LTC4008 4A, High Efficiency, Multi-Chemistry Battery Charger FEATURES DESCRIPTION n The LTC(R)4008 is a constant-current/constant-voltage charger controller. The PWM controller uses a synchronous, quasi-constant frequency, constant off-time architecture that will not generate audible noise even when using ceramic capacitors. Charging current is programmable with a sense resistor and programming resistor to 4% typical accuracy. Charging current can be monitored as a voltage across the programming resistor. An external resistor divider and precision internal reference set the final float voltage. n n n n n n n n n n n n General Purpose Charger Controller High Conversion Efficiency: Up to 96% Output Currents Exceeding 4A 0.8% Voltage Accuracy AC Adapter Current Limiting Maximizes Charge Rate* Thermistor Input for Temperature Qualified Charging Wide Input Voltage Range: 6V to 28V Wide Output Voltage: 3V to 28V 0.5V Dropout Voltage; Maximum Duty Cycle: 98% Programmable Charge Current: 4% Accuracy Indicator Outputs for Charging, C/10 Current Detection, AC Adapter Present, Input Current Limiting and Faults Charging Current Monitor Output Available in a 20-Pin Narrow SSOP Package APPLICATIONS n n n Notebook Computers Portable Instruments Battery Backup Systems L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks and PowerPath and No RSENSE are trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners. Protected by U.S. Patents including 5723970. TYPICAL APPLICATION 12.3V, 4A Li-Ion Charger INPUT SWITCH DCIN 0V TO 28V 0.1F 140k* VLOGIC 100k 100k ICL ACP LTC4008 BATMON DCIN VFB INFET ICL CLP ACP/SHDN FAULT TGATE FLAG FLAG BGATE NTC PGND 32.4k RT 15k* 150k 0.47F ITH 6.04k GND 0.12F NOTE: * 0.25% TOLERANCE ALL OTHER RESISTORS ARE 1% TOLERANCE 0.1F 0.02 SYSTEM LOAD 4.99k 20F CLN FAULT THERMISTOR 10k NTC The LTC4008 includes a thermistor sensor input that will suspend charging if an unsafe temperature condition is detected and will automatically resume charging when battery temperature returns to within safe limits; a FAULT pin indicates this condition. A FLAG pin indicates when charging current has decreased below 10% of the programmed current. An external sense resistor programs AC adapter current limiting. The ICL pin indicates when the charging current is being reduced by input current limiting so that the charging algorithm can adapt. Q1 10H Q2 0.025 20F Li-Ion BATTERY CSP BAT 3.01k 3.01k PROG 0.0047F 26.7k Q1: Si4431BDY Q2: FDC645N CHARGING CURRENT MONITOR 4008 TA01 4008fb 1 LTC4008 ABSOLUTE MAXIMUM RATINGS (Note 1) Voltage from DCIN, CLP, CLN to GND.......... +32V/-0.3 V PGND with Respect to GND ...................................0.3V CSP, BAT to GND .......................................... +28V/-0.3V VFB, RT to GND ............................................... +7V/-0.3V NTC .............................................................. +10V/-0.3V ACP/SHDN, FLAG, FAULT, ICL ..................... +32V/-0.3V CLP to CLN ..........................................................+0.5V 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 PIN CONFIGURATION LTC4008 LTC4008-1* TOP VIEW TOP VIEW DCIN 1 20 INFET ICL 2 19 BGATE ACP/SHDN 3 18 PGND RT 4 17 TGATE FAULT 5 16 CLP GND 6 15 CLN VFB 7 14 FLAG NTC 8 13 BATMON ITH 9 12 BAT PROG 10 11 CSP GN PACKAGE 20-LEAD NARROW PLASTIC SSOP DCIN 1 20 NC ICL 2 19 BGATE SHDN 3 18 PGND RT 4 17 TGATE FAULT 5 16 CLP GND 6 15 CLN VFB 7 14 FLAG NTC 8 13 BATMON ITH 9 12 BAT PROG 10 11 CSP GN PACKAGE 20-LEAD NARROW PLASTIC SSOP TJMAX = 125C, JA = 160C/W EXPOSED PAD (PIN #) IS GND, MUST BE SOLDERED TO PCB TJMAX = 150C, JA = 140C/W *The LTC4008EGN-1 does not have the Input FET function ORDER INFORMATION LEAD FREE FINISH TAPE AND REEL PART MARKING PACKAGE DESCRIPTION TEMPERATURE RANGE LTC4008EGN#PBF LTC4008EGN#TRPBF LTC4008EGN 20-Lead Narrow Plastic SSOP -40C to 125C LTC4008EGN-1#PBF LTC4008EGN-1#TRPBF LTC4008EGN-1 20-Lead Narrow Plastic SSOP -40C to 125C Consult LTC Marketing for parts specified with wider operating temperature ranges. Consult LTC Marketing for information on non-standard lead based finish parts. For more information on lead free part marking, go to: http://www.linear.com/leadfree/ For more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/ 4008fb 2 LTC4008 ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. VDCIN = 20V, VBAT = 12V unless otherwise noted. SYMBOL PARAMETER CONDITIONS MIN DCIN Operating Range IQ Operating Current Charging Sum of Current from CLP, CLN, DCIN VTOL Voltage Accuracy (Notes 2, 5) BATMON Error (Note 5) Measured from BAT to BATMON, RLOAD = 100k Charge Current Accuracy (Note 3) VCSP - VBAT Target = 100mV Battery Leakage Current ITOL TYP 6 3 l UNITS 28 V 5 mA 0.8 1.0 % % 80 mV 4 5 % % 20 35 10 A A -0.8 -1.0 0 MAX 35 l -4 -5 DCIN = 0V (LTC4008 Only) ACP/SHDN = 0V l l -10 DCIN Rising, VBAT = 0V l 4.2 4.7 5.5 V l 1 1.6 2.5 V 2 3 Shutdown UVLO Undervoltage Lockout Threshold Shutdown Threshold at ACP/SHDN Operating Current in Shutdown VSHDN = 0V, Sum of Current from CLP, CLN, DCIN mA Current Sense Amplifier, CA1 Input Bias Current Into BAT Pin CMSL CA1/I1 Input Common Mode Low CMSH CA1/I1 Input Common Mode High 11.66 l VDCIN 28V Input Voltage Offset VOS Current Comparators ICMP and IREV ITMAX Maximum Current Sense Threshold (VCSP - VBAT) VITH = 2.5V ITREV 0 V l VCLN - 0.2 -3.5 l A 140 Reverse Current Threshold (VCSP - VBAT) 165 V 3.5 mV 200 mV -30 mV Current Sense Amplifier, CA2 Transconductance 1 mmho Source Current Measured at ITH, VITH = 1.4V -40 A Sink Current Measured at ITH, VITH = 1.4V 40 A 1.4 mmho Current Limit Amplifier Transconductance VCLP Current Limit Threshold ICLN CLN Input Bias Current l 93 100 107 100 mV nA Voltage Error Amplifier, EA Transconductance VREF Reference Voltage Used to Calculate VFLOAT IBEA Input Bias Current Sink Current OVSD Overvoltage Shutdown Threshold as a Percent of Programmed Charger Voltage 1 mmho 1.19 4 Measured at ITH, VITH = 1.4V V 25 36 l 102 107 nA A 110 % 4008fb 3 LTC4008 ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. VDCIN = 20V, VBAT = 12V unless otherwise noted. SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS 0 0.17 0.25 V 25 50 Input P-Channel FET Driver (INFET) (LTC4008 Only) DCIN Detection Threshold (VDCIN - VCLP) DCIN Voltage Ramping Up from VCLP - 0.1V l l Forward Regulation Voltage (VDCIN - VCLP) Reverse Voltage Turn-Off Voltage (VDCIN - VCLP) DCIN Voltage Ramping Down l -60 -25 INFET "On" Clamping Voltage (VCLP - VINFET) IINFET = 1A l 5 5.8 INFET "Off" Clamping Voltage (VCLP - VINFET) IINFET = -25A mV mV 6.5 V 0.25 V Thermistor NTCVR Reference Voltage During Sample Time 4.5 V High Threshold VNTC Rising l NTCVR * 0.48 NTCVR * 0.5 NTCVR * 0.52 V Low Threshold VNTC Falling l NTCVR * 0.115 NTCVR * 0.125 NTCVR * 0.135 V Thermistor Disable Current VNTC 10V 10 A V Indicator Outputs (ACP/SHDN, FLAG, ICL, FAULT C10TOL FLAG (C/10) Accuracy Voltage Falling at PROG ICL Threshold Accuracy VCLP - VCLN VOL VOH Low Logic Level of ACP/SHDN, FLAG, ICL, FAULT IOL = 100A High Logic Level of ACP/SHDN, ICL IOH = -1A IOFF Off State Leakage Current of FLAG, FAULT VOH = 3V IPO Pull-Up Current on ACP/SHDN, ICL V = 0V l l 0.375 0.397 0.420 83 93 105 mV 0.5 V 2.7 V -1 1 -10 A A Oscillator fOSC Regulator Switching Frequency fMIN Regulator Switching Frequency in Drop Out DCMAX Regulator Maximum Duty Cycle 255 300 345 kHz Duty Cycle 98% 20 25 kHz VCSP = VBAT 98 99 % Gate Drivers (TGATE, BGATE) VTGATE High (VCLP - VTGATE) ITGATE = -1mA 50 mV VBGATE High CLOAD = 3000pF 5.6 10 V VTGATE Low (VCLP - VTGATE) CLOAD = 3000pF 5.6 10 V 50 mV VBGATE Low IBGATE = 1mA TGTR TGTF TGATE Transition Time TGATE Rise Time TGATE Fall Time CLOAD = 3000pF, 10% to 90% CLOAD = 3000pF, 10% to 90% 50 50 110 100 ns ns BGTR BGTF BGATE Transition Time BGATE Rise Time BGATE Fall Time CLOAD = 3000pF, 10% to 90% CLOAD = 3000pF, 10% to 90% 40 40 90 80 ns ns VTGATE at Shutdown (VCLP - VTGATE) ITGATE = -1A, DCIN = 0V, CLP = 12V 100 mV VBGATE at Shutdown IBGATE = 1A, DCIN = 0V, CLP = 12V 100 mV Note 1: Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. Exposure to any Absolute Maximum Rating condition for extended periods may affect device reliability and lifetime. Note 2: See Test Circuit. Note 3: Does not include tolerance of current sense resistor or current programming resistor. Note 4: The LTC4008E 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. Note 5: Voltage accuracy includes BATMON error and voltage reference error. Does not include error of external resistor divider. 4008fb 4 LTC4008 TYPICAL PERFORMANCE CHARACTERISTICS (TA = 25C unless otherwise noted) INFET Response Time to Reverse Current VFB vs DCIN 0.05 Vgs OF PFET (2V/DIV) Vgs = 0 Vs OF PFET (5V/DIV) VFB (%) 0 Vs = 0V -0.05 -0.10 -0.15 Id (REVERSE) OF PFET (5A/DIV) -0.20 Id = 0A 6 1.25s/DIV 11 TEST PERFORMED ON DEMOBOARD VCHARGE = 12.6V VIN = 15VDC CHARGER = ON INFET = 1/2 Si4925DY ICHARGE = <10mA 4008 G01 26 4008 G02 BATMON Offset 0.02 16 21 DCIN (V) VOUT vs IOUT 0 BATMON LOAD = 100k VBATTERY - VBATMON (V) -0.02 -0.04 -0.06 -0.08 DCIN = 15V DCIN = 20V DCIN = 24V -0.10 3 8 13 18 BATTERY VOLTAGE (V) 23 OUTPUT VOLTAGE ERROR (%) -0.5 0 -1.0 -1.5 -2.0 -2.5 -3.0 -3.5 -4.0 -4.5 DCIN = 20V VBAT = 12.6V -5.0 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 OUTPUT CURRENT (A) 4008 G04 4008 G03 Disconnect/Reconnect Battery (Load Dump) PWM Frequency vs Duty Cycle 350 3A STEP PWM FREQUENCY (kHz) 300 250 1A STEP VFLOAT 1V/(DIV) 200 1A STEP 150 PROGRAMMED CURRENT = 10% 100 LOAD STATE DCIN = 15V DCIN = 20V DCIN = 24V 50 0 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 DUTY CYCLE (VOUT/VIN) 4008 G05 3A STEP DISCONNECT RECONNECT LOAD CURRENT = 1A, 2A, 3A DCIN = 20V VFLOAT = 12.6V 4008 G06 4008fb 5 LTC4008 TYPICAL PERFORMANCE CHARACTERISTICS (TA = 25C unless otherwise noted) Battery Leakage Current vs Battery Voltage Efficiency at 19VDC VIN 100 VDCIN = 0V 35 16.8V 95 30 12.6V EFFICIENCY (%) BATTERY LEAKAGE CURRENT (A) 40 25 20 15 10 90 85 80 5 75 0 0 5 10 15 20 BATTERY VOLTAGE (V) 25 0.50 30 1.00 1.50 2.00 2.50 CHARGE CURRENT (A) 3.00 4008 G09 4008 G07 Charging Voltage Error TEMP = 27C, ILOAD = 0.120A Efficiency at 12.6V with 15VDC VIN 0.150 100 OUTPUT VOLTAGE ERROR (V) 0.125 EFFICIENCY (%) 95 90 85 80 0.100 0.075 0.050 DCIN = 20V 0.025 DCIN = 15V 0 -0.025 -0.050 -0.075 -0.100 -0.125 75 0.50 1.00 1.50 2.00 2.50 CHARGE CURRENT (A) 3.00 4008 G10 -0.150 0 2 4 6 8 10 12 14 16 18 20 22 CHARGING VOLTAGE (V) 4008 G11 4008fb 6 LTC4008 PIN FUNCTIONS DCIN (Pin 1): External DC Power Source Input. Bypass this pin with at least 0.01F. See Applications Information section. ICL (Pin 2): Input Current Limit Indicator. Active low digital output. Internal 10A pull-up to 3.5V. Pulled low if the charger current is being reduced by the input current limiting function. The pin is capable of sinking at least 100A. If VLOGIC > 3.3V, add an external pull-up. 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 shutdown by pulling this pin below 1V. The pin is capable of sinking at least 100A. If VLOGIC > 3.3V, add an external pull-up. (LTC4008-1: ACP function disabled.) RT (Pin 4): Thermistor Clocking Resistor. Use a 150k resistor as a nominal value. This resistor is always required. If this resistor is not present, the charger will not start. FAULT (Pin 5): Active low open-drain output that indicates that charger operation has suspended due to the thermistor exceeding allowed values. A pull-up resistor is required if this function is used. The pin is capable of sinking at least 100A. GND (Pin 6): Ground for Low Power Circuitry. VFB (Pin 7): Input of Voltage Feedback Error Amplifier, EA, in the Block Diagram. NTC (Pin 8): 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 and the FAULT pin is driven low 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 9): Control Signal of the Inner Loop of the Current Mode PWM. Higher ITH voltage corresponds to higher charging current in normal operation. A 6k 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. PROG (Pin 10): Current Programming/Monitoring Input/ Output. An external resistor to GND programs the peak charging current in conjunction with the current sensing resistor. 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 PROG to ground is required to filter higher frequency components. The maximum program resistance to ground is 100k. Values higher than 100k can cause the charger to shut down. CSP (Pin 11): Current Amplifier CA1 Input. The CSP and BAT pins 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 12): Battery Sense Input and the Negative Reference for the Current Sense Resistor. BATMON (Pin 13): Output Voltage Representing Battery Voltage. Switched off to reduce standby current drain when AC is not present. An external voltage divider from BATMON to VFB sets the charger float voltage. Recommended minimum load resistance is 100k. FLAG (Pin 14): Active low open-drain output that indicates when charging current has declined to 10% of max programmed current. A pull-up resistor is required if this function is used. The pin is capable of sinking at least 100A. This function is latching. To clear it, user must cycle the ACP/SHDN pin. CLN (Pin 15): Negative Input to the Input Current Limiting Amplifier CL1. The threshold is set at 100mV below the voltage at the CLP pin. When used to limit input current, a filter is needed to filter out the switching noise. If no current limit function is desired, connect this pin to CLP. CLP (Pin 16): This pin serves as a positive reference for the input current limit amplifier, CL1. It also serves as the power supply for the IC. TGATE (Pin 17): Drives the top external PMOSFET of the battery charger buck converter. PGND (Pin 18): High Current Ground Return for BGATE Driver. BGATE (Pin 19): Drives the bottom external N-MOSFET of the battery charger buck converter. INFET (Pin 20): Drives the gate of the external input P-MOSFET. (LTC4008-1: No Connection) 4008fb 7 LTC4008 BLOCK DIAGRAM 0.1F VIN DCIN INFET* Q3 1 5.8V 20 * * - + *NOT USED IN THE LTC4008-1 CLP ACP/SHDN 3 CONTROL BLOCK FAULT 5 TBAD OSCILLATOR 4 THERMISTOR 8 150k RT NTC 32.4k 10k NTC 0.47F C/10 FLAG 14 BATMON 397mV + 35mV 6 - GND - 11.67A 13 + CLN - 16 15 gm = 1.4m 11 CSP 20F 3k 9k CL1 100mV + gm = 1m - 0.1F 5k - 7 3k RSENSE CA1 RCL EA + CLP VFB gm = 1m BAT - + 1.19V 12 CA2 ICL 2 + DCIN OSCILLATOR WATCHDOG DETECT tOFF 20F 1.19V 9 + 1.28V - OV ITH 6K BUFFERED ITH /5 0.12F CLP 17 Q S R Q2 BGATE PGND 19 PWM LOGIC ICMP -+ - TGATE + Q1 CHARGE 18 IREV - 17mV L1 + 10 PROG 4.7nF RPROG 26.7k 4008 BD 4008fb 8 LTC4008 TEST CIRCUIT 7 VFB LTC4008 + VREF + EA - - 13 BATMON 11 CSP 12 BAT 9 90.325k ITH + LT1055 - 9.675k 0.6V 4008 TC OPERATION OVERVIEW The LTC4008 is a synchronous current mode PWM step down (buck) switcher 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 CSP and BAT pins. The final float voltage is programmed with an external resistor divider and the internal 1.19V reference voltage. Charging begins when the potential at the DCIN pin rises above the voltage at BAT (and the UVLO voltage) and the ACP/SHDN pin is high. An external thermistor network is sampled at regular intervals. If the thermistor value exceeds design limits, charging is suspended and the FAULT pin is set low. If the thermistor value returns to an acceptable value, charging resumes and the FAULT pin is set high. An external resistor on the RT pin sets the sampling interval for the thermistor. As 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 C/10 comparator will indicate this condition by latching the FLAG pin low. If this condition is caused by an input current limit condition, described below, then the FLAG indicator will be inhibited. 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. Forcing ACP/SHDN low, or removing the voltage from DCIN, will also clear the FLAG pin if it is low. Table 1. Truth Table For Indicator States MODE DCIN ACP/SHDN FLAG** FAULT** ICL Shutdown by low adapter voltage (Disabled on LTC4008-1) <BAT LOW HIGH HIGH LOW Normal charging >BAT HIGH HIGH HIGH* HIGH* Input current limited charging >BAT HIGH HIGH* HIGH* LOW Charger shut down due to thermistor out of range >BAT HIGH X LOW HIGH X Forced LOW HIGH HIGH LOW >BAT + <UVL HIGH HIGH HIGH* LOW Shut down by ACP/SHDN pin (USER) Shut down by undervoltage lockout *Most probable condition, **Open-drain output, HIGH = Open with pull-up, X = Don't care 4008fb 9 LTC4008 OPERATION Input FET (LTC4008) The input FET circuit performs two functions. It enables the charger if the input voltage is higher than the CLP 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 VCLP , 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 external 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 CLP drops to less than 25mV, the input FET is turned off slowly. If the voltage between DCIN and CLP 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. Input FET (LTC4008-1) The input FET circuit is disabled for the LTC4008-1. There is no low current shutdown mode when DCIN falls below the CLP pin. The ACP/SHDN pin functions only to shut down the charger. Battery Charger Controller The LTC4008 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 V -V = DCIN BAT VDCIN * fOSC to set the bottom MOSFET on time. This activity is diagrammed in Figure 1. OFF TGATE ON ON tOFF BGATE OFF TRIP POINT SET BY ITH VOLTAGE INDUCTOR CURRENT 4008 F01 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 RPROG at the PROG pin and adjusts ITH until: VREF V - V + 11.67A * 3.01k = CSP BAT RPROG 3.01k therefore, V 3.01k ICHARGE(MAX) = REF - 11.67A * RPROG RSENSE The voltage at BATMON is divided down by an external 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 PROG will decrease in direct proportion. The voltage at PROG is then given by: VPROG = (ICHARGE * RSENSE + 11.67A * 3.01k) * RPROG 3.01k The accuracy of VPROG will range from 0% to ITOL. VPROG is plotted in Figure 2. The amplifier CL1 monitors and limits the input current, normally from the AC adapter to a preset level (100mV/RCL). At input current limit, CL1 will decrease the ITH voltage, thereby reducing charging current. The ICL indicator output will go low when this condition is detected and the FLAG indicator will be inhibited if it is not already low. 4008fb 10 LTC4008 OPERATION Charger Startup 1.2 1.19V 1.0 VPROG (V) 0.8 0.6 0.4 0.309V 0.2 0 0 20 40 60 80 ICHARGE (% OF MAXIMUM CURRENT) 100 4008 F02 Figure 2. VPROG vs ICHARGE If the charging current decreases below 10% to 15% of programmed current, while engaged in input current limiting, BGATE will be forced low to prevent the charger from discharging the battery. Audible noise can occur in this mode of operation. An overvoltage comparator guards against voltage transient overshoots (>7% of programmed value). In this case, both MOSFETs are turned off until the overvoltage condition is cleared. This feature is useful for batteries which "load dump" themselves by opening their protection switch to perform functions such as calibration or pulse mode charging. 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 (100mV/RSENSE). 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. LTC4008 R10 32.4k 8 RTH 10k NTC C7 0.47F CLK - NTC S1 + 60k + - - PWM Watchdog Timer There is a watchdog timer that observes the activity on the BGATE and TGATE pins. If TGATE stops switching for more than 40s, the watchdog activates and turns off the top MOSFET for about 400ns. The watchdog engages to prevent very low frequency operation in dropout which is a potential source of audible noise when using ceramic input and output capacitors. ~4.5V 45k + 15k D Q TBAD C 4008 F03 Figure 3 4008fb 11 LTC4008 OPERATION 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: 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 = 26s, tSAMPLE = 127.5 * 20 * RRT * 17.5pF = 6.7ms, for RRT = 150k for RRT = 150k 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 + R10 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, FAULT pin is set low and the timer will be suspended until TBAD returns to zero (see Figure 4). CLK (NOT TO SCALE) tHOLD VOLTAGE ACROSS THERMISTOR tSAMPLE COMPARATOR HIGH LIMIT VNTC COMPARATOR LOW LIMIT 4008 F04 Figure 4 4008fb 12 LTC4008 APPLICATIONS INFORMATION Charger Current Programming The basic formula for charging current is: ICHARGE(MAX) = VREF * 3.01k / RPROG - 0.035V RSENSE VREF = 1.19V. This leaves two degrees of freedom: RSENSE and RPROG. The 3.01k input resistors must not be altered since internal currents and voltages are trimmed for this value. Pick RSENSE by setting the average voltage between CSP and BAT to be close to 100mV during maximum charger current. Then RPROG can be determined by solving the above equation for RPROG. RPROG = VREF * 3.01k RSENSE * ICHARGE(MAX) + 0.035V Table 2. Recommended RSNS and RPROG Resistor Values IMAX (A) RSENSE () 1% RSENSE (W) RPROG (k) 1% 1.0 0.100 0.25 26.7 2.0 0.050 0.25 26.7 3.0 0.033 0.5 26.7 4.0 0.025 0.5 26.7 Charging current can be programmed by pulse width modulating RPROG with a switch Q1 to RPROG at a frequency higher than a few kHz (Figure 5). CPROG must be increased to reduce the ripple caused by the RPROG switching. The compensation capacitor at ITH will probably need to be LTC4008 PROG 10 CPROG RPROG RZ 102k 5V 0V Q1 2N7002 4008 F05 Figure 5. PWM Current Programming increased also to improve stability and prevent large overshoot currents during start-up conditions. Charging current will be proportional to the duty cycle of the switch with full current at 100% duty cycle and zero current when Q1 is off. Maintaining C/10 Accuracy The C/10 comparator threshold that drives the FLAG pin has a fixed threshold of approximately VPROG = 400mV. This threshold works well when RPROG is 26.7k, but will not yield a 10% charging current indication if RPROG is a different value. There are situations where a standard value of RSENSE will not allow the desired value of charging current when using the preferred RPROG value. In these cases, where the full-scale voltage across RSENSE is within 20mV of the 100mV full-scale target, the input resistors connected to CSP and BAT can be adjusted to provide the desired maximum programming current as well as the correct FLAG trip point. For example, the desired max charging current is 2.5A but the best RSENSE value is 0.033. In this case, the voltage across RSENSE at maximum charging current is only 82.5mV, normally RPROG would be 30.1k but the nominal FLAG trip point is only 5% of maximum charging current. If the input resistors are reduced by the same amount as the full-scale voltage is reduced then, R4 = R5 = 2.49k and RPROG = 26.7k, the maximum charging current is still 2.5A but the FLAG trip point is maintained at 10% of full scale. There are other effects to consider. The voltage across the current comparator is scaled to obtain the same values as the 100mV sense voltage target, but the input referred sense voltage is reduced, causing some careful consideration of the ripple current. Input referred maximum comparator threshold is 117mV, which is the same ratio of 1.4x the DC target. Input referred IREV threshold is scaled back to -24mV. The current at which the switcher starts will be reduced as well so there is some risk of boost activity. These concerns can be addressed by using a slightly larger inductor to compensate for the reduction of tolerance to ripple current. 4008fb 13 LTC4008 APPLICATIONS INFORMATION Battery Conditioning Table 3 Some batteries require a small charging current to condition them when they are severely depleted. The charging current is switched to a high rate after the battery voltage has reached a "safe" voltage to do so. Figure 6 illustrates how to do this 2-level charging. When Q1 is on, the charger current is set to maximum. When Q1 is off, the charging current is set to 10% of the maximum. R9 (k) 0.25% R8 (k) 0.25% 8.2 24.9 147 8.4 26.1 158 12.3 15 140 12.6 16.9 162 16.4 11.5 147 16.8 13.3 174 Soft-Start LTC4008 PROG 10 CPROG 0.0047F R1 26.7k Q1 2N7002 FLOAT VOLTAGE (V) R2 53.6k 4008 F06 Figure 6. 2-Level Current Programming Charger Voltage Programming A resistor divider, R8 and R9 (see Figure 10), programs the final float voltage of the charger. The equation for float voltage is (the input bias current of EA is typically -4nA and can be ignored): VFLOAT = VREF (1 + R8/R9) It is recommended that the sum of R8 and R9 not be less than 100k. Accuracy of the LTC4008 voltage reference is 0.8% at 25C, and 1% over the full temperature range. This leads to the possibility that very accurate (0.1%) resistors might be needed for R8 and R9. Actually, the temperature of the LTC4008 will rarely exceed 50C near the float voltage because charging currents have tapered to a low level, so 0.25% resistors will normally provide the required level of overall accuracy. Table 3 contains recommended values for R8 and R9 for popular float voltages. The LTC4008 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. Kemet T495 series of "Surge Robust" low ESR tantalums are rated for high surge conditions such as battery to ground. 4008fb 14 LTC4008 APPLICATIONS INFORMATION 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 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: 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 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 4 as a guide for selecting the correct inductor value for your application. Table 4 MAXIMUM AVERAGE CURRENT (A) INPUT VOLTAGE (V) MINIMUM INDUCTOR VALUE (H) 1 20 40 20% 1 >20 56 20% 2 20 20 20% 2 >20 30 20% 3 20 15 20% 3 >20 20 20% 4 20 10 20% 4 >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. 4008fb 15 LTC4008 APPLICATIONS INFORMATION 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 so the duty cycles for the top and bottom MOSFETs are given by: Synchronous Switch Duty Cycle = (VIN - VOUT)/VIN. 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 MOSFET power dissipations at maximum output current are given by: The diode may be omitted if the efficiency loss can be tolerated. Main Switch Duty Cycle = VOUT/VIN PMAIN = VOUT/VIN(IMAX)2(1 + T)RDS(ON) + k(VIN)2(IMAX)(CRSS)(fOSC) PSYNC = (VIN - VOUT)/VIN(IMAX)2(1 + T)RDS(ON) Where T 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 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 = QGD/VDS is usually specified in the MOSFET characteristics. 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 Pchannel efficiency generally improves with a larger MOSFET. Using asymmetrical MOSFETs may achieve cost savings or efficiency gains. Calculating IC Power Dissipation The power dissipation of the LTC4008 is dependent upon the gate charge of the top and bottom MOSFETs (QG1 & 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) + IQ) Example: VDCIN = 19V, fOSC = 345kHz, QG1 = QG2 = 15nC, IQ = 5mA PD = 292mW Adapter Limiting An important feature of the LTC4008 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 4008fb 16 LTC4008 APPLICATIONS INFORMATION used, with closed-loop feedback ensuring that adapter load current remains within limits. Amplifier CL1 in Figure 7 senses the voltage across RCL, connected between the CLP and CLN 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, CLN should be connected to CLP. Note that the ICL pin will be asserted when the voltage across RCL is 93mV, before the adapter limit regulation threshold. VIN LTC4008 CLP - CL1 16 15nF 100mV + RCL* CLN + 5k CIN TO SYSTEM LOAD 15 4008 F07 *RCL = 100mV ADAPTER CURRENT LIMIT Figure 7. Adapter Current Limiting Setting Input Current Limit To set the input current limit, you need to know the minimum wall adapter current rating. Subtract 7% 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 * 7%) LTC4008 R9 NTC 8 C7 RTH 4008 F08 Figure 8. Voltage Divider Thermistor Network Table 5. Common RCL Resistor Values ADAPTER RATING (A) RCL VALUE* () 1% RCL POWER DISSIPATION (W) RCL POWER RATING (W) 1.5 0.06 0.135 0.25 1.8 0.05 0.162 0.25 2 0.045 0.18 0.25 2.3 0.039 0.206 0.25 2.5 0.036 0.225 0.5 2.7 0.033 0.241 0.5 3 0.03 0.27 0.5 *Values shown above are rounded to nearest standard value. 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 8. 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) 4008fb 17 LTC4008 APPLICATIONS INFORMATION LTC4008 Example #2: 100k NTC R9 NTC 8 C7 R9A RTH 4008 F09 Figure 9. General Thermistor Network 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 9 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: 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 For NTC thermistors: R9 = 6 RTH(LOW) * RTH(HIGH)/(RTH(LOW) - RTH(HIGH)) R9A = 6 RTH(LOW) * RTH(HIGH)/(RTH(LOW) - 7 * RTH(HIGH)) Where 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)) Where RTH(HIGH) > 7 * RTH(LOW) 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) 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 = tHOLD/(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 = 150k C7 = 0.28F 0.27F (nearest value) 4008fb 18 LTC4008 APPLICATIONS INFORMATION 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. Generally, a 301k resistor will work for DCIN less than 15V. A 499k resistor is recommended for DCIN between 15V and 24V. Using the LTC4008-1 (Refer to Figure 10) The LTC4008-1 is intended for applications where the battery power is fully isolated from the charger and wall adapter connections. An example application is a system with multiple batteries such that the charger's output power passes through a downstream power path or selector system. Typically these systems also provide isolation and control the wall adapter power. To reduce cost in such systems, the LTC4008-1 removes the requirement for the wall adapter INFET function or blocking diode. Wall adapter or ACP detection is also removed along with micropower shutdown mode. Asserting of the SHDN pin only puts the charger into standby mode. Failure to isolate the battery power from ANY of the LTC4008-1 pins when wall adapter power is removed or lost will only drain the battery at the IC quiescent current rate. More specifically, high current is drawn from the DCIN, CLP and CLN pins. Suggested devices to isolate power from the charger include simple diodes, electrical or mechanical switches or power path control devices such as the LTC4412 low loss PowerPathTM controller. Because the switcher operation is continuous under nearly all conditions, precautions must be taken to prevent the charger from boosting the input voltage above maximum voltage values on the input capacitors or adapter. Z1 and Q3 will shut down the charger if the input voltage exceeds a safe value. 4008fb 19 LTC4008 APPLICATIONS INFORMATION DCIN 0V TO 28V C1 0.1F R8 140k 0.25% R12 100k ICL FAULT FLAG R10 32.4k 1% Z1 Q3 2N7002 R13 1.5k C7 0.47F THERMISTOR 10k NTC RCL 0.02 1% SYSTEM LOAD BATMON DCIN LTC4008-1 VFB VLOGIC R11 100k C4 15nF R1 4.99k 1% RT 150k R9 15k 0.25% R7 6.04k 1% C6 0.12F ICL CLP SHDN CLN FAULT TGATE FLAG BGATE NTC PGND RT CSP ITH BAT GND C2 20F L1 10H Q1 Q2 D2 RSENSE 0.025 1% Q4 D1 C3 20F R26 150k Li-Ion BATTERY R4 3.01k 1% R5 3.01k 1% PROG C5 0.0047F R6 28.7k 1% Q5 2N7002 CHARGE 4008 F10 D1: MBRS130T3 D2: SBM540 Q1: Si4431BDY Q2: FDC645N Q4: Si7423DN Z1 VALUE SIZED FOR ABSOLUTE MAXIMUM ADAPTER VOLTAGE Figure 10. Typical LTC4008-1 Application (12.3V/4A) 4008fb 20 LTC4008 APPLICATIONS INFORMATION 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 11.) 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 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. 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 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. 4008fb 21 LTC4008 APPLICATIONS INFORMATION DIRECTION OF CHARGING CURRENT SWITCH NODE L1 VBAT RSENSE VIN C2 HIGH FREQUENCY CIRCULATING PATH D1 C3 BAT 4008 F12 BAT CSP 4008 F11 Figure 11. High Speed Switching Path Figure 12. Kelvin Sensing of Charging Current PACKAGE DESCRIPTION GN Package 20-Lead Plastic SSOP (Narrow .150 Inch) (Reference LTC DWG # 05-08-1641) .337 - .344* (8.560 - 8.738) .045 p.005 20 19 18 17 16 15 14 13 12 .254 MIN .150 - .165 .0165 p.0015 11 .229 - .244 (5.817 - 6.198) .058 (1.473) REF .150 - .157** (3.810 - 3.988) .0250 BSC 1 RECOMMENDED SOLDER PAD LAYOUT .015 p .004 s 45o (0.38 p 0.10) .0075 - .0098 (0.19 - 0.25) 2 3 4 5 6 7 8 .0532 - .0688 (1.35 - 1.75) 9 10 .004 - .0098 (0.102 - 0.249) 0o - 8o TYP .016 - .050 (0.406 - 1.270) NOTE: 1. CONTROLLING DIMENSION: INCHES INCHES 2. DIMENSIONS ARE IN (MILLIMETERS) .008 - .012 (0.203 - 0.305) TYP .0250 (0.635) BSC 3. DRAWING NOT TO SCALE *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 GN20 (SSOP) 0204 4008fb 22 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. LTC4008 REVISION HISTORY (Revision history begins at Rev B) REV DATE DESCRIPTION B 7/10 Updated Figure 5 and Figure 6. PAGE NUMBER 13, 14 4008fb 23 LTC4008 TYPICAL APPLICATION NiMH/4A Battery Charger Q3 INPUT SWITCH DCIN 0V TO 20V C1 0.1F R8 147k 0.25% VLOGIC R11 100k R12 100k ICL ACP BATMON DCIN VFB INFET ICL LTC4008 CLP ACP/SHDN FAULT FLAG R10 32.4k 1% TGATE FLAG BGATE NTC PGND THERMISTOR 10k NTC RT 150k GND SYSTEM LOAD C2 20F L1 10H Q1 Q2 RSENSE 0.025 1% D1 C3 20F CSP BAT ITH R7 6.04k 1% RCL 0.02 1% CLN FAULT RT R9 C7 13.3k 0.47F 0.25% C4 0.1F R1 4.99k 1% R4 3.01k 1% R5 3.01k 1% PROG C5 0.0047F R6 26.7k 1% C6 0.12F NiMH BATTERY PACK CHARGING CURRENT MONITOR D1: MBRS130T3 Q1: Si4431BDY Q2: FDC645N 4008 TA02 RELATED PARTS PART NUMBER DESCRIPTION (R) COMMENTS LT 1511 3A Constant-Current/Constant-Voltage Battery Charger High Efficiency, Minimum External Components to Fast Charge Lithium, NIMH and NiCd Batteries LT1513 Sepic Constant- or Programmable-Current/ConstantVoltage Battery Charger Charger Input Voltage May be Higher, Equal to or Lower Than Battery Voltage, 500kHz Switching Frequency LT1571 1.5A Switching Charger 1- or 2-Cell Li-Ion, 500kHz or 200kHz Switching Frequency, Termination Flag LTC1628-PG 2-Phase, Dual Synchronous Step-Down Controller Minimizes CIN and COUT , Power Good Output, 3.5V VIN 36V LTC1709 Family 2-Phase, Dual Synchronous Step-Down Controller with VID Up to 42A Output, Minimum CIN and COUT , Uses Smallest Components for Intel and AMD Processors LTC1729 Li-Ion Battery Charger Termination Controller Trickle Charge Preconditioning, Temperature Charge Qualification, Time or Charge Current Termination, Automatic Charger and Battery Detection, and Status Output LT1769 2A Switching Battery Charger Constant-Current/Constant-Voltage Switching Regulator, Input Current Limiting Maximizes Charge Current LTC1778 Wide Operating Range, No RSENSETM Synchronous Step-Down Controller 2% to 90% Duty Cycle at 200kHz, Stable with Ceramic COUT LTC1960 Dual Battery Charger/Selector with SPI Interface Simultaneous Charge or Discharge of Two Batteries, DAC Programmable Current and Voltage, Input Current Limiting Maximizes Charge Current LTC3711 No RSENSE Synchronous Step-Down Controller with VID 3.5V VIN 36V, 0.925V VOUT 2V, for Transmeta, AMD and Intel Mobile Processors LTC4006 Small, High Efficiency, Fixed Voltage, Lithium-Ion Battery Charger with Termination Complete Charger for 3- or 4-Cell Li-Ion Batteries, AC Adapter Current Limit and Thermistor Sensor, 16-Pin Narrow SSOP Package LTC4007 High Efficiency, Programmable Voltage Battery Charger with Termination Complete Charger for 3- or 4-Cell Li-Ion Batteries, AC Adapter Current Limit, Thermistor Sensor and Indicator Outputs LTC4100 Smart Battery Charger Controller SMBus Rev 1.1 Compliant 4008fb 24 Linear Technology Corporation LT 0710 REV B * PRINTED IN USA 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 FAX: (408) 434-0507 www.linear.com (c) LINEAR TECHNOLOGY CORPORATION 2003