LTC3440 Micropower Synchronous Buck-Boost DC/DC Converter U FEATURES DESCRIPTIO ■ The LTC®3440 is a high efficiency, fixed frequency, BuckBoost DC/DC converter that operates from input voltages above, below or equal to the output voltage. The topology incorporated in the IC provides a continuous transfer function through all operating modes, making the product ideal for single lithium-ion, multicell alkaline or NiMH applications where the output voltage is within the battery voltage range. ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ Single Inductor Fixed Frequency Operation with Battery Voltages Above, Below or Equal to the Output Synchronous Rectification: Up to 96% Efficiency 25μA Quiescent Current in Burst Mode® Operation Up to 600mA Continuous Output Current No Schottky Diodes Required (VOUT < 4.3V) VOUT Disconnected from VIN During Shutdown 2.5V to 5.5V Input and Output Range Programmable Oscillator Frequency from 300kHz to 2MHz Synchronizable Oscillator Burst Mode Enable Control <1μA Shutdown Current Small Thermally Enhanced 10-Pin MSOP and (3mm × 3mm) DFN Packages U APPLICATIO S ■ ■ ■ ■ Palmtop Computers Handheld Instruments MP3 Players Digital Cameras The device includes two 0.19Ω N-channel MOSFET switches and two 0.22Ω P-channel switches. Switching frequencies up to 2MHz are programmed with an external resistor and the oscillator can be synchronized to an external clock. Quiescent current is only 25μA 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, soft-start control, thermal shutdown and current limit. The LTC3440 is available in the 10-pin thermally enhanced MSOP and (3mm × 3mm) DFN packages. , LT, LTC and LTM are registered trademarks of Linear Technology Corporation. Burst Mode is a registered trademark of Linear Technology Corporation. Protected by U.S. Patents including 6404251, 6166527. U TYPICAL APPLICATIO Li-Ion to 3.3V at 600mA Buck-Boost Converter L1 10μH 4 SW1 SW2 LTC3440 6 7 VIN VOUT Li-Ion + 2 C1 * 10μF 1 SHDN/SS FB MODE/SYNC VC RT RT 60.4k *1 = Burst Mode OPERATION 0 = FIXED FREQUENCY GND 94 R1 340k 9 C2 22μF C5 1.5nF 10 5 R3 15k EFFICIENCY (%) 8 VOUT = 3.3V 98 IOUT = 100mA 96 fOSC = 1MHz VOUT 3.3V 600mA 3 VIN = 2.7V TO 4.2V Efficiency vs VIN 100 92 90 88 86 84 R2 200k 82 80 C1: TAIYO YUDEN JMK212BJ106MG C2: TAIYO YUDEN JMK325BJ226MM L1: SUMIDA CDRH6D38-100 2.5 3440 TA01 3.0 3.5 4.0 VIN (V) 4.5 5.0 5.5 3440 TA02 3440fb 1 LTC3440 W W W AXI U U ABSOLUTE RATI GS (Note 1) VIN, VOUT Voltage........................................ – 0.3V to 6V SW1, SW2 Voltage ..................................... – 0.3V to 6V VC, RT, FB, SHDN/SS, MODE/SYNC Voltage .................................. – 0.3V 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 U U W PACKAGE/ORDER I FOR ATIO TOP VIEW 10 VC RT 1 MODE/SYNC 2 SW1 3 SW2 4 7 VIN GND 5 6 VOUT 9 FB 11 8 SHDN/SS DD PACKAGE 10-LEAD (3mm × 3mm) PLASTIC DFN EXPOSED PAD (PIN 11) IS GND MUST BE SOLDERED TO PCB TJMAX = 125°C, θJA = 43°C/ W, θJC = 3°C/ W ORDER PART NUMBER LTC3440EDD 10 9 8 7 6 VC FB SHDN/SS VIN VOUT MS PACKAGE 10-LEAD PLASTIC MSOP DD PART MARKING LTC3440EMS MS PART MARKING TJMAX = 125°C, θJA = 130°C/ W 1 LAYER BOARD θJA = 100°C/ W 4 LAYER BOARD θJC = 45°C/ W LBKT 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 1 2 3 4 5 RT MODE/SYNC SW1 SW2 GND LTNP 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 = VOUT = 3.6V, RT = 60k, unless otherwise noted. PARAMETER CONDITIONS MIN TYP MAX UNITS 2.4 2.5 V 2.5 5.5 V 2.5 5.5 V Input Start-Up Voltage ● Input Operating Range ● Output Voltage Adjust Range ● ● 1.196 Feedback Voltage Feedback Input Current VFB = 1.22V 1.22 1.244 V 1 50 nA Quiescent Current, Burst Mode Operation VC = 0V, MODE/SYNC = 3V (Note 3) 25 40 μA Quiescent Current, Shutdown SHDN = 0V, Not Including Switch Leakage 0.1 1 μA Quiescent Current, Active VC = 0V, MODE/SYNC = 0V (Note 3) 600 1000 μA NMOS Switch Leakage Switches B and C 0.1 5 μA PMOS Switch Leakage Switches A and D 0.1 10 μA NMOS Switch On Resistance Switches B and C 0.19 Ω PMOS Switch On Resistance Switches A and D 0.22 Ω 75 % % Input Current Limit Maximum Duty Cycle Boost (% Switch C On) Buck (% Switch A On) ● 1 ● ● 55 100 Minimum Duty Cycle ● Frequency Accuracy ● MODE/SYNC Threshold MODE/SYNC Input Current A 0 0.8 1 0.4 VMODE/SYNC = 5.5V 0.01 1.2 % MHz 2 V 1 μA 3440fb 2 LTC3440 ELECTRICAL CHARACTERISTICS The ● denotes specifications that apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VIN = VOUT = 3.6V, RT = 60k, unless otherwise noted. PARAMETER CONDITIONS MIN TYP Error Amp AVOL MAX UNITS 90 dB Error Amp Source Current 15 μA Error Amp Sink Current 380 μA SHDN/SS Threshold When IC is Enabled When EA is at Maximum Boost Duty Cycle SHDN/SS Input Current VSHDN = 5.5V Note 1: Absolute Maximum Ratings are those values beyond which the life of the device may be impaired. Note 2: The LTC3440E is guaranteed to meet performance specifications from 0°C to 70°C. Specifications over the – 40°C to 85°C operating ● 0.4 1 2.2 1.5 V V 0.01 1 μA temperature range are assured by design, characterization and correlation with statistical process controls. Note 3: Current measurements are performed when the outputs are not switching. U W TYPICAL PERFOR A CE CHARACTERISTICS Li-Ion to 3.3V Efficiency (fOSC = 300kHz) 90 Burst Mode OPERATION 80 60 EFFICIENCY (%) VIN = 2.5V VIN = 3.3V 50 40 70 VIN = 4.2V VIN = 2.5V VIN = 3.3V 10 60 50 VIN = 3.3V 1 40 30 10 100 1 OUTPUT CURRENT (mA) 1000 20 0.1 70 fOSC = 1MHz 1 10 100 OUTPUT CURRENT (mA) 3440 G01 40 0.1 1000 20 0.1 fOSC = 2MHz 10 100 1 OUTPUT CURRENT (mA) Switch Pins on the Edge of Buck/Boost and Approaching Boost Switch Pins on the Edge of Buck/Boost and Approaching Buck SW1 2V/DIV SW2 2V/DIV SW2 2V/DIV SW2 2V/DIV VIN = 3.42V VOUT = 3.3V IOUT = 250mA 50ns/DIV 3440 G05 1000 3440 G03 SW1 2V/DIV 3440 G04 VIN = 3.3V 50 SW1 2V/DIV 50ns/DIV VIN = 4.2V 3440 G02 Switch Pins During Buck/Boost VIN = 3.78V VOUT = 3.3V IOUT = 250mA VIN = 2.5V 60 30 30 fOSC = 300kHz 20 0.1 POWER LOSS (mW) 70 80 100 80 VIN = 4.2V Burst Mode OPERATION 90 Burst Mode OPERATION EFFICIENCY (%) 90 100 1000 100 100 EFFICIENCY (%) Li-Ion to 3.3V Efficiency (fOSC = 2MHz) Li-Ion to 3.3V Efficiency, Power Loss (fOSC = 1MHz) VIN = 4.15V VOUT = 3.3V IOUT = 250mA 50ns/DIV 3440 G06 3440fb 3 LTC3440 U W TYPICAL PERFOR A CE CHARACTERISTICS Switch Pins in Buck Mode SW1 2V/DIV Buck VIN = 5V SW1 2V/DIV VOUT 10mV/DIV AC Coupled SW2 2V/DIV Boost VIN = 2.5V 250ns/DIV 3440 G07 VIN = 2.5V VOUT = 3.3V IOUT = 250mA Active Quiescent Current 5 35 65 TEMPERATURE (°C) 95 VIN = VOUT = 3.6V 30 20 10 –55 125 –25 5 35 65 TEMPERATURE (°C) 95 3440 G10 125 3440 G13 5 35 65 TEMPERATURE (°C) 95 VIN = VOUT = 3.6V SWITCHES B AND C 0.20 0.10 –55 –25 5 35 65 TEMPERATURE (°C) 125 Feedback Voltage 1.236 0.15 95 –25 3440 G12 FEEDBACK VOLTAGE (V) 0.95 5 35 65 TEMPERATURE (°C) 5 –55 125 0.25 NMOS RDS(ON) (Ω) FREQUENCY (MHz) 1.05 –25 10 NMOS RDS(ON) 0.30 VIN = VOUT = 3.6V 0.90 –55 15 3440 G11 Output Frequency 1.00 3440 G09 20 E/A SOURCE CURRENT (μA) VIN + VOUT CURRENT (μA) 450 1μs/DIV Error Amp Source Current VIN = VOUT = 3.6V 500 –25 L = 10μH COUT = 22μF IOUT = 250mA fOSC = 1MHz 3440 G08 40 VIN = VOUT = 3.6V 400 –55 250ns/DIV Burst Mode Quiescent Current 550 1.10 Buck/Boost VIN = 3.78V SW2 2V/DIV VIN = 5V VOUT = 3.3V IOUT = 250mA VIN + VOUT CURRENT (μA) VOUT Ripple During Buck, Buck/Boost and Boost Modes Switch Pins in Boost Mode 95 125 3440 G14 VIN = VOUT = 3V 1.216 1.196 –55 –25 5 35 65 TEMPERATURE (°C) 95 125 3440 G15 3440fb 4 LTC3440 U W TYPICAL PERFOR A CE CHARACTERISTICS Feedback Voltage Line Regulation Error Amp Sink Current 430 E/A SINK CURRENT (μA) LINE REGULATION (dB) VIN = VOUT = 2.5V TO 5.5V 80 70 60 –55 –25 5 35 65 TEMPERATURE (°C) 95 0.30 VIN = VOUT = 3.6V 410 390 370 –25 5 35 65 TEMPERATURE (°C) 95 Minimum Start Voltage 80 75 5 35 65 TEMPERATURE (°C) 95 125 3440 G19 5 35 65 TEMPERATURE (°C) 95 125 Current Limit 3000 VIN = VOUT = 3.6V PEAK SWITCH 2500 CURRENT LIMIT (A) MINIMUM START VOLTAGE (V) DUTY CYCLE (%) 85 –25 3440 G18 2.40 VIN = VOUT = 3.6V RT = 60k –25 0.10 –55 125 3440 G17 Boost Max Duty Cycle 70 –55 0.20 0.15 3440 G16 90 VIN = VOUT = 3.6V SWITCHES A AND D 0.25 350 –55 125 PMOS RDS(ON) PMOS RDS(ON) (Ω) 90 2.35 2.30 2000 AVERAGE INPUT 1500 2.25 –55 –25 5 35 65 TEMPERATURE (°C) 95 125 3440 G20 1000 –55 –25 5 35 65 TEMPERATURE (°C) 95 125 3440 G21 3440fb 5 LTC3440 U U U PI FU CTIO S RT (Pin 1): Timing Resistor to Program the Oscillator Frequency. The programming frequency range is 300kHz to 2MHz. fOSC = 6 • 1010 Hz RT MODE/SYNC (Pin 2): MODE/SYNC = External CLK : Synchronization of the internal oscillator. A clock frequency of twice the desired switching frequency and with a pulse width between 100ns and 2μs is applied. The oscillator free running frequency is set slower than the desired synchronized switching frequency to guarantee sync. The oscillator RT component value required is given by: RT = 8 • 1010 fSW ages over 4.3V, a Schottky diode is required from SW2 to VOUT to ensure the SW pin does not exhibit excess voltage. GND (Pin 5): Signal and Power Ground for the IC. VOUT (Pin 6): Output of the Synchronous Rectifier. A filter capacitor is placed from VOUT to GND. VIN (Pin 7): Input Supply Pin. Internal VCC for the IC. A ceramic bypass capacitor as close to the VIN pin and GND (Pin 5) is required. SHDN/SS (Pin 8): Combined Soft-Start and Shutdown. Grounding this pin shuts down the IC. Tie to >1.5V to enable the IC and > 2.5V to ensure the error amp is not clamped from soft-start. An RC from the shutdown command signal to this pin will provide a soft-start function by limiting the rise time of the VC pin. where fSW = desired synchronized switching frequency. FB (Pin 9): Feedback Pin. Connect resistor divider tap here. The output voltage can be adjusted from 2.5V to 5.5V. The feedback reference voltage is typically 1.22V. SW1 (Pin 3): Switch Pin Where the Internal Switches A and B are Connected. Connect inductor from SW1 to SW2. An optional Schottky diode can be connected from SW1 to ground. Minimize trace length to keep EMI down. VC (Pin 10): Error Amp Output. A frequency compensation network is connected from this pin to the FB pin to compensate the loop. See the section “Compensating the Feedback Loop” for guidelines. SW2 (Pin 4): Switch Pin Where the Internal Switches C and D are Connected. For applications with output volt- Exposed Pad (Pin 11, DFN Package Only): Ground. This pin must be soldered to the PCB and electrically connected to ground. 3440fb 6 LTC3440 W BLOCK DIAGRA SW1 3 4 SW2 SW A SW D 7 6 SW B GATE DRIVERS AND ANTICROSS CONDUCTION –0.4A SW C – + VOUT 2.5V TO 5.5V VOUT + VIN 2.5V TO 5.5V ISENSE AMP REVERSE CURRENT LIMIT SUPPLY CURRENT LIMIT – + UVLO + RT RT + 1.22V R1 – PWM COMPARATORS 9 CLAMP – 10 1 FB + 2.4V PWM LOGIC AND OUTPUT PHASING – – + 2.7A ERROR AMP VC OSC R2 SYNC SLEEP Burst Mode OPERATION CONTROL SHUTDOWN 8 SHDN/SS RSS VIN 5μs DELAY CSS MODE/SYNC 2 1 = Burst Mode OPERATION 0 = FIXED FREQUENCY 5 GND 3440 BD 3440fb 7 LTC3440 U OPERATIO The LTC3440 provides high efficiency, low noise power for applications such as portable instrumentation. The LTC proprietary topology allows input voltages above, below or equal to the output voltage by properly phasing the output switches. The error amp output voltage on the VC pin determines the output duty cycle of the switches. Since the VC pin is a filtered signal, it provides rejection of frequencies from well below the switching frequency. The low RDS(ON), low gate charge synchronous switches provide high frequency pulse width modulation control at high efficiency. Schottky diodes across the synchronous switch D and synchronous switch B are not required, but provide a lower drop during the break-before-make time (typically 15ns). The addition of the Schottky diodes will improve peak efficiency by typically 1% to 2% at 600kHz. High efficiency is achieved at light loads when Burst Mode operation is entered and when the IC’s quiescent current is a low 25μA. LOW NOISE FIXED FREQUENCY OPERATION Oscillator The frequency of operation is user programmable and is set through a resistor from the RT pin to ground where: ⎛ 6e10⎞ f=⎜ ⎟ Hz ⎝ RT ⎠ An internally trimmed timing capacitor resides inside the IC. The oscillator can be synchronized with an external clock applied to the MODE/SYNC pin. A clock frequency of twice the desired switching frequency and with a pulse width between 100ns and 2μs is applied. The oscillator RT component value required is given by: RT = 8 • 1010 fSW where fSW = desired synchronized switching frequency. For example to achieve a 1.2MHz synchronized switching frequency the applied clock frequency to the MODE/SYNC pin is set to 2.4MHz and the timing resistor, RT, is set to 66.5k (closest 1% value). Error Amp The error amplifier is a voltage mode amplifier. The loop compensation components are configured around the amplifier to provide loop compensation for the converter. The SHDN/SS pin will clamp the error amp output, VC, to provide a soft-start function. Supply Current Limit The current limit amplifier will shut PMOS switch A off once the current exceeds 2.7A typical. The current amplifier delay to output is typically 50ns. Reverse Current Limit The reverse current limit amplifier monitors the inductor current from the output through switch D. Once a negative inductor current exceeds – 400mA typical, the IC will shut off switch D. Output Switch Control Figure 1 shows a simplified diagram of how the four internal switches are connected to the inductor, VIN, VOUT and GND. Figure 2 shows the regions of operation for the LTC3440 as a function of the internal control voltage, VCI. The VCI voltage is a level shifted voltage from the output of the error amp (VC pin) (see Figure 5). The output switches are properly phased so the transfer between operation modes is continuous, filtered and transparent to the user. When VIN approaches VOUT the Buck/Boost region is reached where the conduction time of the four switch region is typically 150ns. Referring to Figures 1 and 2, the various regions of operation will now be described. VIN VOUT 7 6 PMOS D PMOS A SW1 SW2 3 4 NMOS B VOUT NMOS C 3440 F01 Figure 1. Simplified Diagram of Output Switches 3440fb 8 LTC3440 U OPERATIO 75% DMAX BOOST V4 (≈2.05V) A ON, B OFF BOOST REGION PWM CD SWITCHES DMIN BOOST DMAX BUCK V3 (≈1.65V) FOUR SWITCH PWM BUCK/BOOST REGION The input voltage, VIN, where the four switch region begins is given by: VIN = VOUT V 1 – (150ns • f) V2 (≈1.55V) The point at which the four switch region ends is given by: D ON, C OFF PWM AB SWITCHES BUCK REGION V1 (≈0.9V) 0% DUTY CYCLE 3440 F02 INTERNAL CONTROL VOLTAGE, VCI Figure 2. Switch Control vs Internal Control Voltage, VCI Buck Region (VIN > VOUT) Switch D is always on and switch C is always off during this mode. When the internal control voltage, VCI, is above voltage V1, output A begins to switch. During the off time of switch A, synchronous switch B turns on for the remainder of the time. Switches A and B will alternate similar to a typical synchronous buck regulator. As the control voltage increases, the duty cycle of switch A increases until the maximum duty cycle of the converter in Buck mode reaches DMAX_BUCK, given by: DMAX_BUCK = 100 – D4SW % where D4SW = duty cycle % of the four switch range. D4SW = (150ns • f) • 100 % where f = operating frequency, Hz. Beyond this point the “four switch,” or Buck/Boost region is reached. Buck/Boost or Four Switch (VIN ~ VOUT) When the internal control voltage, VCI, is above voltage V2, switch pair AD remain on for duty cycle DMAX_BUCK, and the switch pair AC begins to phase in. As switch pair AC phases in, switch pair BD phases out accordingly. When the VCI voltage reaches the edge of the Buck/Boost range, at voltage V3, the AC switch pair completely phase out the BD pair, and the boost phase begins at duty cycle D4SW. VIN = VOUT(1 – D) = VOUT(1 – 150ns • f) V Boost Region (VIN < VOUT) Switch A is always on and switch B is always off during this mode. When the internal control voltage, VCI, is above voltage V3, switch pair CD will alternately switch to provide a boosted output voltage. This operation is typical to a synchronous boost regulator. The maximum duty cycle of the converter is limited to 75% typical and is reached when VCI is above V4. 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 25μA. In this mode the output ripple has a variable frequency component that depends upon load current. During the period where the device is delivering energy to the output, the peak current will be equal to 400mA typical and the inductor current will terminate at zero current for each cycle. In this mode the maximum average output current is given by: IOUT(MAX)BURST ≈ 0.1 • VIN A VOUT + VIN Burst Mode operation is user controlled, by driving the MODE/SYNC pin high to enable and low to disable. The peak efficiency during Burst Mode operation is less than the peak efficiency during fixed frequency because the part enters full-time 4-switch mode (when servicing the output) with discontinuous inductor current as illustrated in Figures 3 and 4. During Burst Mode operation, the control loop is nonlinear and cannot utilize the control 3440fb 9 LTC3440 U OPERATIO voltage from the error amp to determine the control mode, therefore full-time 4-switch mode is required to maintain the Buck/Boost function. The efficiency below 1mA becomes dominated primarily by the quiescent current and not the peak efficiency. The equation is given by: Efficiency Burst ≈ Burst Mode Operation to Fixed Frequency Transient Response When transitioning from Burst Mode operation to fixed frequency, the system exhibits a transient since the modes of operation have changed. For most systems this transient is acceptable, but the application may have stringent input current and/or output voltage requirements that dictate a broad-band voltage loop to minimize the transient. Lowering the DC gain of the loop will facilitate the task (10M FB to VC) at the expense of DC load regulation. Type 3 compensation is also recommended to broad band the loop and roll off past the two pole response of the LC of the converter (see Closing the Feedback Loop). ( ηbm) • ILOAD 25μA + ILOAD where (ηbm) is typically 79% during Burst Mode operation for an ESR of the inductor of 50mΩ. For 200mΩ of inductor ESR, the peak efficiency (ηbm) drops to 75%. VIN VOUT 7 6 3 + dI ≈ VIN dT L D – L SW1 4 IINDUCTOR A SW2 B C 400mA 0mA 3440 F03 T1 5 GND Figure 3. Inductor Charge Cycle During Burst Mode Operation VIN VOUT 7 6 3 SW1 – dI ≈ – VOUT L dT + L B D 4 SW2 C IINDUCTOR A 400mA 0mA T2 3440 F04 5 GND Figure 4. Inductor Discharge Cycle During Burst Mode Operation 3440fb 10 LTC3440 U OPERATIO SOFT-START The soft-start function is combined with shutdown. When the SHDN/SS pin is brought above typically 1V, the IC is enabled but the EA duty cycle is clamped from the VC pin. A detailed diagram of this function is shown in Figure 5. The components RSS and CSS provide a slow ramping voltage on the SHDN/SS pin to provide a soft-start function. ERROR AMP VIN 15μA + VOUT 1.22V R1 FB – 9 TO PWM COMPARATORS R2 CP1 VC SOFT-START CLAMP 10 VCI SHDN/SS RSS ENABLE SIGNAL 8 3440 F05 CSS + CHIP ENABLE – 1V Figure 5. Soft-Start Circuitry U W U U APPLICATIO S I FOR ATIO COMPONENT SELECTION L1 Inductor Selection LTC3440 1 RT 2 MODE/SYNC 3 SW1 4 D2 SW2 D1 5 GND VC 10 FB 9 SHDN/SS 8 VIN 7 VOUT 6 R1 R2 VIN C1 L> MULTIPLE VIAS C2 The high frequency operation of the LTC3440 allows the use of small surface mount inductors. The inductor current ripple is typically set to 20% to 40% of the maximum inductor current. For a given ripple the inductance terms are given as follows: VOUT L> GND 3440 F06 Figure 6. Recommended Component Placement. Traces Carrying High Current are Direct. Trace Area at FB and VC Pins are Kept Low. Lead Length to Battery Should be Kept Short ( ) VIN(MIN) • VOUT – VIN(MIN) f • IOUT(MAX) • Ripple • VOUT ( VOUT • VIN(MAX) – VOUT μH, ) f • IOUT(MAX) • Ripple • VIN(MAX) μH where f = operating frequency, MHz 3440fb 11 LTC3440 U W U U APPLICATIO S I FOR ATIO Ripple = allowable inductor current ripple (e.g., 0.2 = 20%) VIN(MIN) = minimum input voltage, V VIN(MAX) = maximum input voltage, V VOUT = output voltage, V IOUT(MAX) = maximum output load current The output capacitance is usually many times larger in order to handle the transient response of the converter. For a rule of thumb, the ratio of the operating frequency to the unity-gain bandwidth of the converter is the amount the output capacitance will have to increase from the above calculations in order to maintain the desired transient response. For high efficiency, choose an inductor with a high frequency core material, such as ferrite, to reduce core loses. 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 2 for a list of component suppliers. The other component of ripple is due to the ESR (equivalent series resistance) of the output capacitor. Low ESR capacitors should be used to minimize output voltage ripple. For surface mount applications, Taiyo Yuden ceramic capacitors, AVX TPS series tantalum capacitors or Sanyo POSCAP are recommended. Table 1. Inductor Vendor Information SUPPLIER PHONE FAX WEB SITE Coilcraft (847) 639-6400 (847) 639-1469 www.coilcraft.com Coiltronics (561) 241-7876 (561) 241-9339 www.coiltronics.com Murata USA: (814) 237-1431 (800) 831-9172 USA: (814) 238-0490 www.murata.com Sumida Output Capacitor Selection The bulk value of the capacitor is set to reduce the ripple due to charge into the capacitor each cycle. The steady state ripple due to charge is given by: %Ripple _ Buck = ( ) % ) % IOUT(MAX) • VOUT – VIN(MIN) • 100 2 COUT • VOUT • f ( Since the VIN pin is the supply voltage for the IC it is recommended to place at least a 4.7μF, low ESR bypass capacitor. Table 2. Capacitor Vendor Information USA: www.japanlink.com/ (847) 956-0666 (847) 956-0702 sumida Japan: 81(3) 3607-5111 81(3) 3607-5144 %Ripple _ Boost = Input Capacitor Selection IOUT(MAX) • VIN(MAX) – VOUT • 100 COUT • VIN(MAX) • VOUT • f SUPPLIER PHONE FAX WEB SITE 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 Optional Schottky Diodes To achieve a 1%-2% efficiency improvement above 50mW, Schottky diodes can be added across synchronous switches B (SW1 to GND) and D (SW2 to VOUT). The Schottky diodes will provide a lower voltage drop during the breakbefore-make time (typically 15ns) of the NMOS to PMOS transition. General purpose diodes such as a 1N914 are not recommended due to the slow recovery times and will compromise efficiency. If desired a large Schottky diode, such as an MBRM120T3, can be used from SW2 to VOUT. A low capacitance Schottky diode is recommended from GND to SW1 such as a Phillips PMEG2010EA or equivalent. where COUT = output filter capacitor, F 3440fb 12 LTC3440 U W U U APPLICATIO S I FOR ATIO Output Voltage > 4.3V Closing the Feedback Loop A Schottky diode from SW to VOUT is required for output voltages over 4.3V. The diode must be located as close to the pins as possible in order to reduce the peak voltage on SW2 due to the parasitic lead and trace inductance. The LTC3440 incorporates voltage mode PWM control. The control to output gain varies with operation region (Buck, Boost, Buck-Boost), but is usually no greater than 15. The output filter exhibits a double pole response is given by: Input Voltage > 4.5V For applications with input voltages above 4.5V which could exhibit an overload or short-circuit condition, a 2Ω/ 1nF series snubber is required between the SW1 pin and GND. A Schottky diode such as the Phillips PMEG2010EA or equivalent from SW1 to VIN should also be added as close to the pins as possible. For the higher input voltages VIN bypassing becomes more critical, therefore, a ceramic bypass capacitor as close to the VIN and GND pins as possible is also required. fFILTER_ POLE = 1 Hz (in Buck mode) 2 • π • L • C OUT fFILTER_ POLE = VIN Hz (in Boost mode) 2π • L • VOUT where COUT is the output filter capacitor. The output filter zero is given by: fFILTER _ ZERO = Operating Frequency Selection There are several considerations in selecting the operating frequency of the converter. The first is, what are 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 and in that case a 2MHz converter frequency may be employed. Other considerations are the physical size of the converter and efficiency. As the operating frequency goes up, the inductor and filter capacitors 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. Additional quiescent current due to the output switches GATE charge is given by: Buck: 500e–12 • VIN • F Boost: 250e–12 • (VIN + VOUT) • F Buck/Boost: F • (750e–12 • VIN + 250e–12 • VOUT) where F = switching frequency 1 2 • π • RESR • COUT Hz where RESR is the capacitor equivalent series resistance. A troublesome feature in Boost mode is the right-half plane zero (RHP), and is given by: 2 fRHPZ VIN = Hz 2 • π • IOUT • L • VOUT The loop gain is typically rolled off before the RHP zero frequency. A simple Type I compensation network can be incorporated to stabilize the loop but at a cost of reduced bandwidth and slower transient response. To ensure proper phase margin, the loop requires to be crossed over a decade before the LC double pole. The unity-gain frequency of the error amplifier with the Type I compensation is given by: fUG = 1 Hz 2 • π • R1 • CP1 Most applications demand an improved transient response to allow a smaller output filter capacitor. To achieve a higher bandwidth, Type III compensation is required. Two zeros are required to compensate for the double-pole response. 3440fb 13 LTC3440 U W U U APPLICATIO S I FOR ATIO 1 Hz 2 • π • 32 e3 • R1 • CP1 Which is extremely close to DC 1 fZERO1 = Hz 2 • π • RZ • CP1 1 fZERO2 = Hz 2 • π •R1 • CZ 1 fPOLE1 ≈ 1 Hz 2 • π • RZ • CP 2 fPOLE2 = VOUT + 1.22V ERROR AMP R1 FB – 9 CP1 VC 10 R2 3440 F07 Figure 7. Error Amplifier with Type I Compensation Restart Circuit VOUT + ERROR AMP – 1.22V R1 CZ1 FB 9 VC CP1 RZ traces and external components. Following the recommendations for output voltage >4.3V and input voltage >4.5V will improve this condition. Additional short-circuit protection can be accomplished with some external circuitry. In an overload or short-circuit condition the LTC3440 voltage loop opens and the error amp control voltage on the VC pin slams to the upper clamp level. This condition forces boost mode operation in order to attempt to provide more output voltage and the IC hits a peak switch current limit of 2.7A. When switch current limit is reached switches B and D turn on for the remainder of the cycle to reverse the volts • seconds on the inductor. Although this prevents current run away, this condition produces four switch operation producing a current foldback characteristic and the average input current drops. The IC is trimmed to guarantee greater than 1A average input current to meet the maximum load demand, but in a short-circuit or overload condition the foldback characteristic will occur producing higher peak switch currents. To minimize this affect during this condition the following circuits can be utilized. For a sustained short-circuit the circuit in Figure 9 will force a soft-start condition. The only design constraint is that R2/C2 time constant must be longer than the softstart components R1/C1 to ensure start-up. R2 10 VIN CP2 3440 F08 R1 1M SOFT-START SO/SS Short-Circuit Improvements The LTC3440 is current limited to 2.7A peak to protect the IC from damage. At input voltages above 4.5V a current limit condition may produce undesirable voltages to the IC due to the series inductance of the package, as well as the R2 1M D1 1N4148 Figure 8. Error Amplifier with Type III Compensation C1 4.7nF M2 NMOS VN2222 C2 10nF M1 NMOS VN2222 VOUT 3440 F09 Figure 9. Soft-Start Reset Circuitry for a Sustained Short-Circuit 3440fb 14 LTC3440 U W U U APPLICATIO S I FOR ATIO Simple Average Input Current Control INPUT_VOLTAGE A simple average current limit circuit is shown in Figure 10. Once the input current of the IC is above approximately 1A, Q1 will start sourcing current into the FB pin and lower the output voltage to maintain the average input current. Since the voltage loop is utilized to perform average current limit, the voltage control loop is maintained and the VC voltage does not slam. The averaging function of current comes from the fact that voltage loop compensation is also used with this circuit. V1 C1 10μF Q1 2N3906 R1 0.5Ω VIN_PIN FB_PIN Figure 10. Simple Input Current Control Utilizing the Voltage Loop U TYPICAL APPLICATIO S 3-Cell to 3.3V at 600mA Converter L1 4.7μH D2 C3 33pF D1 3 VIN = 2.7V TO 4.5V 7 8 3 CELLS 2 C1 * 10μF 1 SW1 SW2 LTC3440 6 VIN VOUT FB MODE/SYNC VC RT GND R1 340k *1 = Burst Mode OPERATION 0 = FIXED FREQUENCY R5 10k 9 10 R3 15k C2 22μF C4 150pF 5 RT f OSC = 1.5MHz 45.3k R2 200k C5 10pF C1: TAIYO YUDEN JMK212BJ106MG C2: TAIYO YUDEN JMK325BJ226MM D1, D2: CENTRAL SEMICONDUCTOR CMDSH2-3 L1: SUMIDA CDR43-4R7M 3440 TA03a 3-Cell to 3.3V Efficiency 100 90 80 70 EFFICIENCY (%) + 4 SHDN/SS VOUT 3.3V 600mA 60 50 40 Burst Mode OPERATION VIN = 2.7V VIN = 4.5V VIN = 3.3V 30 20 10 fOSC = 1.5MHz 0 0.1 1 10 100 OUTPUT CURRENT (mA) 1000 3440 TA03b 3440fb 15 LTC3440 U TYPICAL APPLICATIO S 3-Cell to 5V Boost Converter with Output Disconnect L1 10μH 3-Cell to 5V Boost Efficiency D1** VOUT 5V 300mA 4 SW1 SW2 LTC3440 6 7 VIN VOUT 3 R4 1M 8 + 3 CELLS 2 C1 10μF SD C3 * 0.1μF 1 SHDN/SS FB MODE/SYNC VC RT GND 90 80 R1 619k 9 C2** 22μF 15k 10 5 C4 1.5nF R2 200k RT = 1MHz f 60.4k OSC VIN = 4.5V Burst Mode OPERATION 70 EFFICIENCY (%) VIN = 2.7V TO 4.5V 100 VIN = 3.6V VIN = 2.7V 60 50 40 30 20 10 C1: TAIYO YUDEN JMK212BJ106MG C2: TAIYO YUDEN JMK325BJ226MM D1: ON SEMICONDUCTOR MBRM120T3 L1: SUMIDA CDRH4D28-100 *1 = Burst Mode OPERATION 0 = FIXED FREQUENCY ** LOCATE COMPONENTS AS CLOSE TO IC AS POSSIBLE fOSC = 1MHz 0 1 0.1 10 100 OUTPUT CURRENT (mA) 3440 TA06a 1000 3440 TA06b Low Profile (<1.1mm) Li-Ion to 3.3V at 200mA Converter L1 4.7μH VOUT 3.3V 200mA 4 SW1 SW2 LTC3440 6 7 VIN VOUT 3 VIN = 2.5V TO 4.2V 8 Li-Ion + 2 C1 * 4.7μF 1 SHDN/SS FB MODE/SYNC RT VC GND R1 340k 9 C2 4.7μF 10 5 R3 15k C4 1.5nF RT 30.1k *1 = Burst Mode OPERATION 0 = FIXED FREQUENCY fOSC = 2MHz R2 200k C1: TAIYO YUDEN JMK212BJ475MG C2: TAIYO YUDEN JMK212BJ475MG L1: COILCRAFT LPO1704-472M 3440 TA04a Efficiency 100 90 80 Burst Mode OPERATION EFFICIENCY (%) 70 60 50 40 VIN = 2.5V VIN = 4.2V VIN = 3.3V 30 20 10 0 0.1 1 10 100 OUTPUT CURRENT (mA) 1000 3440 TA04b 3440fb 16 LTC3440 U TYPICAL APPLICATIO S Efficiency of the WCDMA Power Amp Power Supply WCDMA Power Amp Power Supply with Dynamic Voltage Control VOUT = 3.3V – 1.7V • (VDAC – 1.22V) Li-Ion + C1 * 10μF 2 1 FB MODE/SYNC RT VC GND R1 340k 10 R3 15k C4 150pF IOUT = 100mA 94 92 IOUT = 250mA 90 88 IOUT = 600mA 86 84 5 C2** 10μF R2 200k C5 10pF RT 30.1k fOSC = 2MHz *1 = Burst Mode OPERATION 0 = FIXED FREQUENCY ** LOCATE COMPONENTS AS CLOSE TO IC AS POSSIBLE R5 10k R6 200k 9 VOUT = 3.4V 96 EFFICIENCY (%) 4 SHDN/SS VOUT 0.4V TO 5V C3 33pF SW1 SW2 LTC3440 6 7 VIN VOUT 8 98 D1** 3 VIN = 2.5V TO 4.2V 100 DAC L1 3.3μH 82 80 2.5 C1, C2: TAIYO YUDEN JMK212BJ106MM D1: ON SEMICONDUCTOR MBRM120T3 L1: SUMIDA CDRH4D28-3R3 3 4 4.5 3.5 INPUT VOLTAGE (V) 5 3440 TA07a 3440 TA07b GSM Modem Powered from USB or PCMCIA with 500mA Input Current Limit L1 10μH VOUT 3.6V 2A (PULSED) 4 SW1 SW2 LTC3440 6 7 VIN VOUT 3 VIN 2.5V TO 5.5V USB/PCMCIA POWER 500mA MAX RS 0.1Ω 8 2 C1 * 10μF 1 SHDN/SS FB MODE/SYNC VC RT GND R1 392k R6 130k 9 – 10 5 C5 10nF 1/2 LT1490A C6 TO C9 470μF ×4 R2 200k R5 24k + – + 1/2 LT1490A RT 60.4k R4 1k 1N914 2N3906 ICURRENTLIMIT = 1.22 • R4 R5 • RS C1: TAIYO YUDEN JMK212BJ106MG C2: TAIYO YUDEN JMK325BJ226MM L1: SUMIDA CDRH-4D28-100 *1 = Burst Mode OPERATION 0 = FIXED FREQUENCY 3440 TA08 3440fb 17 LTC3440 U PACKAGE DESCRIPTIO DD Package 10-Lead Plastic DFN (3mm × 3mm) (Reference LTC DWG # 05-08-1699) R = 0.115 TYP 6 0.38 ± 0.10 10 0.675 ±0.05 3.50 ±0.05 1.65 ±0.05 2.15 ±0.05 (2 SIDES) 3.00 ±0.10 (4 SIDES) PACKAGE OUTLINE 1.65 ± 0.10 (2 SIDES) PIN 1 TOP MARK (SEE NOTE 6) (DD10) DFN 1103 5 0.25 ± 0.05 0.200 REF 0.50 BSC 2.38 ±0.05 (2 SIDES) RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS 1 0.75 ±0.05 0.00 – 0.05 0.25 ± 0.05 0.50 BSC 2.38 ±0.10 (2 SIDES) BOTTOM VIEW—EXPOSED PAD NOTE: 1. DRAWING TO BE MADE A JEDEC PACKAGE OUTLINE M0-229 VARIATION OF (WEED-2). CHECK THE LTC WEBSITE DATA SHEET FOR CURRENT STATUS OF VARIATION ASSIGNMENT 2. DRAWING NOT TO SCALE 3. ALL DIMENSIONS ARE IN MILLIMETERS 4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.15mm ON ANY SIDE 5. EXPOSED PAD SHALL BE SOLDER PLATED 6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION ON THE TOP AND BOTTOM OF PACKAGE 3440fb 18 LTC3440 U PACKAGE DESCRIPTIO 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) 10 9 8 7 6 3.00 ± 0.102 (.118 ± .004) (NOTE 4) 4.90 ± 0.152 (.193 ± .006) DETAIL “A” 0.497 ± 0.076 (.0196 ± .003) REF 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 3440fb 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 LTC3440 U TYPICAL APPLICATIO Li-Ion to 3.3V at 600mA Buck-Boost Converter Efficiency L1 10μH 220pF 8 Li-Ion 2 + C1 * 10μF 1 SHDN/SS FB MODE/SYNC VC RT GND R1 340k RT 60.4k *1 = Burst Mode OPERATION 0 = FIXED FREQUENCY 2.2k C2 22μF C5 300pF 10 R3 15k 90 80 9 5 100 EFFICIENCY (%) 4 SW1 SW2 LTC3440 6 7 VIN VOUT 3 VIN = 2.8V TO 4.2V VOUT 3.3V 600mA Burst Mode OPERATION 70 60 50 VIN = 4.2V VIN = 3.3V 40 30 R2 200k 20 10 C1: TAIYO YUDEN JMK212BJ106MG C2: TAIYO YUDEN JMK325BJ226MM L1: SUMIDA CDRH4D28-100 0 0.1 3440 TA01 1.0 10 100 OUTPUT CURRENT (mA) 1000 3440 TA05 RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LT1613 550mA(ISW), 1.4MHz, High Efficiency Step-Up DC/DC Converter 90% Efficiency, VIN: 0.9V to 10V, VOUT(MIN) = 34V, IQ = 3mA, ISD = <1μA, ThinSOTTM Package LT1618 1.5A(ISW), 1.25MHz, High Efficiency Step-Up DC/DC Converter 90% Efficiency, VIN: 1.6V to 18V, VOUT(MIN) = 35V, IQ = 1.8mA, ISD = <1μA, MS10 Package LTC1877 600mA(IOUT), 550kHz, Synchronous Step-Down DC/DC Converter 95% Efficiency, VIN: 2.7V to 10V, VOUT(MIN) = 0.8V, IQ = 10μA, ISD = <1μA, MS8 Package LTC1878 600mA(IOUT), 550kHz, Synchronous Step-Down DC/DC Converter 95% Efficiency, VIN: 2.7V to 6V, VOUT(MIN) = 0.8V, IQ = 10μA, ISD = <1μA, MS8 Package LTC1879 1.2A(IOUT), 550kHz, Synchronous Step-Down DC/DC Converter 95% Efficiency, VIN: 2.7V to 10V, VOUT(MIN) = 0.8V, IQ = 15μA, ISD = <1μA, TSSOP16 Package LT1961 1.5A(ISW), 1.25MHz, High Efficiency Step-Up DC/DC Converter 90% Efficiency, VIN: 3V to 25V, VOUT(MIN) = 35V, IQ = 0.9mA, ISD = 6μA, MS8E Package LTC3400/LTC3400B 600mA(ISW), 1.2MHz, Synchronous Step-Up DC/DC Converter 92% Efficiency, VIN: 0.85V to 5V, VOUT(MIN) = 5V, IQ = 19μA/300μA, ISD = <1μA, ThinSOT Package LTC3401 1A(ISW), 3MHz, Synchronous Step-Up DC/DC Converter 97% Efficiency, VIN: 0.5V to 5V, VOUT(MIN) = 6V, IQ = 38μA, ISD = <1μA, MS10 Package LTC3402 2A(ISW), 3MHz, Synchronous Step-Up DC/DC Converter 97% Efficiency, VIN: 0.5V to 5V, VOUT(MIN) = 6V, IQ = 38μA, ISD = <1μA, MS10 Package LTC3405/LTC3405A 300mA(IOUT), 1.5MHz, Synchronous Step-Down DC/DC Converter 95% Efficiency, VIN: 2.7V to 6V, VOUT(MIN) = 0.8V, IQ = 20μA, ISD = <1μA, ThinSOT Package LTC3406/LTC3406B 600mA(IOUT), 1.5MHz, Synchronous Step-Down DC/DC Converter 95% Efficiency, VIN: 2.5V to 5.5V, VOUT(MIN) = 0.6V, IQ = 20μA, ISD = <1μA, ThinSOT Package LTC3411 1.25A(IOUT), 4MHz, Synchronous Step-Down DC/DC Converter 95% Efficiency, VIN: 2.5V to 5.5V, VOUT(MIN) = 0.8V, IQ = 60μA, ISD = <1μA, MS10 Package LTC3412 2.5A(IOUT), 4MHz, Synchronous Step-Down DC/DC Converter 95% Efficiency, VIN: 2.5V to 5.5V, VOUT(MIN) = 0.8V, IQ = 60μA, ISD = <1μA, TSSOP16E Package LTC3441/LTC3443 1.2A(IOUT), 1MHz/0.6MHz, Micropower Synchronous Buck-Boost DC/DC Converter 95% Efficiency, VIN: 2.4V to 5.5V, VOUT(MIN): 2.4V to 5.25V, IQ = 25μA, ISD = <1μA, DFN Package ThinSOT is a trademark of Linear Technology Corporation. 3440fb 20 Linear Technology Corporation LT 0507 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 2001