LTC4006 4A, High Efficiency, Standalone Li-Ion Battery Charger DESCRIPTIO U FEATURES ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ 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: ±4% Accuracy Indicator Outputs for Charging, C/10 Current Detection and AC Adapter Present Charging Current Monitor Output 16-Pin Narrow SSOP Package U APPLICATIO S ■ ■ ■ ■ Notebook Computers Portable Instruments Battery-Backup Systems Standalone Li-Ion Chargers The LTC®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% voltage 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 the 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. The LTC4006 includes a thermistor sensor input that suspends charging if an unsafe temperature condition is detected and automatically resumes charging when the battery temperature returns to within safe limits. , LT, LTC and LTM are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners. Protected by U.S. Patents including 5723970. U TYPICAL APPLICATIO 4A Li-Ion Battery Charger DCIN 0V TO 28V 3A INPUT SWITCH 0.1µF 5k VLOGIC DCIN 100k CHG CHG INFET LTC4006 CLP ACP/SHDN ACP CHARGING CURRENT MONITOR 32.4k 0.0047µF THERMISTOR 10k NTC 0.47µF 309k TIMING RESISTOR (~2 HOURS) 6k 0.12µF CLN IMON TGATE NTC BGATE RT PGND ITH CSP GND BAT 15nF 0.033Ω TO SYSTEM LOAD 20µF 10µH 0.025Ω BATTERY 20µF 4006 TA01 4006fa 1 LTC4006 W U U U W W W ABSOLUTE MAXIMUM RATINGS PACKAGE/ORDER INFORMATION (Note 1) Voltage from DCIN, CLP, CLN, TGATE, INFET, ACP/SHDN, CHG to GND ....................... + 32V to – 0.3V Voltage from CLP to CLN ..................................... ±0.3V CSP, BAT to GND ................................... +28V to – 0.3V RT to GND ................................................. +7V to – 0.3V NTC ........................................................ +10V to – 0.3V Operating Ambient Temperature Range (Note 4) ............................................. – 40°C to 85°C Operating Junction Temperature ......... – 40°C to 125°C Storage Temperature Range ................. – 65°C to 150°C Lead Temperature (Soldering, 10 sec).................. 300°C ORDER PART NUMBER TOP VIEW DCIN 1 16 INFET CHG 2 15 BGATE ACP/SHDN 3 14 PGND RT 4 13 TGATE GND 5 12 CLN NTC 6 11 CLP ITH 7 10 BAT IMON 8 9 LTC4006EGN-2 LTC4006EGN-4 LTC4006EGN-6 GN PART MARKING 40062 40064 40066 CSP GN PACKAGE 16-LEAD PLASTIC SSOP TJMAX = 125°C, θJA = 110°C/W Order Options Tape and Reel: Add #TR Lead Free: Add #PBF Lead Free Tape and Reel: Add #TRPBF Lead Free Part Marking: http://www.linear.com/leadfree/ Consult LTC Marketing for parts specified with wider operating temperature ranges. ELECTRICAL CHARACTERISTICS The ● denotes specifications which apply over the full operating temperature range (Note 4), otherwise specifications are at TA = 25°C. VDCIN = 20V, VBAT = 12V unless otherwise noted. SYMBOL PARAMETER CONDITIONS MIN DCIN Operating Range IDCIN DCIN Operating Current Sum of Current from CLP, CLN, DCIN VTOL Voltage Accuracy (Note 2) LTC4006-6 LTC4006-6 LTC4006-2 LTC4006-2 LTC4006-4 LTC4006-4 ITOL TTOL Current Accuracy (Note 3) TYP 6 MAX UNITS 28 V 3 5 mA 8.4 8.4 12.6 12.6 16.8 16.8 8.467 8.484 12.700 12.726 16.935 16.968 V V V V V V ● 8.333 8.316 12.499 12.474 16.665 16.632 ● –4 –5 4 5 % % VBAT < 6V, VCSP – VBAT Target = 10mV – 60 60 % 6V ≤ VBAT ≤ VLOBAT, VCSP – VBAT Target = 10mV – 40 40 % –15 15 % 35 45 10 µA µA µA 5.5 V VCSP – VBAT Target = 100mV VBAT = 11.5V (LTC4006-2) VBAT = 7.6V (LTC4006-6) VBAT = 12V (LTC4006-4) ● ● Termination Timer Accuracy RRT = 270k ● Battery Leakage Current DCIN = 0V DCIN = 0V DCIN = 20V, VSHDN = 0V, VBAT = 12V ● ● –10 20 25 0 DCIN Rising, VBAT = 0V ● 4.2 4.7 ● 1 Shutdown UVLO Undervoltage Lockout Threshold Shutdown Threshold at ACP/SHDN DCIN Current in Shutdown VSHDN = 0V, Sum of Current from CLP, CLN, DCIN 2.5 2 3 V mA Current Sense Amplifier, CA1 Input Bias Current Into BAT Pin µA 11.67 CMSL CA1/I1 Input Common Mode Low ● CMSH CA1/I1 Input Common Mode High ● 0 V VCLN – 0.2 V 4006fa 2 LTC4006 ELECTRICAL CHARACTERISTICS The ● denotes specifications which apply over the full operating temperature range (Note 4), otherwise specifications are at TA = 25°C. VDCIN = 20V, VBAT = 12V unless otherwise noted. SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS 140 165 200 mV Current Comparators ICMP and IREV ITMAX Maximum Current Sense Threshold (VCSP – VBAT) ITREV Reverse Current Threshold (VCSP – VBAT) VITH = 2.5V ● – 30 mV Current Sense Amplifier, CA2 Transconductance 1 mmho Source Current Measured at ITH, VITH = 1.4V – 40 µA Sink Current Measured at ITH, VITH = 1.4V 40 µA 1.5 mmho Current Limit Amplifier Transconductance VCLP Current Limit Threshold ICLP CLP Input Bias Current ● 93 100 107 100 mV nA Voltage Error Amplifier, EA Transconductance Sink Current OVSD Measured at ITH, VITH = 1.4V Overvoltage Shutdown Threshold as a Percent of Programmed Charger Voltage 1 mmho 36 µA ● 102 107 110 % ● 0 0.17 0.25 V 25 50 Input P-Channel FET Driver (INFET) DCIN Detection Threshold (VDCIN – VCLN) DCIN Voltage Ramping Up from VCLN – 0.1V ● Forward Regulation Voltage (VDCIN – VCLN) Reverse Voltage Turn-Off Voltage (VDCIN – VCLN) DCIN Voltage Ramping Down ● – 60 – 25 INFET “On” Clamping Voltage (VDCIN – VINFET) IINFET = 1µA ● 5 5.8 INFET “Off” Clamping Voltage (VDCIN – VINFET) IINFET = – 25µA mV mV 6.5 V 0.25 V Thermistor NTCVR Reference Voltage During Sample Time 4.5 V High Threshold VNTC Rising ● NTCVR • 0.48 NTCVR • 0.5 NTCVR • 0.52 V Low Threshold VNTC Falling ● NTCVR • 0.115 NTCVR • 0.125 NTCVR • 0.135 V Thermistor Disable Current VNTC ≤ 10V 10 µA Indicator Outputs (ACP/SHDN, CHG) C10TOL C/10 Indicator Accuracy Voltage Falling at PROG ● 0.375 0.400 0.425 V LBTOL LOBAT Threshold Accuracy LTC4006-6 LTC4006-2 LTC4006-4 ● ● ● 4.70 7.27 9.70 4.93 7.5 10 5.14 7.71 10.28 V V V RESTART Threshold Accuracy LTC4006-6 LTC4006-2 LTC4006-4 ● ● ● 7.5 11.35 15.15 7.8 11.7 15.6 7.96 11.94 15.92 V V V VOL Low Logic Level of ACP/SHDN, CHG IOL = 100µA ● 0.5 V VOH High Logic Level of ACP/SHDN IOH = –1µA ● 2.7 ● 15 IPO Pull-Up Current on ACP/SHDN V = 0V IC10 C/10 Indicator Sink Current from CHG VOH = 3V IOFF Off State Leakage Current of CHG VOH = 3V Timer Defeat Threshold at CHG V µA –10 –1 1 25 38 µA 1 µA V 4006fa 3 LTC4006 ELECTRICAL CHARACTERISTICS The ● denotes specifications which apply over the full operating temperature range (Note 4), otherwise specifications are at TA = 25°C. VDCIN = 20V, VBAT = 12V unless otherwise noted. SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS 255 300 345 kHz Oscillator fOSC Regulator Switching Frequency fMIN Regulator Switching Frequency in Drop Out Duty Cycle ≥ 98% 20 25 kHz DCMAX Regulator Maximum Duty Cycle VCSP = VBAT 98 99 % Gate Drivers (TGATE, BGATE) VTGATE High (VCLN – VTGATE) ITGATE = –1mA 50 mV VBGATE High CLOAD = 3000pF 4.5 VTGATE Low (VCLN – VTGATE) CLOAD = 3000pF 4.5 5.6 10 V 5.6 10 V VBGATE Low IBGATE = 1mA 50 mV 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 (VCLN – VTGATE) ITGATE = –1µA, DCIN = 0V, CLN = 12V 100 mV VBGATE at Shutdown IBGATE = 1µA, DCIN = 0V, CLN = 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. Note 4: The LTC4006E is guaranteed to meet performance specifications from 0°C to 70°C. Specifications over the –40°C to 85°C operating temperature range are assured by design, characterization and correlation with statistical process controls. U W TYPICAL PERFOR A CE CHARACTERISTICS INFET Response Time to Reverse Current VOUT vs IOUT Vgs OF PFET (2V/DIV) –0.5 Id (REVERSE) OF PFET (5A/DIV) Id = 0A 1.25µs/DIV TEST PERFORMED ON DEMOBOARD LTC4006-2 VIN = 15VDC CHARGER = ON INFET = 1/2 Si4925DY ICHARGE = <10mA 4006 G01 300 –1.0 PWM FREQUENCY (kHz) Vs = 0V OUTPUT VOLTAGE ERROR (%) Vgs = 0 Vs OF PFET (5V/DIV) PWM Frequency vs Duty Cycle 350 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) 4006 G02 250 200 150 PROGRAMMED CURRENT = 10% 100 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) 4006 G03 4006fa 4 LTC4006 U W TYPICAL PERFOR A CE CHARACTERISTICS Disconnect/Reconnect Battery (Load Dump) Battery Leakage Current vs Battery Voltage 40 1A STEP VFLOAT 1V/(DIV) BATTERY LEAKAGE CURRENT (µA) 3A STEP 1A STEP 3A STEP LOAD STATE DISCONNECT RECONNECT VDCIN = 0V 35 30 25 20 15 10 5 0 LOAD CURRENT = 1A, 2A, 3A DCIN = 20V LTC4006-2 0 5 10 15 20 BATTERY VOLTAGE (V) 25 30 4006 G05 4006 G04 LTC4006-2 Efficiency with 15VDC VIN Efficiency at 19VDC VIN 100 100 LTC4006-4 95 95 EFFICIENCY (%) EFFICIENCY (%) LTC4006-2 90 85 80 90 85 80 75 75 0.50 1.00 1.50 2.00 2.50 CHARGING CURRENT (A) 3.00 4006 G07 0.50 1.00 1.50 2.00 2.50 CHARGING CURRENT (A) 3.00 4006 G08 U U U PI FU CTIO S DCIN (Pin 1): External DC Power Source Input. Bypass this pin with at least 0.01µF. 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 25µA 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 discon- nected 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 10µA 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 0.1µs. 4006fa 5 LTC4006 U U U PI FU CTIO S RT (Pin 4): Timer Resistor. The timer period is set by placing a resistor, RRT, to GND. 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. The timer period is tTIMER = (1hour • RRT/154k) If this resistor is not present, the charger will not start. 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. GND (Pin 5): Ground for low power circuitry. 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. 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. ITH (Pin 7): Control Signal of the Inner Loop of the Current Mode PWM. Higher ITH voltage corresponds to higher charging currrent in normal operation. A 6.04k resistor, in series with a capacitor of at least 0.1µF to GND, provides loop compensation. Typical full-scale output current is 40µA. Nominal voltage range for this pin is 0V to 3V. CLN (Pin 12): Negative Reference for the Input Current Limit Amplifier, CL1. This pin also serves as the power supply for the IC. A 10µF to 22µF 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. 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 V(IMON) = 1.19V when conditioning a depleted battery. Any current sourced or sinked from this pin directly affects the charging current accuracy. If this pin is to be monitored, a high impedance input buffer should be used. 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 11.67µA + VREF – + EA 3k 35mV – 10 BAT 9 CSP 7 ITH + LT1055 – 0.6V 4006 TC 4006fa 6 LTC4006 W BLOCK DIAGRA VIN DCIN 25µA 1 0.1µF INFET Q3 2 CHG 100k VLOGIC 5.8V 16 CLN ACP/SHDN 3 TIMER/CONTROLLER OSCILLATOR 4 THERMISTOR 6 RRT RT ICL TBAD RESTART 32.4k NTC 1.105V 10k NTC 0.47µF LOBAT 397mV C/10 35mV 708mV – 5 3k + GND 11.67µA 10 BAT RSENSE 9 gm = 1m – + 1.19V Ω 15nF CLN – 11 – Ω 9k CL1 100mV 12 gm = 1.5m + RCL CLP 3k CA1 EA 5.1k 20µF CSP + gm = 1m Ω – CA2 + DCIN OSCILLATOR WATCH DOG DETECT tOFF 7 1.28V Q1 TGATE 13 Q S R Q2 BGATE PGND 15 PWM LOGIC ÷5 CHARGE ICMP 6.04k BUFFERED ITH 0.12µF –+ 14 IREV – 17mV L1 ITH – OV + 20µF 1.19V IMON + 8 RIMON1 26.44k 4.7nF RIMON2 52.87k 4006 BD 4006fa 7 LTC4006 U 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. 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 25µA 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 15µA. 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 DCIN and CLN is ever less than – 25mV, then the input FET is turned off in less than 10µs 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. 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 OFF TGATE ON ON tOFF BGATE OFF TRIP POINT SET BY ITH VOLTAGE INDUCTOR CURRENT 4006 F01 Figure 1 4006fa 8 LTC4006 U OPERATIO Table 1. Truth Table for LTC4006 Operation MODE DCIN BAT VOLTAGE BAT CURRENT ACP/SHDN TIMER STATE CHG* Shut Down by Low Adapter Voltage Conditioning a Depleted Battery <BAT >BAT >UVLO <2.5V/Cell LOW HIGH Reset Running HIGH LOW Normal Charging >BAT >2.5V/Cell HIGH Running LOW Input Current Limited Charging >BAT >2.5V/Cell HIGH Running LOW Charger Paused Due to Thermistor Out of Range >BAT X Leakage 10% Programmed Current Programmed Current Programmed Current OFF HIGH Paused Shut Down by ACP/SHDN Pin Terminated by Low-Battery Fault (Note 1) >BAT >BAT X <2.5V/Cell OFF OFF Forced LOW HIGH Reset >T/4 Stopped Top-Off Charging. C/10 is Latched >BAT VFLOAT OFF HIGH Timer is Reset by C/10 Comparator (Latched), then Terminates After 1/4 T >BAT VFLOAT OFF HIGH Terminated by Expired Timer >BAT VFLOAT** OFF HIGH <T/4 After C/10 Comparator Trip. Running >T/4 After C/10 Comparator Trip. Stopped >T Stopped LOW or 25µA (Faulted) HIGH HIGH (Faulted) 25µA X X X X X HIGH (Waiting for Restart) HIGH (Waiting for Restart) Forced LOW >BAT and <UVL >BAT <UVL OFF HIGH Reset HIGH** 2.5V ≤ VBAT ≤3.9V (V/Cell) Programmed Current HIGH Running LOW 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 Note 1: If a depleted battery is inserted while the charger is in this state, the charger must be reset to initiate charging. compares this current against the desired current programmed by RIMON at the IMON pin and adjusts ITH until: The accuracy of VIMON will range from 0% to ITOL. therefore, ⎛ V ⎞ 3kΩ ICHARGE = ⎜ REF – 11.67µA⎟ • ⎝ 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 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 will 1.2 1.19V 1.0 0.8 VIMON (V) VREF V –V + 11.67µA • 3kΩ = CSP BAT RIMON 3kΩ 0.6 0.4 0.309V 0.2 0 R VIMON = (ICHARGE • RSENSE + 11.67µA • 3kΩ) • IMON 3kΩ 0 20 40 60 80 ICHARGE (% OF MAXIMUM CURRENT) 100 4006 F02 Figure 2. VIMON vs ICHARGE 4006fa 9 LTC4006 U OPERATIO Table 2. Truth Table for LTC4006 Operation (Supplemental) NUMBER FROM STATE TO STATE NEXT C/10 LATCH MAX BAT CURRENT ACP/SHDN TIMER STATE 1 Any MSD <BAT 0 OFF LOW Reset 2 MSD HIGH Charge Shutdown >BAT 0 OFF HIGH Reset HIGH 3 SD Shut Down by Undervoltage Lockout >BAT and <UVL OFF HIGH Reset HIGH** SD CONDITION Start Conditioning a Depleted Battery >BAT <2.5V/Cell 10% Programmed Current HIGH 5 CONDITION CONDITION Input Current Limited Condition Charging >BAT <2.5V/Cell <10% Programmed Current (Note 2) HIGH Running LOW 6 CONDITION CONDITION Conditioning a Depleted Battery >BAT <2.5V/Cell 10% Programmed Current HIGH Running LOW 7 CONDITION CONDITION Timer Defeated. (Low-Battery Conditioning Still Functional) >BAT <2.5V/Cell 10% Programmed Current HIGH Ignored Forced LOW 8 CONDITION SD Charger Paused Due to Thermistor Out of Range >BAT <2.5V/Cell OFF HIGH Paused LOW (Faulted) 9 CONDITION SD Timeout in CONDITION Mode >BAT <2.5V/Cell OFF HIGH >T/4 HIGH (Faulted) 10 CONDITION SD Shut Down by ACP/SHDN Pin >BAT <2.5V/Cell OFF Forced LOW Reset HIGH 11 CONDITION CHARGE Start Normal Charging >BAT >2.5V/Cell Programmed Current HIGH Running 12 CHARGE CHARGE Timer Defeated. (Low-Battery Conditioning Still Functional) >BAT >2.5V/Cell Programmed Current HIGH Ignored 13 SD CHARGE Restart >BAT 2.5V ≤ VBAT ≤ 3.9V (V/Cell) Programmed Current HIGH Reset 14 CHARGE CHARGE Top-Off Charging >BAT >3.9V/Cell Programmed Current HIGH Running LOW 15 CHARGE CHARGE C/10 Latch is SET when Battery Current is Less Than 10% of Programmed Current >BAT >2.5V/Cell Programmed Current HIGH Reset 25µA 16 CHARGE CHARGE Top-Off Charging >BAT >3.9V/Cell Programmed Current HIGH Running 25µA 17 CHARGE CHARGE Input Current Limited Charging >BAT >2.5V/Cell <Programmed Current (Note 2) HIGH 18 CHARGE SD Charger Paused Due to Thermistor Out of Range >BAT >2.5V/Cell OFF HIGH Paused LOW or 25µA (Faulted) 19 CHARGE SD Shut Down by ACP/SHDN Pin >BAT >2.5V/Cell 0 OFF Forced LOW Reset HIGH 20 CHARGE SD Terminated by Low-Battery Fault (Note 1) >BAT <2.5V/Cell 0 OFF HIGH >T/4 then Reset HIGH (Faulted) 21 CHARGE SD Terminates After 1/4 T >BAT VFLOAT 1 OFF HIGH >T/4 then Reset HIGH 22 CHARGE SD Terminates After T >BAT VFLOAT** 0 OFF HIGH >T/4 then Reset HIGH MODE DCIN Shut Down by Low Adapter Voltage SD SD, CONDITION, CHARGE 4 BAT VOLTAGE Note 1: If a depleted battery is inserted while the charger is in this state, the charger must be reset to initiate charging. Note 2: See section on “Adapter Limiting”. Note 3: The information contained in this table is supplemental to the LTC4006 data sheet and has not been production qualified. Note 4: Blank fields indicate no change, not considered, or other states impact value. *Open Drain. High when used with pull-up resistor. ** Most probable condition. PRESENT C/10 LATCH 0 0 0 1 1 CHG* LOW Forced LOW LTC4006: State Diagram (Supplemental) 1 MASTER SHUTDOWN ANY 2 SHUTDOWN 4 13 5, 6, 7 3, 8, 9, 10 3, 18, 19, 20, 21, 22 CONDITION 11 CHARGE 12, 14, 15, 16, 17 4006 F15 4006fa 10 LTC4006 U OPERATIO be inhibited if it is not already active. 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. LTC4006 R9 32.4k – 6 RTH 10k NTC C7 0.47µF CLK NTC S1 + 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. 60k + – – 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 100µs. 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: 45k + As the voltage at BAT increases to near the input voltage at DCIN, the converter will attempt to turn on the top MOSFET continuously (“dropout’’). A watchdog timer detects this condition and forces the top MOSFET to turn off for about 300ns at 40µs intervals. This is done to prevent audible noise when using ceramic capacitors at the input and output. Charger Startup ~4.5V 15k D TBAD Q C 4006 F03 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 = 54µs, 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 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: VOLTAGE ACROSS THERMISTOR COMPARATOR HIGH LIMIT VNTC COMPARATOR LOW LIMIT 4006 F04 VRTH(FINAL) 4.5V • RTH = RTH + R9 Figure 4 4006fa 11 LTC4006 U W U U APPLICATIO S I FOR ATIO Alternatively, a normally closed switch can be used to detect when the battery is present (see Figure 8). Charger Current Programming The basic formula for charging current is: 200 180 160 Table 3. Recommended RSENSE Resistor Values tTIMER (MINUTES) ICHARGE(MAX) 100mV = RSENSE 140 120 IMAX (A) RSENSE (Ω) 1% RSENSE (W) 1.0 0.100 0.25 2.0 0.050 0.25 3.0 0.033 0.5 40 4.0 0.025 0.5 20 Setting the Timer Resistor 100 80 60 0 100 150 200 250 300 350 400 450 500 RRT (kΩ) 4006 F05 The charger termination timer is designed for a range of 1 hour to 3 hours with a ±15% uncertainty. The timer is programmed by the resistor RRT using the following equation: tTIMER = 10 • 227 • RRT • 17.5pF (Refer to Figure 5) (seconds) 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. Figure 5. tTIMER vs RRT 3.3V LTC4006 VDD µP OUT IN 200k 33k CHG 2 4006 F06 Figure 6. Microprocessor Interface 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 100µA. When the charge current drops to 10% of the full-scale current (C/10), the N-channel MOSFET is turned off and a weak 25µA 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. LTC4006 ADAPTER POWER 1 DCIN 470k 3 ACP/SHDN 4006 F07 SWITCH CLOSED IF BATTERY CONNECTED Figure 7 ADAPTER POWER LTC4006 1 DCIN 3 ACP/SHDN 4006 F08 SWITCH OPEN WHEN BATTERY CONNECTED Figure 8 4006fa 12 LTC4006 U W U U APPLICATIO S I FOR ATIO Soft-Start The LTC4006 is soft started by the 0.12µF 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 40µA 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 0.12µF 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 1µF 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 20µF) 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 = 10µH, 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 0.2Ω and the battery impedance is raised to 4Ω 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 10µH 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. 4006fa 13 LTC4006 U W U U APPLICATIO S I FOR ATIO Table 4 MAXIMUM AVERAGE CURRENT (A) INPUT VOLTAGE (V) MINIMUM INDUCTOR VALUE (µH) 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. 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: 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 is nearly 100%. The term (1 + δ∆T) is generally given for a MOSFET in the form of a normalized RDS(ON) vs temperature curve, but δ = 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. Main Switch Duty Cycle = VOUT/VIN The diode may be omitted if the efficiency loss can be tolerated. Synchronous Switch Duty Cycle = (VIN – VOUT)/VIN. Calculating IC Power Dissipation The MOSFET power dissipations at maximum output current are given by: PMAIN = VOUT/VIN(I2MAX)(1 + δ∆T)RDS(ON) + k(V2IN)(IMAX)(CRSS)(fOSC) PSYNC = (VIN – VOUT)/VIN(I2MAX)(1 + δ∆T)RDS(ON) Where δ 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 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) 4006fa 14 LTC4006 U W U U APPLICATIO S I FOR ATIO Example: VDCIN = 19V, fOSC = 345kHz, QG1 = QG2 = 15nC. PD = 292mW IDCIN = 5mA 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 5kΩ and 15nF is required to eliminate switching noise. If the current limit is not used, CLP should be connected to CLN. 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 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%) 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 Figure 9). Designing the Thermistor Network LTC4006 100mV – + CLP 11 15nF CL1 5k + RCL* CLN 12 *RCL = 100mV ADAPTER CURRENT LIMIT + CIN AC ADAPTER INPUT VIN TO SYSTEM LOAD 4006 F09 Figure 9. Adapter Current Limiting 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 Table 5. Common RCL Resistor Values ADAPTER RATING (A) –7% ADAPTER RATING (A) RCL VALUE* (Ω) 1% RCL LIMIT (A) RCL POWER DISSIPATION (W) RCL POWER RATING (W) 1.5 1.40 0.068 1.47 0.15 0.25 1.8 1.67 0.062 1.61 0.16 0.25 2.0 1.86 0.051 1.96 0.20 0.25 2.3 2.14 0.047 2.13 0.21 0.25 2.5 2.33 0.043 2.33 0.23 0.50 2.7 2.51 0.039 2.56 0.26 0.50 3.0 2.79 0.036 2.79 0.28 0.50 3.3 3.07 0.033 3.07 0.31 0.50 3.6 3.35 0.030 3.35 0.33 0.50 4.0 3.72 0.027 3.72 0.37 0.50 * Rounded to nearest 5% standard step value. Many non-standard values are popular. 4006fa 15 LTC4006 U W U U APPLICATIO S I FOR ATIO LTC4006 LTC4006 R9 NTC 6 R9 NTC 6 C7 RTH C7 R9A 4006 F10 4006 F11 Figure 10. Voltage Divider Thermistor Network 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)) 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) > 7RTH(LOW) Example #1: 10kΩ NTC with custom limits TLOW = 0°C, THIGH = 50°C RTH = 10k at 25°C, RTH(LOW) = 32.582k at 0°C RTH(HIGH) = 3.635k at 50°C R9 = 24.55k → 24.3k (nearest 1% value) R9A = 99.6k → 100k (nearest 1% value) Example #2: 100kΩ NTC TLOW = 5°C, THIGH = 50°C RTH = 100k at 25°C, RTH(LOW) = 272.05k at 5°C RTH(HIGH) = 33.195k at 50°C R9 = 226.9k → 226k (nearest 1% value) R9A = 1.365M → 1.37M (nearest 1% value) Example #3: 22kΩ PTC TLOW = 0°C, THIGH = 50°C RTH Figure 11. General Thermistor Network RTH = 22k at 25°C, RTH(LOW) = 6.53k at 0°C RTH(HIGH) = 61.4k at 50°C 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 = 0.57µF → 0.56µF (nearest value) 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 10µA with the minimum voltage applied to DCIN and 10V at NTC. Do not exceed 30µA into NTC. Generally, a 301k resistor will work for DCIN less than 15V. A 499k resistor is recommended for DCIN between 15V and 24V. Optional Simple Battery Discharge Path Circuit It is NOT recommended that one permit battery current to flow backwards through RSENSE, inductor and out the TGATE MOSFET internal diode to reach VOUT. The TGATE MOSFET is off when VIN < VBAT. Figure 12 shows an optional high efficiency discharge path for the battery such that VOUT power comes from lossless “diode or” of VIN and VBAT. Normally when VIN > VBAT, P-channel MOSFET Q1B VGS = 4006fa 16 LTC4006 U W U U APPLICATIO S I FOR ATIO selection. If the VIN supply is going to collapse very slowly such that Q1B is not turned on quickly enough for the given load and stay within its PD limits, you should install a suitable Schottky diode in parallel with Q1B. 100k VIN Q1A PCB Layout Considerations VOUT ZENER 18V TGATE Q1B INDUCTOR RSENSE VBAT 4006 F12 Figure 12. Optional Simple High Efficiency Battery Discharge Path 0V keeping Q1B in the off state while P-channel MOSFET Q1A is on. If VIN were to suddenly go away, Q1B internal diode will provide a passive but instant discharge path for battery current to reach VOUT and hold up the load. Q1B internal diode has the same current rating as the FET itself, but has a very high Vf of about a volt such that heat will quickly build up in Q1B if left alone. However as VIN’s voltage falls below VBAT by Q1B’s VGS threshold, Q1B will then turn on shorting out its internal diode removing both the heat and voltage losses created by the diode. When VIN falls to zero volts, Q1B gate will be driven to the same voltage as VBAT providing the lowest possible RDSON value. A zener diode along with a 100k resistor in series with the Q1B gate protects the gate from any hazardous voltage spikes that can exceed Q1B maximum permissible VGS voltage. The zener voltage rating must be less than Q1B VGS(MAX) voltage but greater than VBAT. Since Q1A and Q1B are always at opposite states and share the same load, it is often advantagous to combine both FETs into a single package and save PCB space. The PD rate of the FET that is on is enhanced when the other FET is off. The choice of a combined Q1 should take into account the highest load current conditions of both paths and choose whichever is greater as the driving force behind the MOSFET 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 13.) 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. SWITCH NODE L1 VBAT VIN C2 HIGH FREQUENCY CIRCULATING PATH D1 C3 BAT 4006 F13 Figure 13. High Speed Switching Path 4006fa 17 LTC4006 U W U U APPLICATIO S I FOR ATIO 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. 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 0Ω resistor to tie analog ground to system ground. 5. Place output capacitors next to the sense resistor output and ground. 10. If possible, place all the parts listed above on the same PCB layer. 6. Output capacitor ground connections need to feed into same copper that connects to the input capacitor ground before tying back into system ground. 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. 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. 9. A good rule of thumb for via count for a given high current path is to use 0.5A per via. Be consistent. 12. For best current programming accuracy provide a Kelvin connection from RSENSE to CSP and BAT. See Figure 13 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 4006 F14 CSP BAT Figure 14. Kelvin Sensing of Charging Current 4006fa 18 LTC4006 U PACKAGE DESCRIPTION GN Package 16-Lead Plastic SSOP (Narrow .150 Inch) (Reference LTC DWG # 05-08-1641) .189 – .196* (4.801 – 4.978) .045 ± .005 16 15 14 13 12 11 10 9 .254 MIN .009 (0.229) REF .150 – .165 .229 – .244 (5.817 – 6.198) .0165 ± .0015 .150 – .157** (3.810 – 3.988) .0250 BSC RECOMMENDED SOLDER PAD LAYOUT 1 .015 ± .004 × 45° (0.38 ± 0.10) .007 – .0098 (0.178 – 0.249) 2 3 4 5 6 7 .0532 – .0688 (1.35 – 1.75) 8 .004 – .0098 (0.102 – 0.249) 0° – 8° 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 GN16 (SSOP) 0204 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 4006fa 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. 19 LTC4006 U TYPICAL APPLICATIO 2A Li-Ion Battery Charger Q3 INPUT SWITCH DCIN 0V TO 20V 2.5A C1 0.1µF VLOGIC 1 R3 100k 2 CHG 3 ACP CHARGING CURRENT MONITOR 8 R9 32.4k 6 4 THERMISTOR 10k NTC C5 0.0047µF C7 0.47µF RT 309k TIMING RESISTOR (~2 HOURS) 7 R4 6.04k C6 0.12µF 5 16 INFET LTC4006 11 CHG CLP 12 CLN ACP/SHDN 13 TGATE IMON 15 BGATE NTC 14 PGND RT 9 CSP ITH 10 BAT GND DCIN D1: MBRM140T3 Q1, Q2: Si7501DN Q3: Si5435B R1 5k C4 15nF RCL 0.04Ω TO SYSTEM LOAD C2 20µF Q1 L1 22µH 2A RSENSE 0.05Ω BATTERY Q2 D1 C3 20µF 4006 TA02 RELATED PARTS PART NUMBER LT1511 DESCRIPTION 3A Constant-Current/Constant-Voltage Battery Charger LT1513 SEPIC Constant- or Programmable-Current/ConstantVoltage Battery Charger 2-Phase, Dual Synchronous Step-Down Controller with VID Dual Battery Charger/Selector LTC1709 LTC1760/ LTC1960 LTC1778 LTC3711 LTC3728 LTC4002 LTC4007 LTC4008 Wide Operating Range, No RSENSETM Synchronous Step-Down Controller No RSENSE Synchronous Step-Down Controller with VID 2-Phase, Dual Synchronous Step-Down Controller Li-Ion Battery Charger Controller High Efficiency, Programmable Voltage, Battery Charger with Termination High Efficiency, Programmable Voltage/Current Battery Charger LTC4100 Smart Battery Charger Controller LTC4412 PowerPathTM Ideal Diode or 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 Up to 42A Output, Minimum CIN and COUT, Uses Smallest Components for Intel and AMD Processors Simultaneous Charge or Discharge of Two Batteries, DAC Programmable Current and Voltage, Input Current Limiting Maximizes Charge Current 2% to 90% Duty Cycle at 200kHz, Stable with Ceramic COUT 3.5V ≤ VIN ≤ 36V, 0.925V ≤ VOUT ≤ 2V, for Transmeta, AMD and Intel Mobile Processors Minimizes CIN and COUT, Power Good Output, 3.5V ≤ VIN ≤ 36V 1- and 2-Cell Li-Ion Batteries, VIN ≤ 22V, 500kHz Switching Frequency, 3hr Charge Termination, IOUT ≤ 4A 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 SMBus (Rev 1.1) Compliant, 6.4V ≤ VIN ≤ 26V, SMBus Accelerator Minimizes Bus Errors Very Low Loss Replacement for OR’ing Diodes No RSENSE and PowerPath are trademarks of Linear Technology Corporation. 4006fa 20 Linear Technology Corporation 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com LT 0506 REV A • PRINTED IN USA © LINEAR TECHNOLOGY CORPORATION 2003