DC-DC电源升压芯片1308abfb

LT1308A/LT1308B 1 1308abfb TYPICAL APPLICATION DESCRIPTION High Current, Micropower Single Cell, 600kHz DC/DC Converters The LT®1308A/LT1308B are micropower, fi xed frequency step-up DC/DC converters that operate over a 1V to 10V input voltage range. They are improved versions of the LT1308 and are recommended for use in new designs. The LT1308A features automatic shifting to power sav- ing Burst Mode operation at light loads and consumes just 140μA at no load. The LT1308B features continuous switching at light loads and operates at a quiescent cur- rent of 2.5mA. Both devices consume less than 1μA in shutdown. Low-battery detector accuracy is signifi cantly tighter than the LT1308. The 200mV reference is specifi ed at ±2% at room and ±3% over temperature. The shutdown pin enables the device when it is tied to a 1V or higher source and does not need to be tied to VIN as on the LT1308. An internal VC clamp results in improved transient response and the switch voltage rating has been increased to 36V, enabling higher output voltage applications. The LT1308A/LT1308B are available in the 8-lead SO and the 14-lead TSSOP packages. Converter Effi ciency FEATURES APPLICATIONS n 5V at 1A from a Single Li-Ion Cell n 5V at 800mA in SEPIC Mode from Four NiCd Cells n Fixed Frequency Operation: 600kHz n Boost Converter Outputs up to 34V n Starts into Heavy Loads n Automatic Burst Mode™ Operation at Light Load (LT1308A) n Continuous Switching at Light Loads (LT1308B) n Low VCESAT Switch: 300mV at 2A n Pin-for-Pin Upgrade Compatible with LT1308 n Lower Quiescent Current in Shutdown: 1μA (Max) n Improved Accuracy Low-Battery Detector Reference: 200mV ±2% n Available in 8-Lead SO and 14-Lead TSSOP Packages n GSM/CDMA Phones n Digital Cameras n LCD Bias Supplies n Answer-Back Pagers n GPS Receivers n Battery Backup Supplies n Handheld Computers Figure 1. LT1308B Single Li-Ion Cell to 5V/1A DC/DC Converter VIN SW FB LT1308B L1 4.7μH D1 LBOLBI 47k R2 100k R1* 309k 5V 1A 100pF 1308A/B F01a C1 47μF C2 220μF Li-Ion CELL VC GND SHDNSHUTDOWN C1: AVX TAJC476M010 C2: AVX TPSD227M006 D1: IR 10BQ015 + + L1: MURATA LQH6C4R7 *R1: 887k FOR VOUT = 12V LOAD CURRENT (mA) 1 EF FI CI EN CY (% ) 95 90 85 80 75 70 65 60 55 50 10 100 1000 1308A/B F01b VIN = 4.2V VIN = 1.5V VIN = 2.5V VIN = 3.6V L, LT, LTC, LTM, Burst Mode, Linear Technology and the Linear logo are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners. LT1308A/LT1308B 2 1308abfb ABSOLUTE MAXIMUM RATINGS VIN, SHDN, LBO Voltage ........................................... 10V SW Voltage .............................................. –0.4V to 36V FB Voltage ......................................................... VIN + 1V VC Voltage ................................................................. 2V LBI Voltage ................................................. –0.1V to 1V Current into FB Pin ............................................... ±1mA (Note 1) 1 2 3 4 8 7 6 5 TOP VIEW LBO LBI VIN SW VC FB SHDN GND S8 PACKAGE 8-LEAD PLASTIC SO TJMAX = 125°C, θJA = 190°C/W F PACKAGE 14-LEAD PLASTIC TSSOP 1 2 3 4 5 6 7 TOP VIEW 14 13 12 11 10 9 8 VC FB SHDN GND GND GND GND LBO LBI VIN VIN SW SW SW (NOTE 6) TJMAX = 125°C, θJA = 80°C/W OBSOLETE, FOR INFORMATION PURPOSES ONLY Contact Linear Technology for Potential Replacement PIN CONFIGURATION ORDER INFORMATION LEAD FREE FINISH TAPE AND REEL PART MARKING PACKAGE DESCRIPTION TEMPERATURE RANGE LT1308ACS8#PBF LT1308ACS8#TRPBF 1308A 8-Lead Plastic SO 0°C to 70°C LT1308AIS8#PBF LT1308AIS8#TRPBF 1308AI 8-Lead Plastic SO –40°C to 85°C LT1308BCS8#PBF LT1308BCS8#TRPBF 1308B 8-Lead Plastic SO 0°C to 70°C LT1308BIS8#PBF LT1308BIS8#TRPBF 1308BI 8-Lead Plastic SO –40°C to 85°C LT1308ACF#PBF LT1308ACF#TRPBF LT1308ACF 14-Lead Plastic TSSOP 0°C to 70°C LT1308BCF#PBF LT1308BCF#TRPBF LT1308BCF 14-Lead Plastic TSSOP 0°C to 70°C LEAD BASED FINISH TAPE AND REEL PART MARKING PACKAGE DESCRIPTION TEMPERATURE RANGE LT1308ACS8 LT1308ACS8#TR 1308A 8-Lead Plastic SO 0°C to 70°C LT1308AIS8 LT1308AIS8#TR 1308AI 8-Lead Plastic SO –40°C to 85°C LT1308BCS8 LT1308BCS8#TR 1308B 8-Lead Plastic SO 0°C to 70°C LT1308BIS8 LT1308BIS8#TR 1308BI 8-Lead Plastic SO –40°C to 85°C LT1308ACF LT1308ACF#TR LT1308ACF 14-Lead Plastic TSSOP 0°C to 70°C LT1308BCF LT1308BCF#TR LT1308BCF 14-Lead Plastic TSSOP 0°C to 70°C Consult LTC Marketing for parts specifi ed with wider operating temperature ranges. For more information on lead free part marking, go to: http://www.linear.com/leadfree/ This product is only offered in trays. For more information go to: http://www.linear.com/packaging/ Operating Temperature Range Commercial............................................. 0°C to 70°C Extended Commerial (Note 2) ............ –40°C to 85°C Industrial ........................................... –40°C to 85°C Storage Temperature Range .................. –65°C to 150°C Lead Temperature (Soldering, 10 sec) ................. 300°C LT1308A/LT1308B 3 1308abfb The l denotes the specifi cations which apply over the full operating temperature range, otherwise specifi cations are at TA = 25°C. Commercial Grade 0°C to 70°C. VIN = 1.1V, VSHDN = VIN, unless otherwise noted. ELECTRICAL CHARACTERISTICS SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS IQ Quiescent Current Not Switching, LT1308A Switching, LT1308B VSHDN = 0V (LT1308A/LT1308B) 140 2.5 0.01 240 4 1 μA mA μA VFB Feedback Voltage l 1.20 1.22 1.24 V IB FB Pin Bias Current (Note 3) l 27 80 nA Reference Line Regulation 1.1V ≤ VIN ≤ 2V 2V ≤ VIN ≤ 10V l 0.03 0.01 0.4 0.2 %/V %/V Minimum Input Voltage 0.92 1 V gm Error Amp Transconductance ∆I = 5μA 60 μmhos AV Error Amp Voltage Gain 100 V/V fOSC Switching Frequency VIN = 1.2V l 500 600 700 kHz Maximum Duty Cycle l 82 90 % Switch Current Limit Duty Cycle = 30% (Note 4) 2 3 4.5 A Switch VCESAT ISW = 2A (25°C, 0°C), VIN = 1.5V ISW = 2A (70°C), VIN = 1.5V 290 330 350 400 mV mV Burst Mode Operation Switch Current Limit (LT1308A) VIN = 2.5V, Circuit of Figure 1 400 mA Shutdown Pin Current VSHDN = 1.1V VSHDN = 6V VSHDN = 0V l l l 2 20 0.01 5 35 0.1 μA μA μA LBI Threshold Voltage l 196 194 200 200 204 206 mV mV LBO Output Low ISINK = 50μA l 0.1 0.25 V LBO Leakage Current VLBI = 250mV, VLBO = 5V l 0.01 0.1 μA LBI Input Bias Current (Note 5) VLBI = 150mV 33 100 nA Low-Battery Detector Gain 3000 V/V Switch Leakage Current VSW = 5V l 0.01 10 μA The l denotes the specifi cations which apply over the full operating temperature range, otherwise specifi cations are at TA = 25°C. Industrial Grade –40°C to 85°C. VIN = 1.2V, VSHDN = VIN, unless otherwise noted. SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS IQ Quiescent Current Not Switching, LT1308A Switching, LT1308B VSHDN = 0V (LT1308A/LT1308B) l l l 140 2.5 0.01 240 4 1 μA mA μA VFB Feedback Voltage l 1.19 1.22 1.25 V IB FB Pin Bias Current (Note 3) l 27 80 nA Reference Line Regulation 1.1V ≤ VIN ≤ 2V 2V ≤ VIN ≤ 10V l l 0.05 0.01 0.4 0.2 %/V %/V Minimum Input Voltage 0.92 1 V gm Error Amp Transconductance ∆I = 5μA 60 μmhos AV Error Amp Voltage Gain 100 V/V LT1308A/LT1308B 4 1308abfb ELECTRICAL CHARACTERISTICS LT1308B 3.3V Output Effi ciency LT1308A 3.3V Output Effi ciency LT1308A 5V Output Effi ciency The l denotes the specifi cations which apply over the full operating temperature range, otherwise specifi cations are at TA = 25°C. Industrial Grade –40°C to 85°C. VIN = 1.2V, VSHDN = VIN, unless otherwise noted. SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS fOSC Switching Frequency l 500 600 750 kHz Maximum Duty Cycle l 82 90 % Switch Current Limit Duty Cycle = 30% (Note 4) 2 3 4.5 A Switch VCESAT ISW = 2A (25°C, –40°C), VIN = 1.5V ISW = 2A (85°C), VIN = 1.5V 290 330 350 400 mV mV Burst Mode Operation Switch Current Limit (LT1308A) VIN = 2.5V, Circuit of Figure 1 400 mA Shutdown Pin Current VSHDN = 1.1V VSHDN = 6V VSHDN = 0V l l 2 20 0.01 5 35 0.1 μA μA μA LBI Threshold Voltage l 196 193 200 200 204 207 mV mV LBO Output Low ISINK = 50μA l 0.1 0.25 V LBO Leakage Current VLBI = 250mV, VLBO = 5V l 0.01 0.1 μA LBI Input Bias Current (Note 5) VLBI = 150mV 33 100 nA Low-Battery Detector Gain 3000 V/V Switch Leakage Current VSW = 5V l 0.01 10 μA 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: The LT1308ACS8, LT1308ACF, LT1308BCS8 and LT1308BCF are designed, characterized and expected to meet the industrial temperature limits, but are not tested at –40°C and 85°C. I grade devices are guaranteed over the –40°C to 85°C operating temperature range. Note 3: Bias current fl ows into FB pin. Note 4: Switch current limit guaranteed by design and/or correlation to static tests. Duty cycle affects current limit due to ramp generator (see Block Diagram). Note 5: Bias current fl ows out of LBI pin. Note 6: Connect the four GND pins (Pins 4–7) together at the device. Similarly, connect the three SW pins (Pins 8–10) together and the two VIN pins (Pins 11, 12) together at the device. TYPICAL PERFORMANCE CHARACTERISTICS LOAD CURRENT (mA) 95 90 85 80 75 70 65 60 55 50 1 100 1000 1308A/B G01 10 EF FI CI EN CY (% ) VIN = 1.8V VIN = 2.5V VIN = 1.2V LOAD CURRENT (mA) 95 90 85 80 75 70 65 60 55 50 1 100 1000 1308A/B G02 10 EF FI CI EN CY (% ) VIN = 1.8V VIN = 2.5V VIN = 1.2V LOAD CURRENT (mA) 1 EF FI CI EN CY (% ) 95 90 85 80 75 70 65 60 55 50 10 100 1000 1308A/B G03 VIN = 4.2V VIN = 2.5V VIN = 3.6V VIN = 1.5V LT1308A/LT1308B 5 1308abfb TYPICAL PERFORMANCE CHARACTERISTICS SHDN Pin Bias Current vs Voltage FB, LBI Bias Current vs Temperature Low Battery Detector Reference vs Temperature Oscillator Frequency vs Temperature LT1308A Quiescent Current vs Temperature Feedback Pin Voltage vs Temperature LT1308B 12V Output Effi ciency Switch Current Limit vs Duty Cycle Switch Saturation Voltage vs Current LOAD CURRENT (mA) 90 85 80 75 70 65 60 55 50 1 100 1000 1308A/B G04 10 EF FI CI EN CY (% ) VIN = 5V VIN = 3.3V DUTY CYCLE (%) 0 CU RR EN T LI M IT (A ) 3.0 3.5 80 1308 • G05 2.5 2.0 20 40 60 100 4.0 SWITCH CURRENT (A) 0 SW IT CH V CE SA T (m V) 2.0 85°C 1308 G06 0.5 1.0 1.5 500 400 300 200 100 0 25°C –40°C SHDN PIN VOLTAGE (V) 0 S H D N P IN C UR RE NT (μ A) 50 40 30 20 10 0 8 1308 G07 2 4 6 10 –40°C 25°C 85°C TEMPERATURE (°C) –50 –25 BI AS C UR RE NT (n A) 0 5025 75 100 1308 • G08 80 70 60 50 40 30 20 10 0 LBI FB TEMPERATURE (°C) –50 –25 V R EF (m V) 0 5025 75 100 1308 • G09 203 202 201 200 199 198 197 196 195 TEMPERATURE (°C) –50 –2.5 FR EQ UE NC Y (k Hz ) 0 5025 75 100 1308 • G10 800 750 700 650 600 550 500 450 400 TEMPERATURE (°C) –50 –25 QU IE SC EN T CU RR EN T (μ A) 0 5025 75 100 1308 • G11 180 170 160 150 140 130 120 110 100 TEMPERATURE (°C) –50 –25 V F B (V ) 0 5025 75 100 1308 • G12 1.25 1.24 1.23 1.22 1.21 1.20 1.19 1.18 LT1308A/LT1308B 6 1308abfb PIN FUNCTIONS VC (Pin 1/Pin 1): Compensation Pin for Error Amplifi er. Connect a series RC from this pin to ground. Typical values are 47kΩ and 100pF. Minimize trace area at VC. FB (Pin 2/Pin 2): Feedback Pin. Reference voltage is 1.22V. Connect resistive divider tap here. Minimize trace area at FB. Set VOUT according to: VOUT = 1.22V(1 + R1/R2). SHDN (Pin 3/Pin 3): Shutdown. Ground this pin to turn off switcher. To enable, tie to 1V or more. SHDN does not need to be at VIN to enable the device. GND (Pin 4/Pins 4, 5, 6, 7): Ground. Connect directly to local ground plane. Ground plane should enclose all components associated with the LT1308. PCB copper connected to these pins also functions as a heat sink. For the TSSOP package, connect all pins to ground copper to get the best heat transfer. This keeps chip heating to a minimum. SW (Pin 5/Pins 8, 9, 10): Switch Pins. Connect induc- tor/diode here. Minimize trace area at these pins to keep EMI down. For the TSSOP package, connect all SW pins together at the package. VIN (Pin 6/Pins 11, 12): Supply Pins. Must have local bypass capacitor right at the pins, connected directly to ground. For the TSSOP package, connect both VIN pins together at the package. LBI (Pin 7/Pin 13): Low-Battery Detector Input. 200mV reference. Voltage on LBI must stay between –100mV and 1V. Low-battery detector does not function with SHDN pin grounded. Float LBI pin if not used. LBO (Pin 8/Pin 14): Low-Battery Detector Output. Open collector, can sink 50μA. A 220kΩ pull-up is recommend- ed. LBO is high impedance when SHDN is grounded. (SO/TSSOP) LT1308A/LT1308B 7 1308abfb BLOCK DIAGRAMS Figure 2a. LT1308A/LT1308B Block Diagram (SO-8 Package) Figure 2b. LT1308A/LT1308B Block Diagram (TSSOP Package) – + – +– + – + – + + + Σ COMPARATOR RAMP GENERATOR R BIAS VC 2VBE gm Q2 ×10 Q1 FB FB ENABLE *HYSTERESIS IN LT1308A ONLY 200mV A = 3 FF A2 A1 Q4 * ERROR AMPLIFIER A4 0.03Ω DRIVER SW GND 1308 BD2a Q3Q S 600kHz OSCILLATOR 5 LBO LBI SHDN SHUTDOWN 3 7 1 4 R6 40k R5 40k R1 (EXTERNAL) R3 30k R4 140k 2 VIN VIN VIN VOUT 6 8 R2 (EXTERNAL) – + – +– + – + – + + + Σ COMPARATOR RAMP GENERATOR R BIAS VC 2VBE gm Q2 ×10 Q1 FB FB ENABLE *HYSTERESIS IN LT1308A ONLY 200mV A = 3 FF A2 A1 Q4 * ERROR AMPLIFIER A4 0.03Ω DRIVER SW GND 1308 BD2b Q3Q S 600kHz OSCILLATOR 8 SW 9 SW LBO LBI SHDN SHUTDOWN 3 13 1 4 GND 5 GND 6 GND 7 R6 40k R5 40k R1 (EXTERNAL) R3 30k R4 140k 2 VIN VIN VIN VIN VOUT 11 12 14 R2 (EXTERNAL) 10 LT1308A/LT1308B 8 1308abfb OPERATION The LT1308A combines a current mode, fi xed frequency PWM architecture with Burst Mode micropower opera- tion to maintain high effi ciency at light loads. Operation can be best understood by referring to the block diagram in Figure 2. Q1 and Q2 form a bandgap reference core whose loop is closed around the output of the converter. When VIN is 1V, the feedback voltage of 1.22V, along with an 80mV drop across R5 and R6, forward biases Q1 and Q2’s base collector junctions to 300mV. Because this is not enough to saturate either transistor, FB can be at a higher voltage than VIN. When there is no load, FB rises slightly above 1.22V, causing VC (the error amplifi er’s output) to decrease. When VC reaches the bias voltage on hyster- etic comparator A1, A1’s output goes low, turning off all circuitry except the input stage, error amplifi er and low-battery detector. Total current consumption in this state is 140μA. As output loading causes the FB voltage to decrease, A1’s output goes high, enabling the rest of the IC. Switch current is limited to approximately 400mA initially after A1’s output goes high. If the load is light, the output voltage (and FB voltage) will increase until A1’s output goes low, turning off the rest of the LT1308A. Low frequency ripple voltage appears at the output. The ripple frequency is dependent on load current and output capacitance. This Burst Mode operation keeps the output regulated and reduces average current into the IC, resulting in high effi ciency even at load currents of 1mA or less. If the output load increases suffi ciently, A1’s output remains high, resulting in continuous operation. When the LT1308A is running continuously, peak switch current is controlled by VC to regulate the output voltage. The switch is turned on at the beginning of each switch cycle. When the summation of a signal representing switch current and a ramp generator (introduced to avoid subharmonic oscillations at duty factors greater than 50%) exceeds the VC signal, comparator A2 changes state, resetting the fl ip- fl op and turning off the switch. Output voltage increases as switch current is increased. The output, attenuated by a resistor divider, appears at the FB pin, closing the overall loop. Frequency compensation is provided by an external series RC network connected between the VC pin and ground. Low-battery detector A4’s open-collector output (LBO) pulls low when the LBI pin voltage drops below 200mV. There is no hysteresis in A4, allowing it to be used as an amplifi er in some applications. The entire device is disabled when the SHDN pin is brought low. To enable the converter, SHDN must be at 1V or greater. It need not be tied to VIN as on the LT1308. The LT1308B differs from the LT1308A in that there is no hysteresis in comparator A1. Also, the bias point on A1 is set lower than on the LT1308B so that switching can occur at inductor current less than 100mA. Because A1 has no hysteresis, there is no Burst Mode operation at light loads and the device continues switching at constant frequency. This results in the absence of low frequency output voltage ripple at the expense of effi ciency. The difference between the two devices is clearly illus- trated in Figure 3. The top two traces in Figure 3 shows an LT1308A/LT1308B circuit, using the components indicated in Figure 1, set to a 5V output. Input voltage is 3V. Load current is stepped from 50mA to 800mA for both circuits. Low frequency Burst Mode operation voltage ripple is observed on Trace A, while none is observed on Trace B. At light loads, the LT1308B will begin to skip alternate cycles. The load point at which this occurs can be decreased by increasing the inductor value. However, output ripple will continue to be signifi cantly less than the LT1308A output ripple. Further, the LT1308B can be forced into micropower mode, where IQ falls from 3mA to 200μA by sinking 40μA or more out of the VC pin. This stops switching by causing A1’s output to go low. APPLICATIONS INFORMATION Figure 3. LT1308A Exhibits Burst Mode Operation Output Voltage Ripple at 50mA Load, LT1308B Does Not 1308 F03 VIN = 3V (CIRCUIT OF FIGURE 1) 800mA 50mA TRACE A: LT1308A VOUT, 100mV/DIV AC COUPLED TRACE B: LT1308B VOUT, 100mV/DIV AC COUPLED 200μs/DIV ILOAD LT1308A/LT1308B 9 1308abfb APPLICATIONS INFORMATION Waveforms for a LT1308B 5V to 12V boost converter using a 10μF ceramic output capacitor are pictured in Figures 4 and 5. In Figure 4, the converter is operating in continuous mode, delivering a load current of approximately 500mA. The top trace is the output. The voltage increases as induc- tor current is dumped into the output capacitor during the switch off time, and the voltage decreases when the switch is on. Ripple voltage is in this case due to capacitance, as the ceramic capacitor has little ESR. The middle trace is the switch voltage. This voltage alternates between a VCESAT and VOUT plus the diode drop. The lower trace is the switch current. At the beginning of the switch cycle, the current is 1.2A. At the end of the switch on time, the current has increased to 2A, at which point the switch turns off and the inductor current fl ows into the output capacitor through the diode. Figure 5 depicts converter waveforms at a light load. Here the converter operates in discontinu- ous mode. The inductor current reaches zero during the switch off time, resulting in some ringing at the switch node. The ring frequency is set by switch capacitance, diode capacitance and inductance. This ringing has little energy, and its sinusoidal shape suggests it is free from harmonics. Minimizing the copper area at the switch node will prevent this from causing interference problems. LAYOUT HINTS The LT1308A/LT1308B switch current at high speed, man- dating careful attention to layout for proper p