19-1182; Rev 2; 12/98 NUAL KIT MA ATION U EET L H A S V E S DATA W O L L FO Switch-Mode Lithium-Ion Battery-Charger ____________________________Features ♦ Charges 1 to 4 Lithium-Ion Battery Cells ♦ ±0.75% Voltage-Regulation Accuracy Using 1% Resistors ♦ Provides up to 4A without Excessive Heating ♦ 90% Efficient ♦ Uses Low-Cost Set Resistors and N-Channel Switch ♦ Up to 24V Input ♦ Up to 18V Maximum Battery Voltage ♦ 300kHz PWM Operation: Low-Noise, Small Components ♦ Stand-Alone Operation; No Microcontroller Needed The MAX745 provides all functions necessary for charging lithium-ion battery packs. It provides a regulated charging current of up to 4A without getting hot, and a regulated voltage with only ±0.75% total error at the battery terminals. It uses low-cost, 1% resistors to set the output voltage, and a low-cost N-channel MOSFET as the power switch. The MAX745 regulates the voltage set point and charging current using two loops that work together to transition smoothly between voltage and current regulation. The per-cell battery voltage regulation limit is set between 4.0V and 4.4V using standard 1% resistors, and then the number of cells is set from 1 to 4 by pinstrapping. Total output voltage error is less than ±0.75%. For a similar device with an SMBus™ microcontroller interface and the ability to charge NiCd and NiMH cells, refer to the MAX1647 and MAX1648. For a low-cost lithium-ion charger using a linear-regulator control scheme, refer to the MAX846A. ________________________Applications Lithium-Ion Battery Packs Desktop Cradle Chargers Cellular Phones Notebook Computers Hand-Held Instruments Ordering Information PART TEMP. RANGE MAX745C/D 0°C to +70°C MAX745EAP -40°C to +85°C PIN-PACKAGE Dice* 20 SSOP Pin Configuration appears on last page. *Dice are tested at TA = +25°C. ___________________________________________________Typical Operating Circuit VIN (UP TO 24V) DCIN CELL COUNT SELECT BST CELL0 DHI CELL1 N MAX745 ON OFF VL LX THM/SHDN REF DLO N ICHARGE SETI CS VADJ SET PER CELL VOLTAGE WITH 1% RESISTORS RSENSE STATUS BATT CCV CCI GND IBAT PGND VOUT 1–4 Li+ CELLS (UP TO 18V) SMBus is a trademark of Intel Corp. ________________________________________________________________ Maxim Integrated Products 1 For free samples & the latest literature: http://www.maxim-ic.com, or phone 1-800-998-8800. For small orders, phone 1-800-835-8769. MAX745 General Description MAX745 Switch-Mode Lithium-Ion Battery Charger ABSOLUTE MAXIMUM RATINGS DCIN to GND ............................................................-0.3V to 26V BST, DHI to GND ......................................................-0.3V to 30V BST to LX ....................................................................-0.3V to 6V DHI to LX............................................(LX - 0.3V) to (BST + 0.3V) LX to GND ................................................-0.3V to (DCIN + 0.3V) VL to GND...................................................................-0.3V to 6V CELL0, CELL1, IBAT, STATUS, CCI, CCV, REF, SETI, VADJ, DLO, THM/SHDN to GND ..-0.3V to (VL + 0.3V) BATT, CS to GND .....................................................-0.3V to 20V PGND to GND..........................................................-0.3V to 0.3V VL Current ...........................................................................50mA Continuous Power Dissipation (TA = +70°C) SSOP (derate 8.00mW/°C above +70°C) ......................640mW Operating Temperature Range ...........................-40°C to +85°C Storage Temperature.........................................-60°C to +150°C Lead Temperature (soldering, 10sec) .............................+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 (VDCIN = 18V, VBATT = 8.4V, TA = 0°C to +85°C. Typical values are at TA = +25°C, unless otherwise noted.) PARAMETER CONDITIONS SUPPLY AND REFERENCE DCIN Input Voltage Range 6.0V < VDCIN < 24V, logic inputs = VL VL Output Voltage 6.0V < VDCIN < 24V, no load TA = +25°C 6.0V < VDCIN < 24V REF Output Load Regulation TYP 6 DCIN Quiescent Supply Current REF Output Voltage MIN MAX UNITS 24 V 4 6 mA 5.15 5.40 5.65 V 4.17 4.2 4.23 4.16 4.2 4.24 10 20 mV/mA 330 kHz 0 < IREF < 1mA SWITCHING REGULATOR Oscillator Frequency 270 300 DHI Maximum Duty Cycle 89 93 V % DHI On-Resistance Output high or low 4 7 Ω DLO On-Resistance Output high or low 6 14 Ω BATT Input Current CS Input Current BATT, CS Input Voltage Range VL < 3.2V, VBATT = 12V 5 VL > 5.15V, VBATT = 12V 500 VL < 3.2V, VCS = 12V 5 VL > 5.15V, VCS = 12V 400 4V < VBATT < 16V 0 CS to BATT Offset Voltage (Note 1) CS to BATT Current-Sense Voltage Absolute Voltage Accuracy 2 19 ±1.5 µA V mV SETI = VREF (full scale) 170 185 205 SETI = 400mV 14 18 22 Not including VADJ resistor tolerance -0.65 0.65 With 1% tolerance VADJ resistors -0.75 0.75 _______________________________________________________________________________________ µA mV % Switch-Mode Lithium-Ion Battery Charger (VDCIN = 18V, VBATT = 8.4V, TA = 0°C to +85°C. Typical values are at TA = +25°C, unless otherwise noted.) PARAMETER CONDITIONS MIN ERROR AMPLIFIERS GMV Amplifier Transconductance TYP MAX UNITS 800 µA/V 200 µA/V GMV Amplifier Output Current ±130 µA GMI Amplifier Output Current ±320 µA GMI Amplifier Transconductance CCI Clamp Voltage with Respect to CCV 1.1V < VCCV < 3.5V 25 80 200 mV CCV Clamp Voltage with Respect to CCI 1.1V < VCCI < 3.5V 25 80 200 mV µA CONTROL INPUTS/OUTPUTS CELL0, CELL1 Input Bias Current -1 1 SETI Input Voltage Range (Note 1) 0 VREF VADJ Adjustment Range 10 SETI, VADJ Input Bias Current -10 10 nA 0 VREF V VADJ Input Voltage Range THM/SHDN Rising Threshold V % 2.20 2.3 2.34 V 2.01 2.1 2.19 V STATUS Output Low Voltage Charger in current-regulation mode, STATUS sinking 1mA 0.2 V STATUS Output Leakage Current Charger in voltage-regulation mode, VSTATUS = 5V 1 µA IBAT Output Current vs. Current-Sense Voltage VIBAT = 2V THM/SHDN Falling Threshold µA/mV 0.9 IBAT Compliance Voltage Range 0 2 V ELECTRICAL CHARACTERISTICS (VDCIN = 18V, VBATT = 8.4V, TA = -40°C to +85°C, unless otherwise noted. Limits over temperature are guaranteed by design.) PARAMETER CONDITIONS SUPPLY AND REFERENCE VL Output Voltage 6.0V < VDCIN < 24V, no load REF Output Voltage 6.0V < VDCIN < 24V MAX UNITS 5.10 5.70 V 4.14 4.26 V 260 340 kHz MIN TYP SWITCHING REGULATOR (Note 1) Oscillator Frequency DHI On-Resistance Output high or low 7 Ω DLO On-Resistance Output high or low 14 Ω 165 205 mV -1.0 1.0 % CS to BATT Full-Scale Current-Sense Voltage Absolute Voltage Accuracy Not including VADJ resistors Note 1: When VSETI = 0V, the battery charger turns off. _______________________________________________________________________________________ 3 MAX745 ELECTRICAL CHARACTERISTICS (continued) __________________________________________Typical Operating Characteristics (TA = +25°C, VDCIN = 18V, VBATT = 4.2V, CELL0 = CELL1 = GND, CVL = 4.7µF, CREF = 0.1µF. Circuit of Figure 1, unless otherwise noted.) CURRENT-SENSE VOLTAGE vs. SETI VOLTAGE BATTERY VOLTAGE vs. CHARGING CURRENT 3.0 2.5 2.0 1.5 1.0 R1 = 0.2Ω R16 = SHORT R12 = OPEN CIRCUIT 0.5 0 0 160 140 120 100 80 60 40 20 0 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 0.5 1.5 2.0 2.5 3.0 SETI VOLTAGE (V) REFERENCE VOLTAGE vs. TEMPERATURE VOLTAGE LIMIT vs. VADJ VOLTAGE 4.40 PER-CELL VOLTAGE LIMIT (V) 4.203 4.202 4.201 4.200 4.199 4.198 4.197 3.5 4.45 MAX745/TOC-06 4.204 4.196 4.0 4.35 4.30 4.25 4.20 4.15 4.10 4.05 4.00 4.195 3.95 0 25 50 75 100 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 TEMPERATURE (°C) VADJ VOLTAGE (V) REFERENCE LOAD REGULATION VL LOAD REGULATION 5.45 4.24 REFERENCE VOLTAGE (V) 5.40 5.35 5.30 5.25 5.20 5.15 MAX745/TOC-05 4.25 MAX745/TOC-04 5.50 4.23 4.22 4.21 4.20 4.19 4.18 5.10 4.17 5.05 4.16 4.15 0 0 5 10 15 20 VL OUTPUT CURRENT (mA) 4 1.0 CHARGING CURRENT (A) 4.205 REFERENCE VOLTAGE (V) R1 = 0.2Ω 180 MAX745/TOC-03 BATTERY VOLTAGE (V) 3.5 200 MAX745/TOC-02 4.0 CURRENT-SENSE VOLTAGE (mV) MAX745/TOC-01 4.5 VL OUTPUT VOLTAGE (V) MAX745 Switch-Mode Lithium-Ion Battery Charger 25 0 500 1000 1500 2000 2500 REFERENCE CURRENT (µA) _______________________________________________________________________________________ 3000 Switch-Mode Lithium-Ion Battery Charger PIN NAME FUNCTION 1 IBAT Current-Sense Amplifier’s Analog Current-Source Output. See Monitoring Charge Current section for detailed description. 2 DCIN Charger Input Voltage. Bypass DCIN with a 0.1µF capacitor. 3 VL 4 CCV Voltage-Regulation-Loop Compensation Point 5 CCI Current-Regulation-Loop Compensation Point 6 THM/ SHDN 7 REF 8 VADJ Voltage-Adjustment Pin. VADJ is tied to a 1% tolerance external resistor-divider to adjust the voltage set point by 10%, eliminating the need for precision 0.1% resistors. The input voltage range is 0V to VREF. 9 SETI SETI is externally tied to the resistor-divider between REF and GND to set the charging current. 10 GND Analog Ground 11, 12 CELL1, CELL0 Logic Inputs to Select Cell Count. See Table 1 for cell-count programming. 13 STATUS An open-drain MOSFET sinks current when in current-regulation mode, and is high impedance when in voltage-regulation mode. Connect STATUS to VL through a 1kΩ to 100kΩ pull-up resistor. STATUS may also drive an LED for visual indication of regulation mode (see MAX745 evaluation kit). Leave STATUS floating if not used. 14 BATT Chip Power Supply. Output of the 5.4V linear regulator from DCIN. Bypass VL with a 4.7µF capacitor. Thermistor Sense-Voltage Input. THM/SHDN also performs the shutdown function. If pulled low, the charger turns off. 4.2V Reference Voltage Output. Bypass REF with a 0.1µF or greater capacitor. Battery-Voltage-Sense Input and Current-Sense Negative Input 15 CS 16 PGND Current-Sense Positive Input 17 DLO Low-Side Power MOSFET Driver Output 18 DHI High-Side Power MOSFET Driver Output 19 LX Power Connection for the High-Side Power MOSFET Source 20 BST Power Ground Power Input for the High-Side Power MOSFET Driver _______________Detailed Description The MAX745 is a switch-mode, lithium-ion battery charger that can achieve 90% efficiency. The charge voltage and current are set independently by external resistor-dividers at SETI and VADJ, and at pin connections at CELL0 and CELL1. VADJ is connected to a resistor-divider to set the charging voltage. The output voltage-adjustment range is ±5%, eliminating the need for 0.1% resistors while still achieving 0.75% set accuracy using 1% resistors. The MAX745 consists of a current-mode, pulse-widthmodulated (PWM) controller and two transconductance error amplifiers: one for regulating current (GMI) and the other for regulating voltage (GMV) (Figure 2). The error amplifiers are controlled via the SETI and VADJ pins. Whether the MAX745 is controlling voltage or current at any time depends on the battery state. If the battery is discharged, the MAX745 output reaches the current-regulation limit before the voltage limit, causing the system to regulate current. As the battery charges, the voltage rises to the point where the voltage limit is reached and the charger switches to regulating voltage. The STATUS pin indicates whether the charger is regulating current or voltage. Voltage Control To set the voltage limit on the battery, tie a resistordivider to VADJ from REF. A 0V to V REF change at VADJ sets a ±5% change in the battery limit voltage around 4.2V. Since the 0 to 4.2V range on VADJ results in only a 10% change on the voltage limit, the resistordivider’s accuracy does not need to be as high as the output voltage accuracy. Using 1% resistors for the voltage dividers typically results in no more than 0.1% degradation in output voltage accuracy. VADJ is internally buffered so that high-value resistors can be used to set the output voltage. When the voltage at VADJ is _______________________________________________________________________________________ 5 MAX745 ______________________________________________________________Pin Description MAX745 Switch-Mode Lithium-Ion Battery Charger VREF / 2, the voltage limit is 4.2V. Table 1 defines the battery cell count. The battery limit voltage is set by the following: 1 VREF VADJ − 2 VBATT = cell count x VREF + 9.523 ( ) Solving for VADJ, we get: 9.523 VBATT VADJ = − 9.023VREF (cell count) Set VADJ by choosing a value for R11 (typically 100k), and determine R3 by: R3 = [1 - (VADJ / VREF)] x R11 (Figure 1) Table 1. Cell-Count Programming Table CELL0 CELL1 CELL COUNT GND GND 1 VL GND 2 GND VL 3 VL VL 4 VIN where V REF = 4.2V and cell count is 1, 2, 3, or 4 (Table 1). The voltage-regulation loop is compensated at the CCV pin. Typically, a series-resistor-capacitor combination can be used to form a pole-zero doublet. The pole introduced rolls off the gain starting at low frequencies. The zero of the doublet provides sufficient AC gain at mid-frequencies. The output capacitor (C1) rolls off the mid-frequency gain to below unity. This guarantees stability before encountering the zero introduced by the C1’s equivalent series resistance (ESR). The GMV amplifier’s output is internally clamped to between onefourth and three-fourths of the voltage at REF. Current Control The charging current is set by a combination of the current-sense resistor value and the SETI pin voltage. The current-sense amplifier measures the voltage across the current-sense resistor, between CS and BATT. The current-sense amplifier’s gain is 6. The voltage on SETI is buffered and then divided by 4. This voltage is compared to the current-sense amplifier’s output. Therefore, full-scale current is accomplished by connecting SETI to REF. The full-scale charging current (IFS) is set by the following: IFS = 185mV / R1 (Figure 1) (UP TO 24V) D2 C5 4.7µF IN4148 VL DCIN BST REF R16 C7 0.1µF R15 10k C4 0.1µF C6 0.1µF L1 22µH DHI THM/SHDN M1A 1/2 IRF7303 LX MAX745 R3 100k 1% 1/2 IRF7303 M1B THM 1 DLO SETI R12 D6 MBRS 340T3 D1 MBRS 340T3 PGND VADJ C2, 0.1µF 0.2Ω R1 CS R2 10k BATT CCV R11 100k 1% CCI C3 47nF STATUS GND BATTERY IBAT Figure 1. Standard Application Circuit 6 _______________________________________________________________________________________ C1 68µF Switch-Mode Lithium-Ion Battery Charger PWM Controller The battery voltage or current is controlled by a current-mode, PWM DC/DC converter controller. This controller drives two external N-channel MOSFETs, which control power from the input source. The controller sets the switched voltage’s pulse width so that it supplies the desired voltage or current to the battery. Total component cost is reduced by using a dual, N-channel MOSFET. The heart of the PWM controller is a multi-input comparator. This comparator sums three input signals to determine the switched signal’s pulse width, setting the battery voltage or current. The three signals are the current-sense amplifier’s output, the GMV or GMI error amplifier’s output, and a slope-compensation signal that ensures that the current-control loop is stable. The PWM comparator compares the current-sense amplifier’s output to the lower output voltage of either the GMV or GMI amplifiers (the error voltage). This current-mode feedback reduces the effect of the inductor on the output filter LC formed by the output inductor (L1) and C1 (Figure 1). This makes stabilizing the circuit much easier, since the output filter changes to a first-order RC from a complex, second-order RLC. Monitoring Charge Current The battery-charging current can be externally monitored by placing a scaling resistor (R IBAT) between IBAT and GND. IBAT is the output of a voltage-controlled current source, with output current given by: IBAT = 0.9µA/VSENSE where VSENSE is the voltage across the current-sense resistor (in millivolts) given by: VSENSE = VCS - VBATT = ICHG x R1 The voltage across RIBAT is then given by: R 0.9µA VIBAT = x IBAT ICHG R1 IBAT CURRENT SENSE AV = 6 ON BATT CS DCIN 5.4V REG 4.2 REF REF VL STATUS GMI SETI 1/4 CCI BST DHI CLAMP PWM LOGIC LX VL DLO PGND THM/SHDN GMV VADJ REF 2 CCV CELL0 CELL1 CELL LOGIC GND Figure 2. Functional Diagram _______________________________________________________________________________________ 7 MAX745 RIBAT must be chosen to limit VIBAT to voltages below 2V for the maximum charging current. Connect IBAT to GND if unused. To set currents below full scale without changing R1, adjust the voltage at SETI according to the following formula: ICHG = IFS (VSETI / VREF) A capacitor at CCI sets the current-feedback loop’s dominant pole. While the current is in regulation, CCV voltage is clamped to within 80mV of the CCI voltage. This prevents the battery voltage from overshooting when the voltage setting is changed. The converse is true when the voltage is in regulation and the current setting is changed. Since the linear range of CCI or CCV is about 2V (1.5V to 3.5V), the 80mV clamp results in negligible overshoot when the loop switches from voltage regulation to current regulation, or vice versa. MAX745 Switch-Mode Lithium-Ion Battery Charger MOSFET Drivers Minimum Input Voltage The MAX745 drives external N-channel MOSFETs to switch the input source generating the battery voltage or current. Since the high-side N-channel MOSFET’s gate must be driven to a voltage higher than the input source voltage, a charge pump is used to generate such a voltage. The capacitor (C7) charges through D2 to approximately 5V when the synchronous rectifier (M1B) turns on (Figure 1). Since one side of C7 is connected to LX (the source of M1A), the high-side driver (DHI) drives the gate up to the voltage at BST, which is greater than the input voltage while the high-side MOSFET is on. The input voltage to the charger circuit must be greater than the maximum battery voltage by approximately 2V so the charger can regulate the voltage properly. The input voltage can have a large AC-ripple component when operating from a wall cube. The voltage at the low point of the ripple waveform must still be approximately 2V greater than the maximum battery voltage. Using components as indicated in Figure 1, the minimum input voltage can be determined by the following formula: [VBATT + VD6 + ICHG (RDS(ON) + RL + R1)] VIN x 0.89 where: VIN is the input voltage; The synchronous rectifier (M1B) behaves like a diode but has a smaller voltage drop, improving efficiency. A small dead time is added between the time when the high-side MOSFET is turned off and when the synchronous rectifier is turned on, and vice versa. This prevents crowbar currents during switching transitions. Place a Schottky rectifier from LX to ground (D1, across M1B’s drain and source) to prevent the synchronous rectifier’s body diode from conducting during the dead time. The body diode typically has slower switchingrecovery times, so allowing it to conduct degrades efficiency. D1 can be omitted if efficiency is not a concern, but the resulting increased power dissipation in the synchronous rectifier must be considered. Since the BST capacitor is charged while the synchronous rectifier is on, the synchronous rectifier may not be replaced by a rectifier. The BST capacitor will not fully charge without the synchronous rectifier, leaving the highside MOSFET with insufficient gate drive to turn on. However, the synchronous rectifier can be replaced with a small MOSFET (such as a 2N7002) to guarantee that the BST capacitor is allowed to charge. In this case, the majority of the high charging currents are carried by D1, and not by the synchronous rectifier. Internal Regulator and Reference The MAX745 uses an internal low-dropout linear regulator to create a 5.4V power supply (VL), which powers its internal circuitry. The VL regulator can supply up to 25mA. Since 4mA of this current powers the internal circuitry, the remaining 21mA can be used for external circuitry. MOSFET gate-drive current comes from VL, which must be considered when drawing current for other functions. To estimate the current required to drive the MOSFETs, multiply the sum of the MOSFET gate charges by the switching frequency (typically 300kHz). Bypass VL with a 4.7µF capacitor to ensure stability. The MAX745 internal 4.2V reference voltage must be bypassed with a 0.1µF or greater capacitor. 8 VD6 is the voltage drop across D6 (typically 0.4V to 0.5V); ICHG is the charging current; RDS(ON) is the high-side MOSFET M1A’s on-resistance; RL is the the inductor’s series resistance; R1 is the current-sense resistor R1’s value. __________________Pin Configuration TOP VIEW IBAT 1 20 BST DCIN 2 19 LX VL 3 18 DHI CCV 4 17 DLO CCI 5 MAX745 THM/SHDN 6 15 CS REF 7 VADJ 16 PGND 14 BATT 13 STATUS 8 SETI 9 12 CELL0 GND 10 11 CELL1 SSOP ___________________Chip Information TRANSISTOR COUNT: 1695 SUBSTRATE CONNECTED TO GND _______________________________________________________________________________________