19-1662; Rev 1; 10/00 KIT ATION EVALU E L B AVAILA SOT23, Single-Cell Li+ Battery Charger for Current-Limited Supply ________________________Applications Single-Cell Li+ Portable Applications Wireless Handsets Personal Digital Assistants Digital Cameras Small Hand-Held Equipment Self-Charging Battery Packs Cradle Chargers Features ♦ Small 6-Pin SOT23 Package ♦ Stand-Alone or µP-Controlled Operation ♦ 0.5% Voltage Set-Point Accuracy ♦ Lowest Power Dissipation ♦ Low 4.7V min Input Voltage ♦ Top-Off Charging to Achieve Full Battery Capacity ♦ No Inductor Required ♦ Safely Precharges Near-Dead Cells ♦ Automatic Power-Down when Input Power Removed Ordering Information TEMP. RANGE PINPACKAGE SOT MARK MAX1736EUT42-T -40°C to +85°C 6 SOT23-6 AAHO MAX1736EUT41-T -40°C to +85°C 6 SOT23-6 AANC PART Note: Requires special solder temperature profile described in the Absolute Maximum Ratings Section. Typical Operating Circuit CURRENT-LIMITED VOLTAGE SOURCE Pin Configuration TOP VIEW PFET IN 1 GATE IN GATE 2 MAX1736 6 BATT 5 CT 4 EN BATT BATTERY MAX1736 ON OFF EN CT GND 3 GND SOT23 ________________________________________________________________ Maxim Integrated Products 1 For price, delivery, and to place orders, please contact Maxim Distribution at 1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com. MAX1736 General Description The MAX1736 is a simple, low-cost, single-cell lithiumion (Li+) battery charger for small hand-held applications. When accompanied by a current-limited voltage source (such as a wall cube), the MAX1736 provides simple, accurate charging and termination control for single-cell Li+ batteries. The MAX1736EUT42 is preset to a 4.2V battery regulation voltage, while the MAX1736EUT41 is preset to 4.1V. The MAX1736 initiates charging in one of four ways: battery insertion, charger power-up, battery voltage threshold, and by external manipulation of the EN pin. The device features an internal precharge current source that safely charges near-dead cells, as well as input-supply detection that shuts down the MAX1736 when the supply is removed to minimize battery current drain. The MAX1736 accepts input voltages up to 22V, making it compatible with a wide range of input supplies. It has a single control input yet offers stand-alone and microprocessor-controlled operation. The MAX1736 is packaged in a small SOT23-6 package. An evaluation kit (EV kit) is available to reduce design time. MAX1736 SOT23, Single-Cell Li+ Battery Charger for Current-Limited Supply ABSOLUTE MAXIMUM RATINGS IN, GATE to GND....................................................-0.3V to +26V Operating Temperature Range ...........................-40°C to +85°C BATT, EN, CT to GND ..............................................-0.3V to +6V Storage Temperature Range ..............................-65°C to +150°C GATE to IN................................................................-6V to +0.3V Maximum Junction Temperature ......................................+150°C GATE Continuous Current.................................-10mA to +10mA Lead Temperature (soldering, 10s) (Note 2) ...................+300°C Continuous Power Dissipation (TA = +70°C) (Note 1) 6-Pin SOT23 (derate 8.1mW/°C above +70°C) .............0.65W Note 1: Thermal properties are specified with product mounted on PC board with one square-inch of copper area and still air. Note 2: This device is constructed using a unique set of packaging techniques that impose a limit on the termal profile the device can be exposed to during solder attach and rework. This limit permits only the use of the solder profiles recommended in the industry standard specification, IPC/JEDEC J-STD-020A, paragraph 7.6, Table 3 for the IR/VPR and Convention reflow. Pre-heating is required. Hand or wave soldering is not allowed. 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 (VIN = 10V, VBATT = 4.2V for MAX1736EUT42 or 4.1V for MAX1736EUT41, TA = 0°C to +85°C. Typical values are at TA = +25°C, unless otherwise noted.) (Note 3) PARAMETER CONDITIONS MIN Input Voltage (Note 4) External P-MOSFET off 4.7 Fast-Charge BATT Qualification Threshold BATT rising, transition from precharge to fast charge 2.4 Fast-Charge BATT Qualification Threshold Hysteresis BATT Regulation Voltage BATT Removal Detection Threshold 4.20 4.221 4.121 BATT rising 4.875 5.0 5.1 125 VBATT = 2V 3.5 IN Input Current CCT = 0.33µF GATE Source/Sink Current VBATT = 5.1V V V mV 0.1 1 µA 2 6 µA 0.4 0.75 mA 6 8 mA 0.25 1 mA 20 s 75 100 125 µA 15 30 60 mA µF/A 1.5 2 V EN Logic Low Threshold 2 mV 4.10 BATT Input Current, When Charging CT Pulldown Current V 4.179 EN = GND, VBATT = 0 to 5V EN Logic High Threshold 2.65 4.079 BATT Input Current, Charger Disabled Minimum BATT Bypass Capacitance (Note 6) V MAX1736EUT42 VIN ≤ VBATT - 0.3V GATE Drive Source Current at Battery Removal UNITS 22 MAX1736EUT41 BATT Input Current, Input Power Removed IN Detection Interval (Note 5) 2.5 MAX 70 BATT Removal Detection Threshold Hysteresis Precharge Source Current TYP 1.6 2 _______________________________________________________________________________________ 0.7 V 2.4 µA SOT23, Single-Cell Li+ Battery Charger for Current-Limited Supply (VIN = 10V, VBATT = 4.2V for MAX1736EUT42 or 4.1V for MAX1736EUT41, TA = 0°C to +85°C. Typical values are at TA = +25°C, unless otherwise noted.) PARAMETER CONDITIONS CT Pullup Current MIN -12 TYP MAX -10 -8 UNITS µA Minimum On-Time CCT = 0.33µF 165 ms Minimum Off-Time CCT = 0.33µF 33 ms EN Pullup Resistance 175 350 725 kΩ ELECTRICAL CHARACTERISTICS (VIN = 10V, VBATT = 4.2V for MAX1736EUT42 or 4.1V for MAX1736EUT41, TA = -40°C to +85°C, unless otherwise noted.) (Note 3) PARAMETER CONDITIONS MIN MAX UNITS Input Voltage (Note 4) External P-MOSFET off 4.7 22 V Fast-Charge BATT Qualification Threshold BATT rising, transition from precharge to fast charge 2.4 2.65 V MAX1736EUT42 4.158 4.242 V MAX1736EUT41 4.058 4.142 BATT Removal Detection Threshold BATT rising 4.85 5.125 V BATT Input Current, Input Power Removed VIN ≤ VBATT - 0.3V 1 µA BATT Input Current, Charger Disabled EN = GND, VBATT = 0 to 5V 6 µA 0.75 mA BATT Regulation Voltage BATT Input Current, When Charging Precharge Source Current VBATT = 2V 3 8 mA 1 mA 60 140 µA 10 90 mA IN Input Current GATE Source/Sink Current GATE Drive Source Current at Battery Removal EN Logic High Threshold VBATT = 5.1V 2 EN Logic Low Threshold CT Pulldown Current 1.5 V 0.7 V 2.5 µA CT Pullup Current -12 -8 µA EN Pullup Resistance 170 725 kΩ Note 3: All devices are 100% production tested at TA = +25°C. Limits over the operating temperature range are guaranteed by design. Note 4: The input voltage range is specified with the external PFET off. When charging, the PFET turns on and the input voltage (the output voltage of the constant-current power source) drops to very near the battery voltage. When the PFET is on, IN may be as low as 2.5V. Note 5: Every 20s (for CT = 0.33µF) the MAX1736 turns off the external P-channel MOSFET and samples IN to determine if input power is present. If input power is removed, the charger shuts down. Note 6: For design guidance, not tested. _______________________________________________________________________________________ 3 MAX1736 ELECTRICAL CHARACTERISTICS (continued) Typical Operating Characteristics (TA = +25°C, unless otherwise noted.) MINIMUM OFF-TIME 100 0.15 0.10 0.05 0.00 -0.05 -0.10 MAX1736-03 MAX1736-02 5.8 VBATT = 0 5.7 PRECHARGE CURRENT CURRENT (mA) (mA) PRECHARGE MINIMUM ON-TIME 1000 0.20 BATT VOLTAGE DEVIATION (%) MAX1736 toc01 10,000 PRECHARGE CURRENT vs. INPUT VOLTAGE BATT REGULATION VOLTAGE DEVIATION vs. TEMPERATURE MINIMUM ON/OFF-TIMES vs. CCT MINIMUM ON/OFF-TIME (ms) 5.6 VBATT = 1V 5.5 5.4 VBATT = 2V 5.3 5.2 -0.15 0.1 1 5.1 -0.20 10 -40 -15 CCT (µF) 10 35 60 4 85 9 14 VIN (V) TEMPERATURE (°C) TYPICAL OPERATING WAVEFORMS INPUT DETECTION INTERVAL vs. CCT MAX1736 toc04 1000 IIN 5V/div PFET OFF PFET ON OV VBATT 200mV/div 100 AC-COUPLED IIN 1A/div 10 OA VGATE 10V/div 1 0.1 1 10 10ms/div CCT (µF) 4 _______________________________________________________________________________________ MAX1736 toc05 10 INPUT DETECTION INTERVAL (s) MAX1736 SOT23, Single-Cell Li+ Battery Charger for Current-Limited Supply 19 24 SOT23, Single-Cell Li+ Battery Charger for Current-Limited Supply PIN NAME DESCRIPTION 1 IN 2 GATE Gate Drive for External PMOS Pass Element. The PMOS device should have a VGS threshold of 2.5V or less (see Selecting External Components). 3 GND Ground. Connect the battery’s negative terminal to GND. 4 EN Logic-Level Enable Input. Pull low to disable the MAX1736. EN is internally pulled up to VBATT + 100mV through 350kΩ, but draws no current from BATT. 5 CT Charge Time Control. Sets the minimum on-time, minimum off-time, and the IN detection interval. Place a 0.33µF capacitor between CT and GND for most applications (see Selecting External Components). 6 BATT Input Voltage from Current-Limited Voltage Source (22V max). Bypass to GND with a 0.1µF capacitor. The charging current is set by the current limit of the external power supply. Cell Voltage Monitor Input, Precharge Current Output, and MAX1736 Power Source. Connect BATT to the positive terminal of a single Li+ cell. Bypass BATT with a capacitor to GND (1.5µF per amp of charge current). Detailed Description The MAX1736 provides a simple, safe, low-cost method of charging a single-cell Li+ battery with nearly no heat generation. Combined with a current-limited voltage source, the MAX1736 provides precharge, fast-charge, and top-off-charge capabilities. After constant-current fast charge, top-off safely finishes charging the battery by pulse-width modulating charge current. The top-off on-time is kept below the electrochemical time constant of the cell. The key advantage of this method is that the charge circuit is small and generates minimal heat while providing a safe method of charging to ensure maximum cell life. Figure 1 shows the MAX1736 functional diagram. Precharge To protect Li+ cells from damage that may occur if fast charged from a dead state, the MAX1736 precharges the Li+ cell with 6mA at the start of a charging cycle when the cell voltage is below 2.5V. As soon as the cell voltage reaches 2.5V, the MAX1736 begins fast charging. Fast Charge In fast-charge mode, the MAX1736 turns on the external P-channel MOSFET. Charging current is set by the current limit of the external supply; current is not regulated by the MAX1736. The P-channel MOSFET is used only as a switch, not as a linear regulator. Therefore, the circuit’s power dissipation is minimized, permitting rapid charge cycles with almost no heat generation. The external power supply should have a specified current limit that matches the desired fastcharge current for the Li+ cell. With the P-channel MOSFET on, V IN will be nearly equal to VBATT. To detect that an input supply is connected, the MAX1736 periodically turns the P-channel MOSFET off and checks the voltage at IN. During fast charge, this occurs once every input detection interval (20s with CCT = 0.33µF). During pulsed top-off, input detection occurs more frequently and is continuous when the MOSFET is off (see Selecting External Components). Pulsed Top-Off When the battery approaches full charge, its instantaneous voltage reaches the BATT regulation voltage and pulsed top-off begins. The MAX1736 uses a hysteretic algorithm with a minimum on- and off-time. Cell voltage is sampled with no charging current to minimize errors due to battery and cell protection resistance. If the voltage is below the BATT regulation voltage, the P-channel MOSFET switches on for a minimum on-time. If, at the end of the minimum on-time, the cell voltage is still below the BATT regulation voltage, the switch remains on until the cell voltage reaches the BATT regulation voltage. At that point, the P-channel MOSFET then switches off for at least the minimum off-time. The minimum on-time is set by CT and should be set below the electrochemical time constant of the cell. A CCT value of 0.33µF sets a minimum on-time of 165ms, which is adequate for most Li+ batteries. _______________________________________________________________________________________ 5 MAX1736 Pin Description MAX1736 SOT23, Single-Cell Li+ Battery Charger for Current-Limited Supply IN EN IN GATE IN VBATT + 100mV 6mA 350k 10µA 1.4V 4.2V (4.1V) STATE MACHINE CT BATT 0.4V 5V REF MAX1736EUT42 (MAX1736EUT41) 2µA GND Figure 1. Functional Diagram Once the switch turns off, it remains off for at least the minimum off-time. After the minimum off-time, the Pchannel MOSFET turns on if the cell voltage is lower than the BATT regulation voltage. A C CT value of 0.33µF sets a minimum off-time of 33ms. At the beginning of the pulsed top-off state, charge current is modulated at approximately an 83% duty cycle. Toward the end of top-off, charge current stays off for long periods of time between single “on” pulses. During these final pulses, the instantaneous cell voltage may exceed the BATT regulation voltage by several hundred millivolts, but these pulses are orders of magnitude shorter than the electrochemical time constant of the Li+ cell and do no harm. Pulsed top-off charge ends when the cell voltage no longer falls below the BATT regulation voltage. Figure 2 shows the state machine. external power source, not by the MAX1736. The Pchannel MOSFET in Figure 3’s application circuit is either on or off, allowing the source to be directly connected to the cell or disconnected. Therefore, it is important to choose a power supply with the correct current limit for the cell to be charged. In most applications, this will be a small wall cube with an open-circuit output voltage of 5V to 12V, which is specified as “current limited” or “constant current.” Some low-cost wall cubes may have poor transient characteristics. For these wall cubes, output current may exceed the specified current limit by several times when the load is quickly connected. The MAX1736 limits this current peak by controlling the slew rate of the P-channel MOSFET. See C CT and C GATE for more information. Selecting External Components The P-channel MOSFET switches the current-limited source on and off. Because of the intentionally slow switching times and limited slew rate, the MAX1736 is not particular about the power FET it drives. Specifications to consider when choosing an appropriate Input Power Supply One reason the MAX1736 Li+ charger is so compact and simple is that the charging current is set by the 6 PMOS Switch ____________________________________________________________________________________________________ SOT23, Single-Cell Li+ Battery Charger for Current-Limited Supply MAX1736 CHARGER POWER REMOVED (FROM ANY STATE) (FROM ANY STATE) EN CHARGER POWER PRESENT SHUTDOWN FET: OFF PRECHARGE FET: OFF IOUT = -6mA DISABLED FET: OFF EVERY CYCLE CHARGER POWER PRESENT TOP-OFF FET: PULSED IN DETECTION INTERVAL VBATT > 4.2V VBATT < 2.5V FAST-CHARGE QUAL FET: OFF VBATT < 2.5V TOP-OFF QUAL FET: OFF VBATT ≥ 2.5V EN CHARGER POWER PRESENT FAST-CHARGE FET: ON Figure 2. State Machine FET are the minimum drain-source breakdown voltage and the minimum turn-on threshold voltage (V GS ). Power dissipation during fast charge is approximately RDSON ✕ ICHG2, where ICHG is the current limit set by the input power source. The minimum breakdown voltage (BVDS) must typically be two times the wall cube’s open-circuit voltage. An even larger margin may be necessary if the wall adapter has especially poor transient response. The MAX1736 can operate with input voltages up to 22V. BATT Capacitor Bypass BATT with at least 1.5µF per amp of charge current. If the battery is removed while the P-channel MOSFET is on, a BATT voltage over 5V is quickly sensed, and the FET is immediately turned off. In applications where the cell is removable, very large capacitance values may increase transient currents when the cell is replaced. Therefore, BATT capacitance in excess of 100µF should be avoided. For best system performance with large output capacitance, at least 0.47µF of the total capacitance should be low-ESR ceramic. CCT and CGATE Most applications will use the circuit of Figure 3 with CGATE = 0.22µF, RGATE = 100kΩ, and CCT = 0.33µF. CGATE, RGATE, and the internal 100µA pull-up and pulldown current sources act to slow the switching of the Pchannel MOSFET. This prevents a wall cube with poor transient response from subjecting VIN to excessive voltage when the P-channel MOSFET turns off, and prevents excessive current into the battery when the Pchannel MOSFET turns on. Excessive voltage at VIN can potentially damage the IC, input capacitor, and the PMOS switch. Excessive current into the battery can cause errors in the termination process of the MAX1736 (by raising the instantaneous battery voltage) and may trip the battery’s protection circuitry. In applications utilizing a wall cube with poor transient response, increase the value of CGATE as needed to _______________________________________________________________________________________ 7 further slow switching edges and prevent transient spikes. CCT sets the minimum on-time and off-time according to the following equations: tON(MIN) = 5 ✕ 105 x CCT CURRENT-LIMITED WALL CUBE (800mA) FDC638P PFET 100k 0.22µF tOFF(MIN) = 1 ✕ 105 x CCT GATE Layout Guidelines The MAX1736 controls the GATE slew rate; consequently, PC board layout is not as sensitive to noise as a high-frequency switching regulator. In addition, since cell voltage is sensed both during and between highcurrent pulses, the system is insensitive to ground errors. However, Maxim recommends maintaining large ground area and large traces for high-current paths. Refer to the MAX1736EVKIT for a recommended layout example. BATT IN 2.2µF 0.1µF MAX1736 GND SINGLE Li+ CELL CT 0.33µF Figure 3. Simple Application Circuit Chip Information TRANSISTOR COUNT: 1622 Package Information 6LSOT.EPS MAX1736 SOT23, Single-Cell Li+ Battery Charger for Current-Limited Supply 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. 8 _____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 © 2000 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.