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19-1752; Rev 0; 7/00
KIT ATION EVALU BLE AVAILA
Stand-Alone, Switch-Mode Li+ Battery Charger with Internal 28V Switch
General Description Features
o Stand-Alone Charger for Up to 4 Li+ Batteries o 0.8% Battery Regulation Voltage Accuracy o Low-Dropout 98% Duty Cycle o o o o o o o o Safely Precharges Near-Dead Cells Continuous Voltage and Temperature Monitoring 0.1A Shutdown Battery Current Input Voltage Up to 28V Up to 1.5A Programmable Charge Current Safety Timer Prevents Overcharging Input Current Limiting Space-Saving 28-Pin SSOP
MAX1758
The MAX1758 is a switch-mode lithium-ion (Li+) battery charger that charges one-to-four 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 MAX1758 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 automatically reduces battery-charging current, preventing overload of the input supply and 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-4 by pin strapping. Battery temperature is monitored by an external thermistor to prevent charging outside the acceptable temperature range. The MAX1758 is available in a space-saving 28-pin SSOP package. Use the MAX1758EVKIT to help reduce design time. For a stand-alone charger with a 14V switch, refer to the MAX1757 data sheet. For a charger controller capable of up to 4A charging current, refer to the MAX1737 data sheet.
o 300kHz PWM Oscillator Reduces Noise
Ordering Information
PART MAX1758EAI TEMP. RANGE -40C to +85C PIN-PACKAGE 28 SSOP
Typical Operating Circuit
VIN 6V TO 28V DCIN REF CSSP CSSN HSD LX MAX1758 ISETOUT BST VL ISETIN SYSTEM LOAD
________________________Applications
Li+ Battery Packs Notebook Computers Hand-Held Instruments Desktop Cradle Chargers
Pin Configuration
TOP VIEW
CELL
PGND CS
VL 1 ISETIN 2 ISETOUT 3 THM 4 REF 5 GND 6 VADJ 7 BATT 8 HSD 9 HSD 10 CELL 11 TIMER1 12 TIMER2 13 FAULT 14
28 DCIN 27 CSSP 26 CSSN 25 CCV 24 CCI
VADJ BATT THM CCS THERM CCI Li+ BATTERY 1 TO 4 CELLS
MAX1758
23 CCS 22 BST 21 CS 20 LX
CCV FASTCHG
19 LX 18 PGND 17 SHDN
TIMER2 FAULT TIMER1 FULLCHG
16 FULLCHG 15 FASTCHG
ON OFF SHDN GND
SSOP
________________________________________________________________ Maxim Integrated Products
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Stand-Alone, Switch-Mode Li+ Battery Charger with Internal 28V Switch MAX1758
ABSOLUTE MAXIMUM RATINGS
DCIN, CSSP, CSSN, HSD to GND..........................-0.3V to +30V CSSP to CSSN.......................................................-0.6V to +0.6V BST to GND ............................................................-0.3V to +36V 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 BATT, CS to GND ...................................................-0.3V to +20V CS to BATT Current ............................................................3.5A PGND to GND .......................................................-0.3V to +0.3V VL Source Current...............................................................50mA Continuous Power Dissipation (TA = +70C) 28-Pin SSOP (derate 9.5mW/C above +70C) ...........762mW Operating Temperature Range ...........................-40C to +85C Junction Temperature ......................................................+150C Storage Temperature.........................................-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 = VHSD = VCSSP = VCSSN = 18V, V SHDN = VVL, VCELL = GND, VBATT = VCS = 4.2V, VVADJ = VREF / 2, VISETIN = VISETOUT = VREF, 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 Dropout Threshold, DCIN Falling 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 HSD Off-State Leakage LX Off-State Leakage HSD to LX On-Resistance LX to PGND On-Resistance CS to BATT Current-Sensing Resistance BATT, CS Input Current RCS 6V < VDCIN < 28V Falling edge Rising edge 6V < VDCIN < 28V IVL = 0 to 15mA 6V < VDCIN < 28V 6V < VDCIN < 28V IREF = 0 to 1mA Nondropout fOSC In-dropout, fOSC / 4 VCSSN = VCSSP = VDCIN = 28V, V SHDN = GND VLX = PGND, VHSD = VDCIN = 28V, V SHDN = GND VLX = VHSD = VDCIN =28V, V SHDN = GND VBST = VLX + 4.5V See PWM Controller section Internal resistor between CS and BATT, 1.5A RMS operating V SHDN = GND, VBATT = 19V CELL = REF, VBATT = 15V, any charging state VBATT = 18V, done state 0.075 0.20 5.10 4.179 6 5 0.125 0.30 5.40 44 4.20 2 6 300 98 2 0.1 0.1 260 1 110 0.1 280 150 28 7 0.175 0.40 5.70 65 4.221 6 14 330 10 10 10 450 2 170 5 540 270 V mA V V V mV V mV mV kHz % A A A m m A A A SYMBOL CONDITIONS MIN TYP MAX UNITS
VREF
fOSC
270 97
2
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Stand-Alone, Switch-Mode Li+ Battery Charger with Internal 28V Switch
ELECTRICAL CHARACTERISTICS (continued)
(Circuit of Figure 1, VDCIN = VHSD = VCSSP = VCSSN = 18V, V SHDN = VVL, VCELL = GND, VBATT = VCS = 4.2V, VVADJ = VREF / 2, VISETIN = VISETOUT = VREF, RTHM = 10k, TA = 0C to +85C, unless otherwise noted. Typical values are at TA = +25C.) PARAMETER CS to BATT Hard Current Limit BATT, CS Input Voltage Range VOLTAGE LIMIT ACCURACY Battery Regulation Voltage Absolute Voltage Accuracy BATT Regulation Voltage Adjustment Range ERROR AMPLIFIERS CCV Amplifier Transconductance CCV Amplifier Maximum Output Current BATT Full-Scale Charge Current BATT 1/10-Scale Charge Current (Note 1) BATT Charge Current in Prequalification State CCI Battery Current Sense Gain CCI Amplifier Maximum Output Current CSSP to CSSN Full-Scale Current-Sense Voltage CSSP to CSSN 1/10-Scale Current-Sense Voltage CCS Amplifier Transconductance CCS Amplifier Maximum 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-Temp Current THM High-Temp Current THM COLD Threshold Resistance (Note 2) THM HOT Threshold Resistance (Note 2) VTRT ITLTC ITHTC THM low-temp or high-temp current VTHM = 1.4V VTHM = 1.4V Combines THM low-temp current and THM threshold, VTRT / ITLTC Combines THM high-temp current and THM threshold, VTRT / ITHTC 1.386 46.2 344 26.92 3.819 1.40 49 353 28.70 3.964 1.414 51.5 362 30.59 4.115 V A A k k VISETIN = VREF / 10 VCCS = 2V VCCS = 2V VISETOUT = VREF / 10 VBATT < 2.4V per cell VCCI = 2V VCCI = 2V VCCV = 2V VCCV = 2V 0.4 50 1.35 100 100 60 100 90 5 1.0 100 25 25 200 200 100 10 2.0 115 15 3.0 1.5 150 150 130 1.65 200 200 240 0.7 1.0 mS x cells A A mA mA A/A A mV mV mS A mV mV VBATTR CELL = float, GND, VL, or REF Not including VADJ resistor tolerances With 1% VADJ resistors VADJ = GND VADJ = REF 4.167 -0.8 -1 3.948 4.386 3.979 4.421 4.2 4.233 0.8 1 4.010 4.453 V/cell % V/cell SYMBOL CONDITIONS Instantaneous peak current limit MIN 2.4 0 TYP 2.7 MAX 3.0 19 UNITS A V
MAX1758
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Stand-Alone, Switch-Mode Li+ Battery Charger with Internal 28V Switch MAX1758
ELECTRICAL CHARACTERISTICS (continued)
(Circuit of Figure 1, VDCIN = VHSD = VCSSP = VCSSN = 18V, V SHDN = VVL, VCELL = GND, VBATT = VCS = 4.2V, VVADJ = VREF / 2, VISETIN = VISETOUT = VREF, RTHM = 10k, TA = 0C to +85C, unless otherwise noted. Typical values are at TA = +25C.) PARAMETER BATT Undervoltage Threshold (Note 3) BATT Overvoltage Threshold (Note 4) FULLCHG BATT Current Termination Threshold (Note 5) BATT Recharge Voltage Threshold (Note 6) TIMER1 and TIMER2 Oscillation Frequency Prequalification Timer Fast-Charge Timer Full-Charge Timer Top-Off Timer Temperature Measurement Frequency CONTROL INPUTS/OUTPUTS SHDN Input Voltage High SHDN Input Voltage Low VADJ, ISETIN, ISETOUT Input Voltage Range VADJ, ISETIN, ISETOUT Input Bias Current SHDN Input Bias Current CELL Input Bias Current ISETOUT Shutdown Threshold Voltage (Note 3) For 1 cell CELL Input Voltage For 2 cells (floating) For 3 cells For 4 cells VVADJ, VISETIN, VISETOUT = 0 or 4.2V V SHDN = 0 or VVL VCELL = 0 or VVL VIH VIL 0 -50 -1 -5 150 0 1.5 VREF - 0.3 VVL - 0.4 220 1.4 0.6 VREF 50 1 5 300 0.5 2.5 VREF + 0.3 VVL V V V V nA A A mV SYMBOL CONDITIONS MIN 2.4 4.55 250 TYP 2.5 4.67 330 MAX 2.6 4.8 400 UNITS V/cell V/cell mA % of VBATTR x cell kHz min min min min Hz
94
95
96
2.1 6.25 81 81 40.5 0.98
2.33 7.5 90 90 45 1.12
2.6 8.75 100 100 49.8 1.32
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Stand-Alone, Switch-Mode Li+ Battery Charger with Internal 28V Switch
ELECTRICAL CHARACTERISTICS (continued)
(Circuit of Figure 1, VDCIN = VHSD = VCSSP = VCSSN = 18V, V SHDN = VVL, VCELL = GND, VBATT = VCS = 4.2V, VVADJ = VREF / 2, VISETIN = VISETOUT = VREF, RTHM = 10k, TA = 0C to +85C, unless otherwise noted. Typical values are at TA = +25C.) PARAMETER FASTCHG, FULLCHG, FAULT Output Low Voltage FASTCHG, FULLCHG, FAULT Output High Leakage SYMBOL VOL ISINK = 5mA V FASTCHG, V FULLCHG, V FAULT = 28V, V SHDN = GND CONDITIONS MIN TYP MAX 0.5 1 UNITS V A
MAX1758
ELECTRICAL CHARACTERISTICS
(Circuit of Figure 1, VDCIN = VHSD = VCSSP = VCSSN = 18V, V SHDN = VVL, VCELL = GND, VBATT = VCS = 4.2V, VVADJ = VREF / 2, VISETIN = VISETOUT = VREF, RTHM = 10k, TA = -40C to +85C, unless otherwise noted.) (Note 7) PARAMETER SUPPLY AND REFERENCE DCIN Input Voltage Range VL Output Voltage REF Output Voltage REF Line Regulation SWITCHING REGULATOR PWM Oscillator Frequency HSD to LX On-Resistance LX to PGND On-Resistance CS to BATT Hard Current Limit BATT, CS Input Voltage Range ACCURACY AND ERROR AMPLIFIERS Absolute Voltage Accuracy BATT Regulation Voltage BATT Full-Scale Charge Current BATT 1/10-Scale Charge Current (Note 1) BATT Charge Current in Prequalification State CSSP to CSSN Full-Scale Current-Sense Voltage CSSP to CSSN 1/10-Scale Current-Sense Voltage STATE MACHINE THM Trip Threshold Voltage THM Low-Temp Current VTRT ITLTC THM low - temp or high-temp current VTHM = 1.4V 1.386 46.2 1.414 51.5 V A VSETIN = VREF / 10 VSETOUT = VREF / 10 VBATT < 2.4V per cell Not including VADJ resistor tolerances With 1% VADJ resistors CELL = float, GND, VL, or REF -0.8 -1 4.158 1.3 100 100 85 5 0.8 1 4.242 1.7 200 200 115 15 % V/cell A mA mA mV mV Instantaneous peak current limit 2.2 0 fOSC Nondropout fOSC VBST = VLX + 4.5V 260 340 450 2 3.2 19 kHz m A V 6V < VDCIN < 28V 6V < VDCIN < 28V 6 5.1 4.166 28 5.7 4.242 6 V V V mV SYMBOL CONDITIONS MIN TYP MAX UNITS
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Stand-Alone, Switch-Mode Li+ Battery Charger with Internal 28V Switch MAX1758
ELECTRICAL CHARACTERISTICS (continued)
(Circuit of Figure 1, VDCIN = VHSD = VCSSP = VCSSN = 18V, V SHDN = VVL, VCELL = GND, VBATT = VCS = 4.2V, VVADJ = VREF / 2, VISETIN = VISETOUT = VREF, RTHM = 10k, TA = -40C to +85C, unless otherwise noted.) (Note 7) PARAMETER BATT Undervoltage Threshold (Note 3) BATT Overvoltage Threshold (Note 4) FULLCHG BATT Current Termination Threshold (Note 5) Temperature Measurement Frequency CONTROL INPUTS/OUTPUTS SHDN Input Voltage High SHDN Input Voltage Low Note 1: Note 2: Note 3: Note 4: Note 5: VIH VIL 1.4 0.6 V V SYMBOL CONDITIONS MIN 2.4 4.55 250 0.93 TYP MAX 2.6 4.8 400 1.37 UNITS V/cell V/cell mA Hz
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 peak inductor 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 -40C are guaranteed by design, not production tested.
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Stand-Alone, Switch-Mode Li+ Battery Charger with Internal 28V Switch MAX1758
Typical Operating Characteristics
(Circuit of Figure 1, VDCIN = 18V, V SHDN = VVL, VCELL = GND, VVADJ = VREF/2, VISETIN = VISETOUT = VREF, TA = +25C, unless otherwise noted.)
BATTERY VOLTAGE vs. CHARGING CURRENT
MAX1758 TOC01
CHARGING CURRENT vs. ISETOUT VOLTAGE
MAX1758 TOC02
INPUT CURRENT-SENSE REGULATION VOLTAGE vs. ISETIN VOLTAGE
INPUT CURRENT-SENSE VOLTAGE (mV)
MAX1758 TOC03
4.5 4.0 3.5 BATTERY VOLTAGE (V) 3.0 2.5 2.0 1.5 1.0 0.5 0 0 0.2 0.4 0.6 0.8 1.0 1.2 1.4
1.6 1.4 CHARGING CURRENT (A) 1.2 1.0 0.8 0.6 0.4 0.2 0
120 100 80 60 40 20 0
1.6
0
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
MAX1758 TOC04
REFERENCE VOLTAGE vs. TEMPERATURE
MAX1758 TOC05
REFERENCE LOAD REGULATION
4.201 REFERENCE VOLTAGE (V) 4.200 4.199 4.198 4.197 4.196 4.195 4.194
MAX1758 TOC07
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
4.215 4.210 REFERENCE VOLTAGE (V) 4.205 4.200 4.195 4.190 4.185 -40
4.202
0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 VADJ VOLTAGE (V)
-20
0
20
40
60
80
100
0 100 200 300 400 500 600 700 800 900 1000 REFERENCE LOAD (A)
TEMPERATURE (C)
TIMEOUT vs. TIMER1 CAPACITANCE
MAX1758 TOC08
FAST-CHARGE TIMEOUT vs. TIMER2 CAPACITANCE
MAX1758 TOC09
EFFICIENCY vs. INPUT VOLTAGE
3 CELLS 90 EFFICIENCY (%) 4 CELLS
MAX1758 TOC10
1000 TOP-OFF MODE 100 TIMEOUT (MINUTES) VOLTAGE MODE
1000
100
TIMEOUT (MINUTES)
100
80 2 CELLS 70
10
10
1
PREQUALIFICATION MODE
60
ICHG = 1.0A
0.1 0.1 1 CAPACITANCE (nF) 10
1 0.1 1 CAPACITANCE (nF) 10
50 6 10 14 18 22 26 INPUT VOLTAGE (V)
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Stand-Alone, Switch-Mode Li+ Battery Charger with Internal 28V Switch MAX1758
Pin Description
PIN 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 NAME VL ISETIN ISETOUT THM REF GND VADJ BATT HSD CELL TIMER1 TIMER2 FAULT FASTCHG FULLCHG SHDN PGND LX CS BST CCS CCI CCV CSSN CSSP DCIN FUNCTION Chip Power Supply. Output of the 5.4V linear regulator from DCIN. Bypass VL to GND with 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 qualification temperature range. If unused, connect a 10k resistor from THM to GND. See Thermistor section. 4.2V Reference Voltage Output. Bypass REF to GND with 1F or larger ceramic capacitor. Analog Ground 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. Battery Voltage-Sense Input and Current-Sense Negative Input High-Side Drain. This is the drain of the internal high-side FET. See Figure 3. Cell-Count Programming Input. Connect CELL to GND, REF, or VL to set 1, 3, or 4 cells, or leave unconnected to set 2 cells. Timer1 Adjustment. Connect a capacitor from TIMER1 to GND to set the prequalification, full-charge, and top-off times. See Timers section. Timer2 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. See 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. Power Ground. Current from the low-side power MOSFET switch source flows through PGND. Power Inductor Switching Node and High-Side Power MOSFET Source Battery Current-Sense Positive Input. Connects to internal 0.1 resistor between BATT and CS. High-Side MOSFET Gate Drive Bias. Connect a 0.1F capacitor from BST to LX. Charger Source Current Regulation Loop Compensation Point. See Compensation section. Battery Charge Current Regulation Loop Compensation Point. See Compensation section. Voltage Regulation Loop Compensation Point. See Compensation section. 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 or greater capacitor. See Detailed Description.
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Stand-Alone, Switch-Mode Li+ Battery Charger with Internal 28V Switch MAX1758
MBRS340 D1 INPUT SUPPLY D2 28 DCIN C7 0.1F MAX1758 CSSN 26 C9 0.1F TO VL 17 5 2 R4 C3 1F R5 6 C4 0.1F C17 1nF C1 0.1F 24 C2 0.1F 23 C5 1nF 12 C6 1nF FULL CHARGE FAST CHARGE FAULT TIMER1 THM CCS BATT CCI R6 10k 25 3 7 11 SHDN REF ISETIN ISETOUT VADJ CELL GND CCV 18 BST HSD HSD LX LX 19 VL 1 D3 22 10 9 20 C14 0.1F L1 22H C13 4.7F + C12 0.22F + C10 22F + C11 22F TO SYSTEM LOAD 27 C8 0.1F R1 0.05
CSSP
D4 MBRS340 PGND
CS
19 C16 0.1F 7 C18 0.1F 4 C15 68F Li+ BATTERY 1 TO 4 CELLS
13 15 16 14
THERM TIMER2 FASTCHG FULLCHG FAULT
Figure 1. Typical Application Circuit
Detailed Description
The MAX1758 includes all of the functions necessary to charge 1, 2, 3, or 4 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.
The DC-DC converter uses an internal power MOSFET switch to convert the input voltage to the charging current 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 voltage is measured at the BATT pin. The battery regulation 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.
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Stand-Alone, Switch-Mode Li+ Battery Charger with Internal 28V Switch MAX1758
Table 1. Charging State Table
STATE ENTRY CONDITIONS From initial power-on or from done state if battery voltage < recharge voltage threshold or VDCIN - VBATT < dropout threshold or VBATT > battery overvoltage threshold STATE CONDITIONS
Reset
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 = (fast-charge current / 10), timeout = 7.5min typ (CTIMER1 = 1nF), FASTCHG = low, FULLCHG = high, FAULT = high Undervoltage threshold battery voltage battery regulation voltage, charging current = charge 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 330mA, timeout = 45min typ (CTIMER1 = 1nF), FASTCHG = high, FULLCHG = high, FAULT = high Recharge voltage threshold battery, voltage voltage limit, 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 if charging current 330mA
Done
From top-off state if top-off timer expires
Over/Undertemperature
From fast-charge state or full-charge state if battery temperature is outside limits From reset state if battery temperature maximum battery temperature or 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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Stand-Alone, Switch-Mode Li+ Battery Charger with Internal 28V Switch
The MAX1758 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. 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 the Voltage Regulation 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 continue to charge at a constant voltage until the top-off timer expires when it enters the done state. In the done state, charging stops until the battery voltage drops below the recharge-voltage threshold when 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.
MAX1758
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)
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-4 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 0.1F capacitor at CCI provides suitable performance for most applications.
Voltage Regulator
Li+ batteries require a high-accuracy voltage limit while charging. The MAX1758 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
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Stand-Alone, Switch-Mode Li+ Battery Charger with Internal 28V Switch MAX1758
DCIN CSS LEVEL SHIFT AND GAIN OF 10 ON CS RCS BATT CSI LEVEL SHIFT AND GAIN OF 7 ON GMS ISETIN +1 3Rx Rx GMI ISETOUT +1 3Rx Rx REF/2 BDIV FASTCHG R2 V/I MODE OSCILLATOR, SM, TIMERS THERM CONTROL TEST CIRCUITRY FULLCHG FAULT TIMER 1 TIMER 2 THM TO REF 9R VADJ +1 R R GMV MIN AND CLAMP SUMMING COMPARATOR BLOCK ON PGND CCV CCI CCS BST HSD LEVEL SHIFT DRIVER LX TO BATT ENABLE 5.4V REGULATOR INTERNAL REFERENCE VL REF
CSSP CSSN
REF/2 = ZERO CURRENT
TO BATT CELL CNTRL LOGIC
MAX1758
R
R2 = R(2N -1) WHERE N = CELL NUMBER
GND
Figure 3. MAX1758 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
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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.
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Stand-Alone, Switch-Mode Li+ Battery Charger with Internal 28V Switch MAX1758
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
When the current-sense resistor is chosen, 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 0.1F capacitor at CCS provides suitable performance for most applications.
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
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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.
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Stand-Alone, Switch-Mode Li+ Battery Charger with Internal 28V Switch MAX1758
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 sufficient voltage to fully drive the MOSFET gate even when its source is near the input voltage.
Table 2. Cell-Count Programming Table
CELL GND Float REF VL CELL COUNT (N) 1 2 3 4
Timers
The MAX1758 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).
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 continue counting from where they left off when charging resumes.
Shutdown
When SHDN is pulled low, the MAX1758 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 5A. 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 MAX1758 goes to the power-on reset state, which resets the timers and begins a new charge cycle.
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.
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 100k 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 per-
Thermistor
The intent of THM is to inhibit charging when the battery 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/BC components (2322-640-63103), Cornerstone Sensors (T101D103-CA), and Fenwall Electronics (140-103LAGRB1) work well. The battery temperature is measured at a 1.12Hz rate (CTIMER1 = CTIMER2 = 1nF). Charging pauses briefly to allow accurate measurement.
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Stand-Alone, Switch-Mode Li+ Battery Charger with Internal 28V Switch
cell voltage limit battery regulation voltage is determined, the VADJ voltage is calculated by the equation: VVADJ = (9.5 VBATTR / N) - (9.0 x VREF) CELL is the programming input for selecting cell count N. Table 2 shows how CELL is connected to charge 1, 2, 3, or 4 cells. DC charging current (LIR) can be used to calculate the optimal inductor value: L= VBATT VDCIN(MAX) - VBATT
MAX1758
(
)
VDCIN(MAX) x fOSC x ICHG x LIR
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 f OSC 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: ICIN ICHG 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 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 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 consideration of RMS current and power
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Setting the Input Current limit
A resistor-divider from REF to GND sets 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 RSOURCE 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, note 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.
D - D2
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
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Stand-Alone, Switch-Mode Li+ Battery Charger with Internal 28V Switch
dissipation ratings more critical 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 fOSC x RCS where: COUT is the total output capacitance. VREF is the reference voltage (4.2V). V BATT 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
MAX1758
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. The current loops in most charger designs can be compensated by 0.1F capacitors to ground at CCI and CCS. 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 MAX1758 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 4.7F 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.
where: RESR is the output capacitor ESR. RCS is the current-sense resistor from CS to BATT (100m typ).
Setting the Timers
The MAX1758 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 fastcharge 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 1nF capacitors to TIMER1 and TIMER2. Each timer period is directly proportional to the capacitance at the corresponding pin (see Typical Operating Characteristics).
Chip Information
TRANSISTOR COUNT: 5996
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Package Information
SSOP.EPS
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 (c) 2000 Maxim Integrated Products Printed USA
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is a registered trademark of Maxim Integrated Products.

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