Final Electrical Specifications LTC1731-4.2 Lithium-Ion Linear Battery Charger Controller December 1999 U DESCRIPTION FEATURES ■ ■ ■ ■ ■ ■ ■ ■ ■ The LTC ®1731-4.2 is a complete constant-current/constant-voltage linear charge controller for lithium-ion batteries. Nickel-cadmium (NiCd) and nickel-metal-hydride (NiMH) batteries can also be charged with constant current using external termination. The external sense resistor sets the charge current with 5% accuracy. An internal resistor divider and precision reference set the final float potential with 1% accuracy. The output float voltage is set internally to 4.2V. Complete Linear Charger Controller for 1-Cell Lithium-Ion Batteries 1% Voltage Accuracy Programmable Charge Current C/10 Charge Current Detection Output Programmable Charge Termination Timer Space Saving 8-Pin MSOP Package Automatic Sleep Mode When Input Supply is Removed (Only 7µA Battery Drain) Automatic Trickle Charging of Low Voltage Cells Programmable for Constant-Current-Only Mode When the input supply is removed, the LTC1731-4.2 automatically enters a low current sleep mode, dropping the battery drain current to 5µA. An internal comparator detects the end-of-charge (C/10) condition while a programmable timer, using an external capacitor, sets the total charge time. Fully discharged cells are automatically trickle charged at 10% of the programmed current until cell voltage exceeds 2.5V. U APPLICATIONS ■ ■ ■ ■ Cellular Phones Handheld Computers Charging Docks and Cradles Programmable Current Source The LTC1731-4.2 is available in the 8-pin MSOP and SO packages. , LTC and LT are registered trademarks of Linear Technology Corporation. U TYPICAL APPLICATION 500mA Li-Ion Charger VIN 5V TO 15V MBRM120T3 7 1k VCC SENSE 2 DRV CHRG RSENSE 0.2Ω 8 6 Q1 Si9430DY LTC1731-4.2 3 CTIMER 0.1µF TIMER BAT PROG GND 4 1µF IBAT = 500mA 1 5 RPROG* 19.6k + Li-ION 10µF CELL 1731 TA01 *SHUTDOWN INVOKED BY FLOATING THE PROG PIN Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use. Linear Technology Corporation makes no representation that the interconnection of its circuits as described herein will not infringe on existing patent rights. 1 LTC1731-4.2 W W U W ABSOLUTE MAXIMUM RATINGS (Note 1) Input Supply Voltage (VCC) ................................... 13.2V Input Voltage (SENSE, DRV, BAT, TIMER, PROG) ....................... – 0.3V to (VCC + 0.3V) Output Voltage (CHRG) ......................... – 0.3V to 13.2V Operating Temperature Range (Note 2) .....– 40° to 85°C Storage Temperature Range ................. – 65°C to 150°C Lead Temperature (Soldering, 10 sec).................. 300°C U W U PACKAGE/ORDER INFORMATION ORDER PART NUMBER TOP VIEW BAT CHRG TIMER GND 1 2 3 4 8 7 6 5 SENSE VCC DRV PROG LTC1731EMS8-4.2 MS8 PACKAGE 8-LEAD PLASTIC MSOP MS8 PART MARKING TJMAX = 150°C, θJA = 180°C/W LTKQ ORDER PART NUMBER TOP VIEW BAT 1 8 SENSE CHRG 2 7 VCC TIMER 3 6 DRV GND 4 5 PROG LTC1731ES8-4.2 S8 PART MARKING S8 PACKAGE 8-LEAD PLASTIC SO 173142 TJMAX = 150°C, θJA = 125°C/W Consult factory for Industrial and Military grade parts. ELECTRICAL CHARACTERISTICS The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VCC = 6V unless otherwise noted. SYMBOL PARAMETER CONDITIONS MIN VCC Input Supply Voltage ICC Input Supply Current Charger On, Current Mode Shutdown Mode Sleep Mode (Battery Drain Current) ● ● VBAT Regulated Output Voltage LTC1731-4.2 (5V ≤ VCC ≤ 12V) ● IBAT Current Mode Charge Current RPROG = 19.6k, RSENSE = 0.2Ω RPROG = 19.6k, RSENSE = 0.2Ω RPROG = 97.6k, RSENSE = 0.2Ω TYP 12 V 3 2 20 mA mA µA 4.158 4.2 4.242 500 ● 465 415 70 mA mA mA mA 100 535 585 130 ITRIKL Trickle Charge Current VBAT = 2V, RPROG = 19.6k, ITRIKL = (VCC – VSENSE)/0.2Ω ● 30 50 95 VTRIKL Trickle Charge Threshold Voltage From Low to High ● 2.4 2.457 2.55 VUV VCC Undervoltage Lockout Voltage From Low to High ● 4.1 4.5 ∆VUV VCC Undervoltage Lockout Hysteresis VMSD Manual Shutdown Threshold Voltage 2 200 PROG Pin Low to High PROG Pin High to Low UNITS 1 1 7 ● 4.5 MAX 2.457 2.446 V V V mV V V LTC1731-4.2 ELECTRICAL CHARACTERISTICS The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VCC = 6V unless otherwise noted. SYMBOL PARAMETER CONDITIONS VASD Automatic Shutdown Threshold Voltage (VCC – VBAT) High to Low (VCC – VBAT) Low to High VDIS Voltage Mode Disable Threshold Voltage VTIMER IPROG PROG Pin Current Internal Pull-Up Current, No RPROG PROG Pin Load Regulation PROG Pin Source Current, ∆VPROG ≤ 5mV VPROG PROG Pin Voltage RPROG =19.6k ICHRG CHRG Pin Weak Pull-Down Current VCHRG = 1V VCHRG CHRG Pin Output Low Voltage ICHRG = 5mA IC/10 End of Charge Indication Current Level RPROG = 19.6k, RSENSE = 0.2Ω tTIMER TIMER Accuracy CTIMER = 0.1µF 10 % VCLAMP DRV Pin Clamp Voltage VCLAMP = VCC – VDRV, IDRIVE = 50µA 6.5 V Note 1: Absolute Maximum Ratings are those values beyond which the life of a device may be impaired. MIN TYP MAX UNITS 30 40 54 69 90 100 mV mV ● 5.6 ● 300 V µA 2.5 µA 2.457 70 ● 25 V 100 130 µA 0.6 1.2 V 50 100 mA Note 2: The LTC1731-4.2 is guaranteed to meet performance specifications from 0°C to 70°C. Specifications over the – 40°C to 85°C operating temperature range are assured by design, characterization and correlation with statistical process controls. Guaranteed I grade parts are available, consult factory. U U U PIN FUNCTIONS BAT (Pin 1): Battery Sense Input. A bypass capacitor of at least 10µF is required to keep the loop stable when the battery is not connected. A precision internal resistor divider sets the final float potential on this pin. The resistor divider is disconnected in sleep mode. CHRG (Pin 2): Open-Drain Charge Status Output. When the battery is being charged, the CHRG pin is pulled low by an internal N-channel MOSFET. When the charge current drops to 10% of the full-scale current for at least 0.32 seconds, the N-channel MOSFET turns off and a 100µA current source is connected from the CHRG pin to GND. When the timer runs out or the input supply is removed, the current source will be disconnected and the CHRG pin is forced into a high impedance state. TIMER (Pin 3): Timer Capacitor and Constant-Voltage Mode Disable Input Pin. The timer period is set by placing a capacitor, CTIMER, to GND. The timer period is tTIMER = (CTIMER • 3 hours)/(0.1µF). When the TIMER pin is connected to VCC, the constant-voltage mode is disabled and the chip will operate in constant-current mode only. Short the TIMER pin to GND to disable the internal timer function. GND (Pin 4): Ground. PROG (Pin 5): Charge Current Program and Shutdown Input Pin. The charge current is programmed by connecting a resistor, RPROG to ground. The charge current is IBAT = (VPROG • 800Ω)/(RPROG • RSENSE). The IC can be forced into shutdown by floating the PROG pin and allowing the internal 2.5µA current source to pull the pin above the 2.457V shutdown threshold voltage. DRV (Pin 6): Drive Output Pin for the P-Channel MOSFET or PNP Transistor. The impedance is high at this pin, therefore, a high gain PNP pass transistor should be used. The DRV pin is internally clamped to 8V (max) below VCC. VCC (Pin 7): Positive Input Supply Voltage. When VBAT is within 54mV of VCC, the LTC1731-4.2 is forced into sleep mode, dropping ICC to 7µA. VCC ranges from 4.5V to 12V. Bypass this pin with a 1µF capacitor. SENSE (Pin 8): Current Sense Input. A sense resistor, RSENSE, must be connected from VCC to the SENSE pin. This resistor is chosen using the following equation: RSENSE = (VPROG • 800Ω)/(RPROG • IBAT) 3 LTC1731-4.2 W BLOCK DIAGRA VCC 7 RSENSE SENSE + 2 + – 800Ω 80Ω C1 – CHRG 8 54mV + C4 – – C/10 STOP C/10 TIMER + DRV CA SLP OSCILLATOR BAT – SHDN 3 720Ω LOGIC LBO COUNTER 6 1 C2 + 100µA VREF – + – VA VCC A1 – + + C3 2.5µA VREF 2.457V CHARGE 5 BATTERY CURRENT IBAT = (2.457V • 800Ω)/(RPROG • RSENSE) 4 PROG RPROG GND 4 1731 BD LTC1731-4.2 U OPERATIO The LTC1731-4.2 is a linear battery charger controller. The charge current is programmed by the combination of a program resistor (RPROG) from the PROG pin to ground and a sense resistor (RSENSE) between the VCC and SENSE pins. RPROG sets a program current through an internal trimmed 800Ω resistor setting up a voltage drop from VCC to the input of the current amplifier (CA). The current amplifier servos the gate of the external P-channel MOSFET to force the same voltage drop across RSENSE which sets the charge current. When the potential at the BAT pin approaches the preset float voltage, the voltage amplifier (VA) will start sinking current which shrinks the voltage drop across RSENSE, thus reducing the charge current. Charging begins when the potential at VCC pin rises above the UVLO level and a program resistor is connected from the PROG pin to ground. At the beginning of the charge cycle, if the battery voltage is below 2.457V per cell, the charger goes into trickle charge mode. The trickle charge current is 10% of the full-scale current. If the cell voltage stays low for one quarter of the total charge time, the charge sequence will be terminated immediately. The charger goes into the fast charge constant-current mode after the voltage on the BAT pin rises above 2.457V per cell. In constant-current mode, the charge current is set by the combination of RSENSE and RPROG. When the battery approaches the final float voltage, the charge current will begin to decrease. When the current drops to 10% of the full-scale charge current, an internal comparator will turn off the pull-down N-channel MOSFET at the CHRG pin and connect a weak current source to ground to indicate an end-of-charge (C/10) condition. An external capacitor on the TIMER pin sets the total charge time. After a time-out occurs, the charging will be terminated immediately and the CHRG pin is forced to a high impedance state. To restart the charge cycle, simply remove the input voltage and reapply it, or float the PROG pin momentarily. For batteries like lithium-ion that require accurate final float potential, the internal 2.457V reference, voltage amplifier and the resistor divider provide regulation with ±1% (max) accuracy. For NiMH and NiCd batteries, the LTC1731-4.2 can be turned into a current source by pulling the TIMER pin to VCC. When in the constantcurrent only mode, the voltage amplifier, timer and the trickle charge function are all disabled. When the input voltage is not present, the charger goes into a sleep mode, dropping ICC to 5µA. This greatly reduces the current drain on the battery and increases the standby time. The charger can be shut down by floating the PROG pin. An internal current source will pull it high and clamp at 3.5V. U W U U APPLICATIONS INFORMATION Charge Termination Trickle Charge and Defective Battery Detection The charger is off when any of the following conditions exist: the voltage at the VCC pin is below 4.1V, the voltage at the VCC pin is higher than 4.1V but is less than 54mV above VBAT, or the PROG pin is floating. The DRV pin will be pulled to VCC and the internal resistor divider is disconnected to reduce the current drain on the battery. At the beginning of the charging sequence, if the battery voltage is low (below 2.457V per cell) the charger goes into trickle mode. The charge current is dropped to 10% of the full-scale current. If the low cell voltage persists for one quarter of the total charging time, the battery is considered defective, the charging will be terminated and the CHRG pin output is forced to a high impedance state. Undervoltage Lockout (UVLO) An internal undervoltage lockout circuit monitors the input voltage and keeps the charger in shutdown mode until VCC rises above 4.1V. To prevent oscillation around VCC = 4.1V, the UVLO circuit has built-in hysteresis. Shutdown The LTC1731-4.2 can be forced into shutdown by floating the PROG pin and allowing the internal 2.5µA current source to pull the pin above the 2.457V shutdown 5 LTC1731-4.2 U W U U APPLICATIONS INFORMATION V+ threshold voltage. The DRV pin will then be pulled up to VCC and turn off the external P-channel MOSFET. The internal timer is reset in the shutdown mode. 7 VCC 100k LTC1731-4.2 Programming Charge Current CHRG 2 1k The formula for the battery charge current (see Block Diagram) is: IBAT = (IPROG)(800Ω/RSENSE) = (2.457V/RPROG)(800Ω/RSENSE) where RPROG is the total resistance from the PROG pin to ground. For example, if 0.5A charge current is needed, select a value for RSENSE that will drop 100mV at the maximum charge current. RSENSE = 0.1V/0.5A = 0.2Ω, then calculate: RPROG = (2.457V/500mA)(800Ω/0.2Ω) = 19.656k For best stability over temperature and time, 1% resistors are recommended. The closest 1% resistor value is 19.6k. Programming the Timer The programmable timer is used to terminate the charge. The length of the timer is programmed by an external capacitor at the TIMER pin. The total charge time is: Time = (3 Hours)(CTIMER/0.1µF) The timer starts when the input voltage greater than 4.1V is applied and the program resistor is connected to ground. After a time-out occurs, the CHRG output will turn into a high impedance state to indicate that the charging has stopped. Connecting the TIMER pin to VCC disables the timer and also puts the charger into a constant-current mode. To only disable the timer function, short the TIMER pin to GND. CHRG Status Output Pin When the charge cycle starts, the CHRG pin is pulled down to ground by an internal N-channel MOSFET that can drive an LED. When the battery current drops to 10% of the fullscale current (C/10), the N-channel MOSFET is turned off and a weak 100µA current source to ground is connected to the CHRG pin. After a time-out occurs, the pin will go into a high impedance state. By using two different value pull-up resistors, a microprocessor can detect three states 6 µPROCESSOR I/O I/O 1731 F01 Figure 1. Microprocessor Interface from this pin (charging, C/10 and stop charging). See Figure 1. End of Charge (C/10) The LTC1731-4.2 includes a comparator to monitor the charge current to detect an end-of-charge condition. When the battery current falls below 10% of full scale, the comparator trips and turns off the N-channel MOSFET at the CHRG pin and switches in a 100µA current source to ground. After an internal time delay of 300ms, this state is then latched. This delay will help prevent false triggering due to transient currents. The end-of-charge comparator is disabled in trickle charge mode. Gate Drive Typically the LTC1731-4.2 controls an external P-channel MOSFET to supply current to the battery. The DRV pin is internally clamped to 6.5V below VCC. This feature allows low voltage P-channel MOSFETs with gate to source breakdown voltage rated at 8V to be used. An external PNP transistor can also be used as the pass transistor instead of the P-channel MOSFET. Due to the low current gain of the current amplifier (CA), a high gain Darlington PNP transistor is required to avoid too much charging current error. The gain of the current amplifier is around 0.6µA/mV. For every 1µA of base current, a 1.6mV of gain error shows up at the inputs of CA. With RPROG = 19.6k (100mV across RSENSE), it represents 1.67% of error in charging current. Constant-Current Only Mode The LTC1731-4.2 can be used as a programmable current source by forcing the TIMER pin to VCC. This is particularly useful for charging NiMH or NiCd batteries. In the LTC1731-4.2 U U W U APPLICATIONS INFORMATION constant-current only mode, the timer and voltage amplifier are both disabled. An external termination method is required to properly terminate the charge. pin to keep the ripple voltage low when the battery is disconnected. When a PNP transistor is chosen as the pass transistor, a 1000pF capacitor is required from the DRV pin to VCC. This capacitor is needed to help stablize the voltage loop. A 10µF capacitor at the BAT pin is also recommended when a battery is not present. Stability The charger is stable without any compensation when a P-channel MOSFET is used as the pass transistor. However, a 10µF capacitor is recommended at the BAT U TYPICAL APPLICATION Linear Charger Using a PNP Transistor VIN 5V TO 15V MBRM120T3 R2 1k C1 1nF 7 VCC SENSE 2 DRV CHRG R1 10k RSENSE 0.2Ω Q2 ZTX749 8 6 Q1 2N5087 LTC1731-4.2 3 TIMER BAT PROG CTIMER 0.1µF GND 4 C3 1µF IBAT = 500mA 1 5 RPROG 19.6k + C2 10µF Li-ION CELL 1731 TA02 U PACKAGE DESCRIPTION Dimensions in inches (millimeters) unless otherwise noted. S8 Package 8-Lead Plastic Small Outline (Narrow 0.150) (LTC DWG # 05-08-1610) 0.189 – 0.197* (4.801 – 5.004) 0.010 – 0.020 × 45° (0.254 – 0.508) 0.008 – 0.010 (0.203 – 0.254) 0.053 – 0.069 (1.346 – 1.752) 0°– 8° TYP 0.016 – 0.050 (0.406 – 1.270) 0.014 – 0.019 (0.355 – 0.483) TYP *DIMENSION DOES NOT INCLUDE MOLD FLASH. MOLD FLASH SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE **DIMENSION DOES NOT INCLUDE INTERLEAD FLASH. INTERLEAD FLASH SHALL NOT EXCEED 0.010" (0.254mm) PER SIDE 8 7 6 5 0.004 – 0.010 (0.101 – 0.254) 0.050 (1.270) BSC 0.150 – 0.157** (3.810 – 3.988) 0.228 – 0.244 (5.791 – 6.197) SO8 1298 1 2 3 4 7 LTC1731-4.2 U TYPICAL APPLICATION Low Dropout Linear Charger VIN 4.5V Q1 1/2 Si9934DY R1 50k 7 VCC SENSE 2 DRV CHRG RSENSE 0.2Ω 8 6 Q2 1/2 Si9934DY LTC1731-4.2 3 TIMER BAT PROG CTIMER 0.1µF C1 1µF IBAT = 500mA 1 5 GND 4 RPROG 19.6k + Li-ION CELL C2 10µF 1731 TA03 U PACKAGE DESCRIPTION Dimensions in inches (millimeters) unless otherwise noted. MS8 Package 8-Lead Plastic MSOP (LTC DWG # 05-08-1660) 0.040 ± 0.006 (1.02 ± 0.15) 0.007 (0.18) 0.034 ± 0.004 (0.86 ± 0.102) 0.118 ± 0.004* (3.00 ± 0.102) 8 7 6 5 0° – 6° TYP 0.021 ± 0.006 (0.53 ± 0.015) SEATING PLANE 0.012 (0.30) 0.0256 REF (0.65) BSC 0.006 ± 0.004 (0.15 ± 0.102) 0.118 ± 0.004** (3.00 ± 0.102) 0.193 ± 0.006 (4.90 ± 0.15) MSOP (MS8) 1098 * DIMENSION DOES NOT INCLUDE MOLD FLASH, PROTRUSIONS OR GATE BURRS. MOLD FLASH, PROTRUSIONS OR GATE BURRS SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE ** DIMENSION DOES NOT INCLUDE INTERLEAD FLASH OR PROTRUSIONS. INTERLEAD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE 1 2 3 4 RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LT 1510-5 500kHz Constant-Voltage/Constant-Current Battery Charger Most Compact, Up to 1.5A, Charges NiCd, NiMH, Li-Ion Cells LT1512 SEPIC Battery Charger VIN Can Be Higher or Lower Than Battery Voltage, 1.5A Switch LT1620 Rail-to-Rail Current Sense Amplifier Precise Output Current Programming, Up to 32V VOUT, Up to 10A IOUT LTC1729 Termination Controller for Li-Ion Time or Charge Current Termination, Automatic Charger/Battery Detection, Status Output, Preconditioning, 8-Lead MSOP ® 8 Linear Technology Corporation 1731is, sn1731 LT/TP 1299 4K • PRINTED IN USA 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408)432-1900 ● FAX: (408) 434-0507 ● www.linear-tech.com © LINEAR TECHNOLOGY CORPORATION 1999