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19-1626; Rev 4; 9/07
KIT ATION EVALU E AILABL AV
Stand-Alone Switch-Mode Lithium-Ion Battery-Charger Controller
General Description 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
MAX1737
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.
Ordering Information
PART MAX1737EEI TEMP RANGE -40C to +85C PIN-PACKAGE 28 QSOP
Applications
Notebook Computers Hand-Held Instruments Li+ Battery Packs Desktop Cradle Chargers
INPUT SUPPLY
Typical Operating Circuit
DCIN VL
CSSP CSSN DHI
Pin Configuration
TOP VIEW
VL 1 ISETIN 2 ISETOUT 3 THM 4 REF 5 GND 6 BATT 7 VADJ 8 CCV 9 CCS 10 CCI 11 CELL 12 TIMER1 13 TIMER2 14 28 DCIN 27 CSSP 26 CSSN 25 DHI 24 LX
REF ISETIN ISETOUT CELL VADJ MAX1737
SYSTEM LOAD
LX BST VLO DLO PGND CS RS BATT Li+ BATTERY 1 TO 4 CELLS
MAX1737
23 BST 22 VLO 21 DLO 20 PGND 19 CS 18 SHDN 17 FULLCHG 16 FASTCHG 15 FAULT
ON OFF SHDN GND CCV CCI TIMER1 TIMER2 CCS
THM FASTCHG FULLCHG FAULT
QSOP
________________________________________________________________ Maxim Integrated Products
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Stand-Alone Switch-Mode Lithium-Ion Battery-Charger Controller MAX1737
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 SUPPLY AND REFERENCE DCIN Input Voltage Range DCIN Quiescent Supply Current DCIN to BATT Undervoltage Threshold, DCIN Falling DCIN to BATT Undervoltage 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 DHI, DLO On-Resistance LX Leakage BATT, CS Input Current BATT, CS Input Voltage Range Battery Regulation Voltage (VBATTR) Absolute Voltage Accuracy Battery Regulation Voltage Adjustment Range CELL = float, GND, VL, or REF (Note 1) Not including VADJ resistor tolerances With 1% VADJ resistors VCCV = 2V VVADJ = GND VVADJ = REF LX = VDCIN = 28V, SHDN = GND SHDN = GND, VBATT = 19V CELL = SHDN = VL, VBATT = 17V 0 4.167 -0.8 -1 3.948 4.386 3.979 4.421 4.2 0.1 0.1 225 VBATT = 15V, CELL = VL In dropout fOSC / 4, VCCV = 2.4V, VBATT = 15V, CELL = VL VCSSN = VCSSP = VDCIN = 28V, SHDN = GND 270 97 300 98 2 10 7 10 5 500 19 4.233 +0.8 +1 4.010 4.453 330 kHz % A A A V V/cell % V/cell 6V < VDCIN < 28V IREF = 0 to 1mA 6.0V < VDCIN < 28V IVL = 0 to 15mA 4.179 6.0V < VDCIN < 28V 0.05 0.19 5.10 5.40 44 4.20 2 6 6 5 28 7 0.155 0.40 5.70 65 4.221 6 14 V mA V V V mV V mV mV CONDITIONS MIN TYP MAX UNITS
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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 ERROR AMPLIFIERS CCV Amplifier Transconductance (Note 2) CCV Amplifier Maximum Output Current CS to BATT Current-Sense Voltage CS to BATT Full-Scale Current-Sense Voltage CS to BATT Current-Sense Voltage When in Prequalification State CS to BATT Hard Current-Limit Voltage CSSP to CSSN Current-Sense Voltage CSSP to CSSN Full-Scale Current-Sense Voltage CCI Amplifier Transconductance CCI Amplifier Output Current CCS Amplifier Transconductance CCS Amplifier Output Current CCI, CCS Clamp Voltage with Respect to CCV CCV Clamp Voltage with Respect to CCI, CCS STATE MACHINE THM Trip-Threshold Voltage THM Low-Temperature Current THM High-Temperature Current THM COLD Threshold Resistance (Note 3) THM HOT Threshold Resistance (Note 3) BATT Undervoltage Threshold (Note 4) BATT Overvoltage Threshold (Note 5) BATT Charge Current Full-Charge Termination Threshold CS-BATT (Note 6) BATT Recharge Voltage Threshold (Note 7) TIMER1, TIMER2 Oscillation Frequency Prequalification Timer Fast-Charge Timer Full-Charge Timer THM low-temperature or high-temperature current VTHM = 1.4V VTHM = 1.4V Combines THM low-temperature current and THM rising threshold, VTRT/ITLTC Combines THM high-temperature current and THM rising threshold, VTRT/ITHTC 1.386 46.2 344 26.92 3.819 2.4 4.55 35 94 2.1 6.25 81 81 1.4 49 353 28.70 3.964 2.5 4.67 44 95 2.33 7.5 90 90 1.414 51.5 362 30.59 4.115 2.6 4.8 55 96 2.6 8.75 100 100 V A A k k V/cell V/cell mV % of VBATTR kHz min min min 3 6V < VCSSP < 28V, VISETIN = VREF / 5, VCCS = 2V 6V < VCSSP < 28V, VCCS = 2V VCCI = 2V VCS - VBATT = 0, 400mV ISET = REF, VCCS = 2V VCSSP - VCSSN = 0, 200mV 4.15V < VBATT < 4.25V, VCCV = 2V 3.5V < VBATT < 5V, VCCV = 2V VISETOUT = VREF / 5 VBATT = 3V to 17V, CELL = GND or VL VBATT < 2.4V per cell 0.39 50 30 185 5 355 10 90 0.6 100 1.2 100 25 25 200 200 2 2.6 40 200 10 385 20 105 1 50 215 15 415 30 115 1.4 0.584 0.80 mS A mV mV mV mV mV mV mS A mS A mV mV CONDITIONS MIN TYP MAX UNITS
MAX1737
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Stand-Alone Switch-Mode Lithium-Ion Battery-Charger Controller MAX1737
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 Top-Off Timer Temperature Measurement Frequency CONTROL INPUTS/OUTPUTS SHDN Input Voltage High SHDN Input Voltage Low (Note 8) VADJ, ISETIN, ISETOUT Input Voltage Range VADJ, ISETIN, ISETOUT Input Bias Current SHDN Input Bias Current CELL Input Bias Current ISETIN Adjustment Range ISETOUT Adjustment Range ISETOUT Voltage for ICHG = 0 For 1 cell CELL Input Voltage For 2 cells For 3 cells For 4 cells FASTCHG, FULLCHG, FAULT Output Low Voltage FASTCHG, FULLCHG, FAULT Output High Leakage ISINK = 5mA FASTCHG, FULLCHG, FAULT = 28V; SHDN = GND VVADJ, VISETIN, VISETOUT = 0 or 4.2V SHDN = GND or VL 0 -50 -1 -5 VREF / 5 VREF / 5 150 0 1.5 VREF - 0.3 VVL - 0.4 220 1.4 0.6 VREF 50 1 5 VREF VREF 300 0.5 2.5 VREF + 0.3 VVL 0.5 1 V A V V V V nA A A V V mV 1nF on TIMER1 and TIMER2 CONDITIONS MIN 40.5 0.98 TYP 45 1.12 MAX 49.8 1.32 UNITS min Hz
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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 SUPPLY AND REFERENCE DCIN Input Voltage Range VL Output Voltage REF Output Voltage REF Line Regulation SWITCHING REGULATOR PWM Oscillator Frequency DHI, DLO On-Resistance BATT, CS Input Voltage Range Battery Regulation Voltage (VBATTR) Absolute Voltage Accuracy ERROR AMPLIFIERS CS to BATT Current-Sense Voltage CS to BATT Full-Scale Current-Sense Voltage CS to BATT Current-Sense Voltage When in Prequalification State CS to BATT Hard Current-Limit Voltage CSSP to CSSN Current-Sense Voltage CSSP to CSSN Full-Scale Current-Sense Voltage STATE MACHINE THM Trip-Threshold Voltage THM Low-Temperature Current THM COLD Threshold Resistance (Note 3) BATT Undervoltage Threshold (Note 4) BATT Overvoltage Threshold (Note 5) BATT Charge Current Full-Charge Termination Threshold, CS-BATT (Note 6) Temperature Measurement Frequency 1nF on TIMER1 and TIMER2 THM low-temperature or high-temperature current VTHM = 1.4V Combines THM low-temperature current and THM rising threshold, VTRT/ITLTC 1.386 46.2 26.92 2.4 4.55 35 0.93 1.414 51.5 30.59 2.6 4.8 55 1.37 V A k V/cell V/cell mV Hz 6V < VCSSP < 28V, VISETIN = VREF / 5, VCCS = 2V 6V < VCSSP < 28V, VCCS = 2V VISETOUT = VREF / 5 VBATT = 3V to 17V, CELL = GND or VL VBATT < 2.4V per cell 25 180 3 350 5 85 55 220 17 420 35 115 mV mV mV mV mV mV CELL = float, GND, VL, or REF Not including VADJ resistor tolerances 0 4.158 -1 VBATT = 15V, CELL = VL 260 340 7 19 4.242 1 kHz V V/cell % 6V < VDCIN < 28V 6.0V < VDCIN < 28V 6 5.1 4.166 28 5.7 4.242 6 V V V mV CONDITIONS MIN MAX UNITS
MAX1737
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Stand-Alone Switch-Mode Lithium-Ion Battery-Charger Controller MAX1737
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 CONTROL INPUTS/OUTPUTS SHDN Input Voltage High SHDN Input Voltage Low (Note 8) 1.4 0.6 V V CONDITIONS MIN TYP MAX UNITS
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.
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Stand-Alone Switch-Mode Lithium-Ion Battery-Charger Controller MAX1737
Typical Operating Characteristics
(Circuit of Figure 1, VDCIN = +18V, ISETIN = ISETOUT = REF, VVADJ = VREF / 2, TA = +25C, unless otherwise noted.)
BATTERY VOLTAGE vs. CHARGING CURRENT
CHARGING CURRENT-SENSE VOLTAGE (mV) R18 = 0.1
MAX1737 toc01
CHARGING CURRENT-SENSE VOLTAGE vs. ISETOUT VOLTAGE
MAX1737 toc02
INPUT CURRENT-SENSE VOLTAGE vs. ISETIN VOLTAGE
INPUT CURRENT-SENSE VOLTAGE (mV)
MAX1737 toc03
4.5 4.0 BATTERY VOLTAGE (V) 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0 0
225 200 175 150 125 100 75 50 25 0 0
120 100 80 60 40 20 0
0.5
1.0
1.5
2.0
2.5
0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 ISETOUT VOLTAGE (V)
0
0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 ISETIN VOLTAGE (V)
CHARGING CURRENT (A)
VOLTAGE LIMIT vs. VADJ VOLTAGE
MAX1737 toc04
REFERENCE VOLTAGE vs. TEMPERATURE
MAX1737 toc05
EFFICIENCY vs. INPUT VOLTAGE
MAX1737 toc06
4.45 4.40 4.35 VOLTAGE LIMIT (V) 4.30 4.25 4.20 4.15 4.10 4.05 4.00 3.95 0
4.205 4.200 REFERENCE VOLTAGE (V) 4.195 4.190 4.185 4.180 4.175
100
90 EFFICIENCY (%)
80
70
60
50 -40 -20 0 20 40 60 80 100 8 12 16 TEMPERATURE (C)
CELL = FLOAT (2 CELLS) VBATT = 7V R18 = 0.1 (IBATT = 2A) 20 24 28 INPUT VOLTAGE (V)
0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 VADJ VOLTAGE (V)
REFERENCE LOAD REGULATION
MAX1737 toc07
TIMEOUT vs. TIMER1 CAPACITANCE
MAX1737 toc08
FAST-CHARGE TIMEOUT vs. TIMER2 CAPACITANCE
MAX1737 toc09
4.210 4.208 4.206 REFERENCE VOLTAGE (V) 4.204
1000 TOP-OFF MODE 100 TIMEOUT (MINUTES) FULL-CHARGE MODE
1000
4.202 4.200 4.198 4.196 4.194 4.192 4.190 0 100 200 300 400 500 600 700 800 900 1000 REFERENCE CURRENT (A)
10
TIMEOUT (MINUTES) 10
100
1
PREQUALIFICATION MODE
10
0.1 0.1 1 CAPACITANCE (nF)
1 0.1 1 CAPACITANCE (nF) 10
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Stand-Alone Switch-Mode Lithium-Ion Battery-Charger Controller MAX1737
Pin Description
PIN NAME VL ISETIN ISETOUT THM REF GND BATT VADJ CCV CCS CCI CELL TIMER1 TIMER2 FAULT FASTCHG FULLCHG SHDN CS PGND DLO VLO BST LX DHI CSSN CSSP DCIN FUNCTION 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. 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. 4.2V Reference Voltage Output. Bypass REF to GND with a 1F or larger ceramic capacitor. Analog Ground Battery Voltage-Sense Input and Current-Sense Negative Input 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. Voltage Regulation Loop Compensation Point Input Source Current Regulation Compensation Point Battery-Current Regulation Loop Compensation Point Cell-Count Programming Input. See Table 2 Timer 1 Adjustment. Connect a capacitor from TIMER1 to GND to set the prequalification, full-charge, and top-off times. See Timers section. Timer 2 Adjustment. Connect a capacitor from TIMER2 to GND to set the fast-charge time. See Timers section. Charge Fault Indicator. Open-drain output pulls low when charging terminates abnormally (Table 1). Fast-Charge Indicator. Open-drain output pulls low when charging with constant current. Full-Charge Indicator. Open-drain output pulls low when charging with constant voltage in full-charge state. 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 Synchronous-Rectifier MOSFET Gate-Drive Output Synchronous-Rectifier MOSFET Gate-Drive Bias. Bypass VLO to PGND with a 0.1F capacitor. High-Side MOSFET Gate Drive Bias. Connect a 0.1F or greater capacitor from BST and LX. Power Inductor Switching Node. Connect LX to the high-side MOSFET source. High-Side MOSFET Gate-Drive Output Source Current-Sense Negative Input. See Input Current Regulator section. Source Current-Sense Positive Input. See Input Current Regulator section. 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.
1
2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28
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Stand-Alone Switch-Mode Lithium-Ion Battery-Charger Controller
Detailed Description
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. 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
MAX1737
D1 D2 INPUT SUPPLY 28 C7 0.1F 1 C1 4.7F C2 0.1F 18 SHDN VLO 5 2 R8 C3 1F R9 3 8 12 6 R1 10k 1nF C5 47nF 11 C6 47nF 10 C13 1nF 13 C14 1nF 14 16 FAST CHARGE FULL CHARGE FAULT 17 15 TIMER2 FASTCHG FULLCHG FAULT TIMER1 CCS 4 CCI BATT 7 0.1F CS 19 0.1F Li+ BATTERY (1 TO 4 CELLS) REF ISETIN ISETOUT VADJ CELL GND BST DHI LX 22 D3 23 25 24 21 20 C10 0.1F L1 22H R18 C15 68F C11 0.1F VL DCIN CSSP
27 C8 0.1F R12
MAX1737
CSSN
26 C9 0.1F + C18 22F + C19 22F SYSTEM LOAD
DLO
C4 0.1F
9
CCV
PGND
THERMISTOR
THM
Figure 1. Typical Application Circuit _______________________________________________________________________________________ 9
Stand-Alone Switch-Mode Lithium-Ion Battery-Charger Controller
FASTCHARGE STATE FULLCHARGE STATE TOP-OFF STATE DONE
BATTERY CURRENT
CHARGE I = 1C
BATTERY VOLTAGE FASTCHG OUTPUT OPENDRAIN LOW OPENDRAIN LOW 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)
FULLCHG OUTPUT BATTERY INSERTION OR SHDN HIGH TRANSITION TO VOLTAGE MODE (APPROX 85% CHARGE)
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.
MAX1737
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.
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 capaci10
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
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Stand-Alone Switch-Mode Lithium-Ion Battery-Charger Controller MAX1737
SHDN 160ns
BATT CS REF/42 5x CSI 3R ISETOUT R/9 PREQ
SLOPE COMP STOP SAW BATT
MAX1737
CCI GMI
R SW+ GND SWGATE CONTROL ON PWMCOMP PWMCMP ILIMIT LOWILIM OSC LO DLO PGND DHI LX DLO VLO BST DHI
CSSP CSSN
GND 10x CSS 3R GMS
CS+ CSCCI LVC CCS CCV GND REF/2.6 EA+ EA-
ISETIN R R
REF/2 GND REF/42 R R/2 R/2 R/2
ONE CELL CELL THREE FOUR REF R VADJ 9R GND GMV TWO PWMOSC
160ns
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.
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
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Stand-Alone Switch-Mode Lithium-Ion Battery-Charger Controller MAX1737
SHUTDOWN VDCIN < BATT VBATT < UNDERVOLTAGE THRESHOLD VDCIN > VBATT PREQUAL
FASTCHG = LOW FULLCHG = HIGH FAULT = HIGH FASTCHG = HIGH FULLCHG = HIGH FAULT = HIGH
SHUTDOWN IS ENTERED FROM ALL STATES WHEN SHDN IS LOW.
SHDN HIGH RESET
FASTCHG = HIGH FULLCHG = HIGH FAULT = HIGH
PREQUAL TIMEOUT
FAULT
FASTCHG = HIGH FULLCHG = HIGH FAULT = LOW
VBATT > 2.5V TEMP NOT OK TEMP OK ONCE PER SECOND
FAST-CHARGE TIMEOUT
FAST CHARGE
FASTCHG = LOW FULLCHG = HIGH FAULT = HIGH
VBATT < 0.95 x VBATTR
TEMP OK ONCE PER SECOND TEMP QUAL TEMP NOT OK TEMP OK TEMP OK TEMP NOT OK
VBATT = BATTERY REGULATION VOLTAGE (VBATTR)
FULL CHARGE
FASTCHG = HIGH FULLCHG = LOW FAULT = HIGH
VBATT < 0.95 x VBATTR
ICHARGE < IMIN OR FULL-CHARGE TIMEOUT TOP-OFF
FASTCHG = HIGH FULLCHG = HIGH FAULT = HIGH
DONE
FASTCHG = HIGH FULLCHG = HIGH FAULT = HIGH
TOP-OFF TIMEOUT
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.
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Stand-Alone Switch-Mode Lithium-Ion Battery-Charger Controller MAX1737
Table 1. Charging State Conditions
STATE ENTRY CONDITIONS From initial power on or From done state if battery voltage < recharge voltage threshold or VDCIN - VBATT < 100mV or VBATT > battery overvoltage threshold From reset state if input power, reference, and internal bias are within limits STATE CONDITIONS
Reset
Timers reset, charging current = 0, FASTCHG = high, FULLCHG = high, FAULT = high
Prequalification
Battery voltage undervoltage threshold, charging current = C/20, timeout = 7.5min typ (CTIMER1 = 1nF), FASTCHG = low, FULLCHG = high, FAULT = high Undervoltage threshold battery voltage battery regulation voltage, charging current = current limit, timeout = 90min typ (CTIMER2 = 1nF), FASTCHG = low, FULLCHG = high, FAULT = high Battery voltage = battery regulation voltage, charging current current limit, timeout = 90min typ (CTIMER1 = 1nF), FASTCHG = high, FULLCHG = low, FAULT = high Battery voltage = battery regulation voltage, charging current 10% of current limit, timeout = 45min typ (CTIMER1 = 1nF), FASTCHG = high, FULLCHG = high, FAULT = high Recharge voltage threshold battery voltage battery regulation voltage, charging current = 0, FASTCHG = high, FULLCHG = high, FAULT = high Charge current = 0, timers suspended, FASTCHG = no change, FULLCHG = no change, FAULT = no change
Fast Charge (Constant Current)
From prequalification state if battery voltage > undervoltage threshold
Full Charge (Constant Voltage)
From fast-charge state if battery voltage = battery regulation voltage
Top-Off (Constant Voltage)
From full-charge state if full-charge timer expires or charging current 10% of current limit
Done
From top-off state if top-off timer expires
Over/Under Temperature
From fast-charge state or full-charge state if battery temperature is outside of limits From prequalification state if prequalification timer expires or From fast-charge state if fast-charge timer expires
Fault
Charging current = 0, FASTCHG = high, FULLCHG = high, FAULT = low
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13
Stand-Alone Switch-Mode Lithium-Ion Battery-Charger Controller 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. 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.
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.
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
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
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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. 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.
MAX1737
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
Setting the Charging Current Limit
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. 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.
where f is the switching frequency (300kHz). The peak inductor current is given by: LIR I PEAK = 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 - D2 where I CIN = the input capacitor RMS current, D = PWM converter duty ratio (typically VBATT / VDCIN), and ICHG = battery charging current.
15
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,
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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
MAX1737
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
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
and the synchronous-rectifier MOSFET duty cycle (D) will be 1 - D or: V -V D DCIN BATT VDCIN
______________________________________________________________________________________
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 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.
MAX1737
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.
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,
Chip Information
TRANSISTOR COUNT: 5978
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17
Stand-Alone Switch-Mode Lithium-Ion Battery-Charger Controller MAX1737
Package Information
(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.)
QSOP.EPS
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.
Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 ____________________ 18 (c) 2007 Maxim Integrated Products is a registered trademark of Maxim Integrated Products, Inc.

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