19-2061; Rev 0; 5/01 ABLE KIT AVAIL N IO T A U L EVA Simple, Efficient, 1-Cell Li+ Pulse Charger Features ♦ Simple Design Minimizes Heat The MAX1879 initiates charging in one of three ways: battery insertion, charger power-up, or toggling the THERM pin. Key safety features include continuous voltage and temperature monitoring, a preset charger time-out, and an 8mA precharge current mode to charge near-dead cells. Automatic detection of input power removal shuts down the device, minimizing current drain from the battery. An overall system accuracy of 0.75% ensures that the cell capacity is fully utilized without cycle life degradation. ♦ Restart Charging at 4.0V The MAX1879 is offered in a space-saving 8-pin µMAX package. An evaluation kit (MAX1879EVKIT) is available to help reduce design time. ♦ Pin-Compatible Upgrade to MAX1679 ♦ Low Component Count, No Inductor ♦ Battery-Full Indicator ♦ 0.75% Accurate Battery Regulation ♦ 1.5µA (max) Battery Current Drain with Wall Cube Removed ♦ Continuous Overvoltage and Overtemperature Protection ♦ Safely Precharges Near-Dead Cells ♦ Automatic Power-Down when Power Source is Removed ♦ Charges 1 Cell from as Low as 4.5V Applications Ordering Information Single-Cell Li+ Powered Portables Self-Charging Battery Packs PDAs PART TEMP. RANGE PIN-PACKAGE MAX1879EUA -40°C to +85°C 8-µMAX Cell Phones Cradle Chargers Typical Operating Circuit Pin Configuration TOP VIEW IN 1 8 BATT GATE 2 7 THERM 3 6 GND TSEL 4 5 ADJ CURRENTLIMITED AC WALL ADAPTER LED CHG µMAX GATE IN MAX1879 BATT CHG MAX1879 PULSE WIDTH SELECT INPUT TSEL THERM 1-CELL Li+ BATTERY GND ADJ THERMISTOR ________________________________________________________________ Maxim Integrated Products For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at 1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com. 1 MAX1879 General Description The MAX1879 single-cell lithium-ion (Li+) battery charger utilizes an efficient pulse-charging architecture to minimize power dissipation in portable devices. This architecture combines the efficiency of switch-mode chargers with the simplicity and low cost of linear chargers. This simple device, in conjunction with a current-limited wall cube and a PMOS transistor, allows safe and fast charging of a single Li+ cell. MAX1879 Simple, Efficient, 1-Cell Li+ Pulse Charger ABSOLUTE MAXIMUM RATINGS IN, CHG, GATE to GND..........................................-0.3V to +26V BATT, TSEL, THERM, ADJ to GND...........................-0.3V to +6V GATE to IN................................................................-6V to +0.3V THERM, ADJ to BATT...............................................-6V to +0.3V GATE Continuous Current ................................................ -10mA Continuous Power Dissipation (TA = +70°C) 8-Pin µMAX (derate 4.1mW/°C above +70°C) ............ 330mW Operating Temperature Range ...........................-40°C to +85°C Storage Temperature Range ............................ -65°C to +150°C Lead Temperature (soldering, 10s) ................................ +300°C Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability. ELECTRICAL CHARACTERISTICS (VIN = V CHG = +10V, VBATT = +4.2V, TSEL = GND, GATE = unconnected, ADJ = unconnected, THERM = 10kΩ to GND, TA = 0°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) PARAMETER Input Voltage (Note 1) SYMBOL VIN CONDITIONS MIN TYP MAX UNITS 22 V 2.3 V External PMOS FET off 4.4 Undervoltage Lockout Trip Point BATT rising 2.1 Undervoltage Lockout Trip-Point Hysteresis BATT falling Fast-Charge Qualification Threshold BATT rising, transition from precharge to full current 2.425 2.5 2.575 V Fast-Charge Restart Threshold BATT falling, transition from Done to Prequalification state (Note 2) 3.92 4.00 4.08 V Fast-Charge Reset Threshold Delay (Note 3) Precharge Source Current VBATT = 2V BATT Regulation Voltage 2.2 60 mV 1 ms 5 8 12 mA 4.1685 4.2000 4.2315 V BATT Regulation Adjust Range 4.0 ADJ Source Impedance 9.8 4.2 V 10 10.2 kΩ ADJ Output Voltage No load on ADJ 1.393 1.400 1.407 V BATT Removal Detection Threshold BATT rising 4.875 5 5.125 V BATT Removal Detection Threshold Hysteresis BATT falling 125 BATT Input Current (Note 4) VIN ≤ VBATT - 0.3V 0.1 1.5 µA mV BATT Input Current, Fast-Charge State IBATT VBATT = 4.0V 900 1500 µA BATT Input Current, Done State IBATT VBATT = 4.25V, VIN present 85 200 µA 50 500 µA 700 1200 µA +10 % IN Input Current, Fast-Charge State IIN VBATT = 4.0V, VIN = 4.0V IN Input Current, Done State IIN VBATT = 4.25V, VIN = 22V Timer Accuracy -10 CHG Output Leakage Current V CHG = 22V, CHG = high -1 CHG Output Sink Current V CHG = 1.0V, CHG = low 4 2 5 _______________________________________________________________________________________ +1 µA 6 mA Simple, Efficient, 1-Cell Li+ Pulse Charger (VIN = V CHG = +10V, VBATT = +4.2V, TSEL = GND, GATE = unconnected, ADJ = unconnected, THERM = 10kΩ to GND, TA = 0°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS THERM Sense Current (for hot qualification) 346 352.9 360 µA THERM Sense Current (for cold qualification) 47.8 48.8 49.8 µA THERM Sense Voltage Trip Point 1.379 1.40 1.421 V GATE Source Current VIN = 10V, VGATE = 8V 75 100 125 µA GATE Sink Current VIN = 10V, VGATE = 8V 19 25 31 µA GATE Drive Current at Battery Removal VBATT = 5.1V, gate driven high 18 40 60 mA ELECTRICAL CHARACTERISTICS (VIN = V CHG = +10V, VBATT = +4.2V, TSEL = GND, GATE = unconnected, ADJ = unconnected, THERM = 10kΩ to GN, TA = -40°C to +85°C, unless otherwise noted.) (Note 5) PARAMETER MIN MAX UNITS External PMOS FET off 4.6 22 V Undervoltage Lockout Trip Point BATT rising 2.05 2.35 V Fast-Charge Qualification Threshold BATT rising, transition from precharge to full current 2.35 2.65 V Fast-Charge Restart Threshold BATT falling, transition from Done to Prequalification state (Note 2) 3.88 4.12 Precharge Source Current VBATT = 2V 4.5 4.137 12 4.263 Input Voltage (Note 1) SYMBOL VIN CONDITIONS BATT Regulation Voltage V mA V BATT Regulation Adjust Range 4.0 4.2 V ADJ Source Impedance 9.8 10.2 kΩ ADJ Output Voltage No load on ADJ 1.383 1.417 V BATT Removal Detection Threshold BATT rising 4.85 5.15 V BATT Input Current (Note 4) VIN ≤ VBATT - 0.3V 1.5 µA BATT Input Current, Fast-Charge State IBATT VBATT = 4.0V 1500 µA BATT Input Current, Done State IBATT VBATT = 4.25V, VIN present 300 µA 600 µA IN Input Current, Fast-Charge State IIN VBATT = 4.0V, VIN = 4.0V IN Input Current, Done State IIN VBATT = 4.25V, VIN = 22V 1500 µA CHG Output Leakage Current V CHG = 22V, CHG = high -1 +1 µA CHG Output Sink Current V CHG = 1.0V, CHG = low 4 6 mA _______________________________________________________________________________________ 3 MAX1879 ELECTRICAL CHARACTERISTICS (continued) MAX1879 Simple, Efficient, 1-Cell Li+ Pulse Charger ELECTRICAL CHARACTERISTICS (continued) (V IN = V CHG = +10V, V BATT = +4.2V, TSEL = GND, GATE = unconnected, ADJ = unconnected, THERM = 10kΩ to GND, TA = -40°C to +85°C, unless otherwise noted.) (Note 5) PARAMETER SYMBOL CONDITIONS MIN MAX UNITS THERM Sense Current (for hot qualification) 342 363 µA THERM Sense Current (for cold qualification) 47.3 50.3 µA THERM Sense Voltage Trip Point 1.358 1.442 V GATE Source Current VIN = 10V, VGATE = 8V 60 140 µA GATE Sink Current VIN = 10V, VGATE = 8V 15 35 µA GATE Drive Current at Battery Removal VBATT = 5.1V, gate driven high 15 90 mA Note 1: The input voltage range is specified with the external PMOS FET off. When charging, the PMOS FET turns on, and the input voltage (the output voltage of the current-limited source) drops to very near the battery voltage. When the PFET is on, VIN may be as low as 2.5V. Note 2: Restart Threshold tracks battery regulation voltage adjustment. Note 3: Glitches less than 1ms do not cause a restart. Note 4: This current is less than 1.5µA, even if an external RADJ resistor is connected from ADJ to GND. Note 5: Specifications to -40°C are guaranteed by design and not production tested. 4 _______________________________________________________________________________________ Simple, Efficient, 1-Cell Li+ Pulse Charger 1.010 1.005 1.000 0.995 0.990 0.985 0.980 -40 NORMALIZED TO +25°C 1.0015 1.0010 1.0005 1.0000 0.9995 0.9990 0.9985 0 20 40 TEMPERATURE (°C) 60 80 8.8 8.6 8.4 8.2 VBATT = 0 8.0 7.8 7.6 0.9980 7.4 0.9975 7.2 VBATT = 2V 7.0 0.9970 -20 9.0 MAX1879 toc03 1.0020 MAX1879 toc02 NORMALIZED TO +25°C NORMALIZED REGULATION VOLTAGE NORMALIZED TIMER PERIOD MAX1879 toc01 1.020 1.015 PRECHARGE CURRENT vs. INPUT VOLTAGE NORMALIZED BATTERY REGULATION VOLTAGE vs. TEMPERATURE PRECHARGE CURRENT (mA) NORMALIZED TIMER PERIOD vs. AMBIENT TEMPERATURE -40 -20 0 20 40 TEMPERATURE (°C) 60 80 5 10 15 20 25 VIN (V) Pin Description PIN NAME FUNCTION 1 IN Input Voltage from Current-Limited Voltage Source (+22V max). Bypass to GND with a 0.1µF capacitor. 2 GATE Gate Drive for External PMOS Pass Element. The PMOS device should have a VGS threshold less than 2.5V. See Selecting External Components. 3 CHG Charge Status Indication. A CHG low indicates that the MAX1879 is charging a battery. CHG goes high when the on/off duty cycle falls to 1/8, indicating that the battery is charged to approximately 95% of full capacity. CHG is an open-drain current-limited N-channel MOSFET suitable for directly driving an LED. Connect a pullup resistor to the logic supply to generate a logic-level signal. CHG blinks at 2Hz during the Prequalification state (2.2V < VBATT < 2.5V) and during a temperature fault. 4 TSEL Minimum ON/OFF Pulse Width Selection (Table 2) 5 ADJ Battery Regulation Voltage Adjustment. Bypass to GND with a 1000pF capacitor. Connect a resistor from ADJ to GND to reduce the nominal +4.200V regulation set point. See Adjusting the Battery Regulation Voltage. 6 GND Ground. See Layout Guidelines for information on system grounding. Connect the battery’s negative terminal to GND. 7 THERM 8 BATT Thermistor Temperature-Sensor Input. Connect an NTC thermistor (10kΩ at +25°C) from THERM to GND to allow prequalification of the cell temperature for fast-charge. Replace the thermistor with a 10kΩ resistor if temperature sensing is not required. Cell Voltage Monitor Input, Precharge Current Output, and MAX1879 Power Source. Connect BATT to the positive terminal of a single Li+ cell. Bypass BATT with a capacitor to ground (1.5µF per amp of charge current). _______________________________________________________________________________________ 5 MAX1879 Typical Operating Characteristics (VIN = CHG = +10V, VBATT = +4.2V, THERM = 10kΩ to GND, TA = +25°C, unless otherwise noted.) Simple, Efficient, 1-Cell Li+ Pulse Charger MAX1879 Functional Diagram CURRENT-LIMITED VOLTAGE SOURCE (800mA) PFET REVERSE-CURRENT PROTECTION DIODE IN GATE CHG MAX1879 PRECHARGE CURRENT (8mA) 5mA BATT 10kΩ TSEL STATE MACHINE SEE TABLE 2 FOR PULSE-WIDTH OPTIONS 1:3 ADJ 2.2µF 1.4V 1nF TIMER BATT REMOVED 5V COLD QUAL TEST CURRENT 30kHz OSCILLATOR HOT QUAL TEST CURRENT 1.4V THERM NTC THERMISTOR* *OPTIONAL—REPLACE WITH 10kΩ RESISITOR IF NOT SENSING TEMPERATURE. **RADJ = 410kΩ ±1% FOR 4.1V CELL; LEAVE OPEN FOR 4.2V CELL. 6 _______________________________________________________________________________________ RADJ ** SINGLE Li+ CELL Simple, Efficient, 1-Cell Li+ Pulse Charger SHUTDOWN PMOS FET: OFF LED: OFF CHARGING POWER REMOVED (FROM ANY STATE) CHARGING POWER APPLIED VBATT < 4.0V OR PULL THERM HIGH VBATT > 2.2V POWER-ON RESET 8.0mA PRECHARGE: ON PMOS FET: OFF LED: OFF BATT NOT INSTALLED OR VBATT < 2.2V (ASYNCHRONOUSLY, FROM ANY STATE) PREQUALIFICATION 8.0mA PRECHARGE: ON PMOS FET: OFF LED: 50% DUTY CYCLE, 2Hz VBATT 4.2V TEMPERATURE NOT OK OR VBATT < 2.5V 2.5V < VBATT < 4.2V VBATT < 2.5V VBATT > 4.0V DONE PMOS FET: OFF LED: OFF CHARGE PMOS FET: PULSED LED: ON EVERY 9s TEMPERATURE OK VBATT < 2.5V CHARGE QUALIFICATION PMOS FET: OFF LED: ON TEMPERATURE NOT OK (LED: 50% DUTY CYCLE, 2Hz) BATT REGULATION VOLTAGE (e.g., 4.2V) HAS BEEN REACHED AND FET ON-TIME < 1 FET OFF-TIME 8 TOP-OFF PMOS FET: PULSED LED: OFF TOTAL TIME = 6.25hr EVERY 9S TEMPERATURE OK VBATT < 2.5V TOP-OFF QUALIFICATION PMOS FET: OFF LED: OFF TEMPERATURE NOT OK (LED: OFF) _______________________________________________________________________________________________________ 7 MAX1879 Simplified State Diagram MAX1879 Simple, Efficient, 1-Cell Li+ Pulse Charger Detailed Description Initiating a Charge Cycle The MAX1879 initiates fast-charge upon insertion of a battery or application of an external power source (current-limited AC wall adapter). After charge completion, charging restarts if the cell voltage falls below 4.0V or when THERM is pulled above 1.4V after the charge timer expires (approximately 6.25hr). Before a charge cycle can begin, cell conditions are verified to be within safe limits. The cell voltage must be greater than 2.5V but less than the regulation voltage (default value 4.2V). In addition, the thermistor must indicate an acceptable cell temperature (default range +2.5°C to +47.5°C). See the Applications Information section. Li+ cells can be damaged when fast-charged from a completely dead state. Moreover, a fully discharged cell may indicate a dangerous abnormal cell condition. As a built-in safety feature, the MAX1879 precharges the Li+ cell with 8mA at the start of a charge cycle if the cell voltage is below 2.5V. As soon as the cell reaches 2.5V and the safety conditions are met (see the FastCharge section), fast-charging begins. If the temperature moves outside the programmed range, the charger pauses. When the temperature returns to the safe charging range, the charging cycle continues, and the charge timer resumes counting from the point at which the temperature fault occurred. The timer is not reset. The MAX1879 monitors these conditions throughout the charging cycle. Fast-Charge Once cell conditions are determined to be satisfactory, the MAX1879 fast-charges the Li+ cell by pulling GATE low, turning on the external PMOS FET. Cell charging current is set by the current limit of the external power supply; it is not regulated by the MAX1879. The PMOS FET operates only as a switch, not as a linear regulator. Therefore, power dissipation is minimized, permitting rapid charge cycles with minimal heat generation. The external power supply must have a specified current limit that matches the desired fast-charge current for the Li+ cell. The MAX1879 uses a hysteretic algorithm with minimum on-times and minimum off-times to top-off the cell. The cell voltage is sampled every 2ms. If VBATT is less than the battery regulation voltage, the external PMOS FET turns on or remains on. If the cell voltage is greater than or equal to the battery regulation voltage, the FET turns off and remains off for the minimum off-time. By measuring the cell voltage when the PMOS FET is off as well as when it is on, the MAX1879 eliminates bat8 tery-voltage sensing errors due to charging current flowing through the series resistance of cell protection switches or fuse links in the charging path. Fast-charge continues until the on/off duty cycle falls to 1/8, then the CHG LED turns off, indicating that the battery is charged to approximately 95% of full capacity. Pulsed Top-Off Charge At the beginning of the Top-Off state, the current stays on for a 1/8 duty cycle. As the cell continues to charge, the percentage of time spent in the “current-on” mode decreases. Towards the end of top-off, the current stays off for many cycles between single “on” pulses. During these final pulses, the instantaneous cell voltage may exceed the battery regulation voltage, but the duration of these pulses is several orders of magnitude shorter than the intrinsic chemical time constant of the Li+ cell. This does not harm the cell. Cell top-off is completed when the charging timer expires (approximately 6.25hr). Charge Status with CHG CHG indicates the cell’s charging status. An LED can be connected directly from IN to CHG for a visible indicator. Alternatively, a pullup resistor (100kΩ) from a logic supply to CHG provides a logic-level output. Table 1 relates the LED status to the charger condition. Applications Information The MAX1879 was designed to offer the maximum integration and functionality in the smallest, most basic application circuit possible. The only necessary external components are a current-limited wall cube, a PMOS FET, two small capacitors, and a 10kΩ thermistor/resistor. This simple application circuit appears in Figure 1. Optionally (as shown in Figure 2), an LED can be added as a charge-state indicator, a resistor (RADJ) can be used to trim down the maximum charge voltage Table 1. CHG Output States CONDITION CHG (LED) No battery or no charger, or cell voltage < 2.2V High impedance (LED off) Fast-charge in progress Low (LED on) Top-Off: on/off duty cycle < 1/8 High impedance (LED off) Done (charge complete) High impedance (LED off) Temperature fault LED blinks at 2Hz Prequalification (2.2V < VBATT < 2.5V) LED blinks at 2Hz _______________________________________________________________________________________ Simple, Efficient, 1-Cell Li+ Pulse Charger Adjusting the Battery Regulation Voltage A typical Li+ cell should be charged at a constant current until it reaches a voltage of about 4.2V, then charged at this voltage until the current decays below a predetermined level. The MAX1879 provides a simple way to reduce this maximum target voltage with a single resistor between ADJ and GND. Internally, ADJ connects to a precision 1.4V reference through a 10kΩ resistor. Leave ADJ open for a battery regulation voltage (VBR) of 4.2V; connect a 1% resistor from ADJ to GND to form a voltage-divider for lower battery regulation voltage (VBR′). Select the external value using: RADJ = 10kΩ VBR −1 VBR ′ Selecting Minimum On-Time The minimum pulse on-times can be selected by connecting TSEL as indicated in Table 2. A short pulse time may be preferred to minimize voltage overshoot at the battery and prevent pack overvoltage protection circuitry from prematurely activating. A long minimum on-time may be needed when using AC adapters with high turn-on overshoot to allow charging current to settle before the end of the pulse. Selecting External Components Power Supply One reason the MAX1879 Li+ cell-charging solution is so compact and simple is that the charging current is set by the external power source, not by the MAX1879 charging circuit. The PMOS FET in this application circuit is either on or off, allowing the source to be directly connected to the cell or completely disconnected. Therefore, it is very important to choose a power supply Table 2. TSEL Minimum On-Time Settings A 1% tolerance resistor at ADJ degrades system accuracy by only a fraction of a percent. For example, an RADJ of 410kΩ ±1% reduces the battery regulation voltage by 2.4% (VBR′ = 4.1V from equation above, and (VBR′ - VBR) / VBR = (4.1 - 4.2) / 4.2 = -2.4%). PMOS FET FAIRCHILD FDC638P -4.5A, -20V 0.07Ω AT VGS = -2.5V CURRENT-LIMITED WALL CUBE (800mA, 6V max) Therefore, the additional system error is simply the RADJ tolerance multiplied by the percent change in the battery regulation voltage, or (1%)(2.4%) = 0.024%. TSEL CONNECTION MINIMUM ON-TIME IN TOP-OFF (ms) BATT 34 ADJ 69 GND 137 PMOS FET FAIRCHILD FDC638P -4.5A, -20V 0.07Ω AT VGS = -2.5V CURRENT-LIMITED SCHOTTKY DIODE 30V, 1A WALL CUBE ZETEX ZHCS1000 (800mA, 6V max) GATE GATE IN IN 5mA LED BATT MAX1879 MAX1879 CHG CHG TSEL* ADJ THERM 0.001µF 10kΩ 0.001µF 2.2µF *SEE TABLE 2 FOR TSEL POSITION AND ASSOCIATED TIMER SETTINGS. Figure 1. Simple Application Circuit SINGLE Li+ CELL RADJ 410kΩ 1%** BATT TSEL* ADJ THERM 2.2µF NTC THERMISTOR FENWAL 140-103LAG-RBI (10kΩ AT 25°C) SINGLE Li+ CELL *SEE TABLE 2 FOR TSEL POSITION AND ASSOCIATED TIMER SETTINGS. ** RADJ SETS BATTERY REGULATION VOLTAGE TO 4.10V; LEAVE OPEN FOR 4.2V. Figure 2. Application Circuit Including LED and Thermistor _______________________________________________________________________________________ 9 MAX1879 from 4.2V, and/or a reverse-current-protection diode can be added in line at the source. If the input is shorted, the MAX1879 will not allow current to flow from BATT back through IN to the source. However, the body diode inherent in the enhancementmode FET would still allow the cell to discharge rapidly. To prevent this, add a power Schottky diode between the source and IN as in Figure 4. MAX1879 Simple, Efficient, 1-Cell Li+ Pulse Charger with current limiting. In most applications, this will be a small “wall cube” switching converter with an output voltage limit of about 5V or 6V, which is specified as “current-limited” or “constant current.” PMOS Switch The PMOS FET switches the current-limited source on and off. Because of the intentionally slow switching times and limited slew rate, the MAX1879 is not particular about the power FET it drives. Specifications to consider when choosing an appropriate FET are the minimum drain-source breakdown voltage, the minimum turn-on threshold voltage (VGS), and current-handling and power-dissipation qualities. The minimum breakdown voltage (BVDS) must exceed the open-circuit voltage of the wall cube by at least 25%. Note that this open-circuit voltage may be twice as high as the specified output voltage, depending on the AC adapter type. Thermistor The intent of THERM is to inhibit fast-charging the cell when it is too cold or too hot (+2.5°C ≤ TOK ≤ 47.5°C), using an external thermistor. THERM time multiplexes two sense currents to test for both hot and cold qualification. The thermistor should be 10kΩ at +25°C and have a negative temperature coefficient (NTC); the THERM pin expects 3.97kΩ at +47.5°C and 28.7kΩ at +2.5°C. Connect the thermistor between THERM and GND. If no temperature qualification is desired, replace the thermistor with a 10kΩ resistor. Thermistors by Philips (22322-640-63103), Cornerstone Sensors (T101D103-CA), and Fenwal Electronics (140-103LAGRB1) work well. Bypass Capacitors Bypass the ADJ pin with a 2000pF ceramic capacitor. Bypass BATT with a capacitor with a value of at least 1.5µF per amp of charge current. The MAX1879 has a built-in protection feature that prevents BATT from rising above 5.5V. The device recognizes a rapid rise at BATT, indicating that the cell is being removed with the FET on. A capacitor from BATT to GND that’s too small does not give the MAX1879 adequate time to shut off the FET. BATT may then rise above 6V (towards the open-circuit source voltage), violating the absolute maximum rating and damaging the device. In applications where the cell is removable, very large capacitance values make it increasingly difficult to identify momentary cell removal events and may increase transient currents when the cell is replaced. Therefore, values in excess of 100µF should be avoided in those cases. For best system performance, at least 0.47µF of the total capacitance should be low-ESR ceramic. Layout Guidelines The MAX1879 controls the GATE slew rate. The layout is not as sensitive to noise as a high-frequency switching regulator. In addition, since the cell voltage is sensed both during and between high-current pulses, the system is insensitive to ground drops. However, Maxim recommends establishing good grounding areas and large traces for high-current paths. Chip Information TRANSISTOR COUNT: 4692 SUBSTRATE CONNECTED TO GND 10 ______________________________________________________________________________________ Simple, Efficient, 1-Cell Li+ Pulse Charger 8LUMAXD.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 ____________________ 11 © 2001 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products. MAX1879 Package Information