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19-1545; Rev 0; 9/99
KIT ATION EVALU BLE AVAILA
Single-Cell Li+ Battery Charger for Current-Limited Supply
General Description Features
o Simple Stand-Alone Application Circuit o Lowest Power Dissipation o 8-Pin MAX Package Saves Space o No Inductor Required o 0.75% Overall System Accuracy o Continuous Voltage and Temperature Protection o Safely Precharges Near-Dead Cells o Programmable Safety Timeout o Top-Off Charging to Achieve Full Battery Capacity o Automatic Power-Down when Power Source is Removed
MAX1679
The MAX1679 battery charger for a single lithium-ion (Li+) cell comes in a space-saving 8-pin MAX package. 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. The MAX1679 initiates charging in one of three ways: battery insertion, charger power-up, or external manipulation of the THERM pin. Charging terminates when the average charging current falls to approximately 1% of the fast-charge current, or when the on-chip counter times out. Key safety features include continuous voltage and temperature monitoring, a programmable charger timeout, and a 5mA 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. The MAX1679 evaluation kit (MAX1679EVKIT) is available to help reduce design time.
Ordering Information
PART MAX1679EUA TEMP. RANGE -40C to +85C PIN-PACKAGE 8 MAX
Applications
Single-Cell Li+ Portable Applications Self-Charging Battery Packs PDAs Cell Phones Cradle Chargers
CURRENTLIMITED VOLTAGE SOURCE LED IN GATE BATT BATTERY IN GATE CHG TSEL 1 2 3 4 8 BATT THERM GND ADJ THERMISTOR 7 6 5 TIMER RANGE SELECT PFET
Typical Operating Circuit
Pin Configuration
TOP VIEW
CHG
MAX1679
TSEL THERM GND ADJ
MAX1679
MAX
________________________________________________________________ Maxim Integrated Products
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Single-Cell Li+ Battery Charger for Current-Limited Supply MAX1679
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 = +70C) 8-Pin MAX (derate 4.1mW/C above +70C) ........... 330mW Operating Temperature Range ...........................-40C to +85C Storage Temperature Range ............................ -65C to +150C Lead Temperature (soldering, 10sec) ............................ +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
(VIN = V CHG = +10V, VBATT = +4.2V, TSEL = GND, GATE = unconnected, ADJ = unconnected, THERM = 10k to GND, TA = 0C to +85C, unless otherwise noted. Typical values are at TA = +25C.) PARAMETER Input Voltage (Note 1) Input Voltage for Removable Battery (Note 1) Undervoltage Lockout Trip Point Undervoltage Lockout Trip-Point Hysteresis Fast-Charge Qualification Threshold Fast-Charge Restart Threshold Precharge Source Current BATT Regulation Voltage BATT Regulation Adjust Range ADJ Source Impedance ADJ Output Voltage Battery Removal Detection Threshold Battery Removal Detection Threshold Hysteresis BATT Input Current (Note 2) BATT Input Current, FastCharge State BATT Input Current, Done State IN Input Current, Fast-Charge State IN Input Current, Done State Timer Accuracy CHG Output Leakage Current IBATT IBATT IIN IIN No load on ADJ VBATT rising VBATT falling VIN VBATT -0.3V VBATT = 4V VBATT = 4.25V VBATT = 4V, VIN = 4V VBATT = 4.25V, VIN = 22V See Table 3 V CHG = 22V, CHG = high -10 -1 SYMBOL VIN VIN CONDITIONS External PMOS FET off External PMOS FET off VBATT rising VBATT falling VBATT rising, transition from precharge to full current VBATT falling, transition from DONE to PREQUAL state (Figure 2) VBATT = 2V 2.425 3.783 4 4.1685 4.0 9.8 1.393 4.875 10 1.400 5.0 125 0.1 900 500 30 250 1 1500 1000 100 600 +10 +1 MIN 5 6 2.1 2.2 60 2.500 3.89 5 4.2000 2.575 4.00 6 4.2315 4.2 10.2 1.407 5.125 TYP MAX 22 22 2.3 UNITS V V V mV V V mA V V k V V % mV A A A A A % A
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Single-Cell Li+ Battery Charger for Current-Limited Supply
ELECTRICAL CHARACTERISTICS (continued)
(VIN = V CHG = +10V, VBATT = +4.2V, TSEL = GND, GATE = unconnected, ADJ = unconnected, THERM = 10k to GND, TA = 0C to +85C, unless otherwise noted. Typical values are at TA = +25C.) PARAMETER CHG Output Sink Current THERM Sense Current (for hot qualification) THERM Sense Current (for cold qualification) THERM Sense Voltage Trip Point GATE Source/Sink Current GATE Drive Current at Battery Removal VIN = 10V, VGATE = 8V VBATT = 5.1V, gate driven high SYMBOL CONDITIONS V CHG = 1V, CHG = low MIN 4 346 47.8 1.379 75 20 TYP 5 352.9 48.8 1.40 105 40 MAX 6 360 49.8 1.421 130 60 UNITS mA A A V % A mA
MAX1679
ELECTRICAL CHARACTERISTICS
(VIN = V CHG = +10V, VBATT = +4.2V, TSEL = GND, GATE = unconnected, ADJ = unconnected, THERM = 10k to GND, TA = -40C to +85C, unless otherwise noted.) PARAMETER Input Voltage (Note 1) Input Voltage for Removable Battery (Note 1) Undervoltage Lockout Trip Point Fast-Charge Qualification Threshold Fast-Charge Restart Threshold Precharge Source Current BATT Regulation Voltage BATT Regulation Adjust Range ADJ Source Impedance ADJ Output Voltage Battery Removal Detection Threshold BATT Input Current (Note 2) BATT Input Current, FastCharge State BATT Input Current, Done State IN Input Current, Fast-Charge State IBATT IBATT IIN No load on ADJ VBATT rising VIN VBATT - 0.3V VBATT = 4.0V VBATT = 4.25V VBATT = 4.0V, VIN = 4.0V SYMBOL VIN VIN CONDITIONS External PMOS FET off External PMOS FET off VBATT rising VBATT rising, transition from precharge to full current VBATT falling, transition from DONE to PREQUAL state, Figure 2 VBATT = 2V MIN 5 6 2.05 2.35 3.74 3 4.137 4.0 9.8 1.386 4.850 MAX 22 22 2.35 2.65 4.04 7 4.263 4.2 10.2 1.414 5.150 1 1500 1000 100 UNITS V V V V V mA V V k V V A A A A
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Single-Cell Li+ Battery Charger for Current-Limited Supply MAX1679
ELECTRICAL CHARACTERISTICS (continued)
(VIN = V CHG = +10V, VBATT = +4.2V, TSEL = GND, GATE = unconnected, ADJ = unconnected, THERM = 10k to GND, TA = -40C to +85C, unless otherwise noted.) PARAMETER IN Input Current, Done State Timer Accuracy CHG Output Leakage Current CHG Output Sink Current THERM Sense Current (for hot qualification) THERM Sense Current (for cold qualification) THERM Sense Voltage Trip Point GATE Source/Sink Current GATE Drive Current at Battery Removal VIN = 10V, VGATE = 8V VBATT = 5.1V, gate driven high SYMBOL IIN See Table 3 V CHG = 22V, CHG = high V CHG = 1.0V, CHG = low CONDITIONS VBATT = 4.25V, VIN = 22V -15 -1 4 342 47.3 1.358 60 20 MIN MAX 700 +15 +1 6 363 50.3 1.442 140 90 UNITS A % A mA A A V A mA
Note 1: 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, VIN may be as low as 2.5V. Note 2: BATT Input Current is the supply current to the device. When VIN is removed, the MAX1679 shuts down and the input current is less than 1A, even if there is an external RADJ resistor (ADJ to GND).
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Single-Cell Li+ Battery Charger for Current-Limited Supply
Typical Operating Characteristics
(VIN = V CHG = +10V, VBATT = +4.2V, THERM = 10k to GND, TA = +25C, unless otherwise noted.)
MAX1679
TIMER PERIOD vs. AMBIENT TEMPERATURE
MAX1679 toc01
NORMALIZED BATT REGULATION VOLTAGE vs. TEMPERATURE
MAX1679 toc02
PRECHARGE CURRENT vs. INPUT VOLTAGE
5.8 PRECHARGE CURRENT (mA) 5.6 5.4 5.2 5.0 4.8 4.6 4.4 4.2 4.0 VBATT = 4.1V VBATT = 2V VBATT = 0V
MAX1679 toc03
1.0200 NORMALIZED TO +25C 1.0150 TIMER PERIOD 1.0100 1.0050 1.0000 0.9950 0.9900 -40
1.0015 1.0010 BATT REGULATION VOLTAGE 1.0005 1.0000 0.9995 0.9990 0.9985 0.9980 0.9975 -40 -20 0 20 40 60 80 NORMALIZED TO +25C
6.0
-20
0
20
40
60
80
100
100
5
10
TEMPERATURE (C)
TEMPERATURE (C)
15 VIN (V)
20
25
Pin Description
PIN 1 2 NAME IN GATE FUNCTION Input Voltage from Current-Limited Voltage Source (+22V max). Bypass to GND with a 0.1F capacitor. The cell charging current is set by the current limit of the external power supply. Gate Drive for External PMOS Pass Element. The PMOS device should have a VGS threshold of 2.5V or less. See Selecting External Components. Charge Status Indication. CHG is an open-drain, current-limited N-channel MOSFET suitable for directly driving an LED. Connect a pull-up resistor to BATT to generate a logic-level signal. See Table 2 for CHG output states. Maximum Total Charge-Time Selection. See Table 3 for timer options. 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 setpoint. See Adjusting the Battery Regulation Voltage. Ground. See Layout Guidelines for information on system grounding. Connect the battery's negative terminal to GND. Thermistor Temperature-Sensor Input. Connect a thermistor from THERM to GND to prequalify the cell temperature for fast-charge. Drive THERM high (> +1.4V) during Done or Fault states to reset the MAX1679 and reinitiate the charging sequence. Replace the thermistor with a 10k resistor if temperature sensing is not required. Cell Voltage Monitor Input, Trickle-Charge Output, and MAX1679 Power Source. Connect BATT to the positive terminal of a single Li+ cell. Bypass BATT with a capacitor to ground (1.5F per amp of charge current).
3 4 5
CHG TSEL ADJ
6
GND
7
THERM
8
BATT
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Single-Cell Li+ Battery Charger for Current-Limited Supply MAX1679
CURRENT-LIMITED VOLTAGE SOURCE (800mA)
*
REVERSE-CURRENT PROTECTION DIODE IN
PFET
GATE
MAX1679
TRICKLE CHARGE (5mA) 5mA
CHG
BATT 10k TSEL SEE TABLE 3 FOR TIMEOUT OPTIONS TIMER STATE MACHINE 1.4V RADJ ** SINGLE Li+ CELL 1:3 ADJ 2.2F
1nF BATT REMOVED 5V
30kHz OSCILLATOR HOT QUAL TEST CURRENT
COLD QUAL TEST CURRENT
1.4V
THERM
NTC THERMISTOR*
*OPTIONAL **RADJ = 410k 1% FOR 4.1V CELL; LEAVE OPEN FOR 4.2V CELL.
Figure 1. Functional Diagram
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Single-Cell Li+ Battery Charger for Current-Limited Supply MAX1679
CELL NOT INSTALLED (FROM ANY STATE)
WE R PO RGE LIED CHA APP R
SHUTDOWN LED: OFF PMOS FET: OFF
CHARGING POWER REMOVED (FROM ANY STATE)
PREQUALIFICATION LED: 50% DUTY CYCLE, 2Hz PMOS FET: OFF 5mA PRECHARGE: ON
CELL REMOVAL OR PULL THERM HIGH
VB PULATT < 3.8 L TH 9V O TEM ERM R PER HIGH ATU AND RE O VB K ATT > 2. 5V
FAULT LED: 50% DUTY CYCLE, 2Hz PMOS FET: OFF
E RG HA T-C EOUT S FA TIM
TEMPERATURE NOT OK OR VBATT < 2.5V
E EV RY 7s ec
FAST-CHARGE LED: ON PMOS FET: ON
EO K
FAST-CHARGE QUALIFICATION LED: ON PMOS FET: OFF
TE
MP
E
T RA
UR
CELL VOLTAGE REACHES BATT REGULATION VALUE (e.g., 4.2V)
TEMPERATURE NOT OK
E EV RY
7
c se
TOP OFF LED: ON PMOS FET: PULSED TOP-OFF
OK
FET O FET N TIM E OFF TIM E 1%
TOP-OFF QUALIFICATION LED: ON PMOS FET: OFF
TE
MP
ER
U AT
RE
DONE LED: 12% DUTY CYCLE, 0.25Hz PMOS FET: OFF 5mA CANCELLATION CURRENT ENABLED
TEMPERATURE NOT OK
Figure 2. State Machine Diagram
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Single-Cell Li+ Battery Charger for Current-Limited Supply MAX1679
Detailed Description
Initiating a Charge Cycle
The MAX1679 attempts to initiate fast-charge upon insertion of the battery or application of an external power source (current-limited wall cube). After charge completion, charging restarts when the cell voltage drops below 3.89V or when THERM is pulled above 1.4V. Before a charge cycle can begin, the 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 (the default range is +2.5C to +47.5C). 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 dangerously abnormal cell condition. As a built-in safety feature, the MAX1679 precharges the Li+ cell with 5mA at the start of a charge cycle when the cell voltage is below 2.5V. Typically, 5mA is sufficient to bring a fully discharged 1000mAh Li+ cell up to 2.5V in less than 5 minutes. As soon as the cell's voltage reaches 2.5V and all the other prerequisites are met (see the Fast-Charge section), the MAX1679 begins fast-charging the cell. If the temperature is outside the programmed range, the charger waits. Once all prequalification conditions are met, the charging cycle and timers begin. The MAX1679 continues to monitor these conditions throughout the charging cycle.
Pulsed Top-Off Charge
In the most common case, where fast-charge is terminated because the battery regulation voltage has been reached (that is, the cell is nearly fully charged), the MAX1679 will top off the cell. The MAX1679 uses a hysteretic algorithm with minimum on-times and minimum off-times (Table 3). The cell voltage is sampled every 2ms. If the cell voltage (at BATT) 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 or remains off until the next sample. By also measuring the cell voltage when the PMOS FET is off, the MAX1679 eliminates voltage errors caused by charging current flowing through the series resistance of protection switches or fuse links that may be in the charging path. At the beginning of this top-off state, the current stays on for many consecutive cycles between single off periods. As the cell continues to charge, the percentage of time spent in the "current-on" mode decreases. Toward 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 by several hundred millivolts, but the duration of these pulses is several orders of magnitude shorter than the intrinsic chemical time constant of Li+ cells. This does not harm the cell. Cell top off is completed either when the duty ratio of "on" cycles to "off" cycles falls below 1/64 to 1/256 as set by TSEL (see Table 3), or when the charging timer expires.
Switched 5mA Cancellation Current
When the charge cycle is complete, the MAX1679 replaces current drawn by the BATT pin (to sense battery removal) with a 5mA (nominal) switched current. This current is turned on and off by an on-chip comparator as needed to maintain the battery regulation voltage. The cell is maintained in this manner as long as the battery is inserted and power is connected. This cancellation current is turned off when the MAX1679 is shut down. Note that BATT draws less than 1A from the battery when power is removed.
Fast-Charge
Once all cell conditions are determined to be satisfactory, the MAX1679 begins fast-charging the Li+ cell by turning on the external PMOS FET. The cell charging current is set by the current limit of the external power supply; it is not regulated by the MAX1679. The PMOS FET is used as a simple switch, not as a linear regulator. Therefore, the circuit's power dissipation is minimized, permitting rapid charge cycles with minimal heat generation. The external power supply should have a specified current limit that matches the desired fast-charge current for the Li+ cell. Fast-charge continues until one of the following conditions is reached: 1) cell voltage climbs to the battery regulation voltage (4.2V or as set by ADJ); 2) the fastcharging timer expires (fault condition); or 3) cell temperature rises above +47.5C or falls below +2.5C. If the cell temperature moves outside the specified limits, charging is suspended but not terminated. All timers are paused and charging resumes when the temperature returns to the normal range.
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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 pull-up resistor (typically 100k) from a logic supply to CHG provides a logic-level output. Table 2 relates the status of the CHG to the condition of the charger.
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Single-Cell Li+ Battery Charger for Current-Limited Supply
Applications Information
The MAX1679 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 10k thermistor/resistor. This simple application circuit appears in Figure 3. Optionally (as shown in Figure 4), an LED can be added as a charge-state indicator, a resistor (RADJ) can be used to trim down the maximum charge voltage from 4.2V, and/or a reverse-current-protection diode can be added in line at the source. If the input is shorted, the MAX1679 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.
MAX1679
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 MAX1679 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 10k 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 = 10k VBR -1 VBR '
Table 2. CHG Output States
CONDITION No battery or no charger, or cell voltage < 2.2V Fast-charge or pulsed topoff charge in progress Fast-charge timer expiration or initial prequalification state (VBATT < 2.5V or initial temperature fault) Charge cycle complete CHG High impedance Low (LED on)
A 1% tolerance resistor at ADJ degrades system accuracy by only a fraction of a percent. For example, an RADJ of 410k 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%). 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%.
2Hz, 50% duty factor (LED flashing) LED blinking 0.5sec on (low), 3.5sec off (high impedance)
CURRENT-LIMITED WALL CUBE (800mA, 6V max)
PMOS FET FAIRCHILD FDC638P -4.5A, -20V 0.07 AT VGS = -2.5V
CURRENT LIMITED WALL CUBE (800mA, 6V max)
SCHOTTKY DIODE 30V, 1A ZETEX ZHCS1000
PMOSFET FAIRCHILD FDC638P -4.5A, -20V 0.07 AT VGS = -2.5V GATE
GATE IN IN BATT 5mA LED SINGLE Li+ CELL 0.001F 10k 2.2F CHG RADJ 410k 1%**
MAX1679
BATT SINGLE Li+ CELL
MAX1679
TSEL* ADJ THERM
CHG 0.001F
TSEL* ADJ THERM 2.2F NTC THERMISTOR FENWAL 140-103LAG-RBI (10k AT 25C)
*SEE TABLE 3 FOR TSEL POSITION AND ASSOCIATED TIMER SETTINGS.
*SEE TABLE 3 FOR TSEL POSITION AND ASSOCIATED TIMER SETTINGS. ** RADJ SETS BATTERY REGULATION VOLTAGE TO 4.10V; LEAVE OPEN FOR 4.2V.
Figure 3. Simple Application Circuit
Figure 4. Application Circuit Including LED, Thermistor, and Reverse-Current Protection Diode
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Single-Cell Li+ Battery Charger for Current-Limited Supply MAX1679
Table 3. Timer Option (TSEL) Definitions
TSEL CONNECTION RECOMMENDED CHARGE RATE FASTCHARGE TIME LIMIT (minutes) 55 75 Off TOTAL CHARGE TIME LIMIT (hours) 2.8 3.75 6.25 MIN ON/OFF TIME (IN TOP-OFF) (ms) 70 140 280 ON/OFF DUTY CYCLE FOR DONE INDICATION 1/256 1/128 1/64
BATT ADJ GND
1.5C 1C <1C
Selecting Maximum Charge Time
As a safety feature, fast-charging and pulsed top-off charging will stop if their respective counters time out. The MAX1679 offers a choice of three timeout periods set by TSEL (Table 3). In Table 3, C represents the nominal capacity of the battery cell in ampere hours. Both timers begin upon entering the fast-charge state. The fast-charge timer is disabled upon leaving fastcharge; the total charge timer continues through top-off but is disabled in the done state.
Selecting External Components
Power Supply One reason the MAX1679 Li+ cell-charging solution is so compact and simple is that the charging current is set by the external power source, not by the MAX1679 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 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 advertised as "current-limited" or "constant current." PMOS Switch The PMOS FET is used to switch the current-limited source on and off into the Li+ cell. Because of the intentionally slow switching times and limited slew rate, the MAX1679 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 converter type.
Thermistor The intent of THERM is to inhibit fast-charging the cell when it is too cold or too hot (+2.5C TOK 47.5C), using an external thermistor. THERM 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 THERM pin expects 3.97k at +47.5C and 28.7k at +2.5C. Connect the thermistor between THERM and GND. If no temperature qualification is desired, replace the thermistor with a 10k 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 0.001F ceramic capacitor. Bypass BATT with a capacitor with a value of at least 1.5F per amp of charge current. The MAX1679 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 MAX1679 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 100F should be avoided in those cases. For best system performance, at least 0.47F of the total capacitance should be low-ESR ceramic.
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Single-Cell Li+ Battery Charger for Current-Limited Supply
Layout Guidelines
The MAX1679 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. TRANSISTOR COUNT: 4692 SUBSTRATE CONNECTED TO GND
Chip Information
MAX1679
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Single-Cell Li+ Battery Charger for Current-Limited Supply MAX1679
Package Information
8LUMAXD.EPS
Note: The MAX1679 does not have an exposed pad.
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.
12 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 (c) 1999 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.

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