LTC3442 Micropower Synchronous Buck-Boost DC/DC Converter with Automatic Burst Mode Operation DESCRIPTIO U FEATURES ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ Regulated Output with Input Voltages Above, Below, or Equal to the Output Single Inductor, No Schottky Diodes Required Manual or Programmable Automatic Burst Mode® Operation Programmable Average Input Current Limit Up to 1.2A Continuous Output Current from a Single Lithium-Ion Cell High Efficiency: Up to 95% Output Disconnect in Shutdown 2.4V to 5.5V Input Range 2.4V to 5.25V Output Range 35µA Quiescent Current in Burst Mode Operation Programmable Frequency from 300kHz to 2MHz <1µA Shutdown Current Small, Thermally Enhanced 12-Lead (4mm × 3mm) DFN Package U APPLICATIO S ■ ■ ■ ■ ■ ■ ■ The LTC®3442 is a highly efficient, fixed frequency, BuckBoost DC/DC converter, which operates from input voltages above, below, and 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 a single Lithium-Ion or multicell alkaline applications where the output voltage is within the battery voltage range. The device includes two 0.10Ω N-channel MOSFET switches and two 0.10Ω P-channel switches. Operating frequency and average input current limit can each be programmed with an external resistor. Quiescent current is only 35µA in Burst Mode operation, maximizing battery life in portable applications. Automatic Burst Mode operation allows the user to program the load current for Burst Mode operation, or to control it manually. Other features include 1µA shutdown current, programmable soft-start, peak current limit and thermal shutdown. The LTC3442 is available in a low profile, thermally enhanced 12-lead (4mm × 3mm × 0.75mm) DFN package. PDA/‘SMART’ Phones Handheld Computers MP3 Players Handheld Instruments Digital Cameras Wireless Handsets USB Peripherals , LTC and LT are registered trademarks of Linear Technology Corporation. Burst Mode is a registered trademark of Linear Technology Corporation. All other trademarks are the property of their respective owners. Protected by U.S. Patents, including 6404251, 6166527. U TYPICAL APPLICATIO Efficiency vs VIN 4.7µH 100 300mA LOAD SW2 VIN VOUT 1M Li-Ion 340k LTC3442 SHDN/SS FB RLIM VC 0.01µF 2.2k 22µF 15k RT 71.5k SGND 1A LOAD 80 70 220pF 470pF 10µF VOUT 3.3V 1.2A 90 EFFICIENCY (%) VIN 2.5V TO 4.2V SW1 60 VOUT = 3.3V L = 4.7µH F = 600kHz BURST PGND 0.01µF 200k 50 200k 2.5 3442 TA01a 3.0 3.5 4.0 VIN (V) 4.5 5.0 5.5 3442 • TA01b 3442fa 1 LTC3442 U W W W ABSOLUTE AXI U RATI GS U W U PACKAGE/ORDER I FOR ATIO (Note 1) TOP VIEW VIN, VOUT Voltage........................................... – 0.3 to 6V SW1, SW2 Voltage DC ................................................................. – 0.3 to 6V Pulsed <100ns ............................................... – 0.3 to 7V SHDN/SS, BURST Voltage ............................. – 0.3 to 6V Operating Temperature (Note 2) ............. – 40°C to 85°C Maximum Junction Temperature (Note 4) ............ 125°C Storage Temperature Range ................. – 65°C to 125°C SHDN/SS 1 12 FB RT 2 11 VC SGND 3 SW1 4 9 VIN PGND 5 8 VOUT SW2 6 7 BURST 13 10 RLIM DE12 PACKAGE 12-LEAD (4mm × 3mm) PLASTIC DFN 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 ORDER PART NUMBER DE PART MARKING LTC3442EDE 3442 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/ 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, RT = 64.9k, unless otherwise noted. PARAMETER CONDITIONS MIN Input Start-Up Voltage ● Output Voltage Adjust Range ● 2.4 Feedback Voltage ● 1.19 Feedback Input Current VFB = 1.22V TYP MAX UNITS 2.3 2.4 V 5.25 V 1.22 1.25 V 1 50 nA Quiescent Current – Burst Mode Operation VFB = 1.22V, BURST = 0V (Note 3) 35 60 µA Quiescent Current – Shutdown SHDN = 0V, VOUT = 0V, Not Including Switch Leakage 0.1 1 µA Quiescent Current – Active BURST = VIN (Note 3) 600 1100 µA NMOS Switch Leakage Switches B and C 0.1 2 µA PMOS Switch Leakage Switches A and D 0.1 3 µA NMOS Switch On Resistance Switches B and C 0.10 Ω PMOS Switch On Resistance Switches A and D 0.10 Ω ● Input Current Limit 3 A Reverse Current Limit 0.5 A Burst Mode Operation Current Limit 0.9 A 70 100 88 % % 570 670 Max Duty Cycle Boost (% Switch C On) Buck (% Switch A In) ● ● Min Duty Cycle ● Frequency Accuracy ● 2 0 % 770 kHz Error Amp AVOL 90 dB Error Amp Source Current 11 µA Error Amp Sink Current 300 µA Burst Threshold (Falling) 0.88 V Burst Threshold (Rising) 1.12 V 3442fa 2 LTC3442 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, RT = 64.9k, unless otherwise noted. PARAMETER CONDITIONS MIN TYP Burst Current Ratio Ratio of IOUT to IBURST 20,000 Input Current Ratio Ratio of IIN to IRLIM, IIN = 0.5A 70,000 RLIM Threshold When IC is Enabled When EA is at Max Boost Duty Cycle SHDN/SS Input Current VSHDN = 5.5V ● U W TYPICAL PERFOR A CE CHARACTERISTICS 100 Burst Mode 90 OPERATION 70 VIN = 2.5V 60 VIN = 5V VIN = 2.5V FIXED FREQUENCY 40 100 70 POWER LOSS 60 10 FIXED FREQUENCY 50 40 30 VOUT = 3.3V 600kHz 1 10 100 LOAD (mA) 1000 10000 30 Average Input Current Limit vs Frequency (Normalized) 15 0.40 0.30 0.20 VIN = 5V % CHANGE (NORMALIZED) 0.50 4 2 0 –2 –4 10 VOUT SHORTED 5 VOUT DROPS 10% 0 –5 –6 0.10 0.00 3442 G03 VOUT = 3.3V 6 1MHz 0.60 VIN = 3.6V VOUT = 3.3V 80 400 600 800 1000 1200 1400 1600 1800 2000 FREQUENCY (kHz) 8 VIN = 3.6V VOUT = 3.3V RLIM = 133k 0.70 WITHOUT SCHOTTKY DIODES 86 Average Input Current Limit vs VIN (Normalized) % CHANGE (NORMALIZED) RLIM VOLTAGE (V) 0.80 88 3442 G02 Input Current Mirror Linearity 0.90 90 82 0.1 10000 10 100 1000 LOAD CURRENT (mA) 3442 G01 1.00 µA 84 VIN = 3.6V VOUT = 3.3V 1 1 WITH SCHOTTKY DIODES 92 1 20 0.1 0.01 94 80 EFFICIENCY (%) EFFICIENCY (%) 80 VIN = 3.3V V V 96 EFFICIENCY (%) Burst Mode 90 OPERATION V = 5V IN 1.4 2.4 Efficiency vs Frequency 1000 POWER LOSS (mW) VIN = 3.3V 0.7 2.2 (TA = 25°C unless otherwise specified). Efficiency and Power Loss vs Load Efficiency vs Load 100 0.4 V 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. 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 LTC3442E is guaranteed to meet performance specifications from 0°C to 85°C. Specifications over –40°C to 85°C operating temperature range are assured by design, characterization and correlation with statistical process controls. 20 0.1 UNITS 0.95 SHDN/SS Threshold 50 MAX 0 .05 .10 .15 .20 .25 .30 .35 .40 .45 .50 INPUT CURRENT (A) 3442 G04 –8 2.5 3.0 3.5 4.0 4.5 5.0 VIN (V) 3442 G05 –10 0.50 0.75 1.00 1.25 1.50 FREQUENCY (MHz) 1.75 2.00 3442 TA01b 3442fa 3 LTC3442 U W TYPICAL PERFOR A CE CHARACTERISTICS Burst Mode Quiescent Current vs VIN Quiescent Current vs VIN (Fixed Frequency Mode) 45 VIN QUIESCENT CURRENT (µA) 2.0 MHz 3.0 1.5 MHz 2.5 1.0 MHz 2.0 1.5 0.5 MHz 1.0 NO SWITCHING 0.5 3.0 40 INPUT CURRENT (A) 3.5 VIN QUIESCENT CURRENT (mA) Peak Current Clamp vs VIN 3.5 50 4.0 35 30 25 20 15 10 2.0 1.5 1.0 0.5 0.0 2.5 0 3.0 3.5 4.0 VIN (V) 4.5 5.0 2.5 5.5 3.0 3.5 4.0 VIN (V) 4.5 5.0 5.5 Automatic Burst Mode Threshold vs RBURST 150 2.29 4% 2.28 3% 2.27 2% 120 110 100 90 80 70 ENTER Burst Mode OPERATION 60 150 175 200 RBURST (kΩ) 225 CHANGE FROM 25°C 5% MINIMUM START VOLTAGE (V) 2.30 130 2.26 2.25 2.24 2.23 35 65 5 TEMPERATURE (°C) 95 125 1.5% 0.8% SW1 2V/DIV CHANGE FROM 25°C 0.4% SW2 2V/DIV 0.2% 0.0% –2.0% –0.4% 50ns/DIV VIN = 2.9V VOUT = 3.3V AT 500mA –0.6% –2.0% –55 –35 –15 –0.8% 5 25 45 65 85 105 125 TEMPERATURE (°C) 3442 G13 Switch Pins Before Entering Boost Mode VIN = VOUT = 3.3V 0.6% –1.5% 5 25 45 65 85 105 125 TEMPERATURE (°C) 3442 G12 Feedback Voltage vs Temperature (Normalized) 1.0% –1.0% –5% –55 –35 –15 3442 G11 2.0% –0.5% VIN = VOUT = 3.3V –2% –3% –25 5.5 0% –4% Frequency Change vs Temperature (Normalized) 0.0% 5.0 –1% 2.21 3442 G10 0.5% 4.5 1% 2.22 2.20 –55 250 1.0% 4.0 VIN (V) Average Input Current Limit vs Temperature (Normalized) Minimum Start Voltage vs Temperature LEAVE Burst Mode OPERATION 3.5 3442 G09 160 140 3.0 3442 G08 3442 G07 CHANGE FROM 25°C 2.5 5 0.0 2.5 LOAD CURRENT (mA) (TA = 25°C unless otherwise specified). –1.0% –55 –35 –15 3442 G15 5 25 45 65 85 105 125 TEMPERATURE (°C) 3442 G14 3442fa 4 LTC3442 U W TYPICAL PERFOR A CE CHARACTERISTICS (TA = 25°C unless otherwise specified). Switch Pins Entering Buck-Boost Mode Switch Pins in Buck-Boost Mode Output Ripple at 1A Load SW1 2V/DIV SW1 2V/DIV VIN = 2.7V VIN = 3.3V SW2 2V/DIV SW2 2V/DIV VIN = 4.2V 1µs/DIV 50ns/DIV VIN = 3.3V VOUT = 3.3V AT 500mA Load Transient Response in Fixed Frequency Mode, No Load to 1A Load Transient Response in Auto Burst Mode Operation, No Load to 1A VOUT 100mV/DIV VOUT 100mV/DIV LOAD 0.5A/DIV LOAD 0.5A/DIV 100µs/DIV VIN = 3.6V VOUT = 3.3V COUT = 47µF, X5R CERAMIC 3442 G17 50ns/DIV VIN = 4.2V VOUT = 3.3V AT 500mA 3442 G16 3442 G19 3442 G18 VOUT 20mV/DIV AC COUPLED Burst Mode Operation VOUT 50mV/DIV INDUCTOR CURRENT 0.5A/DIV 100µs/DIV VIN = 3.6V VOUT = 3.3V COUT = 47µF, X5R CERAMIC + 100µF LOW ESR TANTALUM 3442 G20 Transition from Burst Mode Operation to Fixed Frequency Mode 20µs/DIV COUT = 100µF LOW ESR TANTALUM 3442 G21 Pulsed Overload Using Average Input Current Limit VOUT 2V/DIV VOUT 50mV/DIV RLIM PIN 0.5V/DIV INDUCTOR CURRENT 0.5A/DIV INDUCTOR CURRENT 0.5A/DIV 200µs/DIV COUT = 100µF LOW ESR TANTALUM 3442 G22 1ms/DIV 3442 G23 RLIM = 133k CLIM = .001µF 3442fa 5 LTC3442 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. For Burst Mode operation, this pin must be pulled up to within 0.5V of VIN. An RC network from the shutdown command signal to this pin will provide a soft-start function by limiting the rise time of the VC pin. RT (Pin 2): Programs the Frequency of the Internal Oscillator. Place a resistor from this pin to ground. See the Applications Information section for component value selection. SGND (Pin 3): Signal Ground for the IC. SW1 (Pin 4): Switch Pin Where Internal Switches A and B are Connected. Connect inductor from SW1 to SW2. An optional Schottky diode can be connected from SW1 to ground for a moderate efficiency improvement. Minimize trace length to reduce EMI. PGND (Pin 5, 13): Power Ground for the Internal NMOS Power Switches. The exposed pad must be soldered to PCB ground to provide both electrical contact and a good thermal contact to the PCB. SW2 (Pin 6): Switch Pin Where Internal Switches C and D are Connected. An optional Schottky diode can be connected from SW2 to VOUT for a moderate efficiency improvement. Minimize trace length to reduce EMI. BURST (Pin 7): Used to set the Automatic Burst Mode Operation Threshold. Place a resistor and capacitor in parallel from this pin to ground. See the Applications Information section for component value selection. For manual control, ground the pin to force Burst Mode operation, connect to VOUT to force fixed frequency mode. 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. VIN (Pin 9): Input Supply Pin. Internal VCC for the IC. A 10µF ceramic capacitor is recommended as close to VIN and SGND as possible. RLIM (Pin 10): Sets the Average Input Current Limit Threshold. Place a resistor and capacitor in parallel from this pin to ground. See the Applications Information section for component value selection. VC (Pin 11): Error Amp Output. A frequency compensation network is connected from this pin to FB to compensate the loop. During Burst Mode operation, VC is internally connected to a hold circuit. 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. 3442fa 6 LTC3442 W W SI PLIFIED BLOCK DIAGRA SW1 SW2 4 6 SW D SW A 8 SW C – SW B GATE DRIVERS AND ANTICROSS CONDUCTION VOUT + VIN 9 REVERSE AMP – RLIM 10 AV = 6 1V + + AVERAGE ILIM Gm = 1/60k – 3A – PWM LOGIC 2.3V – 11 VC UVLO + + PWM COMPARATORS – VIN AUTOMATIC BURST MODE CONTROL AND VC HOLD SLEEP RT 2 12 FB + – 5A 1.22V ERROR AMP – + + PEAK CURRENT LIMIT OSC 7 VIN SHDN/SS 1 SHUTDOWN SOFT-START VREF VCC SS BURST 1.22V VREF THERMAL SHUTDOWN SHUTDOWN 2 6 PGND SGND 3442 BD 3442fa 7 LTC3442 U OPERATIO The LTC3442 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 VC determines the output duty cycle of the switches. Since VC 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 voltage drop during the break-before-make time (typically 15ns). 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 the IC’s quiescent current drops to a low 35µA. Internal Current Limit There are three different current limit circuits in the LTC3442. Two have internally fixed thresholds which vary inversely with VIN, the third is externally programmable, and does not vary with input voltage. The first circuit is a high speed peak current limit amplifier that will shut off switch A if the current exceeds 5A typical. The delay to output of this amplifier is typically 50ns. A second amplifier will begin to source current into the FB pin to drop the output voltage once the peak input current exceeds 3A typical. This method provides a closed loop means of clamping the input current. During conditions where VOUT is near ground, such as during a short-circuit or during startup, this threshold is cut in half, providing a foldback feature. For this current limit feature to be most effective, the Thevenin resistance from FB to ground should be greater than 100kΩ. LOW NOISE FIXED FREQUENCY OPERATION Externally Programmable Current Limit Oscillator The frequency of operation is programmed by an external resistor from RT to ground, according to the following equation: f (kHz) = 43, 300 RT(kΩ) Error Amp The error amplifier is a voltage mode amplifier. The loop compensation components are configured around the amplifier (from FB to VC) to obtain stability of the converter. For improved bandwidth, an additional RC feedforward network can be placed across the upper feedback divider resistor. The voltage on SHDN/SS clamps the error amp output, VC, to provide a soft-start function. The third current limit circuit is programmed by an external resistor on RLIM. This circuit works by mirroring the input current in switch A, averaging it by means of the external RC network on RLIM, and comparing the resulting voltage with an internal reference. If the voltage on RLIM starts to exceed 0.95V, a Gm amplifier will clamp VC, lowering VOUT to maintain control of the input current. This allows the user to program a maximum average input current, for applications such as USB, where the current draw from the bus must be limited to 500mA. The resistor and capacitor values are determined by the following equations: ( RLIM(kΩ) = CLIM(µF) ≥ ⎛ 2 • VIN – VOUT 70 • ⎜ 0.86 + ⎜ 40 ⎝ )⎞⎟ ⎟ ⎠ IIN(AMPS) 0.1 RLIM(kΩ) The programmable current limit feature is disabled in Burst Mode operation. 3442fa 8 LTC3442 U OPERATIO Reverse Current Limit During fixed frequency operation, the LTC3442 operates in forced continuous conduction mode. The reverse current limit amplifier monitors the inductor current from the output through switch D. Once the negative inductor current exceeds 500mA typical, the IC will shut off switch D. Four-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 LTC3442 as a function of the internal control voltage, VCI. Depending on the control voltage, the IC will operate in either buck, buck/boost or boost mode. The VCI voltage is a level shifted voltage from the output of the error amp (VC) (see Figure 5). The four power switches are properly phased so the transfer between operating modes is continuous, smooth and transparent to the user. When VIN approaches VOUT the buck/boost region is reached where VIN VOUT 9 8 SW1 SW2 4 6 NMOS C NMOS B 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. PMOS D PMOS A 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. 3442 F01 Figure 1. Simplified Diagram of Output Switches 88% DMAX BOOST V4 (≈2.05V) 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: A ON, B OFF BOOST REGION PWM CD SWITCHES DMIN BOOST DMAX BUCK V3 (≈1.65V) FOUR SWITCH PWM BUCK/BOOST REGION VOUT 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 VIN = 3442 F02 VIN = VOUT(1 – D) = VOUT(1 – 150ns • f) V INTERNAL CONTROL VOLTAGE, VCI Figure 2. Switch Control vs Internal Control Voltage, VCI 3442fa 9 LTC3442 U OPERATIO 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. VIN VOUT 9 8 A 4 SW1 – dI ≈ – VOUT L dt D + L 6 SW2 B C IINDUCTOR Boost Region (VIN < VOUT) 900mA 0mA T2 3442 F04 5 GND BURST MODE OPERATION Figure 4. Inductor Discharge Cycle During Burst Mode Operation Burst Mode operation occurs 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 35µA of quiescent current from VIN. In this mode the output ripple has a variable frequency component that depends upon load current, and will typically be about 2% peak-to-peak. Burst Mode operation ripple can be reduced slightly by using more output capacitance (47µF or greater). Another method of reducing Burst Mode operation ripple is to place a small feed-forward capacitor across the upper resistor in the VOUT feedback divider network (as in Type III compensation). During the period where the device is delivering energy to the output, the peak switch current will be equal to 900mA 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: 0.2 • VIN IOUT(MAX)BURST ≈ A VOUT + VIN Note that the peak efficiency during Burst Mode operation is less than the peak efficiency during fixed frequency VIN VOUT 9 8 4 + SW1 dI ≈ VIN dt L L B D – 6 SW2 C IINDUCTOR A 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. The Burst Mode operation efficiency is given by: EFFICIENCY ≅ n • ILOAD 35µA + ILOAD where n is typically 82% during Burst Mode operation. Automatic Burst Mode Operation Control Burst Mode operation can be automatic or manually controlled with a single pin. In automatic mode, the IC will enter Burst Mode operation at light load and return to fixed frequency operation at heavier loads. The load current at which the mode transition occurs is programmed using a single external resistor from the BURST pin to ground, according to the following equations: 17.6 RBURST 22.4 Leave Burst Mode: I = RBURST Enter Burst Mode: I = 900mA 0mA T1 3442 F03 5 GND where RBURST is in kΩ and IBURST is the load transition Figure 3. Inductor Charge Cycle During Burst Mode Operation 3442fa 10 LTC3442 U OPERATIO current in Amps. Do not use values of RBURST greater than 250k. For automatic operation, a filter capacitor should also be connected from BURST to ground to prevent ripple on BURST from causing the IC to oscillate in and out of Burst Mode operation. The equation for the minimum capacitor value is: CBURST(MIN) ≥ COUT • VOUT 60, 000 where CBURST(MIN) and COUT are in µF In the event that a load transient causes the feedback pin to drop by more than 4% from the regulation value while in Burst Mode operation, the IC will immediately switch to fixed frequency mode and an internal pull-up will be momentarily applied to BURST, rapidly charging the BURST cap. This prevents the IC from immediately reentering Burst Mode operation once the output achieves regulation. Manual Burst Mode Operation For manual control of Burst Mode operation, the RC network connected to BURST can be eliminated. To force fixed frequency mode, BURST should be connected to VOUT. To force Burst Mode operation, BURST should be grounded. When commanding Burst Mode operation manually, the circuit connected to BURST should be able to sink up to 2mA. For optimum transient response with large dynamic loads, the operating mode should be controlled manually by the host. By commanding fixed frequency operation prior to a sudden increase in load, output voltage droop can be minimized. Note that if the load current applied during forced Burst Mode operation (BURST pin is grounded) exceeds the current that can be supplied, the output voltage will start to droop and the IC will automatically come out of Burst Mode operation and enter fixed frequency mode, raising VOUT. Once regulation is achieved, the IC will then enter Burst Mode operation once again, and the cycle will repeat, resulting in about 4% output ripple. Note that Burst Mode operation is inhibited during soft-start. Burst Mode Operation to Fixed Frequency Transient Response In Burst Mode operation, the compensation network is not used and VC is disconnected from the error amplifier. During long periods of Burst mode operation, leakage currents in the external components or on the PC board could cause the compensation capacitor to charge (or discharge), which could result in a large output transient when returning to fixed frequency mode of operation, even at the same load current. To prevent this, the LTC3442 incorporates an active clamp circuit that holds the voltage on VC at an optimal voltage during Burst Mode operation. This minimizes any output transient when returning to fixed frequency mode operation. For optimum transient 3442fa 11 LTC3442 U OPERATIO response, Type 3 compensation is also recommended to broad band the control loop and roll off past the two pole response of the output LC filter. (See Closing the Feedback Loop.) detailed diagram of this function is shown in Figure 5. The components RSS and CSS provide a slow ramping voltage on SHDN/SS to provide a soft-start function. To ensure that VC is not being clamped, SHDN/SS must be raised above 2.4V. To enable Burst Mode operation, SHDN/SS must be raised to within 0.5V of VIN. Soft-Start The soft-start function is combined with shutdown. When the SHDN/SS pin is brought above 1V typical, the IC is enabled but the EA duty cycle is clamped from VC. A 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 + 3442 F05 CHIP ENABLE – 1V Figure 5. Soft-Start Circuitry 3442fa 12 LTC3442 U W U U APPLICATIO S I FOR ATIO COMPONENT SELECTION where f = operating frequency, Hz ∆IL = maximum allowable inductor ripple current, A VIN 1 SHDN/SS FB 12 VIN(MIN) = minimum input voltage, V 2 RT VC 11 VIN(MAX) = maximum input voltage, V 3 SGND RLIM 10 4 SW1 VIN 9 VOUT = output voltage, V VIN VOUT 8 5 PGND VOUT IOUT(MAX) = maximum output load current Figure 6. Recommended Component Placement. Traces Carrying High Current Should be Short and Wide. 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. For high efficiency, choose a ferrite inductor with a high frequency core material 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 shielded inductor. See Table 1 for a suggested list of inductor suppliers. Inductor Selection Output Capacitor Selection The high frequency operation of the LTC3442 allows the use of small surface mount inductors. The inductor ripple current is typically set to 20% to 40% of the maximum inductor current. For a given ripple the inductance terms are given as follows: The bulk value of the output filter 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 = BURST 7 6 SW2 GND RT L BOOST > L BUCK > MULTIPLE VIAS 3442 F06 VIN(MIN) • ( VOUT – VIN(MIN) ) VOUT f • ∆ IL • VOUT • ( VIN(MAX ) – VOUT ) f • ∆ IL • VIN(MAX ) IOUT(MAX) • (VOUT – VIN(MIN) ) •100 COUT • VOUT 2 • f H % % RIPPLE_BUCK = IOUT(MAX) • (VIN(MAX) – VOUT ) •100 H COUT • VIN(MAX) • VOUT • f % where COUT = output filter capacitor in Farads and f = switching frequency in Hz. Table 1. Inductor Vendor Information SUPPLIER PHONE FAX WEB SITE Coilcraft (847) 639-6400 (847) 639-1469 www.coilcraft.com CoEv Magnetics (800) 227-7040 (650) 361-2508 www.circuitprotection.com/magnetics.asp Murata (814) 237-1431 (800) 831-9172 (814) 238-0490 www.murata.com Sumida USA: (847) 956-0666 Japan: 81(3) 3607-5111 USA: (847) 956-0702 Japan: 81(3) 3607-5144 www.sumida.com TDK (847) 803-6100 (847) 803-6296 www.component.tdk.com TOKO (847) 297-0070 (847) 699-7864 www.tokoam.com 3442fa 13 LTC3442 U W U U APPLICATIO S I FOR ATIO The output capacitance is usually many times larger than the minimum value in order to handle the transient response requirements 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. 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 or TDK ceramic capacitors, AVX TPS series tantalum capacitors or Sanyo POSCAP are recommended. See Table 2 for contact information. 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. Note that Burst Mode operation is inhibited at output voltages below 1.6V typical. Output Voltage > 4.3V A Schottky diode from SW2 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 Capacitor Selection Input Voltage > 4.5V Since VIN is the supply voltage for the IC, as well as the input to the power stage of the converter, it is recommended to place at least a 4.7µF, low ESR ceramic bypass capacitor close to the VIN and SGND pins. It is also important to minimize any stray resistance from the converter to the battery or other power source. 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 SW1 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 SGND pins as possible is also required. Optional Schottky Diodes 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) improving efficiency. Use a surface mount Schottky diode such as an MBRM120T3 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. Operating Frequency Selection Higher operating frequencies allow the use of a smaller inductor and smaller input and output filter capacitors, thus reducing board area and component height. However, higher operating frequencies also increase the IC’s total quiescent current due to the gate charge of the four switches, as given by: Buck: Iq = (0.8 • VIN • f) mA Output Voltage < 2.4V Boost: Iq = [0.4 • (VIN + VOUT) • f] mA The LTC3442 can operate as a buck converter with output Buck/Boost: Iq = [f • (1.2 • VIN + 0.4 • VOUT)] mA Table 2. Capacitor Vendor Information SUPPLIER PHONE FAX WEB SITE AVX (803) 448-9411 (803) 448-1943 www.avxcorp.com Murata (814) 237-1431 (800) 831-9172 (814) 238-0490 www.murata.com Sanyo (619) 661-6322 (619) 661-1055 www.sanyovideo.com Taiyo Yuden (408) 573-4150 (408) 573-4159 www.t-yuden.com TDK (847) 803-6100 (847) 803-6296 www.component.tdk.com 3442fa 14 LTC3442 U W U U APPLICATIO S I FOR ATIO where f = switching frequency in MHz. Therefore frequency selection is a compromise between the optimal efficiency and the smallest solution size. fUG = 1 Hz 2 • π • R1 • CP1 referring to Figure 7. Closing the Feedback Loop VOUT The LTC3442 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, as given by: 1.22V ERROR AMP R1 FB – 12 CP1 VC R2 11 3442 F07 1 f FILTER—POLE = 2 • π • L • COUT Hz Figure 7. Error Amplifier with Type I Compensation (in buck mode) f FILTER—POLE = + VIN 2 • VOUT • π • L • COUT Hz (in boost mode) where L is in henries and COUT is in farads. The output filter zero is given by: 1 f FILTER— ZERO = Hz 2 • π • RESR • COUT where RESR is the equivalent series resistance of the output cap. A troublesome feature in boost mode is the right-half plane zero (RHP), given by: 2 VIN f RHPZ = 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 using Type I compensation, the loop must 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: Most applications demand an improved transient response to allow a smaller output filter capacitor. To achieve a higher bandwidth, Type III compensation is required, providing two zeros to compensate for the double-pole response of the output filter. Referring to Figure 8, the location of the poles and zeros are given by: 1 fPOLE1 ≅ Hz 2 • π • 32e3 • R1 • CP1 (which is extremely close to DC) 1 Hz 2 • π • RZ • CP1 1 fZERO2 = Hz 2 • π • R1 • CZ1 1 fPOLE2 = Hz 2 • π • RZ • CP2 fZERO1 = where resistance is in ohms and capacitance is in farads. VOUT + ERROR AMP – 1.22V R1 CZ1 FB 12 VC CP1 RZ R2 11 CP2 3442 F08 Figure 8. Error Amplifier with Type III Compensation 3442fa 15 LTC3442 U TYPICAL APPLICATIO S 1MHz Li-Ion to 3.3V at 1.2A Converter with Manual Mode Control (and Peak Current Limit Only) L1 3.3µH 2.5V TO 4.2V SW2 LTC3442 VOUT VIN SW1 1M CIN 10µF SHDN/SS FB RLIM VC RT Li-Ion 0.01µF BURST 15k 2.2k COUT 22µF 220pF 470pF PGND SGND 43.2k 340k VOUT 3.3V 1.2A 200k CIN: TAIYO YUDEN JMK212BJ106MG COUT: TAIYO YUDEN JMK325BJ226MM L1: TDK RLF7030T-3R3M4R BURST FIXED FREQ 3442 TA02 Multi-Input 3.3V at 600mA Boost Converter for Portable Applications with Automatic Burst Mode Operation and Average Input Current Limit for USB Powered Devices 2Ω L1 4.7µH 1nF Li-Ion D1 MBRM120T3 2.5V TO 5.5V USB/5V CIN 10µF SW1 VIN SHDN/SS 1M RLIM 143k 2N7002 USB PRESENT SW2 LTC3442 VOUT RT 0.01µF RSNUB** 1Ω 1nF 143k SGND 64.9k 340k FB VC BURST 15k 2.2k 220pF 470pF PGND 200k 200k VOUT 3.3V 600mA COUT 22µF 0.01µF **A SNUBBER RESISTOR IS REQUIRED TO PREVENT CIN: TAIYO YUDEN JMK212BJ106MG RINGING IF THERE IS SIGNIFICANT INPUT INDUCTANCE, COUT: TAIYO YUDEN JMK325BJ476MM L1: TDK RLF7030T-4R7M3R4 SUCH AS FROM A USB CABLE 3442 TA03 3442fa 16 LTC3442 U TYPICAL APPLICATIO S High Efficiency Li-Ion Powered Constant Current LED Driver with Open-LED Protection 3.3µH R5 7.87k VIN 2.5V TO 4.2V SW1 SW2 VIN VOUT VOUT ILED = 500mA LTC3442 *OFF ON SHDN/SS FB RLIM VC 1nF 10µF RT R4 2k SGND 57.6k OPEN LED VOLTAGE LIMIT = (R4+R5)*0.95/R4 LHXL-PW03 4.7µF R2 200k BURST PGND R3 95.3k 47pF R1 301k R2 = R1/1.5 ILED = 24 • (R1+R2+R3)/(R1 • R3) AMPS 3442 TA04a * NOTE: THE SHDN/SS VOLTAGE MUST BE NO MORE THAN 0.5V BELOW VIN WHEN ENABLED. LED Driver Efficiency vs LED Current 100 98 VIN = 3.6V 750kHz 96 EFFICIENCY (%) 94 92 90 88 86 84 82 80 0.1 1.0 LED CURRENT (A) 3442 TA04b 3442fa 17 LTC3442 U TYPICAL APPLICATIO S High Current LED Driver with Low/High Current Range for Pulsed Applications; LED Current is 0.5A with 1.5A Pulse 3.3µH R5 7.87k VIN 2.7V TO 4.2V SW1 SW2 VIN VOUT VOUT ILED = 500mA/1.5A LTC3442 *OFF ON SHDN/SS FB 10µF 6.3V 1nF RLIM R2 20k VC 10µF 6.3V R2 200k RT R4 2k 57.6k LHXL-PW03 BURST PGND SGND OPEN LED VOLTAGE LIMIT = (R4+R5) • 0.95/R4 LOW HI 95.3k 1nF 40.2k 2N7002 R1 301k R2 = R1/1.5 ILED = 24 • (R1+R2+R3)/(R1 • R3) AMPS (OR: ILED = 40/R3 + .08) 3442 TA05 * NOTE: THE SHDN/SS VOLTAGE MUST BE NO MORE THAN 0.5V BELOW VIN WHEN ENABLED. 3442fa 18 LTC3442 U PACKAGE DESCRIPTIO UE/DE 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 6 0.25 ± 0.05 3.30 ±0.10 (2 SIDES) 0.00 – 0.05 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 3442fa 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 LTC3442 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 Package LT1618 1.5A (ISW), 1.25MHz, High Efficiency Step-Up DC/DC Converter VIN: 1.6V to 18V, VOUT(MAX) = 35V, IQ = 1.8mA, ISD < 1µA, MS10 Package LT1930/LT1930A 1A (ISW), 1.2MHz/2.2MHz, High Efficiency Step-Up DC/DC Converter VIN: 2.6V to 16V, VOUT(MAX) = 34V, IQ = 4.2mA/5.5mA, ISD < 1µA, ThinSOT Package LT1935 2A (ISW), 1.2MHz, 38V Step-Up DC/DC Converter VIN: 2.3V to 16V, VOUT(MAX) = 38V, IQ = 3mA, ISD < 1µA, ThinSOT Package LT1946/LT1946A 1.5A (ISW), 1.2MHz/2.7MHz, High Efficiency Step-Up DC/DC Converter VIN: 2.45V to 16V, VOUT(MAX) = 34V, IQ = 3.2mA, ISD < 1µA, MS8 Package LT1961 1.5A (ISW), 1.25MHz, High Efficiency Step-Up DC/DC Converter VIN: 3V to 25V, VOUT(MAX) = 35V, IQ = 0.9mA, ISD = 6µA, MS8E Package ® LTC3400/LTC3400B 600mA (ISW), 1.2MHz Synchronous Step-Up DC/DC Converter VIN: 0.85V to 5V, VOUT(MAX) = 5V, IQ = 19µA/300µA, ISD < 1µA, ThinSOT Package LTC3401/LTC3402 VIN: 0.5V to 5V, VOUT(MAX) = 6V, IQ = 38µA, ISD < 1µA, MS Package 1A/2A (ISW), 3MHz Synchronous Step-Up DC/DC Converter LTC3405/LTC3405A 300mA (IOUT), 1.5MHz Synchronous Step-Down DC/DC Converter VIN: 2.7V to 6V, VOUT(MIN) = 0.8V, IQ = 20µA, ISD ≤ 1µA, MS10 Package LTC3406/LTC3406B 600mA (IOUT), 1.5MHz Synchronous Step-Down DC/DC Converter VIN: 2.5V to 5.5V, VOUT(MIN) = 0.6V, IQ = 20µA, ISD ≤ 1µA, ThinSOT Package LTC3407 600mA (IOUT), 1.5MHz Dual Synchronous Step-Down DC/DC Converter VIN: 2.5V to 5.5V, VOUT(MIN) = 0.6V, IQ = 40µA, ISD ≤ 1µA, MS Package LTC3411 1.25A (IOUT), 4MHz Synchronous Step-Down DC/DC Converter VIN: 2.5V to 5.5V, VOUT(MIN) = 0.8V, IQ = 60µA, ISD ≤ 1µA, MS Package LTC3412 2.5A (IOUT), 4MHz Synchronous Step-Down DC/DC Converter VIN: 2.5V to 5.5V, VOUT(MIN) = 0.8V, IQ = 60µA, ISD ≤ 1µA, TSSOP16E Package LTC3421 3A (ISW), 3MHz Synchronous Step-Up DC/DC Converter VIN: 0.5V to 4.5V, VOUT(MAX) = 5.25V, IQ = 12µA, ISD < 1µA, QFN Package LTC3425 5A (ISW), 8MHz Multiphase Synchronous Step-Up DC/DC Converter VIN: 0.5V to 4.5V, VOUT(MAX) = 5.25V, IQ = 12µA, ISD < 1µA, QFN Package LTC3429 600mA (ISW), 500kHz Synchronous Step-Up DC/DC Converter VIN: 0.5V to 4.4V, VOUT(MIN) = 5V, IQ = 20µA, ISD < 1µA, QFN Package LTC3436 3A (ISW), 1MHz, 34V Step-Up DC/DC Converter VIN: 3V to 25V, VOUT(MAX) = 34V, IQ = 0.9mA, ISD < 6µA, TSSOP-16E Package LTC3440 600mA (IOUT), 2MHz Synchronous Buck-Boost DC/DC Converter VIN: 2.5V to 5.5V, VOUT(MIN) = 5.5V, IQ = 25µA, ISD < 1µA, MS, DFN Packages LTC3441 600mA (IOUT), 2MHz Synchronous Buck-Boost DC/DC Converter VIN: 2.5V to 5.5V, VOUT(MIN) = 5.5V, IQ = 25µA, ISD < 1µA, DFN Package LTC3443 1.2A (IOUT), 600kHz Synchronous Buck-Boost DC/DC Converter VIN: 2.4V to 5.5V, VOUT(MIN) = 5.25V, IQ = 28µA, ISD < 1µA, MS Package LT3467 1.1A (ISW), 1.3MHz, High Efficiency Step-Up DC/DC Converter VIN: 2.6V to 16V, VOUT(MAX) = 40V, IQ = 1.2mA, ISD < 1µA, ThinSOT Package ThinSOT is a trademark of Linear Technology Corporation. 3442fa 20 Linear Technology Corporation LT 0306 REV A • PRINTED IN USA 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com © LINEAR TECHNOLOGY CORPORATION 2004