LTC1980 Combination Battery Charger and DC/DC Converter U FEATURES DESCRIPTIO ■ The LTC®1980 integrates PWM power control for charging a battery and converting the battery voltage to a regulated output or simultaneously charging the battery while powering a system load from an unregulated AC wall adapter. Combining these features into a single IC produces a smaller area and lower cost solution compared to presently available multi-IC solutions. The LTC1980 shares the discrete components for both the battery charger and the DC/DC converter thus minimizing size and cost relative to dual controller solutions. Both the battery charger and DC/DC converter use a current mode flyback topology for high efficiency and excellent transient response. Optional Burst Mode operation and power-down mode allow power density, efficiency and output ripple to be tailored to the application. ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ Single Controller IC Includes Battery Charger Plus DC/DC Converter Wall Adapter Voltage May be Above or Below Battery Voltage LDO Controller Allows Simultaneous Charging and Regulating from Wall Adapter Input Standalone Li-Ion Battery Charger Including Charge Termination, Overvoltage Protection, Shorted-Cell Detection and Battery Recharge Selectable 4.1V, 4.2V, 8.2V and 8.4V Float Voltages Simple NiMH and NiCd Battery Charger Pin Programmable Regulator Burst Mode® Operation and Shutdown for High Efficiency High Efficiency Current Mode 300kHz PWM Reduced Component Architecture Undervoltage Protection and Soft-Start Ensures Start-Up with Current Limited Wall Adapter Small 24-Pin SSOP Package The LTC1980 provides a complete Li-Ion battery charger with charge termination timer, preset Li-Ion battery voltages, overvoltage and undervoltage protection, and userprogrammable constant-current charging. Automatic battery recharging, shorted-cell detection, and open-drain C/10 and wall plug detect outputs are also provided. User programming allows NiMH and NiCd battery chemistries to be charged as well. U APPLICATIO S ■ ■ ■ Digital Cameras Handheld Computers Personal Digital Assistants 1W to 10W Uninterruptable Power Supplies , LTC and LT are registered trademarks of Linear Technology Corporation. Burst Mode is a registered trademark of Linear Technology Corporation. Patents Pending. U ■ TYPICAL APPLICATIO Li-Ion Charger and DC/DC Converter Using One IC 3.3V Regulator Efficiency vs Load Current POWER FLOW 90 CHARGING BATTERY OPERATION Li-Ion BATTERY UNREGULATED WALL ADAPTER INPUT (3V TO 10V) • BAT-FET • EFFICIENCY (%) SYSTEM POWER 85 REG-FET LDO/ SWITCH SYSTEM LOAD DC/DC CONVERTERS LTC1980 1980 TA01 3.3V 80 75 70 VBAT = 3.6V TA = 25°C FIGURE 5 65 1.8V 1.5V 60 10 100 LOAD CURRENT (mA) 1000 1980 G04 1980f 1 LTC1980 W W W AXI U U U W PACKAGE/ORDER I FOR ATIO U ABSOLUTE RATI GS (Note 1) VREG to GND ............................................. –0.5V to 12V VBAT to GND ............................................. –0.5V to 12V PROG, ISENSE .............................................. –0.5V to 5V PROGT, REGFB, VC, BATT1, BATT2 TIMER, SS ............................................ –0.5V to VBIAS2 LDOFB, LDODRV .................................... –0.5V to VREG WA, VBIAS1, REG ....................................... –0.5V to 12V MODE ................................................... –0.5V to VBIAS1 VBIAS2 ......................................................... –0.5V to 5V OVP ............................................................ –0.5V to 5V PGND to GND .................................... Connect Together Operating Ambient Temperature Range (Note 2) ................................................. – 40°C to 85°C Storage Temperature Range ................. – 65°C to 125°C Lead Temperature (Soldering, 10 sec)................ 300°C ORDER PART NUMBER TOP VIEW PROG 1 24 SS PROGT 2 23 OVP REGFB 3 22 CAOUT VC 4 21 ISENSE LDOFB 5 20 GND LDODRV 6 19 VBIAS2 VREG 7 18 VBAT WA 8 17 TIMER BATT1 9 16 MODE BATT2 10 LTC1980EGN 15 REG RGTDR 11 14 BGTDR PGND 12 13 VBIAS1 GN PACKAGE 24-LEAD NARROW PLASTIC SSOP TJMAX = 125°C, θJA = 85°C/W Consult LTC Marketing for parts specified with wider operating temperature ranges. ELECTRICAL CHARACTERISTICS The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VBAT = 2.4V, VREG = 5V, VBAT unloaded. SYMBOL PARAMETER CONDITIONS MIN TYP VBAT Positive Supply Voltage, VBAT VREG Positive Supply Voltage, VREG VFB Feedback Voltage REGFB Tied to VC VPROGT Voltage on PROGT Pin PROGT Tied to VC IBURST Burst Mode Operation Supply Current, Quiescent, VREG Regulator Mode, REGFB = 1.5V IHIGH Supply Current, Quiescent, VREG Regulator Mode, REGFB = 0V ISHDN Supply Current in Shutdown Mode, VREG Mode = 0V VUVL Positive-Going Undervoltage Lockout Voltage From Either VBAT or VREG VUVHYS Undervoltage Lockout Hysteresis From Either VBAT or VREG ISS Soft-Start Ramp Current BATT1 = 0, BATT2 = 0, Charger Mode VFLOAT0 Output Float Voltage in Constant Voltage Mode BATT1 = 0, BATT2 = 0 ● 4.059 4.1 4.141 V VFLOAT1 Output Float Voltage in Constant Voltage Mode BATT1 = 1, BATT2 = 0 ● 4.158 4.2 4.242 V VFLOAT2 Output Float Voltage in Constant Voltage Mode BATT1 = 0, BATT2 = 1 (Note 3) ● 8.118 8.2 8.282 V VFLOAT3 Output Float Voltage in Constant Voltage Mode BATT1 = 1, BATT2 = 1 (Note 3) ● 8.316 8.4 8.484 V VFLOAT4 Output Float Voltage in Constant Voltage Mode BATT1 = Open, BATT2 = Don’t Care Measured from OVP Input ● 1.207 1.225 1.243 V VRCHG0 Recharge Threshold, Delta Voltage with Respect to Float Voltage BATT2 = 0, BATT1 = 0 or 1 200 mV VRCHG1 Recharge Threshold, Delta Voltage with Respect to Float Voltage BATT2 = 1, BATT1 = 0 or 1 400 mV 2.85 10 2.85 ● MAX UNITS V 10 V 1.194 1.225 1.256 V 1.194 1.225 1.256 V 0.75 ● 2.45 mA 2 4.3 mA 15 µA 2.7 2.85 V 100 mV 10 µA 1980f 2 LTC1980 ELECTRICAL CHARACTERISTICS The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VBAT = 2.4V, VREG = 5V, VBAT unloaded. SYMBOL PARAMETER CONDITIONS MIN TYP MAX VRCHG2 Recharge Threshold, Delta Voltage with Respect to Float Voltage, Measured at OVP BATT 1 = Open VLT0 Charger Shorted Cell Threshold BATT2 = 0 2.55 2.7 2.8 V VLT1 Charger Shorted Cell Threshold BATT2 = 1 5.2 5.4 5.65 V IBLDO Input Bias Current, Low Dropout Regulator Measured at LDOFB Pin 1.0 µA gmldo Transconductance, Low Dropout Regulator Measured from LDOFB to LDODRV 350 µmhos VOLLDO Output Low Voltage, Low Dropout Regulator VOHLDO Output High Voltage, Low Dropout Regulator IOUTLDO Low Dropout Regulator Output Current, Source/Sink AVOL Error Amplifier Open-Loop Voltage Gain IBEA Error Amplifier Input Bias Current –0.1 0.1 µA VOLEA Error Amplifier Output Low Voltage 0 0.5 V VOHEA Error Amplifier Output High Voltage 1.4 2 V IOUT Error Amplifier Output Source Current Error Amplifier Output Sink Current gmflt Float Voltage Error Amplifier Transconductance IBFLT Float Voltage Error Amplifier Input Current (Measured at OVP Input) VOS1 Current Amplifier Offset Voltage IBIS Input Bias Current, ISENSE Input AVCA Current Amplifier Voltage Gain RPROG PROG Pin On Resistance 400 Ω IPROG PROG Pin Leakage Current 100 nA fS Switching Frequency tr, tf Driver Output Transition Times CL = 15pF 10 ns tBREAK Driver Output Break Times VBAT = VREG = 10V 100 ns fTIMER Timer Frequency C = 1000pF 4.5 kHz ITIMER1 TIMER Pin Source Current –4 µA ITIMER2 TIMER Pin Sink Current 4 µA RREG REG On Resistance 68 Ω IREGPD REG Pull-Down Current IREGLK REG Leakage Current VVTHREG REG Logic Threshold VIL1 Digital Input Low Voltage, Negative-Going, Wall Adapter (WA) VREG = 5V 1.185 VIH1 Digital Input High Voltage, Positive-Going, Wall Adapter (WA) VREG = 5V 1.195 VIL2 Digital Input Low Voltage, BATT1 VIH2 Digital Input High Voltage, BATT1 60 mV 0.1 VREG – 0.1 From REGFB to VC SS = Open V µA 60 dB mA mA 65 µmhos –0.1 0.1 µA –6 6 mV 2.55 V/V –100 Measured from ISENSE to CAOUT Pin 2.3 ● V ±20 0.5 –1.2 Measured from OVP to SS, Charger Mode, BATT1 = Open UNITS 260 2 2.44 300 5 µA 340 9 60 0.3 µA nA 1.3 V 1.221 1.247 V 1.226 1.257 V 100 VBIAS2 –100 kHz mV V 1980f 3 LTC1980 ELECTRICAL CHARACTERISTICS The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C.VBAT = 2.4V, VREG = 5V, VBAT unloaded. SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS VP2 Digital Input Pull-Up Voltage, BATT1 BATT1 Input Floating VIL3 Digital Input Low Voltage, BATT2 0.3 V VIH3 Digital Input High Voltage, BATT2 II1 Digital Input Current, WA –5 5 µA II2 Digital Input Current, BATT1 –10 10 µA II3 Digital Input Current, BATT2 –1 1 µA 1.6 V 2 Note 1: Absolute Maximum Ratings are those values beyond which the life of a device may be impaired. Note 2: The LTC1980E is guaranteed to meet performance specifications from 0°C to 70°C. Specifications over the –40°C to 85°C operating V temperature range are assured by design, characterization and correlation with statistical process controls. Note 3: TA = 0°C to 70°C. U W TYPICAL PERFOR A CE CHARACTERISTICS Switching Frequency Variance vs Temperature Regulator Load Regulation 1.2240 1.5 1.2235 1.0 –0.2 0.5 –0.4 1.2230 1.2225 1.2220 1.2215 1.2210 1.2205 –40 –15 10 35 TEMPERATURE (°C) 60 0 ∆VREG (%) FREQUENCY VARIANCE (%) FEEDBACK REFERENCE VOLTAGE (V) Feedback Reference Voltage vs Temperature 0 –0.8 –1.0 –1.0 –15 60 10 35 TEMPERATURE (°C) 90 90 85 85 80 80 75 70 VBAT = 3.6V TA = 25°C FIGURE 5 10 100 LOAD CURRENT (mA) –1.2 1000 1980 G04 0 100 500 200 300 400 LOAD CURRENT (mA) 1980 G03 5V Regulator Efficiency vs Load Current EFFICIENCY (%) EFFICIENCY (%) 3.3V Regulator Efficiency vs Load Current 60 85 1980 G02 1980 G01 65 –0.6 –0.5 –1.5 –40 85 VBAT = 4.2V VREG ≅ 3.3V TA = 25°C FIGURE 5 Regulator Load Step Response VREG 50mV/DIV 75 IL 500mA/DIV 70 VBAT = 3.6V TA = 25°C R8 = 309k FIGURE 5 65 60 10 100 LOAD CURRENT (mA) 1000 VBAT = 3.6V 100µs/DIV VREG ≅ 3.3V IL = 100mA TO 500mA TA = 25°C FIGURE 5 1980 G06 1980 G05 1980f 4 LTC1980 U W TYPICAL PERFOR A CE CHARACTERISTICS Typical ISENSE Waveforms, Regulator Typical BGTDR and RGTDR Waveforms Typical Operation with Burst Mode Operation Disabled VREG 50mV/DIV BGTDR 1V/DIV ISENSE 20mV/DIV PIN 21 FIGURE 5 ISENSE 50mV/DIV RGTDR 1V/DIV VBAT = 3.6V VREG = 3.3V TA = 25°C IL = 500mA 1980 G07 1µs/DIV VBAT = 3.6V VREG = 3.3V IL = 500mA TA = 25°C FIGURE 5 1µs/DIV 1980 G08 VREG 50mV/DIV VLDO 0.1V/DIV 1980 G10 200µs/DIV 1980 G09 VREG 1V/DIV VREG 1V/DIV BGTDR 2V/DIV 1µs/DIV Regulator Output Transient Response—Wall Adapter “Hot Plugged” Regulator Output Transient Response—Wall Adapter Removal Burst Mode Circuit Operation VBAT = 3.6V VREG = 3.3V IL = 10mA TA = 25°C FIGURE 5 VBAT = 3.6V VREG ≅ 3.3V IL = 500mA MODE = VBIAS1 TA = 25°C FIGURE 5 VLDO 0.5V/DIV VBAT = 3.6V 500µs/DIV VREG = 3.3V VLDO = 3.1V ILDO = 200mA VWALL ADAPTER = 6V TO 0V TA = 25°C FIGURE 5 1980 G11 VBAT = 3.6V 500µs/DIV VREG = 3.3V VLDO = 3.1V ILDO = 200mA VWALL ADAPTER = 0V TO 6V TA = 25°C FIGURE 5 1980 G12 Typical CTIMER Waveform Mode Pin Input Current vs VIN MODE PIN INPUT CURRENT (µA) 1.5 VBAT = 2.4V VREG = 5V 1.0 TA = 25°C 0.5 TIMER 100mV/DIV PIN 17 0 –0.5 –1.0 –1.5 CTIMER = 0.24µF TA = 25°C 0 0.5 1.0 1.5 2.0 MODE PIN VIN (V) 2.5 5ms/DIV 1980 G14 3.0 1980 G13 1980f 5 LTC1980 U U U PI FU CTIO S PROG (Pin 1): Charge Current Ratio Programming Pin. Programs the full charge current when the charger is in the constant current mode. A resistor placed between the PROG pin and the PROGT pin (Pin 2) determines the charge current. The PROG pin connects to an open drain MOSFET which turns on for full current and is off when trickle charging. PROGT (Pin 2): Trickle Charge Programming Pin. Programs the trickle charge current for a deeply discharged battery. Two resistors are used, one between the PROGT pin and CAOUT (Pin 22) and another from PROGT to ground. A capacitor between the PROGT pin and VC (Pin 4) provides compensation for the constant current feedback loop. REGFB (Pin 3): DC/DC Converter Feedback Pin. This pin is used to program the DC/DC converter output voltage when the LTC1980 is in the DC/DC (regulator) converter mode. An external resistor divider from VREG to REGFB to ground programs the output voltage. The virtual reference voltage (VREF) on this pin is 1.225V. A series RC from the REGFB pin to VC (Pin 4) provides pole-zero compensation for the regulator outer loop. VC (Pin 4): Control Signal of the Inner Loop of the Current Mode PWM. A common current mode loop is used by the battery charger and voltage regulator functions. Minimum duty factor (measured on BGTDR (Pin 14) in regulator mode and RGTDR (Pin 11) in charger mode) occurs at approximately 1V. Duty factor increases as VC increases. This part includes slope compensation, so there is some variation in VC for minimum and maximum duty factor as VREG or VBAT is varied. LDOFB (Pin 5): Low Dropout Regulator Feedback Pin. This pin is used to program the low dropout linear regulator output voltage. An external resistor divider from the output of the LDO regulator (drain of the external MOSFET) to LDOFB to ground programs the output voltage. The virtual reference voltage on this pin is 1.225V. LDODRV (Pin 6): Low Dropout Error Amplifier Output. This pin drives the gate of an external PMOS pass transistor. This pin is pulled up to VREG (shutting off the pass transistor) if MODE (Pin 16) is grounded or if undervoltage occurs. VREG (Pin 7): Connection Point to the DC/DC Converter Side of the Combo Charger/Converter Circuit. WA (Pin 8): Wall Adapter Comparator Input. An external resistor divider from the wall adapter output to WA to ground sets the threshold which determines if charging can occur. If the wall adapter is below this threshold, the LTC1980 assumes the wall adapter is not present and the charger shuts down. Wall adapter sense threshold is set higher than the DC/DC converter output voltage to insure correct operation. BATT1 (Pin 9): Logic Input Pin for Selecting Preprogrammed Li-Ion Charge Voltage. See Truth Table logic settings. BATT2 (Pin 10): Logic Input Pin for Selecting Preprogrammed Li-Ion Charge Voltage. The following combinations of BATT1 and BATT2 select the correct LiIon charge voltage. See Truth Table. BATT2 BATT1 FLOAT VOLTAGE 0 0 4.1V 0 1 4.2V 1 0 8.2V 1 1 8.4V Don’t Care Open Externally Set Via OVP Logic 1 = VBIAS2 (Pin 19), Logic 0 = GND RGTDR (Pin 11): DC/DC Converter (Regulator) Side Gate Drive Pin. This pin provides gate drive to the external MOSFET (REG-FET) that connects to VREG via the transformer. PGND (Pin 12): Power Ground. Refer to the Applications Information section for proper use of ground and power ground connections. VBIAS1 (Pin 13): Internally Generated Power Bus. Bypass this pin with a 1µF or larger ceramic capacitor (or other low ESR capacitor) to PGND (Pin 12). Do not connect any load to this pin. BGTDR (Pin 14): DC/DC Converter (Battery) Side Gate Drive Pin. This pin provides gate drive to the external MOSFET (BAT-FET) that connects to VBAT via the transformer. 1980f 6 LTC1980 U U U PI FU CTIO S REG (Pin 15): Bidirectional Regulator Mode Control Pin. A pull-up resistor is required between this pin and VBIAS2. This pin is open when charging normally, has a weak pulldown (approximately 5µA) when conditioning the battery and a strong pull-down when in regulator mode. Pulling this pin low forces the IC into regulator mode. MODE (Pin 16): Selects different operating modes in both charger and DC/DC converter configurations. Also enables and disables Burst Mode operation. See Mode Pin Operation table in Application section. TIMER (Pin 17): A timing capacitor on this pin determines the normal charge time for charge termination. C(µF) = 0.25 • Time (Hours) VBAT (Pin 18): This pin connects to the positive terminal of the battery and the battery side of the power converter. VBIAS2 (Pin 19): Internally Generated Voltage. Bypass this pin with a 1µF or larger ceramic capacitor (or other low ESR capacitor). Do not connect any load to this pin. GND (Pin 20): Signal Ground. This pin should Kelvinconnect to the current sense resistor (RSENSE). ISENSE (Pin 21): Current Sense Input Pin. Connects internally to a current amplifier and zero current comparator. This pin should Kelvin-connect to the current sense resistor (RSENSE) . CAOUT (Pin 22): Current Amplifier Output. A program resistor connects between this pin and PROGT (Pin 2) to set the charge current (in constant-current mode). OVP (Pin 23): Overvoltage Protection. This pin connects to the tap on an optional external voltage divider connected across the battery. This allows nonstandard float voltages to be used for the battery charger. Overvoltage, restart and undervoltage thresholds will also be affected by the external voltage division ratio. To use this pin, BATT1 (Pin 9) must float. SS (Pin 24): Soft-Start. A capacitor between this pin and ground sets the battery charge ramp rate. Battery charge current is very low the moment after the converter switches from DC/DC converter (regulator) mode to battery charger mode then ramps up to final battery charge current from there. This insures that the wall adapter is not loaded down with a large inrush current that could prevent correct battery charger operation. The same capacitor, which sets the soft-start ramp rate, also sets the compensation for the battery float voltage control loop. 1980f 7 LTC1980 W BLOCK DIAGRA VBIAS1 LDOFB LDODRV CAOUT 13 5 6 22 REF_UVL 21 ISENSE + – GM VREF VMAX VREF + VREF – VBIAS2 19 + I=O COMP – UVL VDD REG 7 + – + – VBAT 18 VREG REFERENCE + – VREF VREF SR_EN DIS MODE 16 L H MODE VM S H = BURST MODE OPERATION OFF OPEN = BURST MODE OPERATION ON L = DISABLE VC DUMP XFMR VREF OSC + VREG VBAT 4 AC 11 RGTDR Q RAMP R PWM COMP 14 BGTDR 12 PGND – PROGT 2 REGFB 3 BATT1 9 VREF + VREF – AC SLEEP EA + – WAKE BURST VREF + CONDITION BATTERY OVP 23 – BATT2 10 VREF + RECHARGE TIMEOUT TIMER SHORT CYCLE START – VREF 17 TIMER + – WA 8 5µA REG 15 VREF 1 PROG + GM – GND 20 REG 24 SS 1980 BD 1980f 8 LTC1980 U OPERATIO The LTC1980 is an IC designed to provide a regulated voltage to a system load from an unregulated or regulated wall adapter, or from a battery and also charge a battery, thereby providing an uninterruptable power source for the system. When the wall adapter is present it provides power to the system load and, if needed, a portion of the power can be used to simultaneously charge the battery. If the wall adapter is removed, the LTC1980 uses the battery as a power source to continue providing a regulated output voltage to power the system. Combining these two functions into a single IC reduces circuit area compared to presently available solutions (Figure 1). The unique bidirectional power converter topology (Figure 2) accounts for much of the area savings. A transformer based design allows the wall adapter voltage to be less than or greater than the battery voltage. The LTC1980 includes a 300kHz DC/DC PWM converter that operates in two modes. The first mode is when the wall adapter is present and the LTC1980 is used to charge the battery using a constant-current/constant-voltage charge scheme. The second mode is when the wall adapter is removed and the battery powers the LTC1980 and the DC/DC converter generates a regulated output voltage. Existing Methods CHARGE TERMINATION Using the LTC1980 BATTERY CHARGER FROM WALL ADAPTER FROM WALL ADAPTER LTC1980-BASED POWER DESIGN POWER ROUTING LOW DROPOUT REGULATOR PWM REGULATOR TO SYSTEM LOAD DC/DC CONVERTERS 1980 F01 TO SYSTEM LOAD DC/DC CONVERTERS Figure 1. Portable Power Systems WALL ADAPTER T1 Li-Ion BATTERY • BAT-FET ISENSE • REG-FET T1 Li-Ion BATTERY • BAT-FET SYSTEM LOAD DC/DC CONVERTERS RS ISENSE LTC1980 • REG-FET SYSTEM LOAD DC/DC CONVERTERS RS LTC1980 1980 F02a 1980 F02a (a) Battery Charger Mode (b) DC/DC Converter Mode (Wall Adapter Removed) Figure 2. LTC1980 Bidirectional Power Conversion 1980f 9 LTC1980 U OPERATIO Lithium-Ion Battery Charger Operation With the wall adapter power applied, the LTC1980 operates as a constant-current/constant-voltage PWM battery charger, with a portion of the adapter current used for charging and the rest flowing to the system load through an optional low dropout regulator. A charge cycle begins when the voltage at VREG exceeds the undervoltage lockout threshold level and the IC is enabled via the MODE pin. If the battery has been deeply discharged and the battery voltage is less than 2.7V, the charger will begin with the programmed trickle charge current. When the battery exceeds 2.7V, the charger begins the constant-current portion of the charge cycle with the charge current equal to the programmed level. As the battery accepts charge, the voltage increases. When the battery voltage reaches the recharge threshold, the programmable timer begins. Constant-current charging continues until the battery approaches the programmed charge voltage of 4.1V or 4.2V/cell at which time the charge current will begin to drop, signaling the beginning of the constant-voltage portion of the charge cycle. The charger will maintain the programmed preset float voltage across the battery until the timer terminates the charge cycle. During trickle charging, if the battery voltage remains below 2.7V for 1/4 of the total programmed charge time, the battery may be defective and the charge cycle ends. Also, if a battery open circuit is detected, the charge cycle ends immediately. The charger can be shut down by pulling the REG pin low, although the timer will continue until it times out. Power Converter Operation from Battery When the AC adapter is removed, the LTC1980 operates as a DC/DC PWM converter using the battery for input power to provide a regulated output voltage for the system load. The LTC1980 is a current mode switcher. This means that the switch duty cycle is directly controlled by switch current rather than by output voltage or current. Battery charger operation will be described for the simplified diagram (Figure 3). At the start of the oscillator cycle, latch U9 is set causing M2 to turn on. When switch current reaches a predetermined level M2 turns off and M1 turns on. This level is set by the control voltage at the output of error amplifier U10. U1 VOLTAGE SELECTION B1 VREG T1 C1 SN1 SNUBBER NETWORK BDRIVE U4 DRIVERS R1 – U2 R2 RDRIVE M1 M2 WALL ADAPTER C2 SN2 SNUBBER NETWORK + + + C6 R12 – VBAT TO SYSTEM LOAD DIRECTION SENSE TYPICAL WAVEFORM – U5 + R4 + ZC VREF CURRENT AMPLIFIER VREF U7 OSC R5 S R + + U6 – R13 U9 Q U8 – – R6 SW1 PWM C3 R7 – R8 SW2 SW3 + C4 U10 R10 – R9 EA R11 U12 C5 + U11 REFERENCE VREF 1980 F03 Figure 3. Simplified Diagram—Power Converter 1980f 10 LTC1980 U OPERATIO Transformer current is sensed across RS, gained up via U6 and sampled through switch SW1. The current in R7 is a scaled-down replica of the battery charging current pulses from the transformer. During battery charging, switch SW2 is in the down position connecting R7, R8, R9 and C4 to the inverting input of amplifier U10 forming an integrator which closes the outer loop of the converter and establishes constant current charging. U12 is a gm amplifier that clamps U10 as the battery float voltage is reached. R10 and R11 set the float voltage and C5 compensates this loop and provides a soft-start function. DC/DC Converter Operation When the LTC1980 is operating as a DC/DC converter, M1 turns on at the start of the oscillator cycle. When transformer current reaches a predetermined level set by U10’s output voltage, M1 turns off and M2 turns on. SW2 is in the up position forming an integrator with zero, which compares the output voltage (via R1 and R2 to reference U11 establishing the output voltage. U W U U APPLICATIO S I FOR ATIO Setting Battery Charge Current Referring to the simplified schematic in Figure 4, the average current through R7 must equal the current through RTRKL with switch SW3 open. This leads to the equation for setting the trickle charge current: RTRKL = VREF • R7 ITRICKLE • RS • A V where AV = 2.44 and VREF = 1.225V. The suggested value for R7 is 10k. Setting the Float Voltage Pin selectable 4.1V, 4.2V, 8.2V, and 8.4V Li-Ion float voltages are available. Other float voltages may be set via external resistors. The following combinations of logic inputs BATT1 and BATT2 determine the float voltage. Normal charge current is set via the parallel combination of RTRKL and RCHRG which leads to the following equation for RCHRG BATT2 BATT1 FLOAT VOLTAGE 0 0 4.1V 0 1 4.2V 1 0 8.2V VREF • R7 1 1 8.4V Don’t Care Open Externally Set via OVP RCHRG = (INORMAL – ITRICKLE) • RS • A V where logic 0 = GND and logic 1 = VBIAS2 (Pin 19) VREF 1.225V ISENSE 21 I + U6 AV = 2.44 RS 20 – R7 10k SW1 2 VC U10 PROGT 22 CAOUT C4 + 4 – RCHRG RTRKL GND PROG 1 SW3 20 1980 F04 Figure 4. Battery Charger Current Control Loop 1980f 11 LTC1980 U W U U APPLICATIO S I FOR ATIO An external resistor divider (Figure 3) can be used to program other float voltages. Resistor values are found using the following equation: R10 = R11 • (VFLOAT – VREF)/VREF where VREF = 1.225V. The suggested value for R11 is 100k. Use 1% or better resistors. Setting DC/DC Converter Output Voltage From Figure 5, select the following resistors based on output voltage VREG: R8 = R14 • (VREG – VREF)/VREF where VREF = 1.225V, suggested value for R14 is 100k, 1%. LDO Operation The LTC1980 provides an uninterrupted power supply for the system load. When a wall adapter is connected and operating, power is taken from the wall adapter to charge the batteries and supply power to the system. In applications where an unregulated wall adapter is used but a regulated voltage is needed by the system, an external Pchannel MOSFET pass transistor may be added to the LTC1980 to create a low dropout linear regulator. From Figure 5, select the following resistors based on the output voltage VLDO: R5 = R6 • (VLDO – VREF)/VREF where VREF = 1.225V, suggested value for R6 is 100k, 1%. This is the voltage that will be seen when operating from a higher voltage wall adapter. When operating from the batteries (as a regulator), the load will see either this voltage or the voltage set by the PWM regulator, whichever is less, minus any drops in the pass transistor. Placing a large-valued capacitor from the drain of this MOSFET to ground creates output compensation. Wall Adapter Comparator Threshold From Figure 5, select the following resistors based on the wall adapter comparator threshold VWATH: R15 = R7(VWATH – VIH1)/VIH1 where VIH1= 1.226V, suggested value for R7 is 100k. Use 1% resistors. MODE Pin Operation The following truth table describes MODE pin operation. Burst Mode operation is disabled during battery charging to reduce broadband noise inherent in Burst Mode operation. (Refer to the LT1307 data sheet for details). POWER FLOW MODE PIN Battery Charger 0 Battery Charger Open OPERATING MODE Disabled Enabled Continuous Battery Charger 1 Enabled Continuous DC/DC converter 0 Disabled DC/DC converter Open DC/DC converter 1 Enabled Burst Mode Operation Enabled Continuous Logic 1 = VBIAS1 (Pin 13) Logic 0 = GND The MODE pin should be decoupled with 200pF to ground when left open. Snubber Design The values given in the applications schematics have been found to work quite well for most applications. Care should be taken in selecting other values for your application since efficiency may be impacted by a poor choice. For a detailed look at snubber design, Application Note 19 is very helpful. Frequency Compensation Load step testing can be used to empirically determine compensation. Application Note 25 provides information on the technique. To adjust the compensation for the DC/ DC converter, adjust C12 and R13 (in Figure 5). Battery charger current loop compensation is set by C11 and battery charger float voltage compensation is set by C8. Component Selection Basics The application circuits work well for most 1- and 2-cell Li-Ion, 0.5A to 1A output current designs. The next section highlights the component selection process. More information is available in Application Note 19. 1980f 12 LTC1980 U W U U APPLICATIO S I FOR ATIO Current Sense Resistor Voltage drop in the current sense resistor should be limited to approximately ±100mV with respect to ground at max load currents in all modes. This value strikes a reasonable balance between providing an adequate low current signal, while keeping the losses from this resistor low. For applications where the inputs and output voltages may be low, a somewhat lower drop can be used (in order to reduce conduction losses slightly). The LTC1980 has several features, such as leading-edge blanking, which make application of this part easier to use. However for best charge current accuracy, the current sense resistor should be Kelvin sensed. MOSFETs The LTC1980 uses low side MOSFET switches. There are two very important advantages. First, N-channel MOSFETs are used—this generally means that efficiency will be higher than a comparable on-resistance P-channel device (because less gate charge is required). Second, low VT (‘logic-level’) MOSFETs with relatively low absolute maximum VGS ratings can be used, even in higher voltage applications. Refer to Application Note 19 for information on determining MOSFET voltage and current ratings. Transformer Turns ratio affects the duty factor of the power converter which impacts current and voltage stress on the power MOSFETs, input and output capacitor RMS currents and transformer utilization (size vs power). Using a 50% duty factor under nominal operating conditions usually gives reasonable results. For a 50% duty factor, the turns ratio is: N = VREG/VBAT N should be calculated for the design operating as a DC/DC converter and as a battery charger. The final turns ratio should be chosen so that it is approximately equal to the average of the two calculated values for N. In addition choose a turns ratio which can be made from the ratio of small integers. This allows bifilar windings to be used in the transformer which can reduce the leakage inductance, reduce the need for aggressive snubber design and for this reason improve efficiency. Avoid transformer saturation under all operating conditions and combinations (usually the biggest problems occur at high output currents and extreme duty cycles. Also check these conditions for battery charging and regulation modes. Finally, in low voltage applications, select a transformer with low winding resistance. This will improve efficiency at heavier loads. Capacitors Check the RMS current rating on your capacitors on both sides of your circuit. Low ESR and ESL is recommended for lowest ripple. OS-CON capacitors (from Sanyo) work very well in this application. Diodes In low voltage applications, Schottky diodes should be placed in parallel with the drain and source of the MOSFETs in the PWM supply. This prevents body diode turn on and improves efficiency by eliminating loss from reverse recovery in these diodes. It also reduces conduction loss during the RGTDR/BGTDR break interval. The LTC1980 can operate to voltages as low as 2.8V. Suitable Schottky diodes include the ZHCS1000 (VF = 420mV at IF = 1A) and SL22/23 (VF = 440mV at IF = 2A) for most 500mA to 1A output current applications. Vendor List VENDOR COMPONENTS TELEPHONE BH Electronics Transformers 952-894-9590 Coiltronics/Cooper Electronic Transformers 561-752-5000 Fairchild Semiconductor MOSFETs Schottky Rectifiers 800-341-0392 Vishay (General Semiconductor) MOSFETs Schottky Rectifiers 631-847-3000 Sanyo OS-CON Capacitors 408-749-9714 Sumida Electric USA Transformers 847-956-0666 Vishay (Siliconix) MOSFETs 408-988-8000 1980f 13 LTC1980 U TYPICAL APPLICATIO BH511-1014 VBAT + 4.1V Li-Ion BATTERY + VREG C1 5.1Ω 68µF + 5.1Ω 1nF D1* IN5819 3.3V WALL ADAPTER C4 68µF OPTIONAL PASS TRANSISTOR FOR LDO FDC636P 1nF 1/2 FDC6401N DCOUT VLDO 3.1V 1/2 FDC6401N SYSTEM LOAD DC/DC CONVERTERS C6 470µF 50mΩ RSENSE 20 GND 21 ISENSE 18 V 23 BAT OVP 3 REGFB 22 CAOUT PROG 1 R10 110k R11 1M VOUT R5 154k 14 12 BGTDR PGND R9 10k ACIN 11 RGTDR 7 6 5 LDODRV LDQFB VREG 15 REG 16 MODE 9 BATT1 10 BATT2 LTC1980 PROGT 2 VC C11 1nF TIMER 4 17 C7 0.27µF R6 100k 8 WA SS VBIAS1 24 13 C8 0.1µF 200pF R7 100k R8 169k VBIAS2 C9 1µF R15 300k 19 C10 1µF R12 100k R14 100k C12 82pF *OPTIONAL DIODE FOR SHORTED WALL ADAPTER TERMINAL PROTECTION R13 806k 1980 F05 Figure 5. 4.1V/1A Li-Ion Battery Charger and 3.3V DC/DC Converter 1980f 14 LTC1980 U PACKAGE DESCRIPTIO GN Package 24-Lead Plastic SSOP (Narrow .150 Inch) (Reference LTC DWG # 05-08-1641) .337 – .344* (8.560 – 8.738) 24 23 22 21 20 19 18 17 16 15 1413 .033 (0.838) REF .045 ±.005 .229 – .244 (5.817 – 6.198) .254 MIN .150 – .157** (3.810 – 3.988) .150 – .165 1 .0165 ± .0015 2 3 4 5 6 7 8 9 10 11 12 .0250 TYP RECOMMENDED SOLDER PAD LAYOUT .015 ± .004 × 45° (0.38 ± 0.10) .007 – .0098 (0.178 – 0.249) .053 – .068 (1.351 – 1.727) .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) .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 GN24 (SSOP) 0502 1980f 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. 15 LTC1980 RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LT1170/LT1171/LT1172 5A/3A/1.25A Flyback Regulators Isolated Flyback Mode LT1571 200kHz/500kHz Switching Battery Charger Up to 1.5A Charge Current; Preset and Adjustable Battery Voltages LTC1729 Lithium-Ion Battery Charger Termination Controllers Time or Charge Current Termination, Preconditioning 8-Lead MSOP LTC1731 Lithium-Ion Linear Battery Charger Controller Simple Charger uses External FET, Features Preset Voltages, C/10 Charger Detection and Programmable Timer LTC1732 Lithium-Ion Linear Battery Charger Controller Simple Charger uses External FET, Features Preset Voltages, C/10 Charger Detection and Programmable Timer, Input Power Good Indication LTC1733 Monolithic Lithium-Ion Linear Battery Charger Standalone Charger with Programmable Timer, Up to 1.5A Charge Current LTC1734 Lithium-Ion Linear Battery Charger in ThinSOTTM Simple ThinSOT Charger, No Blocking Diode, No Sense Resistor Needed LTC1734L Lithium-Ion Linear Battery Charger Controller 50mA to 180mA, No Blocking Diode, No Sense Resistor Needed LTC1760 Dual Battery Charger/Selector with SMBus Interface Complete SMBus Charger/Selector for Two Smart Batteries LTC1960 Dual Battery Charger/Selector with SPI Complete Dual-Battery Charger/Selector System, Easy Interface with Microcontroller, Extends Run Time by 10%, reduces Charge Time by 50% LTC4002 Wide VIN Range Li-Ion Battery Charger 1-, 2-Cell Batteries, Switch Mode Charger, Up to µA Charge Current, 4.7V ≤ VIN ≤ 22V LTC4007 4A Standalone Multiple Cell Li-Ion Battery Charger 6V ≤ VIN ≤ 28V, 3- or 4-Cell, Up to 96% Efficiency LTC4050 Lithium-Ion Linear Battery Charger Controller Simple Charger uses External FET, Thermistor Input for Battery Temperature Sensing LTC4052 Lithium-Ion Linear Battery Pulse Charger Fully Integrated, Standalone Pulse Charger, Minimal Heat Dissipation, Overcurrent Protection LTC4411 2.6A Low Loss Ideal Diode in ThinSOT Very Low Loss Replacement for Power Supply ORing Diodes, 2.6V to 5.5V Supply Voltage, ThinSOT Package LTC4412 Ideal Diode or PowerPathTM Very Low Loss Replacement for Power Supply ORing Diodes, Enternal Pass Element, 3V to 28V Supply Voltage,ThinSOT Package ThinSOT and PowerPath are trademarks of Linear Technology Corporation. 1980f 16 Linear Technology Corporation LT/TP 0604 1K • PRINTED IN USA 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com © LINEAR TECHNOLOGY CORPORATION 2003