LTC3402 2A, 3MHz Micropower Synchronous Boost Converter U FEATURES DESCRIPTIO ■ The LTC®3402 is a high efficiency, fixed frequency, stepup DC/DC converter that operates from an input voltage below 1V. The device includes a 0.16Ω N-channel MOSFET switch and a 0.18Ω P-channel synchronous rectifier. Switching frequencies up to 3MHz are programmed with an external timing resistor and the oscillator can be synchronized to an external clock. An external Schottky diode is optional but will slightly improve efficiency. ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ Synchronous Rectification: Up to 97% Efficiency 2A Switch Current Rating Fixed Frequency Operation Up to 3MHz Wide Input Range: 0.5V to 5V Very Low Quiescent Current: 38μA (Burst Mode® Operation) 2.6V to 5.5V Adjustable Output Voltage 0.85V (Typ) Start-Up Voltage No External Schottky Diode Required (VOUT < 4.3V) Synchronizable Switching Frequency Burst Mode Enable Control Antiringing Control Reduces Switching Noise PGOOD Output OPTI-LOOP® Compensation Very Low Shutdown Current: < 1μA Small 10-Pin MSOP Package Quiescent current is only 38μA in Burst Mode operation, maximizing battery life in portable applications. Burst Mode operation is user controlled and can be enabled by driving the MODE/SYNC pin high. If the MODE/SYNC pin has either a clock or is driven low, then fixed frequency switching is enabled. Other features include a 1μA shutdown, antiringing control, open-drain power good output, thermal shutdown and current limit. The LTC3402 is available in the 10-lead thermally enhanced MSOP package. Lower current applications should use the 1A rated LTC3401 synchronous boost converter. Applications that require VOUT < 2.6V should use the LTC3424. U APPLICATIO S ■ ■ ■ ■ ■ ■ Cellular Telephones Handheld Computers MP3 Players 2-Way Pagers GPS Receivers Battery Backup Supplies CCFL Backlights , LT, LTC and LTM are registered trademarks of Linear Technology Corporation. Burst Mode and OPTI-LOOP are registered trademarks of Linear Technology Corporation. U ■ TYPICAL APPLICATIO All Ceramic Capacitor 2-Cell to 3.3V at 1A Step-Up Converter L1 2.2μH 3 10 +2 CELLS 2 6 C1 10μF 1 100 VOUT 3.3V 1A LTC3402 VIN SHDN SW VOUT MODE/SYNC FB PGOOD Rt Rt 30.1k VC GND 4 R2 909k 7 C2 44μF (2 × 22μF) 8 9 5 C3 470pF R5 82k Burst Mode OPERATION 80 1MHz CONSTANT FREQUENCY 70 60 50 40 30 20 R1 549k 10 C4 4.7pF C1: TAIYO YUDEN JMK212BJ106MG 0 = FIXED FREQ C2: TAIYO YUDEN JMK325BJ226MM 1 = Burst Mode OPERATION L1: COILCRAFT: D03316P-222 90 EFFICIENCY (%) VIN = 1.8V to 3V Efficiency 0 VIN = 2.4V WITH SCHOTTKY 0.1 1 10 IOUT (mA) 100 1000 3402 TA02 3402 TA01 3402fb 1 LTC3402 W W W AXI U U ABSOLUTE RATI GS U U W PACKAGE/ORDER I FOR ATIO (Note 1) VIN, VOUT Voltages ...................................... – 0.5V to 6V SW Voltage ................................................. – 0.5V to 6V VC, Rt Voltages ......................... – 0.5V to (VOUT + 0.3V) PGOOD, SHDN, FB, MODE Voltages ........... – 0.5V to 6V Operating 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 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/ ORDER PART NUMBER TOP VIEW Rt MODE VIN SW GND 1 2 3 4 5 10 9 8 7 6 SHDN VC FB VOUT PGOOD MS PACKAGE 10-LEAD PLASTIC MSOP LTC3402EMS MS PART MARKING TJMAX = 125°C θJA = 130°C/ W 1 LAYER BOARD θJA = 100°C/ W 4 LAYER BOARD LTSK Consult LTC Marketing for parts specified with wider operating temperature ranges. ELECTRICAL CHARACTERISTICS The ● denotes specifications that apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VIN = 1.2V, VOUT = 3.3V unless otherwise noted. PARAMETER CONDITIONS Minimum Start-Up Voltage ILOAD = <1mA Minimum Operating Voltage (Note 4) MIN TYP MAX UNITS 0.85 1.0 V 0.5 V 5.5 V 1.25 1.28 V ● Output Voltage Adjust Range ● 2.6 Feedback Voltage ● 1.22 Feedback Input Current VFB = 1.25V 1 50 nA Quiescent Current—Burst Mode Operation VC = 0V, MODE/SYNC = 3.3V (Note 3) 38 65 μA Quiescent Current—SHDN SHDN = 0V, Not Including Switch Leakage 0.1 1 μA Quiescent Current—Active VC = 0V, MODE/SYNC = 0V, Rt = 300k (Note 3) 440 800 μA NMOS Switch Leakage 0.1 5 μA PMOS Switch Leakage 0.1 10 μA NMOS Switch On Resistance 0.16 Ω PMOS Switch On Resistance 0.18 Ω 2.5 A NMOS Current Limit ● 2 ● 80 NMOS Burst Current Limit Maximum Duty Cycle Rt = 15k A 85 % ● Minimum Duty Cycle Switching Frequency 0.66 Rt = 15k MODE/SYNC Input High ● 0 1.6 2 2.4 1.4 0.4 VMODE/SYNC = 5.5V Error Amp Transconductance ΔI = – 5μA to 5μA, VC = VFB PGOOD Threshold Referenced to Feedback Voltage 0.01 1 –9 V μA μmhos 85 –6 MHz V MODE/SYNC Input Low MODE/SYNC Input Current % – 12 % 3402fb 2 LTC3402 ELECTRICAL CHARACTERISTICS The ● denotes specifications that apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VIN = 1.2V, VOUT = 3.3V unless otherwise noted. PARAMETER CONDITIONS PGOOD Low Voltage IPGOOD = 1mA VOUT = 1V, IPGOOD = 20μA MIN PGOOD Leakage VPGOOD = 5.5V SHDN Input High VIN = VSHDN TYP MAX UNITS 0.1 0.1 0.2 0.4 V V 0.01 1 μA 1 V SHDN Input Low SHDN Input Current VSHDN = 5.5V 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 LTC3402E 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 0.01 0.4 V 1 μA with statistical process controls. Note 3: Current is measured into the VOUT pin since the supply current is bootstrapped to the output pin and in the application will reflect to the input supply by (VOUT/VIN) • I/Efficiency. The outputs are not switching. Note 4: Once the output is started, the IC is not dependent upon the VIN supply. U W TYPICAL PERFOR A CE CHARACTERISTICS (TA = 25°C unless otherwise noted) SW Pin and Inductor Current (IC) in Discontinuous Mode. Ringing Control Circuitry Eliminates High Frequency Ringing Switching Waveform on SW Pin IL 50mA/DIV 0A SW 1V/DIV Transient Response 5mA to 50mA VOUT 100mV/DIV SW 1V/DIV 50mA IOUT 5mA 0V 50ns/DIV 200ns/DIV 3402 G01 Transient Response 50mA to 500mA COUT = 22μF L = 3.3μH fOSC = 1MHz 3402 G02 VOUT AC 100mV/DIV 550mA SW 1V/DIV 3402 G03 Burst Mode Operation Burst Mode Operation VOUT 200mV/DIV 200μs/DIV VOUT AC 100mV/DIV SW 1V/DIV 50mA COUT = 22μF L = 3.3μH fOSC = 1MHz 200μs/DIV 3402 G04 VIN = 1.2V 5ms/DIV VOUT = 3.3V COUT = 100μF IOUT = 250μA MODE/SYNC PIN = HIGH 3402 G05 VIN = 1.2V 200μs/DIV VOUT = 3.3V COUT = 100μF IOUT = 20mA MODE/SYNC PIN = HIGH 3402 G06 3402fb 3 LTC3402 U W TYPICAL PERFOR A CE CHARACTERISTICS Converter Efficiency 1.2V to 3.3V Converter Efficiency 2.4V to 3.3V 300kHz Burst Mode OPERATION Burst Mode OPERATION 40 1MHz 300kHz 60 EFFICIENCY (%) 50 80 3MHz 70 1MHz 60 50 40 70 50 40 30 20 20 20 10 10 10 10 100 1 OUTPUT CURRENT (mA) 30 0 0.1 1000 10 100 1 OUTPUT CURRENT (mA) VIN = 3.6V 0 1000 0.1 1 100 10 LOAD CURRENT (mA) 3402 G08 3402 G07 Start-Up Voltage vs IOUT 500 1MHz FIXED FREQUENCY 60 30 0 0.1 Burst Mode OPERATION 90 80 3MHz 70 EFFICIENCY (%) 100 90 EFFICIENCY (%) 90 14 TA = 25°C 1000 3402 G10 Efficiency Loss Without Schottky vs Frequency Current Limit 3.4 TA = 25°C 12 3.2 10 3.0 300 200 CURRENT (A) 400 EFFICIENCY LOSS (%) OUTPUT CURRENT (mA) Converter Efficiency 3.6V to 5V 100 100 80 (TA = 25°C unless otherwise noted) 8 6 2.8 2.6 4 2.4 2 2.2 100 0 0.8 0.9 1 1.1 VIN (V) 1.2 1.3 0 0.2 1.4 2.2 1.0 1.4 1.8 FREQUENCY (MHz) 0.6 3402 G09 2.6 2.0 –55 3.0 –15 25 65 TEMPERATURE (°C) 3402 G12 3402 G11 EA FB Voltage NMOS RDS(ON) Oscillator Frequency Accuracy 1.28 2.10 105 125 0.30 Rt = 15k 1.27 VOUT = 3.3V 0.25 1.26 1.25 1.24 RESISTANCE (Ω) FREQUENCY (MHz) VOLTAGE (V) 2.05 2.00 1.95 –15 25 65 TEMPERATURE (°C) 105 125 3402 G13 1.90 –55 0.15 0.10 1.23 1.22 –55 0.20 –15 25 65 TEMPERATURE (°C) 105 125 3402 G14 0.05 –55 –15 25 65 TEMPERATURE (°C) 105 125 3402 G22 3402fb 4 LTC3402 U W TYPICAL PERFOR A CE CHARACTERISTICS (TA = 25°C unless otherwise noted) PMOS RDS(ON) 0.30 VOUT = 3.3V 1.10 1.05 0.25 1.0 1.00 0.20 0.15 VOLTAGE (V) 0.95 VOLTAGE (V) RESISTANCE (Ω) Shutdown Threshold Start-Up Voltage 1.1 0.9 0.8 0.90 0.85 0.80 0.75 0.10 0.7 0.70 0.05 –55 0.6 –55 0.65 –15 25 65 TEMPERATURE (°C) 105 125 –15 25 65 TEMPERATURE (°C) 3402 G16 PGOOD Threshold 25 65 TEMPERATURE (°C) 105 125 3402 G18 VOUT Turn-Off Voltage Burst Mode Operation Current 2.50 44 –7.5 2.45 42 –8.0 2.40 40 –9.0 –9.5 –10.0 –10.5 2.35 VOLTAGE (V) CURRENT (μA) –8.5 38 36 2.30 2.25 2.20 2.15 34 –11.0 2.10 32 –11.5 –12.0 –55 –15 3402 G17 –7.0 PERCENT FROM VFB (%) 0.60 –55 105 125 –15 25 65 TEMPERATURE (°C) 105 125 3402 G19 30 –55 2.05 –15 25 65 TEMPERATURE (°C) 105 125 3402 G20 2.00 –55 –15 25 65 TEMPERATURE (°C) 105 125 3402 G21 3402fb 5 LTC3402 U U U PI FU CTIO S Rt (Pin 1): Timing Resistor to Program the Oscillator Frequency. fOSC = 3 • 1010 Hz Rt MODE/SYNC (Pin 2): Burst Mode Select and Oscillator Synchronization. MODE/SYNC = High. Enable Burst Mode operation. The inductor peak inductor current will be 1/3 the current limit value and return to zero current on each cycle. During Burst Mode operation the operation is variable frequency, providing a significant efficiency improvement at light loads. It is recommended the Burst Mode operation only be entered once the part has started up. MODE/SYNC = Low. Disable Burst Mode operation and maintain low noise, constant frequency operation. MODE/SYNC = External CLK. Synchronization of the internal oscillator and Burst Mode operation disable. A clock pulse width of 100ns to 2μs is required to synchronize. VIN (Pin 3): Input Supply Pin. SW (Pin 4): Switch Pin. Connect inductor and Schottky diode here. For applications with output voltages over 4.3V, a Schottky diode is required to ensure that the SW pin voltage does not exceed its absolute maximum rating. Minimize trace length to keep EMI and high ringing down. For discontinuous inductor current, a controlled impedance is placed from SW to VIN from the IC to eliminate high frequency ringing due to the resonant tank of the inductor and SW node capacitance, therefore reducing EMI radiation. GND (Pin 5): Signal and Power Ground for the IC. PGOOD (Pin 6): Power Good Comparator Output. This open-drain output is low when VFB < – 9% from its regulation voltage. VOUT (Pin 7): Output of the Synchronous Rectifier and Bootstrapped Power Source for the IC. A ceramic capacitor of at least 1μF is required and should be located as close to the VOUT and GND pins as possible (Pins 7 and 5). FB (Pin 8): Feedback Pin. Connect resistor divider tap here. The output voltage can be adjusted from 2.6V to 5V. The feedback reference voltage is typically 1.25V. VC (Pin 9): Error Amp Output. A frequency compensation network is connected to this pin to compensate the loop. See the section “Compensating the Feedback Loop” for guidelines. SHDN (Pin 10): Shutdown. Grounding this pin shuts down the IC. Tie to >1V to enable (VIN or digital gate output). To operate with input voltages below 1V once the converter has started, a 1M resistor from SHDN to VIN and a 5M resistor from SHDN to VOUT will provide sufficient hysteresis. During shutdown, the output voltage will hold up to VIN minus a diode drop due to the body diode of the PMOS synchronous switch. If the application requires a complete disconnect during shutdown, refer to the section “Output Disconnect Circuits.” 3402fb 6 LTC3402 W BLOCK DIAGRA + 3 1V TO VOUT + 0.3V VIN SW 4 ANTIRING P SHDN 10 SHUTDOWN ANTICROSS COND + N 10mV ISENSE AMP CURRENT LIMIT VOUT + IZERO AMP + 5 2.8A TYP 1.25V – + ERROR AMP – CURRENT COMP – R1 8 FB + PWM LOGIC + SLEEP Σ – 9 VC Burst Mode CONTROL Rt VOUT 2.6V TO 5.5V + – – GND 7 1 OSC R2 2 MODE/SYNC SLOPE COMP – POK 6 N 1.25V – 9% 3402 BD 3402fb 7 + LTC3402 U W U U APPLICATIO S I FOR ATIO DETAILED DESCRIPTION The LTC3402 provides high efficiency, low noise power for applications such as portable instrumentation. The current mode architecture with adaptive slope compensation provides ease of loop compensation with excellent transient load response. The low RDS(ON), low gate charge synchronous switches provide the pulse width modulation control at high efficiency. The Schottky diode across the synchronous PMOS switch provides a lower drop during the break-before-make time (typically 20ns) of the NMOS to PMOS transition. The addition of the Schottky diode will improve efficiency (see graph “Efficiency Loss Without Schottky vs Frequency”). While the IC’s quiescent current is a low 38μA, high efficiency is achieved at light loads when Burst Mode operation is entered. Low Voltage Start-Up The LTC3402 is designed to start up at input voltages of typically 0.85V. The device can start up under some load, (see graph Start-Up vs Input Voltage). Once the output voltage exceeds a threshold of 2.3V, then the IC powers itself from VOUT instead of VIN. At this point, the internal circuitry has no dependency on the input voltage, eliminating the requirement for a large input capacitor. The input voltage can drop below 0.5V without affecting the operation, but the limiting factor for the application becomes the availability of the power source to supply sufficient energy to the output at the low voltages. Low Noise Fixed Frequency Operation Oscillator. The frequency of operation is set through a resistor from the Rt pin to ground where f = 3 • 1010/Rt. An internally trimmed timing capacitor resides inside the IC. The oscillator can be synchronized with an external clock inserted on the MODE/SYNC pin. When synchronizing the oscillator, the free running frequency must be set to approximately 30% lower than the desired synchronized frequency. Keeping the sync pulse width below 2μs will ensure that Burst Mode operation is disabled. Current Sensing. Lossless current sensing converts the peak current signal to a voltage to sum in with the internal slope compensation. This summed signal is compared to the error amplifier output to provide a peak current control command for the PWM. The slope compensation in the IC is adaptive to the input and output voltage. Therefore, the converter provides the proper amount of slope compensation to ensure stability and not an excess causing a loss of phase margin in the converter. Error Amp. The error amplifier is a transconductance amplifier with gm = 0.1ms. A simple compensation network is placed from the VC pin to ground. Current Limit. The current limit amplifier will shut the NMOS switch off once the current exceeds its threshold. The current amplifier delay to output is typically 50ns. Zero Current Amp. The zero current amplifier monitors the inductor current to the output and shuts off the synchronous rectifier once the current is below 50mA, preventing negative inductor current. Antiringing Control. The anitringing control will place an impedance across the inductor to damp the ringing on the SW pin during discontinuous mode operation. The LCSW ringing (L = inductor, CSW = capacitance on the switch pin) is low energy, but can cause EMI radiation. Burst Mode Operation Burst Mode operation is when the IC delivers energy to the output until it is regulated and then goes into a sleep mode where the outputs are off and the IC is consuming only 38μA. In this mode, the output ripple has a variable frequency component with load current and the steady state ripple will be typically below 3%. During the period where the device is delivering energy to the output, the peak current will be equal to 1/6 the current limit value and the inductor current will terminate at zero current for each cycle. In this mode the maximum output current is given by: I OUT(MAXBURST) ≈ VIN Amps 6 • VOUT Burst Mode operation is user controlled by driving the MODE/SYNC pin high to enable and low to disable. It is recommended that Burst Mode operation be entered after the part has started up. 3402fb 8 LTC3402 U W U U APPLICATIO S I FOR ATIO Table 1. Inductor Vendor Information COMPONENT SELECTION SUPPLIER Inductor Selection The high frequency operation of the LTC3402 allows the use of small surface mount inductors. The minimum inductance value is proportional to the operating frequency and is limited by the following constraints: VIN(MIN) • VOUT(MAX) – VIN(MIN) 3 L > μH and L > H f f • Ripple • VOUT(MAX) where f = Operating Frequency (Hz) Ripple = Allowable Inductor Current Ripple (A) VIN(MIN) = Minimum Input Voltage (V) VOUT(MAX) = Maximum Output Voltage (V) The inductor current ripple is typically set to 20% to 40% of the maximum inductor current. PHONE FAX WEBSITE Coilcraft (847) 639-6400 (847) 639-1469 www.coilcraft.com Coiltronics (516) 241-7876 (516) 241-9339 www.coiltronics.com Murata (814) 237-1431 (800) 831-9172 (814) 238-0490 www.murata.com Sumida USA: (847) 956-0666 (847) 956-0702 Japan: 81-3-3607-5111 81-3-3607-5144 www.japanlink.com sumida Output Capacitor Selection The output voltage ripple has several components. The bulk value of the capacitor is set to reduce the ripple due to charge into the capacitor each cycle. The max ripple due to charge is given by: VRBULK = IP • VIN V COUT • VOUT • f where IP = Peak Inductor Current Rt SHDN MODE VC VIN FB VOUT SW POK GND The ESR can be a significant factor for ripple in most power converters. The ripple due to capacitor ESR is simply given by: VRCESR = IP • RESR V where VOUT RESR = Capacitor Series Resistance 3402 F01 Figure 1. Recommended Component Placement. Traces Carrying High Current Are Direct. Trace Area FB and VC Pins Are Kept Low. Lead Length to Battery Should be Kept Short For high efficiency, choose an inductor with a high frequency core material, such as ferrite, to reduce core losses. The inductor should have low ESR (equivalent series resistance) to reduce the I2R losses and must be able to handle the peak inductor current without saturating. Molded chokes or chip inductors usually do not have enough core to support the peak inductor currents in the 1A to 2A region. To minimize radiated noise, use a toroid, pot core or shielded bobbin inductor. See Table 1 for suggested components and Table 1 for a list of component suppliers. Low ESR capacitors should be used to minimize output voltage ripple. For surface mount applications, AVX TPS series tantalum capacitors and Sanyo POSCAP or TaiyoYuden ceramic X5R or X7R type capacitors are recommended. For through-hole applications Sanyo OS-CON capacitors offer low ESR in a small package size. See Table 2 for a list of component suppliers. In some layouts it may be required to place a 1μF low ESR capacitor as close to the VOUT and GND pins as possible. Table 2. Capacitor Vendor Information SUPPLIER PHONE FAX WEBSITE AVX (803) 448-9411 (803) 448-1943 www.avxcorp.com Sanyo (619) 661-6322 (619) 661-1055 www.sanyovideo.com Taiyo Yuden (408) 573-4150 (408) 573-4159 www.t-yuden.com 3402fb 9 LTC3402 U W U U APPLICATIO S I FOR ATIO The input filter capacitor reduces peak currents drawn from the input source and reduces input switching noise. Since the IC can operate at voltages below 0.5V once the output is regulated, then demand on the input capacitor is much less and in most applications a 4.7μF is recommended. Output Diode For applications with output voltages over 4.3V, a Schottky diode is required to ensure that the SW pin voltage does not exceed its absolute maximum rating. The Schottky diode across the synchronous PMOS switch provides a lower drop during the break-before-make time (typically 20ns) of the NMOS to PMOS transition. The Schottky diode improves peak efficiency (see graph “Efficiency Loss Without Schottky vs Frequency). Use of a Schottky diode such as a MBR0520L, 1N5817 or equivalent. Since slow recovery times will compromise efficiency, do not use ordinary rectifier diodes. Operating Frequency Selection There are several considerations in selecting the operating frequency of the converter. The first is determining the sensitive frequency bands that cannot tolerate any spectral noise. For example, in products incorporating RF communications, the 455kHz IF frequency is sensitive to any noise, therefore switching above 600kHz is desired. Some communications have sensitivity to 1.1MHz. In this case, a 2MHz converter frequency may be employed. The second consideration is the physical size of the converter. As the operating frequency goes up, the inductor and filter caps go down in value and size. The trade off is in efficiency since the switching losses due to gate charge are going up proportional with frequency. For example in Figure 2, for a 2.4V to 3.3V converter, the efficiency at 100mA is 5% less at 2MHz compared to 300kHz. Another operating frequency consideration is whether the application can allow “pulse skipping.” In this mode, the minimum on time of the converter cannot support the duty cycle, so the converter ripple will go up and there will be a low frequency component of the output ripple. In many applications where physical size is the main criterion then running the converter in this mode is acceptable. In applications where it is preferred not to enter this mode, then the maximum operating frequency is given by: fMAX _ NOSKIP = VOUT – VIN Hz VOUT • tON(MIN) where tON(MIN) = minimum on time = 120ns. 100 90 Burst Mode OPERATION 80 3MHz 70 EFFICIENCY (%) Input Capacitor Selection 60 300kHz 1MHz 50 40 30 20 10 0 0.1 1 10 100 OUTPUT CURRENT (mA) 1000 3402 G08 Figure 2. Converter Efficiency 2.4V to 3.3V Reducing Output Capacitance with a Load Feed Forward Signal In many applications the output filter capacitance can be reduced for the desired transient response by having the device commanding the change in load current, (i.e. system microcontroller), inform the power converter of the changes as they occur. Specifically, a “load feed forward” signal coupled into the VC pin gives the inner current loop a head start in providing the change in output current. The transconductance of the LTC3402 converter at the VC pin with respect to the inductor current is typically 170mA/100mV, so the amount of signal injected is proportional to the anticipated change of inductor current with load. The outer voltage loop performs the remainder of the correction, but because of the load feed forward signal, the range over which it must slew is greatly reduced. This results in an improved transient response. A logic level feed forward signal, VFF, is coupled through components C5 and R6. The amount of feed forward 3402fb 10 LTC3402 U W U U APPLICATIO S I FOR ATIO signal is attenuated with resistor R6 and is given by the following relationship: ⎛ V • R5 • VIN • 1.5⎞ R6 ≈ ⎜ FF ⎟ – R5 ⎝ VOUT • ΔIOUT ⎠ The output filter zero is given by: fFILTERZERO = VOUT 10 2 6 1 LTC3402 SHDN SW VOUT MODE/SYNC FB PGOOD Rt VC GND 7 9 C3 R6 Hz 2 2πLVO The typical error amp compensation is shown in Figure 4. The equations for the loop dynamics are as follows: C5 3.3nF fPOLE1 ≈ VFF 3402 F03 Figure 3 Closing the Feedback Loop The LTC3402 used current mode control with internal adaptive slope compensation. Current mode control eliminates the 2nd order filter due to the inductor and output capacitor exhibited in voltage mode controllers, and simplifies it to a single-pole filter response. The product of the modulator control to output DC gain plus the error amp open-loop gain equals the DC gain of the system. GDC = GCONTROLOUTPUT • GEA VIN RO At heavy loads this gain increase with phase lag can occur at a relatively low frequency. The loop gain is typically rolled off before the RHP zero frequency. 8 R5 LOAD FEED FORWARD SIGNAL 2 fRHPZ = 4 5 1 Hz 2 • π • 20 • 106 • CC1 which is extremelyclose to DC 1 Hz 2 • π • RZ • CC1 1 fPOLE2 ≈ Hz 2 • π • RZ • CC2 f ZERO1 = Refer to AN76 for more closed-loop examples. VOUT + ERROR AMP – 2 • VIN GCONTROL = , GEA ≈ 2000 IOUT 1.25V R1 FB 8 R2 VC 9 CC1 The output filter pole is given by: fFILTERPOLE = IOUT Hz π • VOUT • COUT Hz A troublesome feature of the boost regulator topology is the right half plane zero (RHP) and is given by: VIN VIN 2 • π • RESR • COUT where RESR is the capacitor equivalent series resistance. where ΔIOUT = load current change. 3 1 CC2 RZ 3402 F04 Figure 4 where COUT is the output filter capacitor. 3402fb 11 LTC3402 UU OUTPUT DISCO ECT CIRCUITS Single Cell Output Disconnect ZETEX FMMT717 VIN = 0.9V TO 1.5V 3 10 2 6 1 LTC3402 4 SW VIN 8 MODE/SYNC FB PGOOD C5 1μF 9 VC Rt RB* 7 VOUT SHDN VOUT 5 GND 3402 TA03 (VOUT – VINMIN – 0.7V) • 100 *SET RB TO FORCE BETA OF ≤100; RB = IOUTMAX 0 = FIXED FREQUENCY 1 = Burst Mode OPERATION Dual Cell Output Disconnect Allowing Full Load Start-Up IRLML6401 VIN = 1.8V TO 3V R7 1M VOUT 3 10 2 6 1 LTC3402 VIN SHDN SW VOUT MODE/SYNC FB PGOOD Rt VC GND 4 RG 1M 7 8 C5 1μF 9 5 2N2222 3402 TA04 0 = FIXED FREQUENCY 1 = Burst Mode OPERATION 3402fb 12 LTC3402 U TYPICAL APPLICATIO S Single Cell to 3V at 500mA, All Ceramic Capacitor, 3MHz Step-Up Converter 3 10 +1 2 CELL 6 C1 3.3μF 1 LTC3402 SW VIN VOUT SHDN MODE/SYNC FB PGOOD VC Rt GND 90 D1 4 R2 866k 7 8 C2 10μF 70 3MHz FIXED FREQUENCY 60 50 40 30 20 9 C3 470pF 5 C4 20pF 10 R1 619k 0 0.1 R5 39k Rt 10k Burst Mode OPERATION 80 VOUT 3V 500mA EFFICIENCY (%) VIN = 0.9V TO 1.5V R3 1M R4 5.1M L1 2.2μH Efficiency 1 10 100 OUTPUT CURRENT (mA) 1000 3402 TA05b C1: TAIYO YUDEN JMK212BJ335MG C2: TAIYO YUDEN JMK325BJ106MM D1: ON SEMICONDUCTOR MBRM120T3 L1: COILCRAFT DO1608-222 0 = FIXED FREQUENCY 1 = Burst Mode OPERATION 3404 TA05a Li-Ion to 5V at 300mA, 1MHz Step-Up Converter R3 1M 3 10 Li-Ion 2 6 C1 4.7μF 1 LTC3402 VIN SHDN SW VOUT MODE/SYNC FB PGOOD Rt Rt 30.1k 0 = FIXED FREQUENCY 1 = Burst Mode OPERATION 100 D1* VC GND VOUT 5V 600mA 4 R2 1.65M 7 8 C2* 22μF 80 70 1MHz FIXED FREQUENCY 60 50 40 30 9 5 Burst Mode OPERATION 90 EFFICIENCY (%) L1 10μH VIN = 2.5V TO 4.2V Efficiency C3 470pF R5 82k 20 C4 4.7pF 10 R1 549k *LOCATE COMPONENTS AS CLOSE TO IC AS POSSIBLE C1: TAIYO YUDEN JMK212BJ475MG C2: TAIYO YUDEN JMK325BJ226MM D1: ON SEMICONDUCTOR MBRM120T3 L1: SUMIDA CDH53-100 0 VIN = 3.6V 0.1 1 100 10 LOAD CURRENT (mA) 1000 3402 G10 3402 TA07a 3402fb 13 LTC3402 U TYPICAL APPLICATIO S High Efficiency, Compact CCFL Supply with Remote Dimming C3 27pF 1kV 10 1 2 4 3 CCFL R1 300Ω VIN = 2.5V TO 4.2V 5 6 T1 C2 Q1 0.22μF Q2 L1 33μF D1 R5 Li-Ion 1M 3 10 2 6 C1 10μF 1 D4 LTC3402 VIN SHDN SW VOUT MODE/SYNC FB PGOOD Rt VC GND R4 20k DIMMING INPUT 0V TO 2.5V 4 7 D2 D3 8 R2 10k 9 5 Rt 150k C5 1μF R3 1k C4 0.1μF 3402 TA06 C1: TAIYO YUDEN JMK212BJ106MG C2: PANASONIC ECH-U D1: ZETEX ZHCS-1000 D2 TO D4: 1N4148 L1: SUMIDA CD-54-330MC Q1, Q2: ZETEX FMMT-617 T1: SUMIDA C1Q122 CCFL BACKLIGHT APPLICATION CIRCUITS CONTAINED IN THIS DATA SHEET ARE COVERED BY U.S. PATENT NUMBER 5408162 AND OTHER PATENTS PENDING 3402fb 14 LTC3402 U PACKAGE DESCRIPTION MS Package 10-Lead Plastic MSOP (Reference LTC DWG # 05-08-1661) 0.889 ± 0.127 (.035 ± .005) 5.23 (.206) MIN 3.20 – 3.45 (.126 – .136) 3.00 ± 0.102 (.118 ± .004) (NOTE 3) 0.50 0.305 ± 0.038 (.0197) (.0120 ± .0015) BSC TYP RECOMMENDED SOLDER PAD LAYOUT 0.254 (.010) 0.497 ± 0.076 (.0196 ± .003) REF 10 9 8 7 6 3.00 ± 0.102 (.118 ± .004) (NOTE 4) 4.90 ± 0.152 (.193 ± .006) DETAIL “A” 0° – 6° TYP GAUGE PLANE 1 2 3 4 5 0.53 ± 0.152 (.021 ± .006) DETAIL “A” 0.86 (.034) REF 1.10 (.043) MAX 0.18 (.007) SEATING PLANE 0.17 – 0.27 (.007 – .011) TYP 0.50 (.0197) BSC 0.127 ± 0.076 (.005 ± .003) MSOP (MS) 0603 NOTE: 1. DIMENSIONS IN MILLIMETER/(INCH) 2. DRAWING NOT TO SCALE 3. DIMENSION DOES NOT INCLUDE MOLD FLASH, PROTRUSIONS OR GATE BURRS. MOLD FLASH, PROTRUSIONS OR GATE BURRS SHALL NOT EXCEED 0.152mm (.006") PER SIDE 4. DIMENSION DOES NOT INCLUDE INTERLEAD FLASH OR PROTRUSIONS. INTERLEAD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.152mm (.006") PER SIDE 5. LEAD COPLANARITY (BOTTOM OF LEADS AFTER FORMING) SHALL BE 0.102mm (.004") MAX 3402fb 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 LTC3402 U TYPICAL APPLICATIO Triple Output Converter D2 D3 D4 D5 8V 2mA 0.1μF R3 1M 3 10 + 2 2 CELLS 6 C1 4.7μF 1 LTC3402 SW VIN SHDN VOUT MODE/SYNC FB PGOOD Rt 4.7μF VC GND VOUT 3.3V 500mA 4 R2 909k 7 8 C2 22μF 9 5 C3 470pF R5 82k Rt 30.1k 0 = FIXED FREQ 1 = Burst Mode OPERATION 0.1μF D1 L1 2.2μH VIN =1.8V TO 3V 0.1μF R1 549k C4 4.7pF 3402 TA08 0.1μF D6 C1: TAIYO YUDEN JMK212BJ475MG C2: TAIYO YUDEN JMK325BJ226MM D1: ON SEMICONDUCTOR MBRM120T3 D2 TO D7: ZETEX FMND7000 DUAL DIODE L1: SUMIDA CD43-2R2M 4.7μF D7 –2.5V 1mA RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LT®1306 Sync, Fixed Frequency, Step-Up DC/DC Converter Internal 2A Switches; VIN As Low As 1.8V LT1308A/LT1308B High Current, Micropower, Single Cell 600kHz DC/DC Converter 5V at 1A with Single Li-Ion Cell, VOUT to 34V LT1613 1.4MHz, Single Cell DC/DC Converter in SOT-23 VIN As Low As 1.1V, 3V at 30mA from Single Cell LT1615 Micropower Step-Up DC/DC Converter in SOT-23 IQ = 20μA, 1μA Shutdown Current, VIN As Low As 1V LT1619 High Efficiency Boost DC/DC Controller 1A Gate Drive, 1.1V to 20V Input, Separate VCC for Gate Drive LTC1872 SOT-23 Boost DC/DC Controller 550kHz, 2.5V to 9.8V Input LT1930/LT1930A 1.2MHz/2.2MHz DC/DC Converters in SOT-23 VIN = 2.6V to 16V, 5V at 450mA from 3.3V Input LT1949 600kHz, 1A Switch PWM DC/DC Converter 1A, 0.5Ω, 30V Internal Switch, VIN As Low As 1.5V, Low-Battery Detect Active in Shutdown LTC3400 Single Cell, High Current (600mA), Micropower, Synchronous 1.2MHz Step-Up DC/DC Converter VIN = 0.85V to 5.5V, Up to 92% Efficiency Synchronizable Oscillator from 100kHz to 1.2MHz, ThinSOT Package LTC3401 Single Cell, High Current (1A), Micropower, Synchronous 3MHz Step-Up DC/DC Converter VIN = 0.5V to 5V, Up to 97% Efficiency Synchronizable Oscillator from 100kHz to 3MHz, 10-Lead MSOP Package LTC3424 Single Cell, High Current (2A), Micropower, Synchronous 3MHz Step-Up DC/DC Converter VOUT = 1.5V, Up to 97% Efficiency Synchronizable Oscillator from 100kHz to 3MHz, 10-Lead MSOP Package 3402fb 16 Linear Technology Corporation LT 0607 REV B • PRINTED IN USA 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com © LINEAR TECHNOLOGY CORPORATION 2000