EVALUATION KIT AVAILABLE MAX1737 Stand-Alone Switch-Mode Lithium-Ion Battery-Charger Controller General Description 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. 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. Applications Features Stand-Alone Charger for Up to Four Li+ Cells 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 90% Conversion Efficiency Ordering Information PART TEMP. RANGE PIN-PACKAGE MAX1737EEI -40C to +85C 28 QSOP Typical Operating Circuit INPUT SUPPLY Notebook Computers Hand-Held Instruments Li+ Battery Packs Desktop Cradle Chargers VL REF Pin Configuration CSSP CSSN MAX1737 VL 1 28 DCIN CELL 27 CSSP VADJ ISETOUT 3 26 CSSN THM 4 REF 5 MAX1737 23 BST 22 VLO VADJ 8 21 DLO CCV 9 20 PGND CCS 10 19 CS CS CELL 12 17 FULLCHG TIMER1 13 16 FASTCHG TIMER2 14 15 FAULT RS CCS BATT CCV 18 SHDN QSOP DLO 24 LX GND 6 CCI 11 LX PGND 25 DHI BATT 7 SYSTEM LOAD VLO ISETOUT ISETIN 2 DHI BST ISETIN TOP VIEW 19-1626; Rev 5; 7/17 DCIN ON OFF THM CCI FASTCHG TIMER1 FULLCHG TIMER2 FAULT SHDN GND Li+ BATTERY 1 TO 4 CELLS 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 28 V 7 mA SUPPLY AND REFERENCE DCIN Input Voltage Range DCIN Quiescent Supply Current 6 6.0V < VDCIN < 28V 5 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 270 300 330 kHz 97 98 SWITCHING REGULATOR PWM Oscillator Frequency VBATT = 15V, CELL = VL LX Maximum Duty Cycle In dropout fOSC / 4, VCCV = 2.4V, VBATT = 15V, CELL = VL 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 www.maximintegrated.com 10 A 7 W LX = VDCIN = 28V, SHDN = GND 0.1 10 A SHDN = GND, VBATT = 19V 0.1 5 A 225 500 CELL = SHDN = VL, VBATT = 17V BATT, CS Input Voltage Range Battery Regulation Voltage (VBATTR) % 0 V 4.233 V/cell 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 4.2 19 VVADJ = GND 3.948 3.979 4.010 VVADJ = REF 4.386 4.421 4.453 % V/cell Maxim Integrated 2 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 VISETOUT = VREF / 5 50 CS to BATT Current-Sense Voltage 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 CCI Amplifier Output Current VCS - VBATT = 0, 400mV 100 CCS Amplifier Transconductance ISET = REF, VCCS = 2V 1.2 2 2.6 mS CCS Amplifier Output Current VCSSP - VCSSN = 0, 200mV A 100 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 kW THM HOT Threshold Resistance (Note 3) Combines THM high-temperature current and THM rising threshold, VTRT/ITHTC 3.819 3.964 4.115 kW 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 www.maximintegrated.com 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 A -5 5 ISETIN Adjustment Range VREF/5 VREF V ISETOUT Adjustment Range VREF/5 VREF V 300 mV CELL Input Bias Current ISETOUT Voltage for ICHG = 0 CELL Input Voltage FASTCHG, FULLCHG, FAULT Output Low Voltage 150 0 0.5 For 2 cells 1.5 2.5 For 3 cells V REF 0.3 VREF + 0.3 For 4 cells VVL 0.4 ISINK = 5mA FASTCHG, FULLCHG, FAULT Output High FASTCHG, FULLCHG, FAULT = 28V; Leakage SHDN = GND www.maximintegrated.com 220 For 1 cell - V VVL 0.5 V 1 A Maxim Integrated 4 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 TYP 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 340 kHz 7 W 0 19 V 4.158 4.242 V/cell 6V < VDCIN < 28V SWITCHING REGULATOR PWM Oscillator Frequency VBATT = 15V, CELL = VL 260 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 3 17 mV ERROR AMPLIFIERS CS to BATT Current-Sense Voltage When in VBATT < 2.4V per cell Prequalification State 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 kW 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 www.maximintegrated.com 1nF on TIMER1 and TIMER2 Maxim Integrated 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 Note Note Note Note Note 1: Battery Regulation Voltage = Number of Cells x (3.979V + 0.10526 x VVADJ). 2: This transconductance is for one cell. Divide by number of cells to determine actual transconductance. 3: See Thermistor section. 4: Below this threshold, the charger reverts to prequalification mode and ICHG is reduced to about 5% of full scale. 5: Above this threshold, the charger returns to reset. 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 5A (max), but internal IC bias current remains on. Note 9: Specifications to -40C are guaranteed by design and not production tested. www.maximintegrated.com Maxim Integrated 6 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 2.0 1.5 1.0 0.5 1.0 1.5 2.0 0 0 4.200 4.190 4.15 4.185 4.10 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 4.175 MAX1737 toc03 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 90 80 70 60 -40 -20 0 20 40 60 80 50 100 CELL = FLOAT (2 CELLS) VBATT = 7V R18 = 0.1 (IBATT = 2A) 8 12 16 20 24 VADJ VOLTAGE (V) TEMPERATURE (C) INPUT VOLTAGE (V) REFERENCE LOAD REGULATION TIMEOUT vs. TIMER1 CAPACITANCE FAST-CHARGE TIMEOUT vs. TIMER2 CAPACITANCE 4.208 4.206 TOP-OFF MODE FULL-CHARGE MODE 100 TIMEOUT (MINUTES) 4.204 4.202 4.200 4.198 4.196 4.194 10 PREQUALIFICATION MODE 1 1000 TIMEOUT (MINUTES) 1000 MAX1737 toc07 0 0 100 4.180 4.00 20 EFFICIENCY vs. INPUT VOLTAGE 4.205 EFFICIENCY (%) 4.20 40 ISETIN VOLTAGE (V) 4.195 4.25 60 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 REFERENCE VOLTAGE vs. TEMPERATURE 4.05 REFERENCE VOLTAGE (V) 25 VOLTAGE LIMIT vs. VADJ VOLTAGE 4.30 4.210 50 ISETOUT VOLTAGE (V) 4.35 3.95 75 CHARGING CURRENT (A) 4.40 VOLTAGE LIMIT (V) 2.5 MAX1737 toc04 4.45 0.5 100 80 28 MAX1737 toc09 0 125 MAX1737 toc05 0 150 100 MAX1737 toc06 2.5 175 120 INPUT CURRENT-SENSE VOLTAGE (mV) 3.0 200 INPUT CURRENT-SENSE VOLTAGE vs. ISETIN VOLTAGE MAX1737 toc08 BATTERY VOLTAGE (V) 3.5 225 MAX1737 toc02 MAX1737 toc01 R18 = 0.1 4.0 REFERENCE VOLTAGE (V) 4.5 CHARGING CURRENT-SENSE VOLTAGE (mV) BATTERY VOLTAGE vs. CHARGING CURRENT 100 10 4.192 4.190 0 100 200 300 400 500 600 700 800 900 1000 REFERENCE CURRENT (A) www.maximintegrated.com 0.1 0.1 1 CAPACITANCE (nF) 10 1 0.1 1 10 CAPACITANCE (nF) Maxim Integrated 7 MAX1737 Stand-Alone Switch-Mode Lithium-Ion Battery-Charger Controller Pin Description PIN NAME FUNCTION 1 VL Chip Power Supply. Output of the 5.4V linear regulator from DCIN. Bypass VL to GND with a 2.2F or larger ceramic capacitor. 2 ISETIN Input Current Limit Adjust. Use a voltage-divider to set the voltage between 0 and VREF. See Input Current Regulator section. 3 ISETOUT Battery Charging Current Adjust. Use a voltage-divider to set the voltage between 0 and VREF. See Charging Current Regulator section. 4 THM Thermistor Input. Connect a thermistor from THM to GND to set a qualification temperature range. If unused, connect a 10kWresistor 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 Cell-Count Programming Input. See Table 2 Shutdown Input. Drive SHDN low to disable charging. Connect SHDN to VL for normal operation. 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. www.maximintegrated.com Battery Current-Sense Positive Input. See Charging Current Regulator section. Power Ground Maxim Integrated 8 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 INPUT SUPPLY D2 28 C7 0.1F 1 C2 0.1F C1 4.7F 18 DCIN CSSP MAX1737 VL CSSN 2 R8 3 C3 1F 8 12 R9 C4 0.1F 6 R1 10k 9 1nF C5 47nF C6 47nF C13 1nF C14 1nF 10 13 14 16 FAST CHARGE FULL CHARGE FAULT REF ISETIN ISETOUT VADJ CELL GND CCV BST DHI LX DLO PGND CS 11 17 15 C8 0.1F R12 26 C9 0.1F + SHDN VLO 5 27 C18 22F + C19 22F SYSTEM LOAD 22 23 D3 25 24 C10 0.1F C11 0.1F L1 22H R18 C15 68F 21 20 THERMISTOR 19 0.1F Li+ BATTERY (1 TO 4 CELLS) CCI BATT 7 0.1F CCS TIMER1 THM 4 TIMER2 FASTCHG FULLCHG FAULT Figure 1. Typical Application Circuit www.maximintegrated.com 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- www.maximintegrated.com 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 current-sense 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 10 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 PREQ SW+ GND GND CSSP 10x CSS CSSN CCI GMS ISETIN CCS LVC R/2 R/2 GND REF/2.6 CCV R CS+ ON PWMCOMP EA+ DHI DLO LOWILIM OSC LO DHI LX ILIMIT EA- DLO VLO PGND REF/42 R/2 160ns ONE CELL PWMCMP BST REF/2 GND R GATE CONTROL CS- 3R R SW- PWMOSC TWO CELL THREE FOUR REF VADJ 9R R GND CCV GMV 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. www.maximintegrated.com 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 Maxim Integrated 11 MAX1737 Stand-Alone Switch-Mode Lithium-Ion Battery-Charger Controller SHUTDOWN VDCIN < BATT SHDN HIGH RESET VBATT < UNDERVOLTAGE THRESHOLD FASTCHG = HIGH FULLCHG = HIGH FAULT = HIGH VDCIN > VBATT PREQUAL FAULT PREQUAL TIMEOUT FASTCHG = LOW FULLCHG = HIGH FAULT = HIGH FASTCHG = HIGH FULLCHG = HIGH FAULT = LOW VBATT > 2.5V TEMP NOT OK TEMP OK TEMP NOT OK TEMP OK FAST-CHARGE TIMEOUT FAST CHARGE ONCE PER SECOND TEMP QUAL DHI AND DLO HELD LOW FOR 800s SHUTDOWN IS ENTERED FROM ALL STATES WHEN SHDN IS LOW. FASTCHG = HIGH FULLCHG = HIGH FAULT = HIGH FASTCHG = LOW FULLCHG = HIGH FAULT = HIGH TEMP OK VBATT < 0.95 x VBATTR VBATT = BATTERY REGULATION VOLTAGE (VBATTR) ONCE PER SECOND FULL CHARGE TEMP OK FASTCHG = HIGH FULLCHG = LOW FAULT = HIGH TEMP NOT OK VBATT < 0.95 x VBATTR 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 across www.maximintegrated.com 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 12 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 www.maximintegrated.com Maxim Integrated 13 MAX1737 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 www.maximintegrated.com Stand-Alone Switch-Mode Lithium-Ion Battery-Charger Controller indicates the charger has completed the fast-charge 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 (140-103LAG-RB1) work well. Charging pauses briefly (DHI and DLO are held Low for 800s) to allow accurate temperature measurement . The battery voltage will have an undershoot when DHI and DLO stop switching during the temperature measurement. The battery voltage will have an overshoot when DHI and DLO resume switching after the temperature measurement. 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 GND Float REF VL CELL COUNT (N) 1 2 3 4 Maxim Integrated 14 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 per-cell battery termination voltage is a function of the battery chemistry and construction; thus, consult the battery manufacturer to determine this voltage. Once the percell voltage limit battery regulation voltage is determined, the VADJ voltage is calculated by the equation: 9.5 x VBATTR = V ADJ - (9.0 x VREF ) 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 A resistor-divider from REF to GND sets the voltage at ISETOUT (VISETOUT). This voltage determines the charging current during the current-regulation fast-charge 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. The charging current ICHG is therefore: 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, Figure 1) between CSSP and CSSN. The full-scale source current is IFSS = 0.1V / R12. The input current limit (IIN) is therefore: V I IN = 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 where f is the switching frequency (300kHz). The peak inductor current is given by: I PEAK = LIR I CHG 1 + 2 Capacitor Selection 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: I CIN I CHG D - D 2 where ICIN = the input capacitor RMS current, D = PWM converter duty ratio (typically VBATT/VDCIN), and ICHG = battery charging current. www.maximintegrated.com Maxim Integrated 15 MAX1737 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 highvalue 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) C OUT > VBATT x f x R CS 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: R x VBATT R ESR < CS 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 www.maximintegrated.com Stand-Alone Switch-Mode Lithium-Ion Battery-Charger Controller 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 full-charge 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 (RDS(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 - VBATT D DCIN VDCIN Maxim Integrated 16 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 R DS(ON) x I CHG 2 The transition loss can be approximated by the equation: VDCIN x I CHG x f x t TR 3 where tTR is the MOSFET transition time. So the total power dissipation of the high-side switch is PTOT = PR + PT. 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 R DS(ON) x I CHG 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, www.maximintegrated.com 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. VL and REF Bypassing 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 Maxim Integrated 17 MAX1737 Stand-Alone Switch-Mode Lithium-Ion Battery-Charger Controller Package Information For the latest package outline information and land patterns (footprints), go to www.maximintegrated.com/packages. Note that a "+", "#", or "-" in the package code indicates RoHS status only. Package drawings may show a different suffix character, but the drawing pertains to the package regardless of RoHS status. PACKAGE TYPE PACKAGE CODE OUTLINE NO. LAND PATTERN NO. 28 QSOP E28+1 21-0055 90-0173 Note: The MAX1737EEI is a 28-pin QSOP and does not have a heat slug. www.maximintegrated.com Maxim Integrated 18 MAX1737 Stand-Alone Switch-Mode Lithium-Ion Battery-Charger Controller Revision History PAGES REVISION NUMBER REVISION DATE 4 5/09 Initial release 5 7/17 Replaced Figure 4 and added information to Thermistor section DESCRIPTION CHANGED 1, 9, 18 12, 14 For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642, or visit Maxim Integrated's website at www.maximintegrated.com. Maxim Integrated cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim Integrated product. No circuit patent licenses are implied. Maxim Integrated 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. Maxim Integrated and the Maxim Integrated logo are trademarks of Maxim Integrated Products, Inc. (c) 2017 Maxim Integrated Products, Inc. 19 Mouser Electronics Authorized Distributor Click to View Pricing, Inventory, Delivery & Lifecycle Information: Maxim Integrated: MAX1737EEI+ MAX1737EEI+T MAX1737EEI-T MAX1737EEI