LT3502/LT3502A 1.1MHz/2.2MHz, 500mA Step-Down Regulators in 2mm × 2mm DFN and MS10 DESCRIPTION FEATURES ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ The LT®3502/LT3502A are current mode PWM step-down DC/DC converters with an internal 500mA power switch, in tiny 8-lead 2mm × 2mm DFN and 10-lead MS10 packages. The wide input voltage range of 3V to 40V makes the LT3502/LT3502A suitable for regulating power from a wide variety of sources, including 24V industrial supplies and automotive batteries. Its high operating frequency allows the use of tiny, low cost inductors and capacitors, resulting in a very small solution. Constant frequency above the AM band avoids interfering with radio reception, making the LT3502A particularly suitable for automotive applications. 3V to 40V Input Voltage Range 500mA Output Current Switching Frequency: 2.2MHz (LT3502A), 1.1MHz (LT3502) 800mV Feedback Voltage Short-Circuit Robust Soft-Start Low Shutdown Current: <2μA Internally Compensated Internal Boost Diode Thermally Enhanced 2mm × 2mm 8-Lead DFN and 10-lead MS10 Package Cycle-by-cycle current limit and frequency foldback provide protection against shorted outputs. Soft-start and frequency foldback eliminates input current surge during start-up. DA current sense provides further protection in fault conditions. An internal boost diode reduces component count. APPLICATIONS ■ ■ ■ ■ Automotive Systems Battery-Powered Equipment Wall Transformer Regulation Distributed Supply Regulation L, LT, LTC and LTM are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners. TYPICAL APPLICATION LT3502A 12VIN Efficiency 3.3V Step-Down Converter 90 80 BD 5VOUT BOOST VIN 1μF 0.1μF 6.8μH SW LT3502A VOUT 3.3V 500mA DA OFF ON 31.6k SHDN FB GND 3.3VOUT 70 10k 10μF EFFICIENCY (%) VIN 4.7V TO 40V 60 50 40 30 20 10 3502 TA01a 0 0 0.1 0.3 0.2 LOAD CURRENT (A) 0.4 0.5 3502 TA01b 3502fc 1 LT3502/LT3502A ABSOLUTE MAXIMUM RATINGS (Note 1) Input Voltage (VIN) ....................................................40V BOOST Voltage .........................................................50V BOOST Pin Above SW Pin...........................................7V FB Voltage ...................................................................6V SHDN Voltage ...........................................................40V BD Voltage ..................................................................7V Operating Junction Temperature Range (Note 2) LT3502AE, LT3502E ...........................–40°C to 125°C LT3502AI, LT3502I .............................–40°C to 125°C Storage Temperature Range...................–65°C to 150°C PIN CONFIGURATION TOP VIEW BD 2 TOP VIEW 8 SW VIN 1 9 FB 3 SHDN 4 SW BOOST NC DA GND 7 BOOST 6 DA 5 GND 10 9 8 7 6 1 2 3 4 5 VIN NC BD FB SHDN MS PACKAGE 10-LEAD PLASTIC MSOP DC PACKAGE 8-LEAD (2mm × 2mm) PLASTIC DFN θJA = 110°C/W θJA = 102°C/W EXPOSED PAD (PIN 9) IS GND, MUST BE SOLDERED TO PCB ORDER INFORMATION LEAD FREE FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE LT3502EDC#PBF LT3502EDC#TRPBF LCLV 8-Lead 2mm × 2mm Plastic DFN –40°C to 125°C LT3502IDC#PBF LT3502IDC#TRPBF LCLV 8-Lead 2mm × 2mm Plastic DFN –40°C to 125°C LT3502AEDC#PBF LT3502AEDC#TRPBF LCLT 8-Lead 2mm × 2mm Plastic DFN –40°C to 125°C LT3502AIDC#PBF LT3502AIDC#TRPBF LCLT 8-Lead 2mm × 2mm Plastic DFN –40°C to 125°C LT3502EMS#PBF LT3502EMS#TRPBF LTDTR 10-Lead Plastic MSOP –40°C to 125°C LT3502IMS#PBF LT3502IMS#TRPBF LTDTR 10-Lead Plastic MSOP –40°C to 125°C LT3502AEMS#PBF LT3502AEMS#TRPBF LTDTS 10-Lead Plastic MSOP –40°C to 125°C LT3502AIMS#PBF LT3502AIMS#TRPBF LTDTS 10-Lead Plastic MSOP –40°C to 125°C Consult LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container. Consult LTC Marketing for information on non-standard lead based finish parts. For more information on lead free part marking, go to: http://www.linear.com/leadfree/ For more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/ 3502fc 2 LT3502/LT3502A ELECTRICAL CHARACTERISTICS The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VIN = 10V, VSHDN = 5V, VBOOST = 15V. PARAMETER CONDITIONS Undervoltage Lockout Quiescent Current at Shutdown MIN TYP MAX 2.6 2.8 3 V 0.5 2 μA 1.5 2 mA 0.8 0.8 0.8 0.8 0.813 0.81 0.816 0.813 VSHDN = 0V Quiescent Current Not Switching Feedback Voltage 2mm × 2mm DFN 2mm × 2mm DFN MS10 MS10 ● ● 0.785 0.79 0.780 0.786 Reference Voltage Line Regulation 0.005 FB Pin Bias Current (Note 5) Switching Frequency IDA < 500mA (LT3502A) IDA < 500mA (LT3502A) IDA < 500mA (LT3502) IDA < 500mA (LT3502) ● ● ● UNITS V V V V %/V 15 50 nA 1.9 1.8 0.9 0.8 2.25 2.25 1.1 1.1 2.7 2.8 1.3 1.4 MHz MHz MHz MHz 70 80 80 90 % % 450 mV Maximum Duty Cycle 100mA Load (LT3502A) 100mA Load (LT3502) Switch VCESAT ISW = 500mA Switch Current Limit (Note 3) 0.9 1.1 A Switch Active Current SW = 10V (Note 4) SW = 0V (Note 5) 95 8 130 30 μA μA BOOST Pin Current ISW = 500mA 10 13 mA Minimum BOOST Voltage Above Switch ISW = 500mA 1.9 2.2 V BOOST Schottky Forward Drop IOUT = 100mA 0.8 1 V DA Pin Current to Stop OSC SHDN Bias Current 0.75 500 VSHDN = 5V VSHDN = 0V SHDN Input Voltage High SHDN Input Voltage Low 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 LT3502EDC and LT3502AEDC are guaranteed to meet performance specifications from 0°C to 125°C junction temperature range. Specifications over the –40°C to 125°C operating junction temperature range are assured by design, characterization and correlation 650 55 mA 80 1 2 μA μA V 0.3 V with statistical process controls. The LT3502IDC and LT3502AIDC are guaranteed over the – 40°C to 125°C operating junction temperature range. Note 3: Current limit guaranteed by design and/or correlation to static test. Slope compensation reduces current limit at higher duty cycle. Note 4: Current flows into pin. Note 5: Current flows out of pin. 3502fc 3 LT3502/LT3502A TYPICAL PERFORMANCE CHARACTERISTICS LT3502A 3.3VOUT Efficiency LT3502A 5VOUT Efficiency 12VIN 70 12VIN 70 24VIN EFFICIENCY (%) 60 50 40 30 24VIN 80 60 50 40 30 40 30 20 10 10 0 0 0.3 0.2 LOAD CURRENT (A) 0 0.5 0.4 0.1 0.3 0.2 LOAD CURRENT (A) 12VIN 1.0 1.0 0.9 0.9 TYPICAL 50 40 30 TYPICAL MINIMUM 0.7 0.6 0.5 0.4 0.3 0.7 0.5 0.4 0.3 20 0.2 10 0.1 0.1 0 0 0.1 0.3 0.4 0.2 LOAD CURRENT (A) 0.5 0 0 10 20 VIN (V) 30 3502 G04 40 TYPICAL 600 MINIMUM 500 0.7 0.5 0.4 0.3 0.6 0.5 0.4 0.3 0.2 0.2 0.1 0.1 30 40 VIN (V) VCE (mV) LOAD CURRENT (A) MINIMUM 0.6 20 30 700 0.8 TYPICAL 0.7 10 20 VIN (V) Switch Voltage Drop 0.9 0 10 3502 G06 LT3502 Maximum Load Current VOUT = 5V, L = 22μH 0.9 0 0 40 3502 G05 LT3502 Maximum Load Current VOUT = 3.3V, L = 15μH 0.8 MINIMUM 0.6 0.2 0 0.5 0.8 LOAD CURRENT (A) LOAD CURRENT (A) 60 0.3 0.4 0.2 LOAD CURRENT (A) LT3502A Maximum Load Current VOUT = 5V, L = 10μH 0.8 24VIN 70 0.1 3502 G03 LT3502A Maximum Load Current VOUT = 3.3V, L = 6.8μH 100 80 0 3502 G02 LT3502 5VOUT Efficiency 90 0.5 0.4 3502 G01 EFFICIENCY (%) 50 10 0.1 12VIN 60 20 0 24VIN 70 20 0 5VIN 90 80 EFFICIENCY (%) 80 EFFICIENCY (%) LT3502 3.3VOUT Efficiency 100 90 90 LOAD CURRENT (A) (TA = 25°C unless otherwise noted) 0 125°C 300 200 100 0 0 10 20 30 40 0 0.2 0.4 0.6 0.8 1.0 SWITCH CURRENT (A) VIN (V) 3502 G07 –40°C 25°C 400 3502 G08 3502 G09 3502fc 4 LT3502/LT3502A TYPICAL PERFORMANCE CHARACTERISTICS UVLO (TA = 25°C unless otherwise noted) Switching Frequency 3.5 Soft-Start (SHDN) 0.9 2.5 LT3502A 0.8 3.0 FREQUENCY (MHz) VIN (V) 2.5 2.0 1.5 1.0 SWITCH CURRENT LIMIT (A) 2.0 1.5 LT3502 1.0 0.5 0.5 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 0 –50 0 50 0 –50 150 100 TEMPERATURE (°C) –0.1 0 50 100 TEMPERATURE (°C) 3502 G10 0 150 200 400 600 800 1000 1200 1400 1600 SHDN PIN VOLTAGE (mV) 3502 G12 3502 G11 SHDN Pin Current Switch Current Limit Switch Current Limit 1.0 300 1.2 0.9 0.8 200 150 100 1.0 SW PEAK CURRENT LIMIT 0.7 CURRENT LIMIT (A) CURRENT LIMIT (A) SHDN PIN CURRENT (μA) 250 DA VALLEY CURRENT LIMIT 0.6 0.5 0.4 0.3 0.2 50 LT3502 0.8 LT3502A 0.6 0.4 0.2 0.1 0 0 5 10 15 20 25 30 35 SHDN PIN VOLTAGE (V) 40 0 –50 45 0 0 LT3502A Maximum VIN for Full Frequency (VOUT = 3.3V) LT3502 Maximum VIN for Full Frequency (VOUT = 3.3V) 45 TA = 25°C 35 TA = 85°C 45 40 40 35 35 30 VIN (V) 25 20 30 TA = 25°C 25 VIN (V) 30 TA = 85°C 20 15 15 10 10 5 5 5 0 0.1 0.2 0.3 0.4 0.5 LOAD CURRENT (A) 0.6 0.7 3502 G16 TA = 85°C 20 15 0 TA = 25°C 25 10 0 100 3502 G15 LT3502A Maximum VIN for Full Frequency (VOUT = 5V) 45 40 50 DUTY CYCLE (%) 3502 G14 3502 G13 VIN (V) 0 150 50 100 TEMPERATURE (°C) 0 0 0.1 0.2 0.3 0.4 0.5 LOAD CURRENT (A) 0.6 0.7 3502 G17 0 0.1 0.2 0.3 0.4 0.5 LOAD CURRENT (A) 0.6 0.7 3502 G18 3502fc 5 LT3502/LT3502A TYPICAL PERFORMANCE CHARACTERISTICS LT3502A Typical Minimum Input Voltage (VOUT = 3.3V) (TA = 25°C unless otherwise noted) LT3502A Typical Minimum Input Voltage (VOUT = 5V) LT3502 Typical Minimum Input Voltage (VOUT = 3.3V) 7 8 7 6 7 6 6 5 5 3 VIN (V) 4 VIN (V) VIN (V) 5 4 4 3 3 2 2 2 1 1 1 0 0.001 0.1 0.01 LOAD CURRENT (A) 1 0 0.001 0.01 0.1 LOAD CURRENT (A) 1 0 0.001 0.1 0.01 LOAD CURRENT (A) 3502 G20 3502 G19 LT3502 Typical Minimum Input Voltage (VOUT = 5V) 1 3502 G21 Continuous Mode Waveform Discontinuous Mode Waveform 8 7 5 VIN (V) VSW 5V/DIV VSW 5V/DIV 6 IL 200mA/DIV 4 3 IL 200mA/DIV VOUT 20mV/DIV VOUT 20mV/DIV 2 1 0 0.001 0.01 0.1 LOAD CURRENT (A) 1 VIN = 12V VOUT = 3.3V L = 6.8μH COUT = 10μF IOUT = 250mA 200ns/DIV 3502 G23 VIN = 12V VOUT = 3.3V L = 6.8μH COUT = 10μF IOUT = 30mA 200ns/DIV 3502 G24 3502 G22 3502fc 6 LT3502/LT3502A PIN FUNCTIONS (DFN/MS) VIN (Pin 1/Pin 10): The VIN pin supplies current to the LT3502/LT3502A’s internal regulator and to the internal power switch. This pin must be locally bypassed. BD (Pin 2/Pin 8): The BD pin is used to provide current to the internal boost Schottky diode. FB (Pin 3/Pin 7): The LT3502/LT3502A regulate their feedback pin to 0.8V. Connect the feedback resistor divider tap to this pin. Set the output voltage according to VOUT = 0.8(1 + R1/R2). A good value for R2 is 10k. SHDN (Pin 4/Pin 6): The SHDN pin is used to put the LT3502 in shutdown mode. Tie to ground to shut down the LT3502/LT3502A. Tie to 2V or more for normal operation. If the shutdown feature is not used, tie this pin to the VIN pin. The SHDN pin also provides soft-start and frequency foldback. To use the soft-start feature, connect R3 and C4 to the SHDN pin. SHDN Pin voltage should not be higher than VIN. GND (Pin 5/Pin 5): Ground Pin. DA (Pin 6/Pin 4): Connect the catch diode (D1) anode to this pin. This pin is used to provide frequency foldback in extreme situations. BOOST (Pin 7/Pin 2): The BOOST pin is used to provide a drive voltage, higher than the input voltage, to the internal bipolar NPN power switch. Connect a boost capacitor from this pin to SW Pin. SW (Pin 8/Pin 1): The SW pin is the output of the internal power switch. Connect this pin to the inductor, catch diode and boost capacitor. 3502fc 7 8 ON OFF VIN C4 R3 C2 4 1 SHDN VIN SLOPE COMP FREQUENCY FOLDBACK OSC INT REG AND UVLO ∑ VC gm S R R2 0.8V Q Q 3 R1 FB DRIVER Q1 GND DA SW BOOST BD 5 6 8 7 2 C1 L1 D1 C3 3502 BD VOUT LT3502/LT3502A BLOCK DIAGRAM 3502fc LT3502/LT3502A OPERATION The LT3502/LT3502A are constant frequency, current mode step-down regulators. An oscillator enables an RS flip-flop, turning on the internal 500mA power switch Q1. An amplifier and comparator monitor the current flowing between the VIN and SW pins, turning the switch off when this current reaches a level determined by the voltage at VC. An error amplifier measures the output voltage through an external resistor divider tied to the FB pin and servos the VC node. If the error amplifier’s output increases, more current is delivered to the output; if it decreases, less current is delivered. An active clamp (not shown) on the VC node provides current limit. The VC node is also clamped to the voltage on the SHDN pin; soft-start is implemented by generating a voltage ramp at the SHDN pin using an external resistor and capacitor. The SHDN pin voltage during soft-start also reduces the oscillator frequency to avoid hitting current limit during start-up. An internal regulator provides power to the control circuitry. This regulator includes an undervoltage lockout to prevent switching when VIN is less than ~3V. The SHDN pin is used to place the LT3502/LT3502A in shutdown, disconnecting the output and reducing the input current to less than 2μA. The switch driver operates from either VIN or from the BOOST pin. An external capacitor and the internal diode are used to generate a voltage at the BOOST pin that is higher than the input supply. This allows the driver to fully saturate the internal bipolar NPN power switch for efficient operation. A comparator monitors the current flowing through the catch diode via the DA pin and reduces the LT3502/ LT3502A’s operating frequency when the DA pin current exceeds the 650mA valley current limit. This frequency foldback helps to control the output current in fault conditions such as shorted output with high input voltage. The DA comparator works in conjunction with the switch peak current limit comparator to determine the maximum deliverable current of the LT3502/LT3502A. The peak current limit comparator is used in normal current mode operations and is used to turn off the switch. The DA valley current comparator monitors the catch diode current and will delay switching until the catch diode current is below the 650mA limit. Maximum deliverable current to the output is therefore limited by both switch peak current limit and DA valley current limit. 3502fc 9 LT3502/LT3502A APPLICATIONS INFORMATION FB Resistor Network The output voltage is programmed with a resistor divider between the output and the FB pin. Choose the 1% resistors according to: V R1= R2 OUT – 1 0.8V R2 should be 20k or less to avoid bias current errors. Reference designators refer to the Block Diagram. Input Voltage Range The input voltage range for the LT3502/LT3502A applications depends on the output voltage and on the absolute maximum ratings of the VIN and BOOST pins. The minimum input voltage is determined by either the LT3502/LT3502A’s minimum operating voltage of 3V, or by its maximum duty cycle. The duty cycle is the fraction of time that the internal switch is on and is determined by the input and output voltages: VOUT + VD DC = VIN – VSW + VD where VD is the forward voltage drop of the catch diode (~0.4V) and VSW is the voltage drop of the internal switch (~0.45V at maximum load). This leads to a minimum input voltage of: V +V VIN(MIN) = OUT D – VD + VSW DCMAX with DCMAX = 0.80 for the LT3502A and 0.90 for the LT3502. The maximum input voltage is determined by the absolute maximum ratings of the VIN and BOOST pins. For fixed frequency operation, the maximum input voltage is determined by the minimum duty cycle DCMIN: V +V VIN(MAX) = OUT D – VD + VSW DCMIN Note that this is a restriction on the operating input voltage for fixed frequency operation; the circuit will tolerate transient inputs up to the absolute maximum ratings of the VIN and BOOST pins. The input voltage should be limited to the VIN operating range (40V) during overload conditions. Minimum On Time The LT3502/LT3502A will still regulate the output at input voltages that exceed VIN(MAX) (up to 40V), however, the output voltage ripple increases as the input voltage is increased. As the input voltage is increased, the part is required to switch for shorter periods of time. Delays associated with turning off the power switch dictate the minimum on time of the part. The minimum on time for the LT3502/LT3502A is 60ns (Figure 1). When the required on time decreases below the minimum on time of 60ns, instead of the switch pulse width becoming narrower to accommodate the lower duty cycle requirement, the switch pulse width remains fixed at 60ns. The inductor current ramps up to a value exceeding the load current and the output ripple increases. The part then remains VSW 20V/DIV IL 500mA/DIV VOUT 100mV/DIV VIN = 33V VOUT = 3.3V L = 6.8μH COUT = 10μF IOUT = 250mA 1μs/DIV 3502 F01 Figure 1. Continuous Mode Operation Near Minimum On Time of 60ns DCMIN = 0.15 for the LT3502A and 0.08 for the LT3502. 3502fc 10 LT3502/LT3502A APPLICATIONS INFORMATION VSW 20V/DIV VSW 20V/DIV IL 500mA/DIV IL 500mA/DIV VOUT 100mV/DIV VOUT 100mV/DIV VIN = 40V VOUT = 3.3V L = 6.8μH COUT = 10μF IOUT = 250mA 1μs/DIV 3502 F02 Figure 2. Pulse Skip Occurs when Required On Time is Below 60ns off until the output voltage dips below the programmed value before it begins switching again (Figure 2). Provided that the load can tolerate the increased output voltage ripple and that the components have been properly selected, operation above VIN(MAX) is safe and will not damage the part. As the input voltage increases, the inductor current ramps up quicker, the number of skipped pulses increases and the output voltage ripple increases. For operation above VIN(MAX) the only component requirement is that the components be adequately rated for operation at the intended voltage levels. Inductor current may reach current limit when operating in pulse skip mode with small valued inductors. In this case, the LT3502/LT3502A will periodically reduce its frequency to keep the inductor valley current to 650mA (Figure 3). Peak inductor current is therefore peak current plus minimum switch delay: VIN – VOUT • 60ns L The part is robust enough to survive prolonged operation under these conditions as long as the peak inductor current does not exceed 1.2A. Inductor current saturation and junction temperature may further limit performance during this operating regime. 900mA + VIN = 40V VOUT = 3.3V L = 6.8μH COUT = 10μF IOUT = 500mA 1μs/DIV 3502 F03 Figure 3. Pulse Skip with Large Load Current Will be Limited by the DA Valley Current Limit. Notice the Flat Inductor Valley Current and Reduced Switching Frequency Inductor Selection and Maximum Output Current A good first choice for the inductor value is: L = 1.6(VOUT + VD) for the LT3502A L = 4.6(VOUT + VD) for the LT3502 where VD is the voltage drop of the catch diode (~0.4V) and L is in μH. With this value there will be no subharmonic oscillation for applications with 50% or greater duty cycle. The inductor’s RMS current rating must be greater than the maximum load current and its saturation current should be about 30% higher. For robust operation during fault conditions, the saturation current should be above 1.2A. To keep efficiency high, the series resistance (DCR) should be less than 0.1Ω. Table 1 lists several vendors and types that are suitable. There are several graphs in the Typical Performance Characteristics section of this data sheet that show the maximum load current as a function of input voltage and inductor value for several popular output voltages. Low inductance may result in discontinuous mode operation, which is okay, but further reduces maximum load current. For details of the maximum output current and discontinuous mode operation, see Linear Technology Application Note 44. 3502fc 11 LT3502/LT3502A APPLICATIONS INFORMATION Table 1 VENDOR Sumida URL www.sumida.com Toko www.toko.com Würth Elektronik www.we-online.com PART SERIES CDRH4D28 CDRH5D28 CDRH8D28 A916CY D585LC WE-TPC(M) WE-PD2(M) WE-PD(S) Catch Diode A low capacitance 500mA Schottky diode is recommended for the catch diode, D1. The diode must have a reverse voltage rating equal to or greater than the maximum input voltage. The Phillips PMEG4005AEA is a good choice; it is related for 500mA continuous forward current and a maximum reverse voltage of 40V. Input Capacitor Bypass the input of the LT3502/LT3502A circuit with a 1μF or higher value ceramic capacitor of X7R or X5R type. Y5V types have poor performance over temperature and applied voltage and should not be used. A 1μF ceramic is adequate to bypass the LT3502/LT3502A and will easily handle the ripple current. However, if the input power source has high impedance, or there is significant inductance due to long wires or cables, additional bulk capacitance may be necessary. This can be provided with a low performance electrolytic capacitor. Step-down regulators draw current from the input supply in pulses with very fast rise and fall times. The input capacitor is required to reduce the resulting voltage ripple at the LT3502/LT3502A and to force this very high frequency switching current into a tight local loop, minimizing EMI. A 1μF capacitor is capable of this task, but only if it is placed close to the LT3502/LT3502A and the catch diode (see the PCB Layout section). A second precaution regarding the ceramic input capacitor concerns the maximum input voltage rating of the LT3502/LT3502A. A ceramic input capacitor combined with trace or cable inductance forms a high INDUCTANCE RATE (μH) 1.2 to 4.7 2.5 to 10 2.5 to 33 2 to 12 1.1 to 39 1 to 10 2.2 to 22 1 to 27 SIZE (mm) 4.5 × 4.5 5.5 × 5.5 8.3 × 8.3 6.3 × 6.2 8.1 × 8 4.8 × 4.8 5.2 × 5.8 7.3 × 7.3 quality (underdamped) tank circuit. If the LT3502/LT3502A circuit is plugged into a live supply, the input voltage can ring to twice its nominal value, possibly exceeding the LT3502/LT3502A’s voltage rating. This situation is easily avoided; see the Hot Plugging Safely section. Output Capacitor The output capacitor has two essential functions. Along with the inductor, it filters the square wave generated by the LT3502/LT3502A to produce the DC output. In this role it determines the output ripple so low impedance at the switching frequency is important. The second function is to store energy in order to satisfy transient loads and stabilize the LT3502/LT3502A’s control loop. Ceramic capacitors have very low equivalent series resistance (ESR) and provide the best ripple performance. A good value is: COUT = 33 for the LT3502A VOUT COUT = 66 for the LT3502 VOUT where COUT is in μF. Use an X5R or X7R type and keep in mind that a ceramic capacitor biased with VOUT will have less than its nominal capacitance. This choice will provide low output ripple and good transient response. Transient performance can be improved with a high value capacitor, but a phase lead capacitor across the feedback resistor, R1, may be required to get the full benefit (see the Compensation section). 3502fc 12 LT3502/LT3502A APPLICATIONS INFORMATION For small size, the output capacitor can be chosen according to: 25 COUT = VOUT where COUT is in μF. However, using an output capacitor this small results in an increased loop crossover frequency and increased sensitivity to noise. High performance electrolytic capacitors can be used for the output capacitor. Low ESR is important, so choose one that is intended for use in switching regulators. The ESR should be specified by the supplier and should be 0.1Ω or less. Such a capacitor will be larger than a ceramic capacitor and will have a larger capacitance, because the capacitor must be large to achieve low ESR. Table 2 lists several capacitor vendors. Figure 4 shows the transient response of the LT3502A with several output capacitor choices. The output is 3.3V. The load current is stepped from 150mA to 400mA and back to 150mA, and the oscilloscope traces show the output voltage. The upper photo shows the recommended value. The second photo shows the improved response (less voltage drop) resulting from a larger output capacitor and a phase lead capacitor. The last photo shows the response to a high performance electrolytic capacitor. Transient performance is improved due to the large output capacitance. BOOST Pin Considerations Capacitor C3 and the internal boost diode are used to generate a boost voltage that is higher than the input voltage. In most cases a 0.1μF capacitor will work well. Figure 5 shows two ways to arrange the boost circuit. The BOOST pin must be at least 2.2V above the SW pin for best efficiency. For outputs of 3V and above, the standard circuit (Figure 5a) is best. For outputs less than 3V and above 2.5V, place a discrete Schottky diode (such as the BAT54) in parallel with the internal diode to reduce VD. The following equations can be used to calculate and minimize boost capacitance in μF: 0.012/(VBD + VCATCH – VD – 2.2) for the LT3502A 0.030/(VBD + VCATCH – VD– 2.2) for the LT3502 VD is the forward drop of the boost diode, and VCATCH is the forward drop of the catch diode (D1). For lower output voltages the BD pin can be tied to an external voltage source with adequate local bypassing (Figure 5b). The above equations still apply for calculating the optimal boost capacitor for the chosen BD voltage. The absence of BD voltage during startup will increase minimum voltage to start and reduce efficiency. You must also be sure that the maximum voltage rating of BOOST pin is not exceeded. Table 2 VENDOR Panasonic PHONE (714) 373-7366 URL www.panasonic.com Kemet (864) 963-6300 www.kemet.com Sanyo (408)794-9714 www.sanyovideo.com Murata AVX (404) 436-1300 www.murata.com www.avxcorp.com Taiyo Yuden (864) 963-6300 www.taiyo-yuden.com PART SERIES Ceramic Polymer, Tantalum Ceramic, Tantalum Ceramic Polymer, Tantalum Ceramic Ceramic, Tantalum Ceramic COMMENTS EEF Series T494,T495 POSCAP TPS Series 3502fc 13 LT3502/LT3502A APPLICATIONS INFORMATION VOUT 32.4k FB IL 0.2A/DIV 10μF VOUT 0.1V/DIV AC COUPLED 10k 10μs/DIV 3502 F04a 10μs/DIV 3502 F04b 10μs/DIV 3502 F04c VOUT 32.4k 50pF IL 0.2A/DIV 10μF ×2 FB VOUT 0.1V/DIV AC COUPLED 10k VOUT 32.4k + FB 10k IL 0.2A/DIV 100μF VOUT 0.1V/DIV AC COUPLED SANYO 4TPB100M Figure 4. Transient Load Response of the LT3502A with Different Output Capacitors as the Load Current is Stepped from 150mA to 400mA. VIN = 12V, VOUT = 3.3V, L = 6.8μH VDD BD BD BOOST VIN VIN LT3502 SW GND BOOST VOUT VIN DA VBOOST – VSW ≅ VOUT MAX VBOOST ≅ VIN + VOUT VIN LT3502 SW GND DA VBOOST – VSW ≅ VIN MAX VBOOST ≅ 2VIN 3502 F05a (5a) VOUT 3502 F05b (5b) Figure 5 3502fc 14 LT3502/LT3502A APPLICATIONS INFORMATION The minimum operating voltage of an LT3502/LT3502A application is limited by the undervoltage lockout (3V) and by the maximum duty cycle as outlined above. For proper start-up, the minimum input voltage is also limited by the boost circuit. If the input voltage is ramped slowly, or the LT3502/LT3502A is turned on with its SHDN pin when the output is already in regulation, then the boost capacitor may not be fully charged. Because the boost capacitor is charged with the energy stored in the inductor, the circuit will rely on some minimum load current to get the boost circuit running properly. This minimum load will depend on the input and output voltages, and on the arrangement of the boost circuit. The minimum load generally goes to zero once the circuit has started. Figure 6 shows plots of minimum load to start and to run as a function of input voltage. In many cases the discharged output capacitor will present a load to the switcher which will allow it to start. The plots show the worst-case situation where VIN is ramping very slowly. At light loads, the inductor current becomes discontinuous and the effective duty cycle can be very high. This reduces the minimum input voltage to approximately 400mV above VOUT. At higher load currents, the inductor current is continuous and the duty cycle is limited by the maximum duty cycle of the LT3502/LT3502A, requiring a higher input voltage to maintain regulation. 7 8 6 7 6 5 4 3 RUN 5 VIN (V) VIN (V) START START RUN 4 3 2 2 1 0 0.001 1 0.1 0.01 LOAD CURRENT (A) 0 0.001 1 0.01 0.1 LOAD CURRENT (A) 3502 G20 3502 G19 (6a) LT3502A Typical Minimum Input Voltage, VOUT = 3.3V (6b) LT3502A Typical Minimum Input Voltage, VOUT = 5V 7 8 6 7 6 RUN START 3 4 3 2 2 1 1 0 0.001 START RUN 5 VIN (V) VIN (V) 5 4 1 0.1 0.01 LOAD CURRENT (A) 0 0.001 1 0.01 0.1 LOAD CURRENT (A) 1 3502 G22 3502 G21 (6c) LT3502 Typical Minimum Input Voltage, VOUT = 3.3V (6d) LT3502 Typical Minimum Input Voltage, VOUT = 5V Figure 6 3502fc 15 LT3502/LT3502A APPLICATIONS INFORMATION VSW 10V/DIV RUN SHDN GND IL 500mA/DIV 3502 F07a VOUT 2V/DIV VIN = 12V VOUT = 3.3V L = 6.8μH COUT = 10μF 5μs/DIV VIN = 12V VOUT = 3.3V L = 6.8μH COUT = 10μF 50μs/DIV RUN VSW 10V/DIV 50k SHDN 0.1μF GND IL 500mA/DIV 3502 F07b VOUT 2V/DIV 3502 F07 Figure 7. To Soft Start the LT3502A, Add a Resistor and Capacitor to the SHDN Pin Soft-Start The SHDN pin can be used to soft start the LT3502/LT3502A, reducing the maximum input current during start-up. The SHDN pin is driven through an external RC filter to create a voltage ramp at this pin. Figure 7 shows the start-up waveforms with and without the soft-start circuit. By choosing a large RC time constant, the peak start up current can be reduced to the current that is required to regulate the output, with no overshoot. Choose the value of the resistor so that it can supply 80μA when the SHDN pin reaches 2V. Short and Reverse Protection If the inductor is chosen so that it won’t saturate excessively, the LT3502/LT3502A will tolerate a shorted output. When operating in short-circuit condition, the LT3502/LT3502A will reduce their frequency until the valley current is 650mA (Figure 8a). There is another situation to consider in systems where the output will be held high when the input to the LT3502/LT3502A is absent. This may occur in battery charging applications or in battery backup systems where a battery or some other supply is diode OR-ed with the LT3502/LT3502A’s output. If the VIN pin is allowed to float and the SHDN pin is held high (either by a logic signal or because it is tied to VIN), then the LT3502/LT3502A’s VSW 10V/DIV IL 500mA/DIV VIN = 40V VOUT = 0V L = 6.8μH COUT = 10μF 2μs/DIV 3502 F08a Figure 8a. The LT3502A Reduces its Frequency to Below 500kHz to Protect Against Shorted Output with 40V Input 3502fc 16 LT3502/LT3502A APPLICATIONS INFORMATION D4 VIN BD BOOST VIN VOUT SW LT3502A DA SHDN + FB GND 3502 F08b Figure 8b. Diode D4 Prevents a Shorted Input from Discharging a Backup Battery Tied to the Output; it Also Protects the Circuit from a Reversed Input. The LT3502/LT3502A Runs Only When the Input is Present internal circuitry will pull its quiescent current through its SW pin. This is fine if your system can tolerate a few mA in this state. If you ground the SHDN pin, the SW pin current will drop to essentially zero. However, if the VIN pin is grounded while the output is held high, then parasitic diodes inside the LT3502/LT3502A can pull large currents from the output through the SW pin and the VIN pin. Figure 8b shows a circuit that will run only when the input voltage is present and that protects against a shorted or reversed input. Hot Plugging Safely The small size, robustness and low impedance of ceramic capacitors make them an attractive option for the input bypass capacitor of LT3502/LT3502A circuits. However, these capacitors can cause problems if the LT3502/LT3502A are plugged into a live supply (see Linear Technology Application Note 88 for a complete discussion). The low loss ceramic capacitor combined with stray inductance in series with the power source forms an underdamped tank circuit, and the voltage at the VIN pin of the LT3502/LT3502A can ring to twice the nominal input voltage, possibly exceeding the LT3502/LT3502A’s rating and damaging the part. If the input supply is poorly controlled or the user will be plugging the LT3502/LT3502A into an energized supply, the input network should be designed to prevent this overshoot. Figure 9 shows the waveforms that result when an LT3502/LT3502A circuit is connected to a 24V supply through six feet of 24-gauge twisted pair. The first plot is the response with a 2.2μF ceramic capacitor at the input. The input voltage rings as high as 35V and the input current peaks at 20A. One method of damping the tank circuit is to add another capacitor with a series resistor to the circuit. In Figure 9b an aluminum electrolytic capacitor has been added. This capacitor’s high equivalent series resistance damps the circuit and eliminates the voltage overshoot. The extra capacitor improves low frequency ripple filtering and can slightly improve the efficiency of the circuit, though it is likely to be the largest component in the circuit. An alternative solution is shown in Figure 9c. A 1Ω resistor is added in series with the input to eliminate the voltage overshoot (it also reduces the peak input current). A 0.1μF capacitor improves high frequency filtering. This solution is smaller and less expensive than the electrolytic capacitor. For high input voltages its impact on efficiency is minor, reducing efficiency less than one half percent for a 5V output at full load operating from 24V. Frequency Compensation The LT3502/LT3502A use current mode control to regulate the output. This simplifies loop compensation. In particular, the LT3502/LT3502A does not require the ESR of the output capacitor for stability allowing the use of ceramic capacitors to achieve low output ripple and small circuit size. Figure 10 shows an equivalent circuit for the LT3502/ LT3502A control loop. The error amp is a transconductance amplifier with finite output impedance. The power section, consisting of the modulator, power switch and inductor, is modeled as a transconductance amplifier generating an output current proportional to the voltage at the VC node. Note that the output capacitor integrates this current, and that the capacitor on the VC node (CC) integrates the error amplifier output current, resulting in two poles in the loop. RC provides a zero. With the recommended output capacitor, the loop crossover occurs above the RCCC zero. This simple model works well as long as the value of the inductor is not too high and the loop crossover frequency is much lower than the switching frequency. With a larger ceramic capacitor (very low ESR), crossover may be lower and a phase lead capacitor (CPL) across the feedback divider may improve the phase margin and transient response. Large electrolytic capacitors may have an ESR large enough to create an additional zero, and the phase lead may not be necessary. 3502fc 17 LT3502/LT3502A APPLICATIONS INFORMATION CLOSING SWITCH SIMULATES HOT PLUG IIN VIN DANGER! LT3502 VIN 20V/DIV + RINGING VIN MAY EXCEED ABSOLUTE MAXIMUM RATING OF THE LT3502 2.2μF LOW IMPEDANCE ENERGIZED 24V SUPPLY IIN 5A/DIV STRAY INDUCTANCE DUE TO 6 FEET (2 METERS) OF TWISTED PAIR 20μs/DIV (9a) VIN 20V/DIV LT3502 + 10μF 35V AI.EI. + 2.2μF IIN 5A/DIV (9b) 20μs/DIV 1Ω VIN 20V/DIV LT3502 + 0.1μF 2.2μF IIN 5A/DIV (9c) 20μs/DIV 3502 F09 Figure 9. A Well Chosen Input Network Prevents Input Voltage Overshoot and Ensures Reliable Operation When the LT3502 is Connected to a Live Supply CURRENT MODE POWER STAGE SW gm = +1A/V LT3502 – 0.5V OUT R1 – gm = 100μA/V RC 150k CC 70pF GND ERROR AMPLIFIER + VC CPL FB ESR 800mV C1 + C1 1M R2 3502 F10 Figure 10. Model for Loop Response 3502fc 18 LT3502/LT3502A APPLICATIONS INFORMATION If the output capacitor is different than the recommended capacitor, stability should be checked across all operating conditions, including load current, input voltage and temperature. The LT1375 data sheet contains a more thorough discussion of loop compensation and describes how to test the stability using a transient load. PCB Layout For proper operation and minimum EMI, care must be taken during printed circuit board layout. Figure 11 shows the recommended component placement with trace, ground plane and via locations. Note that large, switched currents flow in the LT3502/LT3502A’s VIN and SW pins, the catch diode (D1) and the input capacitor (C2). The loop formed by these components should be as small as possible and tied to system ground in only one place. These components, along with the inductor and output capacitor, should be placed on the same side of the circuit board, and their connections should be made on that layer. Place a local, unbroken ground plane below these components, and tie this ground plane to system ground at one location, ideally at the ground terminal of the output capacitor C1. The SW and BOOST nodes should be as small as possible. Finally, keep the FB node small so that the ground pin and ground traces will shield it from the SW and BOOST nodes. Include vias near the exposed GND pad of the LT3502/LT3502A to help remove heat from the LT3502/LT3502A to the ground plane. VOUT C1 L1 High Temperature Considerations The die temperature of the LT3502/LT3502A must be lower than the maximum rating of 125°C. This is generally not a concern unless the ambient temperature is above 85°C. For higher temperatures, care should be taken in the layout of the circuit to ensure good heat sinking of the LT3502/LT3502A. The maximum load current should be derated as the ambient temperature approaches 125°C. The die temperature is calculated by multiplying the LT3502/LT3502A power dissipation by the thermal resistance from junction to ambient. Power dissipation within the LT3502/LT3502A can be estimated by calculating the total power loss from an efficiency measurement and subtracting the catch diode loss. Thermal resistance depends on the layout of the circuit board, but 102°C/W and 110ºC/W are typical for the (2mm × 2mm) DFN and MS10 packages respectively. Outputs Greater Than 7V Note that for outputs above 7V, the input voltage range will be limited by the maximum rating of the BOOST pin. The sum of input and output voltages cannot exceed the BOOST pin’s 50V rating. The 15V circuit (Figure 12) shows how to overcome this limitation using an additional zener diode. Other Linear Technology Publications Application notes AN19, AN35 and AN44 contain more detailed descriptions and design information for Buck regulators and other switching regulators. The LT1376 data sheet has a more extensive discussion of output ripple, loop compensation and stability testing. Design Note 100 shows how to generate a bipolar output supply using a buck regulator. C2 VIN C3 BST R1 BD FB SHDN 10V BD VIN 20V TO 40V VIN BOOST C3 0.1μF C2 1μF D1 DA L1 33μH SW LT3502A VOUT 15V 500mA 22pF DA R2 R1 180k GND OFF ON 3502 F11 = VIA SHDN FB GND 3502 F12 Figure 11 R2 10k C1 10μF Figure 12. 15V Step-Down Converter 3502fc 19 LT3502/LT3502A TYPICAL APPLICATIONS 0.8V Step-Down Converter VBD 3V TO 7V VBD 3V TO 7V 0.1μF BD VIN 3V TO 40V C2 1μF VIN BOOST L1 C3 0.1μF 3.3μH SW LT3502A D1 0.1μF BD VIN 3V TO 40V C2 1μF VOUT 0.8V 500mA VIN BOOST C3 0.1μF SW LT3502 DA OFF ON SHDN L1 10μH D1 VOUT 0.8V 500mA DA FB OFF ON SHDN C1 47μF GND C1: JMK212BJ476MG C3: HMK212BJ104MG L1: LQH43CN3R3M03 FB C1 100μF GND C1: JMK316BJ107ML L1: LQH43CN100K03 3502 TA02a 3502 TA02b 1.8V Step-Down Converter VBD 3V TO 7V VBD 3V TO 7V 0.1μF 0.1μF BD VIN 3V TO 40V C2 1μF VIN BOOST L1 C3 0.1μF 4.7μH SW LT3502A D1 DA OFF ON SHDN C2 1μF VOUT 1.8V 500mA VIN BOOST C3 0.1μF SW LT3502 D1 DA R1 12.5k FB GND BD VIN 3V TO 40V OFF ON R2 10k C1: JMK212BJ226MG L1: LQH43CN4R7M03 C1 22μF 3502 TA03a SHDN L1 15μH VOUT 1.8V 500mA R1 12.5k FB GND R2 10k C1: JMK212BJ476MG L1: LQH55DN150M03 C1 47μF 3502 TA03b 3502fc 20 LT3502/LT3502A TYPICAL APPLICATIONS 2.5V Step-Down Converter VBD 3V TO 7V VBD 3V TO 7V 0.1μF BD VIN 3.5V TO 40V C2 1μF VIN BOOST L1 C3 0.1μF 6.8μH SW LT3502A D1 DA OFF ON SHDN BD VIN 3.5V TO 40V C2 1μF VOUT 2.5V 500mA VIN BOOST C3 0.1μF LT3502 D1 DA R1 21.3k SHDN OFF ON R2 10k C1: JMK212BJ226MG L1: LQH43DN6R8M03 L1 15μH SW FB GND 0.1μF C1 22μF VOUT 2.5V 500mA R1 21.3k FB R2 10k GND C1 22μF C1: JMK212BJ226MG L1: LQH55DN150M03 3502 TA04a 3502 TA04b 3.3V Step-Down Converter BD VIN 4.7V TO 40V VIN BOOST C2 1μF SW LT3502A D1 DA OFF ON L1 C3 0.1μF 6.8μH SHDN VIN BOOST C3 0.1μF C2 1μF VOUT 3.3V 500mA SW LT3502 D1 DA R1 31.6k FB GND BD VIN 4.5V TO 40V OFF ON R2 10k C1: LMK316BJ106ML-BR L1: LQH43CN6R8M03 C1 10μF 3502 TA05a SHDN L1 15μH VOUT 3.3V 500mA R1 31.6k FB GND R2 10k C1: JMK212BJ226MG L1: LQH55DN150M03 C1 22μF 3502 TA05b 3502fc 21 LT3502/LT3502A PACKAGE DESCRIPTION DC Package 8-Lead Plastic DFN (2mm × 2mm) (Reference LTC DWG # 05-08-1719 Rev Ø) 0.70 ±0.05 2.55 ±0.05 1.15 ±0.05 0.64 ±0.05 (2 SIDES) PACKAGE OUTLINE 0.25 ± 0.05 0.45 BSC 1.37 ±0.05 (2 SIDES) RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED R = 0.05 TYP 2.00 ±0.10 (4 SIDES) PIN 1 BAR TOP MARK (SEE NOTE 6) R = 0.115 TYP 5 8 0.40 ± 0.10 0.64 ± 0.10 (2 SIDES) PIN 1 NOTCH R = 0.20 OR 0.25 × 45° CHAMFER (DC8) DFN 0106 REVØ 4 0.200 REF 1 0.23 ± 0.05 0.45 BSC 0.75 ±0.05 1.37 ±0.10 (2 SIDES) 0.00 – 0.05 BOTTOM VIEW—EXPOSED PAD NOTE: 1. DRAWING IS NOT A JEDEC PACKAGE OUTLINE 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 3502fc 22 LT3502/LT3502A PACKAGE DESCRIPTION MS Package 10-Lead Plastic MSOP (Reference LTC DWG # 05-08-1661) 0.889 ± 0.127 (.035 ± .005) 5.23 (.206) MIN 3.20 – 3.45 (.126 – .136) 3.00 ± 0.102 (.118 ± .004) (NOTE 3) 0.50 0.305 ± 0.038 (.0197) (.0120 ± .0015) BSC TYP RECOMMENDED SOLDER PAD LAYOUT 0.254 (.010) 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 0.1016 ± 0.0508 (.004 ± .002) MSOP (MS) 0307 REV E 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 3502fc 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. 23 LT3502/LT3502A TYPICAL APPLICATION 5V Step-Down Converter BD VIN 6.7V TO 40V VIN BOOST C3 0.1μF C2 1μF SW LT3502A D1 DA OFF ON L1 10μH SHDN VIN BOOST C3 0.1μF C2 1μF VOUT 5V 500mA LT3502 R1 52.3k R2 10k C1 10μF C1: LMK316BJ106ML-BR L1: LQH43CN100K03 OFF ON L1 22μH SW D1 DA FB GND BD VIN 6.4V TO 40V SHDN R1 52.3k FB GND R2 10k C1: LMK316BJ106ML-BR L1: LQH43CN100K03 3502 TA06a VOUT 5V 500mA C1 22μF 3502 TA06b RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LT1766 60V, 1.2A (IOUT), 200kHz, High Efficiency Step-Down DC/DC Converter VIN: 5.5V to 60V, VOUT(MIN) = 1.2V, IQ = 2.5mA, ISD = 25μA, TSSOP16/TSSOP16E Packages LT1933 500mA (IOUT), 500kHz, Step-Down Switching Regulator in SOT-23 VIN: 3.6V to 36V, VOUT(MIN) = 1.2V, IQ = 1.6mA, ISD < 1μA, ThinSOTTM Package LT1936 36V, 1.4A (IOUT), 500kHz, High Efficiency Step-Down DC/DC Converter VIN: 3.6V to 36V, VOUT(MIN) = 1.2V, IQ = 1.9mA, ISD < 1μA, MS8E Package LT1940 Dual 25V, 1.4A (IOUT), 1.1MHz, High Efficiency Step-Down DC/DC Converter VIN: 3.6V to 25V, VOUT(MIN) = 1.20V, IQ = 3.8mA, ISD < 30μA, TSSOP16E Package LT1976/LT1977 60V, 1.2A (IOUT), 200kHz/500kHz High Efficiency StepDown DC/DC Converters with Burst Mode® Operation VIN: 3.3V to 60V, VOUT(MIN) = 1.20V, IQ = 100μA, ISD < 1μA, TSSOP16E Package LTC 3407/LTC3407-2 Dual 600mA/800mA, 1.5MHz/2.25MHz, Synchronous Step-DownDC/DC Converters VIN: 2.5V to 5.5V, VOUT(MIN) = 0.6V, IQ = 40μA, ISD <1μA, 3mm × 3mm DFN, MS10E Package LT3434/LT3435 60V, 1.2A (IOUT), 200kHz/500kHz High Efficiency StepDown DC/DC Converters with Burst Mode Operation VIN: 3.3V to 60V, VOUT(MIN) = 1.20V, IQ = 100μA, ISD < 1μA, TSSOP16E Package LT3437 60V, 400mA (IOUT), Micropower Step-Down DC/DC Converter with Burst Mode Operation VIN: 3.3V to 60V, VOUT(MIN) = 1.25V, IQ = 100μA, ISD < 1μA, DFN Package LT3493 36V, 1.4A (IOUT), 750kHz, High Efficiency Step-Down DC/DC Converter VIN: 3.6V to 36V, VOUT(MIN) = 0.8V, IQ = 1.9mA, ISD < 1μA, DFN Package LT3501 Dual 25V, 3A (IOUT), 1.5MHz, High Efficiency Step-Down DC/DC Converter VIN: 3.3V to 25V, VOUT(MIN) = 0.8V, IQ = 3.7mA, ISD < 10μA, TSSOP20E Package LT3503 20V, 1A (IOUT), 2.2MHz, High Efficiency Step-Down DC/DC Converter VIN: 3.6V to 20V, VOUT(MIN) = 0.78V, IQ = 1.9mA, ISD < 1μA, 2mm × 3mm DFN Package LT3505 36V, 1.2A (IOUT), 3MHz, High Efficiency Step-Down DC/DC Converter VIN: 3.6V to 36V, VOUT(MIN) = 0.78V, IQ = 2mA, ISD < 2μA, 3mm × 3mm DFN, MS8E Packages LT3506/LT3506A Dual 25V, 1.6A (IOUT), 575kHz/1.1MHz, High Efficiency Step-Down DC/DC Converters VIN: 3.6V to 25V, VOUT(MIN) = 0.8V, IQ = 3.8mA, ISD < 30μA, 4mm × 5mm DFN Package LT3508 Dual 36V, 1.4A (IOUT), 2.5MHz, High Efficiency Step-Down DC/DC Converter VIN: 3.6V to 36V, VOUT(MIN) = 0.8V, IQ = 4.3mA, ISD < 1μA, 4mm × 4mm QFN, TSSOP16E Packages LT3510 Dual 25V, 2A (IOUT), 1.5MHz, High Efficiency Step-Down DC/DC Converter VIN: 3.3V to 25V, VOUT(MIN) = 0.8V, IQ = 3.7mA, ISD < 10μA, TSSOP20E Package LTC3548 Dual 400mA + 800mA, 2.25MHz Synchronous Step-Down DC/DC Converter VIN: 2.5V to 5.5V, VOUT(MIN) = 0.6V, IQ = 40μA, ISD < 1μA, 3mm × 3mm DFN, MS10E Packages Burst Mode is a registered trademark of Linear Technology Corporation. ThinSOT is a trademark of Linear Technology Corporation. 3502fc 24 Linear Technology Corporation LT 0908 REV C • PRINTED IN USA 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com © LINEAR TECHNOLOGY CORPORATION 2007