Maxim Integrated MAX1737 Stand-Alone Switch-Mode Lithium-Ion Battery-Charger Controller For the high-side switch, the worst-case power dissipation due to on-resistance occurs at the minimum source voltage VDCIN(MIN) and the maximum battery voltage VBATT(MAX), and can be approximated by the equation: PR VBATT(MAX) VDCIN(MIN) x RDS(ON) x ICHG 2 VL and REF Bypassing The transition loss can be approximated by the equation: V x ICHG x f x t TR PT DCIN 3 where tTR is the MOSFET transition time. So the total power dissipation of the high-side switch is PTOT = PR + PT. The worst-case synchronous-rectifier power occurs at the minimum battery voltage VBATT(MIN) and the maximum source voltage VDC(MAX), and can be approximated by: PDL VDCIN(MAX) - VBATT(MIN) VDCIN(MAX) x RDS(ON) x ICHG 2 There is a brief dead time where both the high-side switch and synchronous rectifier are off. This prevents crowbar currents that flow directly from the source voltage to ground. During the dead time, the inductor current will turn on the synchronous-rectifier MOSFET body diode, which may degrade efficiency. To prevent this, Maxim Integrated connect a Schottky rectifier across the drain source of the synchronous rectifier to stop the body diode from conducting. The Schottky rectifier may be omitted, typically degrading the efficiency by approximately 1% to 2%, causing a corresponding increase in the low-side synchronous-rectifier power dissipation. The MAX1737 uses an internal linear regulator to drop the input voltage down to 5.4V, which powers the internal circuitry. The output of the linear regulator is the VL pin. The internal linear regulator may also be used to power external circuitry as long as the maximum current and power dissipation of the linear regulator are not exceeded. The synchronous-rectifier MOSFET gate driver (DLO) is powered from VLO. An internal 12 resistor from VL to VLO provides the DC current to power the gate driver. Bypass VLO to PGND with a 0.1F or greater capacitor. A 4.7F bypass capacitor is required at VL to ensure that the regulator is stable. A 1F bypass capacitor is also required between REF and GND to ensure that the internal 4.2V reference is stable. In both cases use a low-ESR ceramic capacitor. Chip Information TRANSISTOR COUNT: 5978 17 MAX1737 Stand-Alone Switch-Mode Lithium-Ion Battery-Charger Controller Package Information QSOP.EPS (The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information go to www.maxim-ic.com/packages.) PACKAGE OUTLINE, QSOP .150", .025" LEAD PITCH 21-0055 F 1 1 Note: The MAX1737EEI is a 28-pin QSOP and does not have a heat slug. Revision History Pages changed at Rev 4: 1, 9, 18 Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim reserves the right to change the circuitry and specifications without notice at any time. The parametric values (min and max limits) shown in the Electrical Characteristics table are guaranteed. Other parametric values quoted in this data sheet are provided for guidance. 18 (c) Maxim Integrated 160 Rio Robles, San Jose, CA 95134 USA 1-408-601-1000 Maxim Integrated The Maxim logo and Maxim Integrated are trademarks of Maxim Integrated Products, Inc.