 |
|
| If you can't view the Datasheet, Please click here to try to view without PDF Reader . |
|
|
|
| If you can't view the Datasheet, Please click here to try to view without PDF Reader . |
|
|
| Datasheet File OCR Text: |
| Final Electrical Specifications LTC4006 4A, High Efficiency, Standalone Li-Ion Battery Charger May 2003 FEATURES s s s s s s s DESCRIPTIO s s s s s s s Complete Charger Controller for 2-, 3- or 4-Cell Lithium-Ion Batteries High Conversion Efficiency: Up to 96% Output Currents Exceeding 4A 0.8% Accurate Preset Voltages: 8.4V, 12.6V, 16.8V Built-In Charge Termination with Automatic Restart AC Adapter Current Limiting Maximizes Charge Rate* Automatic Conditioning of Deeply Discharged Batteries Thermistor Input for Temperature Qualified Charging Wide Input Voltage Range: 6V to 28V 0.5V Dropout Voltage; Maximum Duty Cycle: 98% Programmable Charge Current: 5% Accuracy Indicator Outputs for Charging, C/10 Current Detection and AC Adapter Present Charging Current Monitor Output 16-Pin Narrow SSOP Package The LTC(R)4006 is a complete constant-current/constantvoltage charger controller for 2-, 3- or 4-cell lithium batteries in a small package using few external components. The PWM controller is a synchronous, quasi-constant frequency, constant off-time architecture that will not generate audible noise even when using ceramic capacitors. The LTC4006 is available in 8.4V, 12.6V and 16.8V versions with 0.8% accuracy. Charging current is programmable with a single sense resistor to 4% typical accuracy. Charging current can be monitored as a representative voltage at the IMON pin. A timer, programmed by an external resistor, sets the total charge time or is reset to 25% of total charge time after C/10 charging current is reached. Charging automatically resumes when cell voltage falls below 3.9V/cell. Fully discharged cells are automatically trickle charged at 10% of the programmed current until the cell voltage exceeds 2.5V/cell. Charging terminates if the low-battery condition persists for more than 25% of the total charge time. LTC4006 includes a thermistor sensor input that suspends charging if an unsafe temperature condition is detected and automatically resumes charging when battery temperature returns to within safe limits. , LTC and LT are registered trademarks of Linear Technology Corporation. *U.S. Patent No. 5,723,970 APPLICATIO S s s s s Notebook Computers Portable Instruments Battery-Backup Systems Standalone Li-Ion Chargers TYPICAL APPLICATIO DCIN 0V TO 28V 3A VLOGIC 4A Li-Ion Battery Charger INPUT SWITCH 0.1F 100k CHG ACP CHARGING CURRENT MONITOR DCIN CHG INFET LTC4006 CLP CLN TGATE BGATE PGND CSP BAT 4006 TA01 5k 15nF 0.033 ACP/SHDN 32.4k 0.0047F IMON NTC RT ITH 6k 0.12F GND THERMISTOR 10k NTC 0.47F 309k TIMING RESISTOR (~2 HOURS) 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. U 20F 10H 0.025 BATTERY 20F U U 4006i 1 LTC4006 ABSOLUTE MAXIMUM RATINGS (Note 1) PACKAGE/ORDER INFORMATION TOP VIEW DCIN CHG ACP/SHDN RT GND NTC ITH IMON 1 2 3 4 5 6 7 8 16 INFET 15 BGATE 14 PGND 13 TGATE 12 CLN 11 CLP 10 BAT 9 CSP Voltage from DCIN, CLP, CLN, TGATE, INFET, ACP/SHDN, CHG to GND ........................... + 32V/- 0.3V CSP, BAT to GND ....................................... +28V/- 0.3V RT to GND ..................................................... +7V/- 0.3V NTC ............................................................ +10V/- 0.3V Operating Ambient Temperature Range (Note 4) ............................................. - 40C to 85C Operating Junction Temperature ......... - 40C to 125C Storage Temperature Range ................. - 65C to 150C Lead Temperature (Soldering, 10 sec).................. 300C ORDER PART NUMBER LTC4006EGN-2 LTC4006EGN-4 LTC4006EGN-6 GN PART MARKING 40062 40064 40066 GN PACKAGE 16-LEAD PLASTIC SSOP TJMAX = 125C, JA = 110C/W Consult LTC Marketing for parts specified with wider operating temperature ranges. ELECTRICAL CHARACTERISTICS SYMBOL IDCIN VTOL PARAMETER DCIN Operating Range DCIN Operating Current Voltage Accuracy The q denotes specifications which apply over the full operating temperature range (Note 4), otherwise specifications are at TA = 25C. VDCIN = 20V, VBAT = 12V unless otherwise noted. CONDITIONS Sum of Current from CLP, CLN, DCIN (Note 2) LTC4006-6 LTC4006-6 LTC4006-2 LTC4006-2 LTC4006-4 LTC4006-4 VCSP - VBAT Target = 100mV VBAT = 11.5V (LTC4006-2) VBAT = 7.6V (LTC4006-6) VBAT = 12V (LTC4006-4) VBAT < 6V, VCSP - VBAT Target = 10mV 6V VBAT VLOBAT, VCSP - VBAT Target = 10mV TTOL Shutdown Battery Leakage Current DCIN = 0V DCIN = 0V DCIN = 20V, VSHDN = 0V DCIN Rising, VBAT = 0V VSHDN = 0V, Sum of Current from CLP, CLN, DCIN q q q q MIN 6 TYP 3 MAX 28 5 8.467 8.484 12.700 12.726 16.935 16.968 4 5 UNITS V mA V V V V V V % % q q q q 8.333 8.316 12.499 12.474 16.665 16.632 -4 -5 8.4 8.4 12.6 12.6 16.8 16.8 ITOL Current Accuracy (Note 3) - 60 - 40 q 60 40 15 15 20 0 4.7 2 30 45 10 5.5 2.5 3 Termination Timer Accuracy RRT = 270k -15 -10 4.2 1 UVLO Undervoltage Lockout Threshold Shutdown Threshold at ACP/SHDN DCIN Current in Shutdown Current Sense Amplifier, CA1 Input Bias Current Into BAT Pin CMSL CMSH CA1/I1 Input Common Mode Low CA1/I1 Input Common Mode High q q 11.67 0 VCLN - 0.2 2 U W U U WW W % % % A A V V mA A V V 4006i LTC4006 ELECTRICAL CHARACTERISTICS SYMBOL ITMAX ITREV PARAMETER Maximum Current Sense Threshold (VCSP - VBAT) Reverse Current Threshold (VCSP - VBAT) Transconductance Source Current Sink Current Current Limit Amplifier Transconductance VCLP ICLP Current Limit Threshold CLP Input Bias Current Transconductance Sink Current OVSD Overvoltage Shutdown Threshold as a Percent of Programmed Charger Voltage DCIN Detection Threshold (VDCIN - VCLN) Forward Regulation Voltage (VDCIN - VCLN) Reverse Voltage Turn-Off Voltage (VDCIN - VCLN) INFET "On" Clamping Voltage (VDCIN - VINFET) INFET "Off" Clamping Voltage (VDCIN - VINFET) Thermistor NTCVR Reference Voltage During Sample Time High Threshold Low Threshold Thermistor Disable Current Indicator Outputs (ACP/SHDN, CHG) C10TOL LBTOL C/10 Indicator Accuracy LOBAT Threshold Accuracy Current Comparators ICMP and IREV The q denotes specifications which apply over the full operating temperature range (Note 4), otherwise specifications are at TA = 25C. VDCIN = 20V, VBAT = 12V unless otherwise noted. CONDITIONS VITH = 2.4V q MIN 140 TYP 165 - 30 1 MAX 200 UNITS mV mV mmho A A mmho Current Sense Amplifier, CA2 Measured at ITH, VITH = 1.4V Measured at ITH, VITH = 1.4V - 40 40 1.5 q 93 100 100 1 107 mV nA mmho A Voltage Error Amplifier, EA Measured at ITH, VITH = 1.4V q 36 102 107 110 % Input P-Channel FET Driver (INFET) DCIN Voltage Ramping Up from VCLN - 0.1V DCIN Voltage Ramping Down IINFET = 1A IINFET = - 25A 4.5 VNTC Rising VNTC Falling VNTC 10V Voltage Falling at PROG LTC4006-6 LTC4006-2 LTC4006-4 LTC4006-6 LTC4006-2 LTC4006-4 IOL = 100A IOH = -1A V = 0V VOH = 3V VOH = 3V q q q q q q q q q q q q q q q q 0 0.17 25 0.25 50 6.5 0.25 V mV mV V V V - 60 5 - 25 5.8 NTCVR * 0.48 NTCVR * 0.115 NTCVR * 0.5 NTCVR * 0.125 NTCVR * 0.52 NTCVR * 0.135 10 V V A V V V V V V V V V A 0.375 4.70 7.27 9.70 7.5 11.35 15.15 2.7 0.400 4.93 7.5 10 7.7 11.7 15.6 0.425 5.10 7.71 10.28 7.9 11.94 15.92 0.5 RESTART Threshold Accuracy VOL VOH IPO IC10 IOFF Low Logic Level of ACP/SHDN, CHG High Logic Level of ACP/SHDN Pull-Up Current on ACP/SHDN C/10 Indicator Sink Current from CHG Off State Leakage Current of CHG Timer Defeat Threshold at CHG -10 15 -1 1 25 38 1 A A V 4006i 3 LTC4006 ELECTRICAL CHARACTERISTICS SYMBOL Oscillator fOSC fMIN DCMAX Regulator Switching Frequency Regulator Switching Frequency in Drop Out Regulator Maximum Duty Cycle VTGATE High (VCLN - VTGATE) VBGATE High VTGATE Low (VCLN - VTGATE) VBGATE Low TGTR TGTF BGTR BGTF TGATE Transition Time TGATE Rise Time TGATE Fall Time BGATE Transition Time BGATE Rise Time BGATE Fall Time VTGATE at Shutdown (VCLN - VTGATE) VBGATE at Shutdown PARAMETER The q denotes specifications which apply over the full operating temperature range (Note 4), otherwise specifications are at TA = 25C. VDCIN = 20V, VBAT = 12V unless otherwise noted. CONDITIONS MIN 255 Duty Cycle 98% VCSP = VBAT ITGATE = -1mA CLOAD = 3000pF CLOAD = 3000pF IBGATE = 1mA CLOAD = 3000pF, 10% to 90% CLOAD = 3000pF, 10% to 90% CLOAD = 3000pF, 10% to 90% CLOAD = 3000pF, 10% to 90% ITGATE = -1A, DCIN = 0V, CLN = 12V IBGATE = 1A, DCIN = 0V, CLN = 12V 50 50 40 40 4.5 4.5 5.6 5.6 20 98 TYP 300 25 99 50 10 10 50 110 100 90 80 100 100 MAX 345 UNITS kHz kHz % mV V V mV ns ns ns ns mV mV Gate Drivers (TGATE, BGATE) Note 1: Absolute Maximum Ratings are those values beyond which the life of a device may be impaired. Note 2: See Test Circuit Note 3: Does not include tolerance of current sense resistor. Note 4: The LTC4006E is guaranteed to meet performance specifications from 0C to 70C. Specifications over the -40C to 85C operating temperature range are assured by design, characterization and correlation with statistical process controls. PI FU CTIO S DCIN (Pin 1): External DC Power Source Input. Bypass this pin with at least 0.01F. See Applications Information section. CHG (Pin 2): Open-Drain Charge Status Output. When the battery is being charged, the CHG pin is pulled low by an internal N-channel MOSFET. When the charge current drops below 10% of programmed current, the N-channel MOSFET turns off and a 25A current source is connected from the CHG pin to GND. When the timer runs out or the input supply is removed, the current source will be disconnected and the CHG pin is forced into a high impedance state. A pull-up resistor is required. The timer function is defeated by forcing this pin below 1V (or connecting it to GND). ACP/SHDN (Pin 3): Open-Drain Output Used to Indicate if the AC Adapter Voltage is Adequate for Charging. Active high digital output. Internal 10A pull-up to 3.5V. The charger can also be inhibited by pulling this pin below 1V. Reset the charger by pulsing the pin low for a minimum of 0.1s. RT (Pin 4): Timer Resistor. The timer period is set by placing a resistor, RRT , to GND. The timer period is tTIMER = (1hour * RRT/154k) If this resistor is not present, the charger will not start. GND (Pin 5): Ground for Low Power Circuitry. 4 U U U 4006i LTC4006 PI FU CTIO S NTC (Pin 6): A thermistor network is connected from NTC to GND. This pin determines if the battery temperature is safe for charging. The charger and timer are suspended if the thermistor indicates a temperature that is unsafe for charging. The thermistor function may be disabled with a 300k to 500k resistor from DCIN to NTC. ITH (Pin 7): Control Signal of the Inner Loop of the Current Mode PWM. Higher ITH voltage corresponds to higher charging current in normal operation. A 6.04k resistor, in series with a capacitor of at least 0.1F to GND, provides loop compensation. Typical full-scale output current is 40A. Nominal voltage range for this pin is 0V to 3V. IMON (Pin 8): Current Monitoring Output. The voltage at this pin provides a linear indication of charging current. Peak current is equivalent to 1.19V. Zero current is approximately 0.309V. A capacitor from IMON to ground is required to filter higher frequency components. If VBAT < 2.5V/cell, then IMON = 1.19V when conditioning a depleted battery. CSP (Pin 9): Current Amplifier CA1 Input. This pin and the BAT pin measure the voltage across the sense resistor, RSENSE, to provide the instantaneous current signals required for both peak and average current mode operation. BAT (Pin 10): Battery Sense Input and the Negative Reference for the Current Sense Resistor. A precision internal resistor divider sets the final float potential on this pin. The resistor divider is disconnected during shutdown. CLP (Pin 11): Positive Input to the Supply Current Limiting Amplifier, CL1. The threshold is set at 100mV above the voltage at the CLN pin. When used to limit supply current, a filter is needed to filter out the switching noise. If no current limit function is desired, connect this pin to CLN. CLN (Pin 12): Negative Reference for the Input Current Limit Amplifier, CL1. This pin also serves as the power supply for the IC. A 10F to 22F bypass capacitor should be connected as close as possible to this pin. TGATE (Pin 13): Drives the top external P-channel MOSFET of the battery charger buck converter. PGND (Pin 14): High Current Ground Return for the BGATE Driver. BGATE (Pin 15): Drives the bottom external N-channel MOSFET of the battery charger buck converter. INFET (Pin 16): Drives the Gate of the External Input PFET. TEST CIRCUIT LTC4006 11.67A U U U + VREF + EA - 35mV 3k - 10 BAT 7 ITH + LT1055 - 4006 TC 0.6V 4006i 5 LTC4006 BLOCK DIAGRA VIN DCIN 0.01F Q3 INFET 16 1 ACP/SHDN 3 TIMER/CONTROLLER ICL TBAD RESTART 1.105V LOBAT 708mV GND 35mV C/10 397mV THERMISTOR 6 OSCILLATOR 4 5 11.67A gm = 1m EA 5.1k RCL 15nF gm = 1.5m CL1 12 + DCIN OSCILLATOR WATCH DOG DETECT tOFF 1.28V gm = 1m 20F OV /5 Q1 13 Q R BGATE PGND CHARGE ICMP Q2 15 14 PWM LOGIC IREV L1 + RIMON1 26.44k RIMON2 52.87k OPERATIO Overview The LTC4006 is a synchronous current mode PWM stepdown (buck) switcher battery charger controller. The charge current is programmed by the sense resistor (RSENSE) between the CSP and BAT pins. The final float voltage is internally programmed to 8.4V (LTC4006-6), 12.6V (LTC4006-2) or 16.8V (LTC4006-4) with better than 0.8% accuracy. Charging begins when the potential at the DCIN pin rises above the voltage at CLN (and the UVLO voltage) and the ACP/SHDN pin is allowed to go high; the CHG pin is set low. At the beginning of the charge cycle, if the cell voltage is below 2.5V, the charger will trickle charge the battery with 10% of the maximum programmed current. 4006i 6 - + TGATE S CLN 100mV CLP - 11 - - CA2 + BUFFERED ITH - 17mV 8 4.7nF IMON + 1.19V + CA1 - - + W 25A 5.8V CLN RT RRT 2 CHG 100k VLOGIC NTC 32.4k 10k NTC 0.47F 3k 10 BAT RSENSE 9 3k CSP 20F 9k 1.19V ITH 6.04k 0.12F 7 -+ 4006 BD U LTC4006 OPERATIO If the cell voltage stays below 2.5V for 25% of the total charge time, the charge sequence will be terminated immediately and the CHG pin will be set to a high impedance. An external thermistor network is sampled at regular intervals. If the thermistor value exceeds design limits, charging is suspended. If the thermistor value returns to an acceptable value, charging resumes. An external resistor on the RT pin sets the total charge time. The timer can be defeated by forcing the CHG pin to a low voltage. As the battery approaches the final float voltage, the charge current will begin to decrease. When the current drops to 10% of the programmed charge current, an internal C/10 comparator will indicate this condition by sinking 25A at the CHG pin. The charge timer is also reset to 25% of the total charge time. If this condition is caused by an input current limit condition, described below, then the C/10 comparator will be inhibited. When a time-out occurs, charging is terminated immediately and the CHG pin changes to a high impedance. The charger will automatically restart if the cell voltage is less than 3.9V. To restart the charge cycle manually, simply remove the input voltage and reapply it, or force the ACP/SHDN pin low momentarily. When the input voltage is not present, the charger goes into a sleep mode, dropping battery current drain to 15A. This greatly reduces the current drain on the battery and increases the standby time. The charger can be inhibited at any time by forcing the ACP/SHDN pin to a low voltage. Input FET The input FET circuit performs two functions. It enables the charger if the input voltage is higher than the CLN pin and provides the logic indicator of AC present on the ACP/SHDN pin. It controls the gate of the input FET to keep a low forward voltage drop when charging and also prevents reverse current flow through the input FET. If the input voltage is less than VCLN, it must go at least 170mV higher than VCLN to activate the charger. When this occurs the ACP/SHDN pin is released and pulled up with an internal load to indicate that the adapter is present. The gate of the input FET is driven to a voltage sufficient to keep a low forward voltage drop from drain to source. If the voltage between DCIN and CLN drops to less than 25mV, the input FET is turned off slowly. If the voltage between U DCIN and CLN is ever less than - 25mV, then the input FET is turned off in less than 10s to prevent significant reverse current from flowing in the input FET. In this condition, the ACP/SHDN pin is driven low and the charger is disabled. Battery Charger Controller The LTC4006 charger controller uses a constant off-time, current mode step-down architecture. During normal operation, the top MOSFET is turned on each cycle when the oscillator sets the SR latch and turned off when the main current comparator ICMP resets the SR latch. While the top MOSFET is off, the bottom MOSFET is turned on until either the inductor current trips the current comparator IREV or the beginning of the next cycle. The oscillator uses the equation: tOFF = VDCIN - VBAT VDCIN * fOSC to set the bottom MOSFET on time. This activity is diagrammed in Figure 1. OFF TGATE ON ON BGATE OFF TRIP POINT SET BY ITH VOLTAGE INDUCTOR CURRENT 4006 F01 tOFF Figure 1 The peak inductor current, at which ICMP resets the SR latch, is controlled by the voltage on ITH. ITH is in turn controlled by several loops, depending upon the situation at hand. The average current control loop converts the voltage between CSP and BAT to a representative current. Error amp CA2 compares this current against the desired current programmed by RIMON at the IMON pin and adjusts ITH until: VREF V -V + 11.67A * 3k = CSP BAT RIMON 3k 4006i 7 LTC4006 OPERATIO MODE Shut Down by Low Adapter Voltage Conditioning a Depleted Battery Normal Charging Input Current Limited Charging Charger Paused Due to Thermistor Out of Range Shut Down by ACP/SHDN Pin Terminated by Low-Battery Fault (Note 1) Top-Off Charging. C/10 is Latched Table 1. Truth Table for LTC4006 Operation DCIN Timer is Reset by C/10 Comparator (Latched), then Terminates After 1/4 T Terminated by Expired Timer Timer Defeated. (Low-Battery Conditioning Still Functional) Shut Down by Undervoltage Lockout Timer Defeated Until VBAT > 3.9V/Cell *Open Drain. High when used with pull-up resistor. **Most probable condition, X = Don't care therefore, V 3k ICHARGE = REF - 11.67A * RIMON RSENSE The voltage at BAT is divided down by an internal resistor divider and is used by error amp EA to decrease ITH if the divider voltage is above the 1.19V reference. When the charging current begins to decrease, the voltage at IMON will decrease in direct proportion. The voltage at IMON is then given by: VIMON = (ICHARGE * RSENSE + 11.67A * 3k) * VIMON is plotted in Figure 2. The amplifier CL1 monitors and limits the input current to a preset level (100mV/RCL). At input current limit, CL1 will decrease the ITH voltage, thereby reducing charging current. When this condition is detected, the C/10 indicator RIMON 3k 8 U >BAT VFLOAT OFF HIGH >BAT VFLOAT** OFF HIGH X >BAT and 4006i LTC4006 OPERATIO 1.2 1.19V 1.0 0.8 VPROG (V) 0.6 0.4 0.2 0 0 20 40 60 80 ICHARGE (% OF MAXIMUM CURRENT) 100 0.309V off for about 300ns at 40s intervals. This is done to prevent audible noise when using ceramic capacitors at the input and output. Charger Startup When the charger is enabled, it will not begin switching until the ITH voltage exceeds a threshold that assures initial current will be positive. This threshold is 5% to 15% of the maximum programmed current. After the charger begins switching, the various loops will control the current at a level that is higher or lower than the initial current. The duration of this transient condition depends upon the loop compensation but is typically less than 100s. Thermistor Detection The thermistor detection circuit is shown in Figure 3. It requires an external resistor and capacitor in order to function properly. The thermistor detector performs a sample-and-hold function. An internal clock, whose frequency is determined by the timing resistor connected to RT, keeps switch S1 closed to sample the thermistor: tSAMPLE = 127.5 * 20 * RRT * 17.5pF = 13.8ms, for RRT = 309k The external RC network is driven to approximately 4.5V and settles to a final value across the thermistor of: VRTH(FINAL) = 4.5V * RTH RTH + R9 U LTC4006 CLK R9 32.4k 6 RTH 10k NTC C7 0.47F - NTC S1 + ~4.5V 60k + - 4006 F02 - + 45k Figure 2. IMON vs ICHARGE 15k D C 4006 F03 Q TBAD Figure 3 This voltage is stored by C7. Then the switch is opened for a short period of time to read the voltage across the thermistor. tHOLD = 10 * RRT * 17.5pF = 54s, for RRT = 309k When the tHOLD interval ends the result of the thermistor testing is stored in the D flip-flop (DFF). If the voltage at NTC is within the limits provided by the resistor divider feeding the comparators, then the NOR gate output will be low and the DFF will set TBAD to zero and charging will continue. If the voltage at NTC is outside of the resistor divider limits, then the DFF will set TBAD to one, the charger will be shut down, and the timer will be suspended until TBAD returns to zero (see Figure 4). CLK (NOT TO SCALE) tHOLD tSAMPLE VOLTAGE ACROSS THERMISTOR VNTC COMPARATOR HIGH LIMIT COMPARATOR LOW LIMIT 4006 F04 Figure 4 4006i 9 LTC4006 APPLICATIO S I FOR ATIO Charger Current Programming The basic formula for charging current is: ICHARGE(MAX) 100mV = RSENSE tTIMER (MINUTES) Table 2. Recommended RSENSE Resistor Values IMAX (A) 1.0 2.0 3.0 4.0 RSENSE () 1% 0.100 0.050 0.033 0.025 RSENSE (W) 0.25 0.25 0.5 0.5 Setting the Timer Resistor The charger termination timer is designed for a range of 1hour to 3 hour with a 15% uncertainty. The timer is programmed by the resistor RRT using the following equation: tTIMER = 227 * RRT * 175pF (Refer to Figure 5) It is important to keep the parasitic capacitance on the RT pin to a minimum. The trace connecting RT to RRT should be as short as possible. CHG Status Output Pin When the charge cycle starts, the CHG pin is pulled down to ground by an internal N-channel MOSFET that can drive more than 100A. When the charge current drops to 10% of the full-scale current (C/10), the N-channel MOSFET is turned off and a weak 25A current source to ground is connected to the CHG 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 from this pin (charging, C/10 and stop charging). See Figure 6. Battery Detection It is generally not good practice to connect a battery while the charger is running. The timer is in an unknown state and the charger could provide a large surge current into the battery for a brief time. The circuit shown in Figure 7 keeps the charger shut down and the timer reset while a battery is not connected. 10 U Alternatively, a normally closed switch can be used to detect when the battery is present (see Figure 8). 200 180 160 140 120 100 80 60 40 20 0 100 150 200 250 300 350 400 450 500 RRT (k) 4006 F05 W UU Figure 5. tTIMER vs RRT 3.3V LTC4006 CHG 200k 33k VDD P OUT IN 4006 F06 Figure 6. Microprocessor Interface ADAPTER POWER 470k LTC4006 DCIN ACP/SHDN 4006 F07 SWITCH CLOSED IF BATTERY CONNECTED Figure 7 ADAPTER POWER LTC4006 DCIN ACP/SHDN 4006 F08 SWITCH OPEN WHEN BATTERY CONNECTED Figure 8 4006i LTC4006 APPLICATIO S I FOR ATIO Soft-Start The LTC4006 is soft started by the 0.12F capacitor on the ITH pin. On start-up, ITH pin voltage will rise quickly to 0.5V, then ramp up at a rate set by the internal 40A pull-up current and the external capacitor. Battery charging current starts ramping up when ITH voltage reaches 0.8V and full current is achieved with ITH at 2V. With a 0.12F capacitor, time to reach full charge current is about 2ms and it is assumed that input voltage to the charger will reach full value in less than 2ms. The capacitor can be increased up to 1F if longer input start-up times are needed. Input and Output Capacitors The input capacitor (C2) is assumed to absorb all input switching ripple current in the converter, so it must have adequate ripple current rating. Worst-case RMS ripple current will be equal to one half of output charging current. Actual capacitance value is not critical. Solid tantalum low ESR capacitors have high ripple current rating in a relatively small surface mount package, but caution must be used when tantalum capacitors are used for input or output bypass. High input surge currents can be created when the adapter is hot-plugged to the charger or when a battery is connected to the charger. Solid tantalum capacitors have a known failure mechanism when subjected to very high turn-on surge currents. Only Kemet T495 series of "Surge Robust" low ESR tantalums are rated for high surge conditions such as battery to ground. The relatively high ESR of an aluminum electrolytic for C1, located at the AC adapter input terminal, is helpful in reducing ringing during the hot-plug event. Refer to Application Note 88 for more information. Highest possible voltage rating on the capacitor will minimize problems. Consult with the manufacturer before use. Alternatives include new high capacity ceramic (at least 20F) from Tokin, United Chemi-Con/Marcon, et al. Other alternative capacitors include OS-CON capacitors from Sanyo. The output capacitor (C3) is also assumed to absorb output switching current ripple. The general formula for capacitor current is: U IRMS V 0.29(VBAT ) 1 - BAT VDCIN = (L1)( f) For example: VDCIN = 19V, VBAT = 12.6V, L1 = 10H, and f = 300kHz, IRMS = 0.41A. EMI considerations usually make it desirable to minimize ripple current in the battery leads, and beads or inductors may be added to increase battery impedance at the 300kHz switching frequency. Switching ripple current splits between the battery and the output capacitor depending on the ESR of the output capacitor and the battery impedance. If the ESR of C3 is 0.2 and the battery impedance is raised to 4 with a bead or inductor, only 5% of the current ripple will flow in the battery. Inductor Selection Higher operating frequencies allow the use of smaller inductor and capacitor values. A higher frequency generally results in lower efficiency because of MOSFET gate charge losses. In addition, the effect of inductor value on ripple current and low current operation must also be considered. The inductor ripple current IL decreases with higher frequency and increases with higher VIN. IL = V 1 VOUT 1- OUT ( f)(L) VIN W UU Accepting larger values of IL allows the use of low inductances, but results in higher output voltage ripple and greater core losses. A reasonable starting point for setting ripple current is IL = 0.4(IMAX). In no case should IL exceed 0.6(IMAX) due to limits imposed by IREV and CA1. Remember the maximum IL occurs at the maximum input voltage. In practice 10H is the lowest value recommended for use. Lower charger currents generally call for larger inductor values. Use Table 3 as a guide for selecting the correct inductor value for your application. 4006i 11 LTC4006 APPLICATIO S I FOR ATIO Table 3 MAXIMUM AVERAGE CURRENT (A) 1 1 2 2 3 3 4 4 INPUT VOLTAGE (V) 20 > 20 20 > 20 20 > 20 20 > 20 MINIMUM INDUCTOR VALUE (H) 40 20% 56 20% 20 20% 30 20% 15 20% 20 20% 10 20% 15 20% Charger Switching Power MOSFET and Diode Selection Two external power MOSFETs must be selected for use with the charger: a P-channel MOSFET for the top (main) switch and an N-channel MOSFET for the bottom (synchronous) switch. The peak-to-peak gate drive levels are set internally. This voltage is typically 6V. Consequently, logic-level threshold MOSFETs must be used. Pay close attention to the BVDSS specification for the MOSFETs as well; many of the logic level MOSFETs are limited to 30V or less. Selection criteria for the power MOSFETs include the "ON" resistance RDS(ON), total gate capacitance QG, reverse transfer capacitance CRSS, input voltage and maximum output current. The charger is operating in continuous mode at moderate to high currents so the duty cycles for the top and bottom MOSFETs are given by: Main Switch Duty Cycle = VOUT/VIN Synchronous Switch Duty Cycle = (VIN - VOUT)/VIN. The MOSFET power dissipations at maximum output current are given by: PMAIN = VOUT/VIN(I2MAX)(1 + T)RDS(ON) + k(V2IN)(IMAX)(CRSS)(fOSC) PSYNC = (VIN - VOUT)/VIN(I2MAX)(1 + T)RDS(ON) Where is the temperature dependency of RDS(ON) and k is a constant inversely related to the gate drive current. Both MOSFETs have I2R losses while the PMAIN equation includes an additional term for transition losses, which are 12 U highest at high input voltages. For VIN < 20V the high current efficiency generally improves with larger MOSFETs, while for VIN > 20V the transition losses rapidly increase to the point that the use of a higher RDS(ON) device with lower CRSS actually provides higher efficiency. The synchronous MOSFET losses are greatest at high input voltage or during a short circuit when the duty cycle in this switch in nearly 100%. The term (1 + T) is generally given for a MOSFET in the form of a normalized RDS(ON) vs temperature curve, but = 0.005/C can be used as an approximation for low voltage MOSFETs. CRSS is usually specified in the MOSFET characteristics; if not, then CRSS can be calculated using CRSS = QGD/VDS. The constant k = 2 can be used to estimate the contributions of the two terms in the main switch dissipation equation. If the charger is to operate in low dropout mode or with a high duty cycle greater than 85%, then the topside P-channel efficiency generally improves with a larger MOSFET. Using asymmetrical MOSFETs may achieve cost savings or efficiency gains. The Schottky diode D1, shown in the Typical Application on the back page, conducts during the dead-time between the conduction of the two power MOSFETs. This prevents the body diode of the bottom MOSFET from turning on and storing charge during the dead-time, which could cost as much as 1% in efficiency. A 1A Schottky is generally a good size for 4A regulators due to the relatively small average current. Larger diodes can result in additional transition losses due to their larger junction capacitance. The diode may be omitted if the efficiency loss can be tolerated. Calculating IC Power Dissipation The power dissipation of the LTC4006 is dependent upon the gate charge of the top and bottom MOSFETs (QG1 and QG2 respectively) The gate charge is determined from the manufacturer's data sheet and is dependent upon both the gate voltage swing and the drain voltage swing of the MOSFET. Use 6V for the gate voltage swing and VDCIN for the drain voltage swing. PD = VDCIN * (fOSC (QG1 + QG2) + IDCIN) 4006i W UU LTC4006 APPLICATIO S I FOR ATIO Example: VDCIN = 19V, fOSC = 345kHz, QG1 = QG2 = 15nC. PD = 292mW Adapter Limiting An important feature of the LTC4006 is the ability to automatically adjust charging current to a level which avoids overloading the wall adapter. This allows the product to operate at the same time that batteries are being charged without complex load management algorithms. Additionally, batteries will automatically be charged at the maximum possible rate of which the adapter is capable. This feature is created by sensing total adapter output current and adjusting charging current downward if a preset adapter current limit is exceeded. True analog control is used, with closed-loop feedback ensuring that adapter load current remains within limits. Amplifier CL1 in Figure 9 senses the voltage across RCL, connected between the CLP and DCIN pins. When this voltage exceeds 100mV, the amplifier will override programmed charging current to limit adapter current to 100mV/RCL. A lowpass filter formed by 5k and 15nF is required to eliminate switching noise. If the current limit is not used, CLP should be connected to CLN. LTC4006 100mV - CL1 + CLP 18 15nF 5k AC ADAPTER INPUT VIN + CLN 19 100mV ADAPTER CURRENT LIMIT RCL* + CIN *RCL = Figure 9. Adapter Current Limiting Setting Input Current Limit To set the input current limit, you need to know the minimum wall adapter current rating. Subtract 5% for the input current limit tolerance and use that current to determine the resistor value. RCL = 100mV/ILIM ILIM = Adapter Min Current - (Adapter Min Current * 5%) U Table 5. Common RCL Resistor Values ADAPTER RATING (A) 1.5 1.8 2 2.3 2.5 2.7 3 RCL VALUE* () 1% 0.06 0.05 0.045 0.039 0.036 0.033 0.03 RCL POWER DISSIPATION (W) 0.135 0.162 0.18 0.206 0.225 0.241 0.27 RCL POWER RATING (W) 0.25 0.25 0.25 0.25 0.5 0.5 0.5 * Values shown above are rounded to nearest standard value. W UU As is often the case, the wall adapter will usually have at least a +10% current limit margin and many times one can simply set the adapter current limit value to the actual adapter rating (see Table 5). Designing the Thermistor Network There are several networks that will yield the desired function of voltage vs temperature needed for proper operation of the thermistor. The simplest of these is the voltage divider shown in Figure 10. Unfortunately, since the HIGH/LOW comparator thresholds are fixed internally, there is only one thermistor type that can be used in this network; the thermistor must have a HIGH/LOW resistance ratio of 1:7. If this happy circumstance is true for you, then simply set R9 = RTH(LOW) If you are using a thermistor that doesn't have a 1:7 HIGH/ LOW ratio, or you wish to set the HIGH/LOW limits to different temperatures, then the more generic network in Figure 11 should work. Once the thermistor, RTH, has been selected and the thermistor value is known at the temperature limits, then resistors R9 and R9A are given by: For NTC thermistors: R9 = 6 RTH(LOW) * RTH(HIGH)/(RTH(LOW) - RTH(HIGH)) R9A = 6 RTH(LOW) * RTH(HIGH)/(RTH(LOW) - 7 * RTH(HIGH)) For PTC thermistors: R9 = 6 RTH(LOW) * RTH(HIGH)/(RTH(HIGH) - RTH(LOW)) R9A = 6 RTH(LOW) * RTH(HIGH)/(RTH(HIGH) - 7 * RTH(LOW)) 4006 F09 4006i 13 LTC4006 APPLICATIO S I FOR ATIO LTC4006 NTC C7 RTH 4006 F10 R9 Figure 10. Voltage Divider Thermistor Network Example #1: 10k NTC with custom limits TLOW = 0C, THIGH = 50C RTH = 10k at 25C, RTH(LOW) = 32.582k at 0C RTH(HIGH) = 3.635k at 50C R9 = 24.55k 24.3k (nearest 1% value) R9A = 99.6k 100k (nearest 1% value) Example #2: 100k NTC TLOW = 5C, THIGH = 50C RTH = 100k at 25C, RTH(LOW) = 272.05k at 5C RTH(HIGH) = 33.195k at 50C R9 = 226.9k 226k (nearest 1% value) R9A = 1.365M 1.37M (nearest 1% value) Example #3: 22k PTC TLOW = 0C, THIGH = 50C RTH = 22k at 25C, RTH(LOW) = 6.53k at 0C RTH(HIGH) = 61.4k at 50C R9 = 43.9k 44.2k (nearest 1% value) R9A = 154k Sizing the Thermistor Hold Capacitor During the hold interval, C7 must hold the voltage across the thermistor relatively constant to avoid false readings. A reasonable amount of ripple on NTC during the hold interval is about 10mV to 15mV. Therefore, the value of C7 is given by: C7 = t HOLD /(R9/7 * -ln(1 - 8 * 15mV/4.5V)) = 10 * RRT * 17.5pF/(R9/7 * - ln(1 - 8 * 15mV/4.5V) Example: R9 = 24.3k RRT = 309k (~2 hour timer) C7 = 0.58F 0.56F (nearest value) 14 U LTC4006 NTC C7 R9A RTH 4006 F11 W UU R9 Figure 11. General Thermistor Network Disabling the Thermistor Function If the thermistor is not needed, connecting a resistor between DCIN and NTC will disable it. The resistor should be sized to provide at least 10A with the minimum voltage applied to DCIN and 10V at NTC. Do not exceed 30A into NTC. Generally, a 301k resistor will work for DCIN less than 15V. A 499k resistor is recommended for DCIN between 15V and 24V. PCB Layout Considerations For maximum efficiency, the switch node rise and fall times should be minimized. To prevent magnetic and electrical field radiation and high frequency resonant problems, proper layout of the components connected to the IC is essential. (See Figure 12.) Here is a PCB layout priority list for proper layout. Layout the PCB using this specific order. 1. Input capacitors need to be placed as close as possible to switching FET's supply and ground connections. Shortest copper trace connections possible. These parts must be on the same layer of copper. Vias must not be used to make this connection. 2. The control IC needs to be close to the switching FET's gate terminals. Keep the gate drive signals short for a clean FET drive. This includes IC supply pins that connect to the switching FET source pins. The IC can be placed on the opposite side of the PCB relative to above. 3. Place inductor input as close as possible to switching FET's output connection. Minimize the surface area of this trace. Make the trace width the minimum amount needed to support current--no copper fills or pours. Avoid running the connection using multiple layers in parallel. Minimize capacitance from this node to any other trace or plane. 4. Place the output current sense resistor right next to the inductor output but oriented such that the IC's 4006i LTC4006 APPLICATIO S I FOR ATIO current sense feedback traces going to resistor are not long. The feedback traces need to be routed together as a single pair on the same layer at any given time with smallest trace spacing possible. Locate any filter component on these traces next to the IC and not at the sense resistor location. 5. Place output capacitors next to the sense resistor output and ground. 6. Output capacitor ground connections need to feed into same copper that connects to the input capacitor ground before tying back into system ground. General Rules 7. Connection of switching ground to system ground or internal ground plane should be single point. If the system has an internal system ground plane, a good way to do this is to cluster vias into a single star point to make the connection. 8. Route analog ground as a trace tied back to IC ground (analog ground pin if present) before connecting to SWITCH NODE L1 VBAT HIGH FREQUENCY CIRCULATING PATH VIN C2 D1 C3 Figure 12. High Speed Switching Path PACKAGE DESCRIPTION GN Package 16-Lead Plastic SSOP (Narrow .150 Inch) (Reference LTC DWG # 05-08-1641) .189 - .196* (4.801 - 4.978) .015 .004 x 45 (0.38 0.10) .007 - .0098 (0.178 - 0.249) .016 - .050 (0.406 - 1.270) 0 - 8 TYP .150 - .157** (3.810 - 3.988) .053 - .068 (1.351 - 1.727) .004 - .0098 (0.102 - 0.249) 16 15 14 13 12 11 10 9 .009 (0.229) REF .045 .005 .229 - .244 .0250 (5.817 - 6.198) (0.635) BSC NOTE: 1. CONTROLLING DIMENSION: INCHES *DIMENSION DOES NOT INCLUDE MOLD FLASH. MOLD FLASH SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE INCHES 2. DIMENSIONS ARE IN (MILLIMETERS) **DIMENSION DOES NOT INCLUDE INTERLEAD FLASH. INTERLEAD FLASH SHALL NOT EXCEED 0.010" (0.254mm) PER SIDE 3. DRAWING NOT TO SCALE .008 - .012 (0.203 - 0.305) U any other ground. Avoid using the system ground plane. CAD trick: make analog ground a separate ground net and use a 0 resistor to tie analog ground to system ground. 9. A good rule of thumb for via count for a given high current path is to use 0.5A per via. Be consistent. 10. If possible, place all the parts listed above on the same PCB layer. 11. Copper fills or pours are good for all power connections except as noted above in Rule 3. You can also use copper planes on multiple layers in parallel too--this helps with thermal management and lower trace inductance improving EMI performance further. 12. For best current programming accuracy provide a Kelvin connection from RSENSE to CSP and BAT. See Figure 12 as an example. It is important to keep the parasitic capacitance on the RT, CSP and BAT pins to a minimum. The traces connecting these pins to their respective resistors should be as short as possible. DIRECTION OF CHARGING CURRENT RSNS BAT 4006 F13 U W UU CSP 4006 F12 BAT Figure 13. Kelvin Sensing of Charging Current .254 MIN .150 - .165 GN16 (SSOP) 0502 1 23 4 56 7 8 .0165 .0015 .0250 TYP RECOMMENDED SOLDER PAD LAYOUT 4006i 15 LTC4006 TYPICAL APPLICATIO DCIN 0V TO 20V 2.5A VLOGIC R3 100k CHG ACP CHARGING CURRENT MONITOR R9 32.4k THERMISTOR 10k NTC C5 0.0047F C7 0.47F RT 309k TIMING RESISTOR (~2 HOURS) RELATED PARTS PART NUMBER LT(R)1511 LT1513 LT1571 LTC1628-PG LTC1709 LTC1729 DESCRIPTION 3A Constant-Current/Constant-Voltage Battery Charger Sepic Constant- or Programmable- Current/ConstantVoltage Battery Charger 1.5A Switching Charger 2-Phase, Dual Synchronous Step-Down Controller 2-Phase, Dual Synchronous Step-Down Controller with VID Li-Ion Battery Charger Termination Controller COMMENTS High Efficiency, Minimum External Components to Fast Charge Lithium, NIMH and NiCd Batteries Charger Input Voltage May be Higher, Equal to or Lower Than Battery Voltage, 500kHz Switching Frequency 1- or 2-Cell Li-Ion, 500kHz or 200kHz Switching Frequency, Termination Flag Minimizes CIN and COUT, Power Good Output, 3.5V VIN 36V Up to 42A Output, Minimum CIN and COUT, Uses Smallest Components for Intel and AMD Processors Trickle Charge Preconditioning, Temperature Charge Qualification, Time or Charge Current Termination, Automatic Charger and Battery Detection, and Status Output Constant-Current/Constant-Voltage Switching Regulator, Input Current Limiting Maximizes Charge Current 2% to 90% Duty Cycle at 200kHz, Stable with Ceramic COUT Simultaneous Charge or Discharge of Two Batteries, DAC Programmable Current and Voltage, Input Current Limiting Maximizes Charge Current 3.5V VIN 36V, 0.925V VOUT 2V, for Transmeta, AMD and Intel Mobile Processors Complete Charger for 3- or 4-Cell Li-Ion Batteries, AC Adapter Current Limit, Thermistor Sensor and Indicator Outputs Constant-Current/Constant-Voltage Switching Regulator, Resistor Voltage/ Current Programming, AC Adapter Current Limit and Thermistor Sensor and Indicator Outputs LT1769 LTC1778 LTC1960 LTC3711 LTC4007 LTC4008 2A Switching Battery Charger Wide Operating Range, No RSENSETM Synchronous Step-Down Controller Dual Battery Charger/Selector with SPI Interface No RSENSE Synchronous Step-Down Controller with VID High Efficiency, Programmable Voltage, Battery Charger with Termination High Efficiency, Programmable Voltage/Current Battery Charger No RSENSE is a trademark of Linear Technology Corporation. 16 Linear Technology Corporation 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 q FAX: (408) 434-0507 q U 2A Li-Ion Battery Charger Q3 INPUT SWITCH C1 0.1F DCIN CHG INFET LTC4006 CLP CLN TGATE BGATE PGND CSP BAT 4006 TA02 R1 5k C4 15nF RCL 0.04 TO LOAD C2 20F Q1 Q2 L1 22H 2A D1 D1: MBRM140T3 Q1, Q3: Si3457 Q2: Si3454 ACP/SHDN IMON NTC RT R4 6.04k C6 0.12F ITH GND RSENSE 0.05 BATTERY C3 20F 4006i LT/TP 0503 1K * PRINTED IN USA www.linear.com (c) LINEAR TECHNOLOGY CORPORATION 2003 |
Price & Availability of LTC4006
 |
|
|
|
|
All Rights Reserved © IC-ON-LINE 2003 - 2022 |
| [Add Bookmark] [Contact Us] [Link exchange] [Privacy policy] |
|
Mirror Sites : [www.datasheet.hk]
[www.maxim4u.com] [www.ic-on-line.cn]
[www.ic-on-line.com] [www.ic-on-line.net]
[www.alldatasheet.com.cn]
[www.gdcy.com]
[www.gdcy.net] |