LTC3443 High Current Micropower 600kHz Synchronous Buck-Boost DC/DC Converter U FEATURES ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ DESCRIPTIO Regulated Output with Input Above, Below or Equal to the Output Single Inductor, No Schottky Diodes High Efficiency: Up to 96% 28µA Quiescent Current in Burst Mode® Operation Up to 1.2A Continuous Output Current from a Single Lithium-Ion True Output Disconnect in Shutdown 2.4V to 5.5V Input Range 2.4V to 5.25V Output Range 600kHz Fixed Frequency Operation Synchronizable Oscillator Selectable Burst Mode or Fixed Frequency Operation <1µA Quiescent Current in Shutdown Small, Thermally Enhanced 12-Lead (4mm × 3mm × 0.8mm) DFN package U APPLICATIO S ■ ■ ■ ■ Handheld Computers Handheld Instruments MP3 Players Digital Cameras The LTC®3443 is a high efficiency, fixed frequency, buckboost DC/DC converter that operates from input voltages above, below or equal to the output voltage. The part is pin for pin compatible with its predecessor, the LTC3441, with a lower operating frequency (600kHz), and a VC pin clamp circuit during Burst Mode operation. The topology incorporated in the IC provides a continuous transfer function through all operating modes, making the product ideal for single Lithium Ion or multicell applications where the output voltage is within the battery voltage range. The device includes two 0.10Ω N-channel MOSFET switches and two 0.11Ω P-channel switches. External Schottky diodes are optional, and can be used for a moderate efficiency improvement. The operating frequency is internally set to 600kHz and can be synchronized up to 1.2MHz. Quiescent current is only 28µA 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 is driven low or with a clock, then fixed frequency switching is enabled. Other features include a 1µA shutdown, soft-start control, thermal shutdown and current limit. The LTC3443 is available in a thermally enhanced 12-lead (4mm × 3mm) DFN Package. , LTC and LT are registered trademarks of Linear Technology Corporation. Burst Mode is a registered trademark of Linear Technology Corporation. U.S. Patent #’s 6404251, 6166527 U TYPICAL APPLICATIO Efficiency vs VIN Li-Ion to 3.3V at 1A Buck-Boost Converter 6µH 220pF SW2 VOUT LTC3443 VIN FB SHDN/SS 10µF PGND 2.2k 44µF (2 × 22µF) 15k VC MODE/SYNC GND Li-Ion PGND 90 340k PVIN VIN 2.5V TO 4.2V 560pF IOUT = 200mA 95 EFFICIENCY (%) SW1 100 VOUT 3.3V 1A IOUT = 1A 85 80 75 70 65 200k 60 55 3443 TA01 50 VOUT = 3.3V 2.7 3.2 3.7 4.2 VIN (V) 4.7 5.2 3443 TA02 sn3443 3443fs 1 LTC3443 W W W AXI U U ABSOLUTE RATI GS U U W PACKAGE/ORDER I FOR ATIO (Note 1) VIN, VOUT Voltage........................................ – 0.3V to 6V SW1, SW2 Voltage DC ...........................................................– 0.3V to 6V Pulsed < 100ns ...................................... – 0.3V to 7V SHDN/SS, MODE/SYNC Voltage ................. – 0.3V to 6V Operating Temperature Range (Note 2) .. – 40°C to 85°C Maximum Junction Temperature (Note 4) ........... 125°C Storage Temperature Range ................ – 65°C to 125°C ORDER PART NUMBER TOP VIEW SHDN/SS 1 12 FB GND 2 11 VC PGND 3 10 VIN SW1 4 9 PVIN SW2 5 8 VOUT PGND 6 7 MODE/SYNC 13 LTC3443EDE DE12 PACKAGE 12-LEAD (4mm × 3mm) PLASTIC DFN DE PART MARKING 3443 TJMAX = 125°C θJA = 53°C/W 1-LAYER BOARD θJA = 43°C/W 4-LAYER BOARD θJC = 4.3°C/W EXPOSED PAD IS PGND (PIN 13) MUST BE SOLDERED TO PCB 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. VIN = VOUT = 3.6V,unless otherwise noted. PARAMETER CONDITIONS MIN Input Start-Up Voltage ● Output Voltage Adjust Range ● 2.4 ● 1.19 Feedback Voltage TYP MAX UNITS 2.3 2.4 V 5.25 V 1.22 1.25 V Feedback Input Current VFB = 1.22V 1 50 nA Quiescent Current—Burst Mode Operation VC = 0V, MODE/SYNC = 3V (Note 3) 28 45 µA Quiescent Current—SHDN VOUT = SHDN = 0V, Not Including Switch Leakage 0.1 1 µA Quiescent Current—Active MODE/SYNC = 0V (Note 3) 520 900 µA NMOS Switch Leakage Switches B and C 0.1 7 µA PMOS Switch Leakage Switches A and D 0.1 10 µA NMOS Switch On Resistance Switches B and C 0.10 Ω PMOS Switch On Resistance Switches A and D Input Current Limit Max Duty Cycle Boost (% Switch C On) Buck (% Switch A In) 0.11 Ω ● 2 3.2 A ● ● 70 100 88 % % 600 Min Duty Cycle ● Frequency Accuracy ● 510 MODE/SYNC Threshold ● 0.4 MODE/SYNC Input Current VMODE/SYNC = 5.5V 0.01 0 % 690 kHz 1.4 V 1 µA Error Amp AVOL 90 dB Error Amp Source Current 14 µA Error Amp Sink Current 300 SHDN/SS Threshold When IC is Enabled SHDN/SS Threshold When EA is at Max Boost Duty Cycle SHDN/SS Input Current VSHDN = 5.5V ● 0.4 µA 1 1.4 V 2 2.4 V 0.01 1 µA sn3443 3443fs 2 LTC3443 ELECTRICAL CHARACTERISTICS Note 1: Absolute Maximum Ratings are those values beyond which the life of a device may be impaired. Note 2: The LTC3443E is guaranteed to meet performance specifications from 0°C to 70°C. Specifications over the –40°C to 85°C operating temperature range are assured by design, characterization and correlation with statistical process controls. Note 3: Current measurements are performed when the outputs are not switching. Note 4: This IC includes overtemperature protection that is intended to protect the device during momentary overload conditions. Junction temperature will exceed 125°C when overtemperature protection is active. Continuous operation above the specified maximum operating junction temperature may result in device degradation or failure. U W TYPICAL PERFOR A CE CHARACTERISTICS (TA = 25°C unless otherwise specified) MODE Transient Response: Burst Mode Operation to Fixed Frequency Li-Ion to 3.3V Efficiency MODE Transient Response: Fixed Frequency to Burst Mode Operation 100 90 EFFICIENCY (%) 80 Burst Mode OPERATION 70 60 VIN = 4.2V VIN = 2.7V VIN = 3.3V 50 VOUT 200mV/DIV AC-COUPLED VOUT 100mV/DIV AC-COUPLED MODE 5V/DIV MODE 5V/DIV 40 VOUT = 3.3V VIN = 3.3V IOUT = 30mA 30 20 500µs/DIV 3443 G03 VOUT = 3.3V VIN = 3.3V IOUT = 30mA 500µs/DIV 3443 G03 10 0 0.1 1.0 10 100 OUTPUT CURRENT (mA) 1000 3443 G01 Load Transient Response, 100mA to 1A VOUT Ripple at 1A Load BUCK VIN = 4.2V VOUT 20mV/DIV AC-COUPLED BUCK-BOOST VIN = 3.3V VOUT 100mV/DIV BOOST VIN = 2.7V 1A IOUT = 1A VOUT = 3.3V 2µs/DIV 3443 G02 100mA 100µs/DIV 3443 G03 sn3443 3443fs 3 LTC3443 U W TYPICAL PERFOR A CE CHARACTERISTICS Switch Pins Entering Buck-Boost Mode Switch Pins in Buck-Boost Mode SW1 2V/DIV SW1 2V/DIV SW2 2V/DIV SW2 2V/DIV VIN = 3.3V VOUT = 3.3V IOUT = 500mA 50ns/DIV 3443 G04 Switch Pins Before Entering Boost Mode (TA = 25°C unless otherwise specified) VIN = 4.2V VOUT = 3.3V IOUT = 500mA Active Quiescent Current 630 620 VIN = VOUT = 3.6V 50ns/DIV VIN = VOUT = 3.6V 1.236 1.231 FEEDBACK VOLTAGE (V) VIN + VOUT CURRENT (µA) SW2 2V/DIV 3443 G05 Feedback Voltage 1.241 610 SW1 2V/DIV VIN = 3V VOUT = 3.3V IOUT = 500mA 50ns/DIV 600 1.226 590 1.221 580 570 1.216 560 1.211 550 1.206 540 3443 G06 1.201 530 520 –55 –25 5 35 65 TEMPERATURE (°C) 95 125 1.196 –55 –25 5 35 65 TEMPERATURE (°C) 95 3443 G08 3443 G07 Burst Mode Quiescent Current Feedback Voltage Line Regulation VIN = VOUT = 3.6V 40 30 20 10 –55 –25 5 35 65 TEMPERATURE (°C) 95 125 3443 G09 Error Amp Source Current 20 VIN = VOUT = 2.4V TO 5.5V EA SOURCE CURRENT (µA) 90 LINE REGULATION (dB) VIN + VOUT CURRENT (µA) 50 80 70 60 –55 –25 5 35 65 TEMPERATURE (°C) 95 125 3443 G10 125 VIN = VOUT = 3.6V 15 10 5 –55 –25 5 35 65 TEMPERATURE (°C) 95 125 3443 G11 sn3443 3443fs 4 LTC3443 U W TYPICAL PERFOR A CE CHARACTERISTICS Error Amp Sink Current Output Frequency 0.70 VIN = VOUT = 3.6V 350 Current Limit 3.4 VIN = VOUT = 3.6V 250 CURRENT LIMIT (A) 300 0.60 3.2 3.0 0.55 200 –55 –25 5 35 65 TEMPERATURE (°C) 95 0.50 –55 125 –25 5 35 65 TEMPERATURE (°C) 95 3443 G12 0.13 PMOS RDS(ON) (Ω) 0.11 0.09 0.07 0.07 –25 5 35 65 TEMPERATURE (°C) 95 125 95 0.05 –50 –25 35 65 5 TEMPERATURE (°C) 3443 G15 125 2.30 VIN = VOUT = 3.6V SWITCHES A AND D 0.13 0.09 5 35 65 TEMPERATURE (°C) Minimum Start Voltage MINIMUM START VOLTAGE (V) 0.15 VIN = VOUT = 3.6V SWITCHES B AND C 0.11 –25 3443 G14 PMOS RDS(ON) 0.15 0.05 –55 2.8 –55 125 3443 G13 NMOS RDS(ON) NMOS RDS(ON) (Ω) VIN = VOUT = 3.6V 0.65 FREQUENCY (MHz) EA SINK CURRENT (µA) 400 (TA = 25°C unless otherwise specified) 95 125 3443 G16 2.25 2.20 2.15 2.10 –55 –25 5 35 65 TEMPERATURE (°C) 95 125 3443 G17 U U U PI FU CTIO S SHDN/SS (Pin 1): Combined Soft-Start and Shutdown. Applied voltage < 0.4V shuts down the IC. Tie to >1.4V to enable the IC and >2.4V 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. GND (Pin 2): Signal Ground for the IC. PGND (Pins 3, 6, 13 Exposed Pad): Power Ground for the Internal NMOS Power Switches. The exposed pad must be soldered to PCB ground for optimal thermal performance. SW1 (Pin 4): 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 this SW1 to ground. Minimize trace length to keep EMI down. SW2 (Pin 5): Switch pin where the internal switches C and D are connected. An optional Schottky diode can be connected from SW2 to VOUT (it is required where VOUT > 4.3V). Minimize trace length to keep EMI down. MODE/SYNC (Pin 7): Burst Mode Select and Oscillator Synchronization. MODE/SYNC = High: Enable Burst Mode Operation. During the period where the IC is supplying energy to the output, the inductor peak inductor current will reach 0.8A and return to zero current on each cycle. In Burst Mode operation the operation is variable frequency, which provides a significant efficiency improvement at light loads. The Burst Mode operation will continue until the pin is driven low. sn3443 3443fs 5 LTC3443 U U U PI FU CTIO S MODE/SYNC = Low: Disable Burst Mode operation and maintain low noise, constant frequency operation . PVIN (Pin 9): Power VIN Supply Pin. A 10µF ceramic capacitor is recommended as close to the PVIN and PGND pins as possible MODE/SYNC = External CLK : Synchronization of the internal oscillator and Burst Mode operation disable. A clock pulse width between 100ns and 2µs and a clock frequency between 1.38MHz and 2.4MHz (twice the desired frequency) is required to synchronize the IC. VIN (Pin 10): Input Supply Pin. Internal VCC for the IC. VC (Pin 11): 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. fOSC = fSYNC/2 VOUT (Pin 8): Output of the Synchronous Rectifier. A filter capacitor is placed from VOUT to GND. A ceramic bypass capacitor is recommended as close to the VOUT and GND pins as possible. FB (Pin 12): Feedback Pin. Connect resistor divider tap here. The output voltage can be adjusted from 2.4V to 5.25V. The feedback reference voltage is typically 1.22V. W BLOCK DIAGRA SW1 10 4 5 SW2 SW D SW A VIN SW B GATE DRIVERS AND ANTICROSS CONDUCTION VOUT ISENSE AMP gm = 1 k 100 – PGND AVERAGE CURRENT LIMIT + 1.22V R1 – PWM COMPARATORS – UVLO + PWM LOGIC AND OUTPUT PHASING ERROR AMP + – FB 12 CLAMP + – 2.4V MODE – + VCC INTERNAL CLAMP THERMAL SHUTDOWN SUPPLY CURRENT LIMIT 4A 8 REVERSE CURRENT LIMIT + 3.2A VOUT 2.4V TO 5.25V –0.4A SW C – 9 + PVIN + VIN 2.4V TO 5.5V VC 600kHz OSC 11 R2 SYNC SLEEP Burst Mode OPERATION CONTROL ÷2 SHUTDOWN SHDN/SS RSS VIN 1 5µs DELAY 7 MODE/SYNC 1 = Burst Mode OPERATION 0 = FIXED FREQUENCY CSS 2 GND 6 PGND 3443 BD sn3443 3443fs 6 LTC3443 U OPERATIO The LTC3443 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%. High efficiency is achieved at light loads when Burst Mode operation is entered and when the IC’s quiescent current is a low 28µA. LOW NOISE FIXED FREQUENCY OPERATION Oscillator The frequency of operation is factory trimmed to 600kHz. 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 of at least 100ns is applied. The oscillator sync range is 690kHz to 1.2MHz (1.38MHz to 2.4MHz sync frequency). Error Amp The error amplifier is a voltage mode amplifier. The loop compensation components are configured around the amplifier to obtain stability of the converter. The SHDN/SS pin will clamp the error amp output, VC, to provide a softstart function. Supply Current Limit The current limit amplifier will shut PMOS switch A off once the current exceeds 4A typical. Before the switch current limit, the average current limit amp (3.2A typical) will source current into the FB pin to drop the output voltage. 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 LTC3443 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. 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 sn3443 3443fs 7 LTC3443 U OPERATIO PVIN VOUT 9 8 VOUT PMOS D PMOS A SW1 SW2 4 5 NMOS B NMOS C 3443 F01 Figure 1. Simplified Diagram of Output Switches 75% DMAX BOOST A ON, B OFF BOOST REGION PWM CD SWITCHES DMIN BOOST DMAX BUCK FOUR SWITCH PWM BUCK/BOOST REGION D ON, C OFF PWM AB SWITCHES BUCK REGION 0% DUTY CYCLE 3443 F02 Figure 2. Switch Control vs Internal Control Voltage, VCI sn3443 3443fs 8 LTC3443 U OPERATIO 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. The input voltage, VIN, where the four switch region begins is given by: VIN = VOUT V 1 – (150ns • f) The point at which the four switch region ends is given by: 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 28µA. 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 800mA typical and the inductor current will terminate at zero current for each cycle. In this mode the typical maximum average output current is given by: IOUT(MAX)BURST ≈ 0.2 • 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 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: 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 88% typical and is reached when VCI is above V4. Efficiency Burst ≈ ( ηbm) • ILOAD 25µA + ILOAD where (ηbm) is typically 80% during Burst Mode operation. sn3443 3443fs 9 LTC3443 U OPERATIO 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. PVIN VOUT PVIN VOUT 9 8 9 8 4 + SW1 dI ≈ VIN L dt L D – 5 SW2 B C A IINDUCTOR A 800mA 4 – dI ≈ – VOUT L dt D + L SW1 5 SW2 B 0mA C IINDUCTOR SOFT-START 800mA 0mA 3443 F03 T1 T2 6 6 GND GND Figure 3. Inductor Charge Cycle During Burst Mode Operation 3443 F04 Figure 4. Inductor Discharge Cycle During Burst Mode Operation ERROR AMP VIN 14µA + VOUT 1.22V R1 FB – 12 VC SOFT-START CLAMP TO PWM COMPARATORS CP1 R2 11 VCI SHDN/SS RSS ENABLE SIGNAL 1 CSS + 3443 F05 CHIP ENABLE – 1V Figure 5. Soft-Start Circuitry sn3443 3443fs 10 LTC3443 U W U U APPLICATIO S I FOR ATIO COMPONENT SELECTION 1 SHDN/SS FB 12 2 GND VC 11 3 PGND VIN 10 4 SW1 PVIN 9 5 SW2 VOUT 8 6 PGND MODE 7 VIN VOUT 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. Table 1. Inductor Vendor Information 3443 F06 MULTIPLE VIAS GND 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. VOUT and VIN Ceramic Capacitors Close to the IC Pins Inductor Selection The high frequency operation of the LTC3443 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: L> L> VIN(MIN)2 • VOUT – VIN(MIN) • 100 ( ) f • IOUT(MAX) • %Ripple • VOUT ( 2 ) VOUT • VIN(MAX) – VOUT • 100 f • IOUT(MAX) • %Ripple • VIN(MAX) H, H where f = operating frequency, Hz %Ripple = allowable inductor current ripple, % VIN(MIN) = minimum input voltage, V VIN(MAX) = maximum input voltage, V VOUT = output voltage, V IOUT(MAX) = maximum output load current 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 USA: www.japanlink.com/ (847) 956-0666 (847) 956-0702 sumida Japan: 81(3) 3607-5111 81(3) 3607-5144 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 _ Boost = %Ripple _ Buck = ( ) % ) % IOUT(MAX) • VOUT – VIN(MIN) • 100 2 COUT • VOUT • f ( IOUT(MAX) • VIN(MAX) – VOUT • 100 COUT • VIN(MAX) • VOUT • f where COUT = output filter capacitor, F 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 sn3443 3443fs 11 LTC3443 U W U U APPLICATIO S I FOR ATIO above calculations in order to maintain the desired transient response. 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. Input Capacitor Selection 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 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 Output Voltage > 4.3V 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. 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 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. Operating Frequency Selection Additional quiescent current due to the output switches GATE charge is given by: Optional Schottky Diodes Buck: 800e–12 • VIN • f The Schottky diodes across the synchronous switches B and D are not required (VOUT < 4.3V), but provide a lower drop during the break-before-make time (typically 15ns) of the NMOS to PMOS transition, improving efficiency. Use a Schottky diode such as a Phillips PMEG2010EA or equivalent. Do not use ordinary rectifier diodes, since the slow recovery times will compromise efficiency. For applications with an output voltage above 4.3V, a Schottky diode is required from SW2 to VOUT. Boost: 400e–12 • (VIN + VOUT) • f Output Voltage < 2.4V The LTC3443 can operate as a buck converter with output voltages as low as 0.4V. The part is specified at 2.4V minimum to allow operation without the requirement of a Schottky diode. Synchronous switch D is powered from VOUT and the RDS(ON) will increase at low output voltages, therefore a Schottky diode is required from SW2 to VOUT to provide the conduction path to the output. Buck/Boost: f • (1200e–12 • VIN + 400e–12 • VOUT) where f = switching frequency Closing the Feedback Loop The LTC3443 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: fFILTER _ POLE = 1 Hz 2 • π • L • COUT where COUT is the output filter capacitor. sn3443 3443fs 12 LTC3443 U W U U APPLICATIO S I FOR ATIO The output filter zero is given by: fFILTER _ ZERO = 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 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 ≈ VIN = Hz 2 • π • IOUT • L • VOUT fPOLE2 = 1 Hz 2 • π • RZ • CP 2 The loop gain is typically rolled off before the RHP zero frequency. VOUT + ERROR AMP 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. 1.22V R1 FB – 12 CP1 VC 11 R2 3443 F07 Figure 7. Error Amplifier with Type I Compensation VOUT + ERROR AMP – 1.22V R1 CZ1 FB 12 VC CP1 RZ R2 11 CP2 3443 F08 Figure 8. Error Amplifier with Type III Compensation sn3443 3443fs 13 LTC3443 U TYPICAL APPLICATIO S Li-Ion to 3.3V at 1.2A Converter L1 6µH 4 9 2.8V TO 4.2V Li-Ion D2 C1 10µF SW2 5 8 VOUT 12 LTC3443 FB 1 11 VC SHDN/SS 7 2 MODE/SYNC GND 3 6 PGND PGND 10 * SW1 D1 PVIN VIN *1 = Burst Mode OPERATION 0 = FIXED FREQUENCY 340k 15k 220pF 2.2k VOUT 3.3V 1.2A C2 44µF (2 × 22µF) 560pF 200k C1: TAIYO YUDEN JMK212BJ106MG C2: TAIYO YUDEN JMK325BJ226MM D1, D2: PHILLIPS PMEG2010EA L1: SUMIDA CDRH6D28-6R0NC 3443 TA03a Efficiency vs Load 100 90 EFFICIENCY (%) 80 Burst Mode OPERATION 70 60 50 40 VIN = 3.6V VIN = 2.8V VIN = 4.2V 30 20 10 WITH SCHOTTKY DIODES: PHILIPS PMEG2010EA 0 0.1 1 10 100 IOUT (mA) 1000 10000 3443 TA03b sn3443 3443fs 14 LTC3443 U PACKAGE DESCRIPTIO DE/UE Package 12-Lead Plastic DFN (4mm × 3mm) (Reference LTC DWG # 05-08-1695) 0.65 ±0.05 3.50 ±0.05 1.70 ±0.05 2.20 ±0.05 (2 SIDES) PACKAGE OUTLINE 0.25 ± 0.05 3.30 ±0.05 (2 SIDES) 0.50 BSC RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS 4.00 ±0.10 (2 SIDES) 7 R = 0.115 TYP 0.38 ± 0.10 12 R = 0.20 TYP PIN 1 TOP MARK (NOTE 6) 3.00 ±0.10 (2 SIDES) 1.70 ± 0.10 (2 SIDES) PIN 1 NOTCH (UE12/DE12) DFN 0603 0.200 REF 0.75 ±0.05 0.00 – 0.05 6 0.25 ± 0.05 3.30 ±0.10 (2 SIDES) 1 0.50 BSC BOTTOM VIEW—EXPOSED PAD NOTE: 1. DRAWING PROPOSED TO BE A VARIATION OF VERSION (WGED) IN JEDEC PACKAGE OUTLINE M0-229 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 sn3443 3443fs 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 LTC3443 RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LT 1613 550mA (ISW) 1.4MHz High Efficiency Step-Up DC/DC Converter VIN: 0.9V to 10V, VOUT(MAX) = 34V, IQ = 3mA, ISD ≤ 1µA, ThinSOTTM LT1616 500mA (IOUT) 1.4MHz High Efficiency Step-Down DC/DC Converter High Efficiency, VIN: 3.6V to 25V, VOUT(MIN) = 1.25V, IQ = 1.9mA, ISD ≤ 1µA, ThinSOT LTC1776 500mA (IOUT) 200kHz High Efficiency Step-Down DC/DC Converter High Efficiency, VIN: 7.4V to 40V, VOUT(MIN) = 1.24V, IQ = 3.2mA, ISD ≤ 30µA, N8, S8 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 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 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 LT1930/LT1930A 1A (ISW) 1.2MHz/2.2MHz High Efficiency Step-Up DC/DC Converter VIN 2.6V to 16V, VOUT(MAX) = 34V, IQ = 5.5mA, ISD ≤ 1µA, ThinSOT ® 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 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 LTC3407 600mA (IOUT) ×2 1.5MHz Dual Synchronous Step-Down DC/DC Converter 96% Efficiency, VIN: 2.5V to 5.5V, VOUT(MIN) = 0.6V, IQ = 40µA, ISD ≤ 1µA, 10-Lead MS 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, 10-Lead MS 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 LTC3440 600mA (IOUT) 2MHz Synchronous Buck-Boost DC/DC Converter 95% Efficiency, VIN: 2.5V to 5.5V, VOUT(MIN) = 2.5V, IQ = 25µA, ISD ≤ 1µA, 10-Lead MS LTC3441 High Current Micropower 1MHz Synchronous Buck-Boost DC/DC Converter 95% Efficiency, VIN: 2.5V to 5.5V, VOUT(MIN) = 2.5V, IQ = 25µA, ISD ≤ 1µA, DFN ThinSOT is a trademark of Linear Technology Corporation. sn3443 3443fs 16 Linear Technology Corporation LT/TP 0504 1K • PRINTED IN USA 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com © LINEAR TECHNOLOGY CORPORATION 2004