19-1754; Rev 0; 6/00 KIT ATION EVALU E L B A AVAIL Stand-Alone, Switch-Mode Li+ Battery Charger with Internal 14V Switch Features ♦ Stand-Alone Charger for Up to 3 Li+ Batteries ♦ ±0.8% Battery Regulation Voltage Accuracy ♦ Low-Dropout 98% Duty Cycle ♦ Safely Precharges Near-Dead Cells ♦ Continuous Voltage and Temperature Monitoring ♦ 0.1µA Shutdown Battery Current ♦ Input Voltage Up to 14V ♦ Up to 1.5A Programmable Charge Current ♦ Input Current Limiting ♦ Space-Saving 28-Pin SSOP ♦ 300kHz PWM Oscillator Reduces Noise Ordering Information PART MAX1757EAI TEMP. RANGE PIN-PACKAGE -40°C to +85°C 28 SSOP Typical Operating Circuit VIN 6V to 14V DCIN CSSP CSSN REF HSD ________________________Applications LX MAX1757 PDAs Desktop Cradle Chargers Li+ Battery Packs Notebook Computers Hand-Held Instruments ISETOUT BST VL Pin Configuration ISETIN PGND TOP VIEW CELL VL 1 28 DCIN ISETTIN 2 27 CSSP ISETOUT 3 26 CSSN THM 4 CS VADJ BATT THM 25 CCV REF 5 GND 6 SYSTEM LOAD CCS 24 CCI MAX1757 THERM 23 CCS VADJ 7 22 BST BATT 8 21 CS HSD 9 20 LX HSD 10 19 LX CELL 11 18 PGND TIMER1 12 17 SHDN TIMER2 13 16 FULLCHG FAULT 14 15 FASTCHG Li+ BATTERY 1 TO 3 CELLS CCI CCV FASTCHG TIMER1 FULLCHG TIMER2 FAULT ON OFF SHDN GND SSOP ________________________________________________________________ Maxim Integrated Products 1 For free samples and the latest literature, visit www.maxim-ic.com or phone 1-800-998-8800. For small orders, phone 1-800-835-8769. MAX1757 General Description The MAX1757 is a switch-mode lithium-ion (Li+) battery charger that charges one to three cells. It provides a regulated charging current accurate to ±10% and a regulated voltage with only a ±0.8% total voltage error at the battery terminals. The internal high-side switch delivers a programmable current of up to 1.5A to charge the battery. The built-in safety timer automatically terminates charging once the adjustable time limit has been reached. The MAX1757 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 (charging + system) and by automatically reducing battery-charging current prevents overload of the input supply, allowing the use of a low-cost wall adapter. The per-cell battery regulation voltage is set between 4.0V and 4.4V using standard 1% resistors. The number of cells is set from 1 to 3 by pin strapping. Battery temperature is monitored by an external thermistor to prevent charging outside the acceptable temperature range. The MAX1757 is available in a space-saving 28-pin SSOP package. Use the MAX1757EVKIT to help reduce design time. For a stand-alone charger with a 28V switch, refer to the MAX1758 data sheet. For a charger controller capable of up to 4A charging current, refer to the MAX1737 data sheet. MAX1757 Stand-Alone, Switch-Mode Li+ Battery Charger with Internal 14V Switch ABSOLUTE MAXIMUM RATINGS BATT, CS, DCIN, CSSP, CSSN, HSD to GND ........-0.3V to +15V CSSP to CSSN.......................................................-0.6V to +0.6V BST to GND ............................................................-0.3V to +21V BST to LX..................................................................-0.3V to +6V LX to PGND ..............................................-0.6V to (VHSD + 0.3V) VL, SHDN, ISETIN, ISETOUT, REF, VADJ, CELL, TIMER1, TIMER2, CCI, CCS, CCV, THM to GND ................-0.3V to +6V FASTCHG, FULLCHG, FAULT to GND ..................-0.3V to +30V CS to BATT Current ............................................................±3.5A PGND to GND .......................................................-0.3V to +0.3V VL Source Current...............................................................50mA Continuous Power Dissipation (TA = +70°C) 28-Pin SSOP (derate 9.5mW/°C above +70°C) ...........762mW Operating Temperature Range ...........................-40°C to +85°C Junction Temperature ......................................................+150°C Storage Temperature Range .............................-65°C to +150°C Lead Temperature (soldering, 10s) .................................+300°C 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 = VHSD = VCSSP = VCSSN = 12V, V SHDN = VVL, VCELL = GND, VBATT = VCS = 4.2V, VVADJ = VREF/2, VISETIN = VISETOUT = VREF, RTHM = 10kΩ, TA = 0°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS SUPPLY AND REFERENCE DCIN Input Voltage Range 6 14 V 5 7 mA 0.075 0.125 0.175 V Rising edge 0.20 0.30 0.40 V 6V < VDCIN < 14V IVL = 0 to 15mA 5.10 5.40 44 5.70 65 V mV 6V < VDCIN < 14V 4.179 4.20 4.221 V 2 6 6 14 mV mV 300 98 2 330 10 kHz % µA 0.1 10 µA DCIN Quiescent Supply Current 6V < VDCIN < 14V DCIN to BATT Dropout Threshold, DCIN Falling Falling edge DCIN to BATT Dropout Threshold, DCIN Rising VL Output Voltage VL Output Load Regulation REF Output Voltage REF Line Regulation REF Load Regulation SWITCHING REGULATOR PWM Oscillator Frequency LX Maximum Duty Cycle CSSN/CSSP Off-State Leakage VREF 6V < VDCIN < 14V IREF = 0 to 1mA fOSC Nondropout fOSC In dropout, fOSC / 4 VCSSN = VCSSP = VDCIN = 14V, V SHDN = GND 270 97 HSD Off-State Leakage VLX = PGND, VHSD = VDCIN = 14V, V SHDN = GND LX Off-State Leakage VLX = VHSD = VDCIN =14V, V SHDN = GND 0.1 10 µA HSD to LX On-Resistance VBST = VLX + 4.5V 150 250 mΩ LX to PGND On-Resistance See PWM Controller section 1 2 Ω 110 170 mΩ CS to BATT Current-Sensing Resistance BATT, CS Input Current 2 RCS Internal resistor between CS and BATT, 1.5A RMS operating V SHDN = GND, VBATT =14V 0.1 5 µA CELL = REF, VBATT = 12V, any charging state 280 540 µA VBATT = 14V, done state 150 270 µA _______________________________________________________________________________________ Stand-Alone, Switch-Mode Li+ Battery Charger with Internal 14V Switch (Circuit of Figure 1, VDCIN = VHSD = VCSSP = VCSSN = 12V, V SHDN = VVL, VCELL = GND, VBATT = VCS = 4.2V, VVADJ = VREF/2, VISETIN = VISETOUT = VREF, RTHM = 10kΩ, TA = 0°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS 2.4 2.7 3.0 A 14 V 4.233 V/cell SWITCHING REGULATOR CS to BATT Hard Current Limit Instantaneous peak current limit BATT, CS Input Voltage Range 0 VOLTAGE LIMIT ACCURACY Battery Regulation Voltage VBATTR CELL = float, GND, or REF Not including VADJ resistor tolerances Absolute Voltage Accuracy With 1% VADJ resistors 4.167 4.2 -0.8 0.8 -1 1 VADJ = GND 3.948 3.979 4.010 VADJ = REF 4.386 4.421 4.453 CCV Amplifier Transconductance VCCV = 2V 0.4 0.7 1.0 CCV Amplifier Maximum Output Current VCCV = 2V ±50 BATT Regulation Voltage Adjustment Range % V/cell ERROR AMPLIFIERS BATT Full-Scale Charge Current mS × cells µA 1.35 1.5 1.65 A BATT 1/10-Scale Charge Current (Note 1) VISETOUT = VREF/10 100 150 200 mA BATT Charge Current in Prequalification State VBATT < 2.4V per cell 100 150 200 mA CCI Battery Current Sense Gain VCCI = 2V 60 130 240 µA/A CCI Amplifier Maximum Output Current VCCI = 2V ±100 CSSP to CSSN Full-Scale Current-Sense Voltage µA 90 100 115 mV 5 10 15 mV 2.0 3.0 mS CSSP to CSSN 1/10-Scale Current-Sense Voltage VISETIN = VREF/10 CCS Amplifier Transconductance VCCS = 2V 1.0 CCS Amplifier Maximum Output Current VCCS = 2V ±100 µA 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 VTRT THM low-temp or high-temp current 1.386 1.40 1.414 V THM Low-Temp Current ITLTC VTHM = 1.4V 46.2 49 51.5 µA THM High-Temp Current ITHTC VTHM = 1.4V 344 353 362 µA THM COLD Threshold Resistance (Note 2) Combines THM low-temp current and THM threshold, VTRT / ITLTC 26.92 28.70 30.59 kΩ THM HOT Threshold Resistance (Note 2) Combines THM high-temp current and THM threshold, VTRT / ITHTC 3.819 3.964 4.115 kΩ _______________________________________________________________________________________ 3 MAX1757 ELECTRICAL CHARACTERISTICS (continued) MAX1757 Stand-Alone, Switch-Mode Li+ Battery Charger with Internal 14V Switch ELECTRICAL CHARACTERISTICS (continued) (Circuit of Figure 1, VDCIN = VHSD = VCSSP = VCSSN = 12V, V SHDN = VVL, VCELL = GND, VBATT = VCS = 4.2V, VVADJ = VREF/2, VISETIN = VISETOUT = VREF, RTHM = 10kΩ, TA = 0°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS BATT Undervoltage Threshold (Note 3) 2.4 2.5 2.6 V/cell BATT Overvoltage Threshold (Note 4) 4.55 4.67 4.8 V/cell FULLCHG BATT Current Termination Threshold (Note 5) 250 330 400 mA BATT Recharge Voltage Threshold (Note 6) 94 95 96 % of VBATTR x cells TIMER1 and 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 Top-Off Timer 40.5 45 49.8 min Temperature Measurement Frequency 0.98 1.12 1.32 Hz STATE MACHINE CONTROL INPUTS/OUTPUTS SHDN Input Voltage High VIH SHDN Input Voltage Low VIL 1.4 VADJ, ISETIN, ISETOUT Input Voltage Range V 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 V SHDN = 0 or VVL -1 1 µA CELL Input Bias Current VCELL = 0 or VVL -5 5 µA 300 mV ISETOUT Shutdown Threshold Voltage (Note 3) 150 For 1 cell CELL Input Voltage For 2 cells (floating) For 3 cells 4 220 0 0.5 1.5 VREF - 0.3 2.5 VREF + 0.3 _______________________________________________________________________________________ V Stand-Alone, Switch-Mode Li+ Battery Charger with Internal 14V Switch (Circuit of Figure 1, VDCIN = VHSD = VCSSP = VCSSN = 12V, V SHDN = VVL, VCELL = GND, VBATT = VCS = 4.2V, VVADJ = VREF/2, VISETIN = VISETOUT = VREF, RTHM = 10kΩ, TA = 0°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS 0.5 V 1 µA CONTROL INPUTS/OUTPUTS FASTCHG, FULLCHG, FAULT Output Low Voltage VOL FASTCHG, FULLCHG, FAULT Output High Leakage ISINK = 5mA V FASTCHG, V FULLCHG, V FAULT = 28V, V SHDN = GND ELECTRICAL CHARACTERISTICS (Circuit of Figure 1, VDCIN = VHSD = VCSSP = VCSSN = 12V, V SHDN = VVL, VCELL = GND, VBATT = VCS = 4.2V, VVADJ = VREF/2, VISETIN = VISETOUT = VREF, RTHM = 10kΩ, TA = -40°C to +85°C, unless otherwise noted.) (Note 7) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS SUPPLY AND REFERENCE DCIN Input Voltage Range VL Output Voltage REF Output Voltage 6V < VDCIN < 14V REF Line Regulation 6V < VDCIN < 14V 6 14 V 5.1 5.7 V 4.166 4.242 V 6 mV SWITCHING REGULATOR PWM Oscillator Frequency fOSC HSD to LX On-Resistance Nondropout fOSC 260 340 kHz 250 mΩ 2 Ω 2.2 3.2 A 0 14 V -0.8 0.8 -1 1 4.158 4.242 V/cell 1.3 1.7 A VBST = VLX + 4.5V LX to PGND On-Resistance CS to BATT Hard Current Limit Instantaneous peak current limit BATT, CS Input Voltage Range ACCURACY AND ERROR AMPLIFIERS Not including VADJ resistor tolerances Absolute Voltage Accuracy With 1% VADJ resistors BATT Regulation Voltage CELL = float, GND, or REF BATT Full-Scale Charge Current % BATT 1/10-Scale Charge Current (Note 1) VISETOUT = VREF/ 10 100 200 mA BATT Charge Current in Prequalification State VBATT < 2.4V per cell 100 200 mA 85 115 mV 5 15 mV CSSP to CSSN Full-Scale Current-Sense Voltage CSSP to CSSN 1/10-Scale Current-Sense Voltage VISETIN = VREF/ 10 STATE MACHINE THM Trip Threshold Voltage VTRT THM low-temp or high-temp current 1.386 1.414 V THM Low-Temp Current ITLTC VTHM = 1.4V 46.2 51.5 µA BATT Undervoltage Threshold (Note 3) 2.4 2.6 V/cell BATT Overvoltage Threshold (Note 4) 4.55 4.8 V/cell _______________________________________________________________________________________ 5 MAX1757 ELECTRICAL CHARACTERISTICS (continued) MAX1757 Stand-Alone, Switch-Mode Li+ Battery Charger with Internal 14V Switch ELECTRICAL CHARACTERISTICS (continued) (Circuit of Figure 1, VDCIN = VHSD = VCSSP = VCSSN = 12V, V SHDN = VVL, VCELL = GND, VBATT = VCS = 4.2V, VVADJ = VREF/2, VISETIN = VISETOUT = VREF, RTHM = 10kΩ, TA = -40°C to +85°C, unless otherwise noted.) (Note 7) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS FULLCHG BATT Current Termination Threshold (Note 5) 250 400 mA Temperature Measurement Frequency 0.93 1.37 Hz CONTROL INPUTS/OUTPUTS SHDN Input Voltage High VIH SHDN Input Voltage Low VIL 1.4 V 0.6 V When VISETOUT = 0, battery charger turns off. See Thermistor section. Below this threshold, charger reverts to a prequalification mode with IBATT reduced to 10% of full scale. Above this threshold, charger is disabled. After full-charge state is complete and BATT current falls below this threshold, FULLCHG output switches high. Battery charging continues until top-off timeout occurs. See Table 1. Note 6: After charging is complete, when BATT voltage falls below this threshold, a new charging cycle is initiated. Note 7: Specifications to -40°C are guaranteed by design, not production tested. Note 1: Note 2: Note 3: Note 4: Note 5: 6 _______________________________________________________________________________________ Stand-Alone, Switch-Mode Li+ Battery Charger with Internal 14V Switch CHARGING CURRENT vs. ISETOUT VOLTAGE 2.0 1.5 0.8 0.6 1.0 0.4 0.5 0.2 0 0 0.4 0.6 0.8 1.0 1.2 1.4 1.6 ISETOUT VOLTAGE (V) VOLTAGE LIMIT vs. VADJ VOLTAGE REFERENCE VOLTAGE vs. TEMPERATURE 4.30 4.25 4.20 4.15 4.10 4.05 0 4.201 4.205 4.200 4.195 4.185 -40 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 4.199 4.198 4.197 4.196 4.194 -20 0 20 40 60 80 0 100 200 300 400 500 600 700 800 900 1000 100 REFERENCE LOAD (µA) TEMPERATURE (°C) VADJ VOLTAGE (V) FAST-CHARGE TIMEOUT vs. TIMER2 CAPACITANCE TIMEOUT vs. TIMER1 CAPACITANCE 100 MAX1757 TOC09 TOP-OFF MODE EFFICIENCY vs. INPUT VOLTAGE 1000 MAX1757 TOC08 1000 2 CELLS 90 10 PREQUALIFICATION MODE 1 100 EFFICIENCY (%) TIMEOUT (MINUTES) VOLTAGE MODE 100 TIMEOUT (MINUTES) 4.200 4.195 4.00 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 4.202 4.190 3.95 20 REFERENCE LOAD REGULATION 4.210 REFERENCE VOLTAGE (V) 4.35 40 ISETIN VOLTAGE (V) 4.215 MAX1757 TOC04 4.40 60 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 CHARGING CURRENT (A) 4.45 80 0 0 REFERENCE VOLTAGE (V) 0.2 MAX1757 TOC05 0 VOLTAGE LIMIT (V) 1.0 MAX1757 TOC07 2.5 100 MAX1757 TOC10 3.0 1.2 120 INPUT CURRENT-SENSE VOLTAGE (mV) 1.4 CHARGING CURRENT (A) 3.5 MAX1757 TOC02 4.0 BATTERY VOLTAGE (V) 1.6 MAX1757 TOC01 4.5 INPUT CURRENT-SENSE REGULATION VOLTAGE vs. ISETIN VOLTAGE MAX1757 TOC03 BATTERY VOLTAGE vs. CHARGING CURRENT 10 80 1 CELL 70 ICHG = 1.0A 60 50 1 0.1 0.1 1 CAPACITANCE (nF) 10 0.1 1 CAPACITANCE (nF) 10 6 8 10 12 14 INPUT VOLTAGE (V) _______________________________________________________________________________________ 7 MAX1757 Typical Operating Characteristics (Circuit of Figure 1, VDCIN = 12V, V SHDN = VVL, VCELL = GND, VVADJ = VREF/2, VISETIN = VISETOUT = VREF, see Figure 1, TA = +25°C, unless otherwise noted.) Stand-Alone, Switch-Mode Li+ Battery Charger with Internal 14V Switch MAX1757 Pin Description 8 PIN NAME FUNCTION 1 VL Chip Power Supply. Output of the 5.4V linear regulator from DCIN. Bypass VL to GND with 2.2µF 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 4 THM Thermistor Input. Connect a thermistor from THM to GND to set qualification temperature range. If unused, connect a 10kΩ resistor from THM to GND. See Thermistor section. 5 REF 4.2V Reference Voltage Output. Bypass REF to GND with 1µF or larger ceramic capacitor. 6 GND Analog Ground 7 VADJ Voltage Adjustment. Use a voltage divider to set the voltage between 0 and VREF to adjust the battery regulation voltage by ±5%. See Battery Regulation Voltage section. 8 BATT Battery Voltage-Sense Input and Current-Sense Negative Input 9, 10 HSD High-Side Drain. This is the drain of the internal high-side FET. See Figure 3. 11 CELL Cell-Count Programming Input. Connect CELL to GND or REF to set 1 or 3 cells, or leave unconnected to set 2 cells. 12 TIMER1 Timer1 Adjustment. Connect a capacitor from TIMER1 to GND to set the prequalification, full-charge, and top-off times. See Timers section. 13 TIMER2 Timer2 Adjustment. Connect a capacitor from TIMER2 to GND to set the fast-charge time. See Timers section. 14 FAULT Charge Fault Indicator. Open-drain output pulls low when charging terminates abnormally. See Table 1. 15 FASTCHG Fast-Charge Indicator. Open-drain output pulls low when charging with constant current. 16 FULLCHG Full-Charge Indicator. Open drain output pulls low when charging with constant voltage in full-charge state. 17 SHDN Shutdown Input. Drive SHDN low to disable charging. Connect SHDN to VL for normal operation. 18 PGND Power Ground. Current from the low-side power MOSFET switch source flows through PGND. 19, 20 LX Power Inductor Switching Node and High-Side Power MOSFET Source 21 CS Battery Current-Sense Positive Input. Connects to internal 0.1Ω resistor between BATT and CS. 22 BST High-Side MOSFET Gate Drive Bias. Connect a 0.1µF capacitor from BST to LX. 23 CCS Charger Source Current Regulation Loop Compensation Point. See Compensation section. 24 CCI Battery Charge Current Regulation Loop Compensation Point. See Compensation section. 25 CCV Voltage Regulation Loop Compensation Point. See Compensation section. 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 0.1µF or greater capacitor. See Detailed Description. Battery Charging Current Adjust. Use a voltage divider to set the voltage between 0 and VREF. See Charging Current Regulator section. _______________________________________________________________________________________ Stand-Alone, Switch-Mode Li+ Battery Charger with Internal 14V Switch MAX1757 MBR5340 INPUT SUPPLY D1 D2 28 DCIN CSSP 27 C7 0.1µF C8 0.1µF R1 0.05Ω MAX1757 CSSN 26 C9 0.1µF 17 TO VL 5 2 R4 3 C3 1µF 7 11 R5 VL ISETIN ISETOUT VADJ R6 10k 25 BST HSD HSD PGND CS CCI CCS BATT 12 FAULT L1 22µH 19 18 21 TIMER1 THM 8 C18 0.1µF C5 1nF FAST CHARGE C14 0.1µF C16 0.1µF 23 FULL CHARGE 9 D4 MBR5340 C2 0.1µF C6 1nF 10 20 C1 0.1µF 24 C11 22µF TO SYSTEM LOAD C13 4.7µF GND C17 1nF C10 22µF + 22 LX CELL CCV C12 0.22µF + D3 REF LX 6 C4 0.1µF SHDN 1 + C15 68µF 4 Li+ BATTERY 1 TO 3 CELLS 13 15 16 14 THERM TIMER2 FASTCHG FULLCHG FAULT Figure 1. Typical Application Circuit General Description The MAX1757 includes all of the functions necessary to charge 1, 2, or 3 Li+ battery cells in series. It includes a step-down 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. rent or voltage. Figure 1 shows the typical application circuit. Figure 2 shows a typical charging sequence and Figure 3 shows the functional diagram. The charging current is set by the voltage at ISETOUT. The battery regulation voltage is measured at the BATT pin. The battery voltage limit 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 limit accuracy is better than 1% while using 1% setting resistors. The DC-DC converter uses an internal power MOSFET switch to convert the input voltage to the charging cur_______________________________________________________________________________________ 9 MAX1757 Stand-Alone, Switch-Mode Li+ Battery Charger with Internal 14V Switch Table 1. Charging State Table STATE ENTRY CONDITIONS STATE CONDITIONS From initial power on Reset or From done state if battery voltage < recharge voltage threshold or VDCIN - VBATT < dropout threshold or VBATT > battery overvoltage threshold Timers reset, charging current = 0, FASTCHG = high, FULLCHG = high, FAULT = high From reset state if input power, reference, and internal bias are within limits Battery voltage ≤ undervoltage threshold, charging current = (fast-charge current / 10), timeout = 7.5min typ (CTIMER1 = 1nF), FASTCHG = low, FULLCHG = high, FAULT = high From prequalification state if battery voltage > undervoltage threshold Undervoltage threshold ≤ battery voltage ≤ battery regulation voltage, charging current = charge 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 ≤ 330mA, 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 If charging current ≤ 330mA Battery voltage = battery regulation voltage, charging current ≤ 330mA 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 ≤ voltage limit, charging current = 0, FASTCHG = high, FULLCHG = high, FAULT = high Over/Undertemperature From fast-charge state or full-charge state if battery temperature is outside limits Charge current = 0, timers suspended, FASTCHG = no change, FULLCHG = no change, FAULT = no change Fault From reset state if battery temperature ≥ maximum battery temperature or Charging current = 0, FASTCHG = high, From prequalification state if prequalification timer expires FULLCHG = high, FAULT = low or From fast-charge state if fast-charge timer expires Prequalification Fast Charge (Constant Current) 10 ______________________________________________________________________________________ Stand-Alone, Switch-Mode Li+ Battery Charger with Internal 14V Switch In the fast-charge state, the FASTCHG output goes low and the batteries charge with a constant current (see 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 and the FAULT output goes low. The fast-charge time limit is set by the TIMER2 capacitor (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 Voltage section). When the charging current drops below 150mA (330mA peak inductor current), or if the full-charge timer expires, the state machine enters the top-off state. In the top-off state, the batteries continues 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, at which time it 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 MAX1757 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 changing the voltage at FASTCHARGE STATE BATTERY CURRENT FULLCHARGE STATE TOP-OFF STATE MAX1757 The MAX1757 includes a state machine that controls the charging algorithm. Figure 4 shows the state diagram. Table 1 is the charging state table. When power is applied, or SHDN input 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, 1/10 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. DONE CHARGE I = 1C BATTERY VOLTAGE FASTCHG OUTPUT OPENDRAIN LOW FULLCHG OUTPUT OPENDRAIN LOW TOP-OFF TIMER TIMES OUT, END OF ALL CHARGE FUNCTIONS BATTERY INSERTION OR SHDN HIGH TRANSITION TO VOLTAGE MODE (APPROX 85% CHARGE) 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 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 1 to 3 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 optimum stability. Charging Current Regulator The charging current-limit regulator limits the charging current. Current is sensed by measuring the voltage across the internal current-sense resistor RCS between BATT and CS. The voltage at ISETOUT adjusts the charging current. Full-scale charging current is achieved when ISETOUT is connected to REF. The charging current error amplifier (GMI) is compensated at CCI. A 0.1µF capacitor at CCI provides suitable performance for most applications. ______________________________________________________________________________________ 11 MAX1757 Stand-Alone, Switch-Mode Li+ Battery Charger with Internal 14V Switch DCIN TO BATT CSS LEVEL SHIFT AND GAIN OF 10 CSSP CSSN ENABLE VL 5.4V REGULATOR INTERNAL REFERENCE REF ON CCV CSI LEVEL SHIFT AND GAIN OF 7 CS RCS BATT CCI CCS BST ON HSD GMS ISETIN LEVEL SHIFT +1 DRIVER LX MIN AND CLAMP 3Rx Rx GMI ISETOUT +1 3Rx Rx REF/2 TO BATT CELL REF/2 = ZERO CURRENT SUMMING COMPARATOR BLOCK ON PGND GMV BDIV FASTCHG CNTRL LOGIC R2 R2 = R(2N - 1) WHERE N = CELL NUMBER R V/I MODE MAX1757 FULLCHG OSCILLATOR, SM, TIMERS THERM CONTROL TEST CIRCUITRY FAULT TIMER 1 TIMER 2 THM TO REF 9R VADJ R +1 R GND Figure 3. Functional Diagram Input Current Regulator The total input current (from a wall cube or other DC source) is the sum of system load 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 will normally fluctuate as portions of the system are powered up or put to sleep. Without input current regulation, the input source must be able to supply the 12 maximum system load 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 regulation voltage to 100mV. ______________________________________________________________________________________ Stand-Alone, Switch-Mode Li+ Battery Charger with Internal 14V Switch VDCIN < BATT MAX1757 SHUTDOWN SHUTDOWN IS ENTERED FROM ALL STATES WHEN SHDN IS LOW. FASTCHG = HIGH FULLCHG = HIGH FAULT = HIGH 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 ONCE PER SECOND TEMP QUAL FULL CHARGE VBATT < 0.95 × VBATTR FASTCHG = HIGH FULLCHG = LOW FAULT = HIGH TEMP OK TEMP OK VBATT < 0.95 × VBATTR VBATT = BATTERY REGULATION VOLTAGE (VBATTR) 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 When choosing the current-sense resistor, note that the voltage drop across this resistor adds to the power loss, reducing efficiency. Reducing the voltage 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 0.1µF capacitor at CCS provides suitable performance for most applications. PWM Controller The PWM controller drives the internal high-side MOSFET to control 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. The current mode PWM controller measures 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 internal N-channel MOSFET switch to step the input voltage down to the battery voltage. The high-side MOSFET gate is driven to a voltage higher than the input source voltage by a bootstrap capacitor. This capacitor (between BST and LX) is charged through a diode from VL when LX is low. An internal N-channel MOSFET turns on momentarily after the high-side switch turns off, pulling LX to PGND to ensure that the bootstrap capacitor charges. The highside MOSFET gate is driven from BST, supplying suffi- ______________________________________________________________________________________ 13 MAX1757 Stand-Alone, Switch-Mode Li+ Battery Charger with Internal 14V Switch cient voltage to fully drive the MOSFET gate even when its source is near the input voltage. Timers The MAX1757 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). 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 cycle (approximately 85% charge) and is operating in voltage mode. The FASTCHG and FULLCHG outputs can be tied together to indicate charging or done (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 only by removing and reapplying the input power, or by pulling SHDN low. Thermistor The intent of THM is to inhibit charging when the battery is too cold or too hot (+2.5°C ≤ TOK ≤ +47.5°C), using an external thermistor. THM time multiplexes two sense currents to test for both hot and cold qualification. The thermistor should be 10kΩ at +25°C and have a negative temperature coefficient (NTC); the THM pin expects 3.97kΩ at +47.5°C and 28.7kΩ at +2.5°C. Connect the thermistor between THM and GND. If no temperature qualification is desired, replace the thermistor with a 10kΩ resistor. Thermistors by Philips/ BCcomponents (2322-640-63103), Cornerstone Sensors (T101D103-CA), and Fenwall Electronics (140103LAG-RB1) work well. The battery temperature is measured at a 1.12Hz rate (CTIMER1 = CTIMER2 = 1nF). Charging is briefly halted to allow accurate measurement. If the temperature goes out of limits while charging is in progress, charging will be suspended until the temperature returns to within the limits. While charging is suspended, the timers will also be suspended but will 14 Table 2. Cell-Count Programming Table CELL CELL COUNT (N) GND 1 Float 2 REF 3 continue counting from where they left off when charging resumes. Shutdown When SHDN is pulled low, the MAX1757 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 5µA. The high-side power MOSFET switch is off. However, the internal linear regulator (VLO) and the reference (REF) remain on. Status outputs FASTCHG, FULLCHG, and FAULT are high impedance. When exiting the shutdown mode, the MAX1757 goes 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 turns off. This prevents battery discharge by the charger during low input voltage conditions. Design Procedure Setting the Battery Regulation Voltage VADJ sets the per-cell voltage limit. To set the VADJ voltage, use a voltage-divider from REF to VADJ. 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 100kΩ for R5 (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: VVADJ = (9.5 VBATTR / N) - (9.0 ✕ VREF) ______________________________________________________________________________________ Stand-Alone, Switch-Mode Li+ Battery Charger with Internal 14V Switch Setting the Charging Current Limit A resistor-divider from REF to GND sets the voltage at ISETOUT (VISETOUT). This determines the charging current during the current-regulation (fast-charge) mode. The full-scale charging current is 1.5A. The charging current (ICHG) is, therefore: VISETOUT ICHG = 1.5A VREF Connect ISETOUT to REF to get the full-scale current limit. where fOSC is the switching frequency (300kHz). The peak inductor current is given by: LIR I PEAK = I ISETOUT1 + 2 Capacitor Selection The input capacitor shunts 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: Setting the Input Current Limit A resistor-divider from REF to GND sets the voltage at ISEVTIN (VISETIN). This sets the maximum source current allowed at any time during charging. The source current I FSS is set by the current-sense resistor R SOURCE between CSSP and CSSN. The full-scale source current is IFSS = 0.1V / R1 (Figure 1). The input current limit (IIN) is therefore: V IIN = IFSS ISETIN VREF Connect ISETIN to REF to get the full-scale input current limit. Short CSSP and CSSN if the input source current limit is not used. In choosing the current-sense resistor, it should be noted that the drop across this resistor adds to the power loss and thus reduces efficiency. However, too low a resistor value may degrade input current-limit accuracy. Inductor Selection The inductor value may be changed for 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, typically, higher inductance will result in higher series resistance and lower saturation current. A good tradeoff 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 fOSC x ICHG x LIR ICIN ≅ ICHG D − D2 where: ICIN is the input capacitor RMS current. D is the PWM converter duty ratio (typically VBATT / VDCIN). ICHG is the battery charging current. The maximum RMS input current occurs at 50% duty cycle; thus, the worst-case input ripple current is 0.5 ✕ 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 input capacitor impedance is critical to preventing AC currents from flowing back into the wall cube. This requirement varies depending on the wall cube impedance and the requirements of any conducted or radiated EMI specifications that must be met. Aluminum electrolytic capacitors are generally the cheapest, but usually are a poor choice for portable devices due to their large size and poor 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, but also higher ESR than ceramic capacitors. This makes it more critical to consider RMS current and power dissipation ratings 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 ______________________________________________________________________________________ 15 MAX1757 CELL is the programming input for selecting cell count N. Table 2 shows how CELL is connected to charge 1, 2, or 3 cells. MAX1757 Stand-Alone, Switch-Mode Li+ Battery Charger with Internal 14V Switch 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 fOSC x RCS where: COUT is the total output capacitance. VREF is the reference voltage (4.2V). VBATT is the maximum battery regulation voltage (typically 4.2V per cell). VDCIN(MIN) is the minimum source input voltage. The maximum output capacitor ESR required for stability is: RESR < RCS x VBATT VREF where: RESR is the output capacitor ESR. RCS is the current-sense resistor from CS to BATT (100mΩ typ). Setting the Timers The MAX1757 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 the fast-charge 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 1nF capacitors to TIMER1 and TIMER2. Each timer period is directly proportional to the capacitance at the corresponding pin (see Typical Operating Characteristics). 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 Diode Selection A Schottky rectifier with a rating of at least 1.5A must be connected from LX to PGND. VL and REF Bypassing The MAX1757 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 of the linear regulator is not exceeded. A 4.7µF bypass capacitor is required at VL to ensure that the regulator is stable. A 1µF 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: 5996 Compensation Each of the three regulation loops—the input current limit, the charging current limit, and the charging voltage limit—can be compensated separately at 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; 0.1µF capacitors to 16 ______________________________________________________________________________________ Stand-Alone, Switch-Mode Li+ Battery Charger with Internal 14V Switch SSOP.EPS Package Information 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. 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