LT3502

LT3502/LT3502A DS (Rev F)

Document overview

• Manufacturer or author: Analog Devices, Inc.
• PDF pages: 25

Technical content

Rev. FFor more information www.analog.comDocument Feedback

FEATURES

APPLICATIONS

DESCRIPTION

1.1MHz/2.2MHz, 500mA Step-Down Regulators in 2mm × 2mm DFN and MS10 The L T®3502/L T3502A 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 L T3502/L T3502A 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 L T3502A particularly suitable for automotive applications. 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 protec- tion in fault conditions. An internal boost diode reduces component count. 3.3V Step-Down Converter n 3V to 40V Input Voltage Range n 500mA Output Current n Switching Frequency: 2.2MHz (L T3502A), 1.1MHz (L T3502) n 800mV Feedback Voltage n Short-Circuit Robust n Soft-Start n Low Shutdown Current: <2µA n Internally Compensated n Internal Boost Diode n Thermally Enhanced 2mm × 2mm 8-Lead DFN and 10-Lead MS10 Package n AEC-Q100 Compliant with Exception n HBM ESD Classification Level 1C n Automotive Systems n Battery-Powered Equipment n Wall T ransformer Regulation n Distributed Supply Regulation L T3502A 12VIN Efficiency VIN 0.1µF

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31.6k 10k 6.8µH SHDN BOOST SW L T3502A BD GND DA FBOFF ON 10µF 1µF VIN 4.7V TO 40V VOUT 3.3V 500mA LOAD CURRENT (A) EFFICIENCY (%) 0.2 0.4 0.5

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0.1 0.3 3.3VOUT5VOUT TYPICAL APPLICATION All registered trademarks and trademarks are the property of their respective owners.

Rev. F For more information www.analog.com PIN CONFIGURATION ABSOLUTE MAXIMUM RATINGS (Note 1) ORDER INFORMATION TOP VIEW VIN BD FB SHDN SW BOOST DA GND DC PACKAGE 8-LEAD (2mm × 2mm) PLASTIC DFN 3 6 θJA = 102°C/W EXPOSED PAD (PIN 9) IS GND, MUST BE SOLDERED TO PCB SW BOOST NC DA GND VIN NC BD FB SHDN TOP VIEW MS PACKAGE 10-LEAD PLASTIC MSOP θJA = 110°C/W Operating Junction Temperature Range (Note 2) LEAD FREE FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE L T3502EDC#TRMPBF L T3502EDC#TRPBF LCLV 8-Lead 2mm × 2mm Plastic DFN –40°C to 125°C L T3502IDC#TRMPBF L T3502IDC#TRPBF LCLV 8-Lead 2mm × 2mm Plastic DFN –40°C to 125°C L T3502AEDC#TRMPBF L T3502AEDC#TRPBF LCL T 8-Lead 2mm × 2mm Plastic DFN –40°C to 125°C L T3502AIDC#TRMPBF L T3502AIDC#TRPBF LCL T 8-Lead 2mm × 2mm Plastic DFN –40°C to 125°C L T3502EMS#PBF L T3502EMS#TRPBF L TDTR 10-Lead Plastic MSOP –40°C to 125°C L T3502IMS#PBF L T3502IMS#TRPBF L TDTR 10-Lead Plastic MSOP –40°C to 125°C L T3502AEMS#PBF L T3502AEMS#TRPBF L TDTS 10-Lead Plastic MSOP –40°C to 125°C L T3502AIMS#PBF L T3502AIMS#TRPBF L TDTS 10-Lead Plastic MSOP –40°C to 125°C AUTOMOTIVE PRODUCTS** L T3502AIDC#WTRMPBF L T3502AIDC#WTRPBF LCL T 8-Lead 2mm × 2mm Plastic DFN –40°C to 125°C For more information on lead free part marking, go to: www.adi.com/leadfree/ For more information on tape and reel specifications, go to: www.adi.com/tapeandreel/ *The temperature grade is identified by a label on the shipping container . Tape and reel specifications. Some packages are available in 500 unit reels through designated sales channels with the #TRMPBF suffix. **Versions of this part are available with controlled manufacturing to support the quality and reliability requirements of automotive applications. These models are designated with a #W suffix. Only the automotive grade products shown are available for use in automotive applications. Contact your local Analog Devices account representative for specific product ordering information and to obtain the specific Automotive Reliability reports for these models.

Rev. FFor more information www.analog.com 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 L T3502EDC and L T3502AEDC 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 ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VIN = 10V, VSHDN = 5V, VBOOST = 15V. with statistical process controls. The L T3502IDC and L T3502AIDC 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. PARAMETER CONDITIONS MIN TYP MAX UNITS Undervoltage Lockout 2.6 2.8 3 V Quiescent Current at Shutdown VSHDN = 0V 0.5 2 µA Quiescent Current Not Switching 1.5 2 mA Feedback Voltage 2mm × 2mm DFN 2mm × 2mm DFN MS10 MS10 l l 0.785 0.79 0.780 0.786 0.8 0.8 0.8 0.8 0.813 0.81 0.816 0.813 V V V V Reference Voltage Line Regulation 0.005 %/V FB Pin Bias Current (Note 5) l 15 50 nA Switching Frequency IDA < 500mA (L T3502A) IDA < 500mA (L T3502A) IDA < 500mA (L T3502) IDA < 500mA (L T3502) l l 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 Maximum Duty Cycle 100mA Load (L T3502A) 100mA Load (L T3502) Switch VCESAT ISW = 500mA 450 mV Switch Current Limit (Note 3) 0.75 0.9 1.1 A Switch Active Current SW = 10V (Note 4) SW = 0V (Note 5) 130 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 500 650 mA SHDN Bias Current VSHDN = 5V VSHDN = 0V 55 80 µA µA SHDN Input Voltage High 2 V SHDN Input Voltage Low 0.3 V L T3502A, 8-Lead Plastic DFN ESD MODEL WITHSTAND THRESHOLD (V) CLASS HBM* ±1500 1C FICDM ±1250 C3 *All pins with the exception of VIN, BST , and SW meet the ±2000V AEC-Q100 standard. ELECTROSTATIC DISCHARGE RATINGS ESD (electrostatic discharge) sensitive device. Charged devices and circuit boards can discharge without detection. Although this product features patented or proprietary protection circuity, damage may occur on devices subjected to high energy ESD. Therefore, proper ESD precautions should be taken to avoid performance degradtion or loss of functionality ESD CAUTION

Rev. F For more information www.analog.com L T3502 Maximum Load Current VOUT = 5V, L = 22µH Switch Voltage Drop L T3502 Maximum Load Current VOUT = 3.3V, L = 15µH SWITCH CURRENT (A) 500 25°C 125°C 600 700 0.8

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0.2 0.4 0.6 1.0 200 100 VCE (mV) –40°C VIN (V) LOAD CURRENT (A) 0.5 0.6 0.7

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0.4 0.3 0.1 10 20 30 0.2 0.9 0.8 MINIMUM TYPICAL VIN (V) LOAD CURRENT (A) 0.5 0.6 0.7

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0.4 0.3 0.1 10 20 30 0.2 0.9 0.8 MINIMUM TYPICAL L T3502 5VOUT Efficiency L T3502A Maximum Load Current VOUT = 3.3V, L = 6.8µH L T3502A Maximum Load Current VOUT = 5V, L = 10µH LOAD CURRENT (A) EFFICIENCY (%) 100 0.4

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0.1 0.2 0.3 0.5 24VIN 12VIN VIN (V) LOAD CURRENT (A) 0.1 0.3 0.4 0.5 1.0 0.7 10 20 TYPICAL

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0.2 0.8 0.9 0.6 30 40 MINIMUM VIN (V) LOAD CURRENT (A) 0.1 0.3 0.4 0.5 1.0 0.7 10 20

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0.2 0.8 0.9 0.6 30 40 MINIMUM TYPICAL TYPICAL PERFORMANCE CHARACTERISTICS L T3502A 3.3VOUT Efficiency L T3502A 5VOUT Efficiency L T3502 3.3VOUT Efficiency LOAD CURRENT (A) EFFICIENCY (%) 0.2 0.4 0.5

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0.1 0.3 24VIN 12VIN LOAD CURRENT (A) EFFICIENCY (%) 0.2 0.4 0.5

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0.1 0.3 80 24VIN 12VIN LOAD CURRENT (A) EFFICIENCY (%) 100 0.4

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0.1 0.2 0.3 0.5 5VIN 24VIN 12VIN (TA = 25°C unless otherwise noted)

Rev. FFor more information www.analog.com Switching Frequency Soft-Start (SHDN)UVLO TEMPERATURE (°C) –50 2.0 2.5 3.5 100

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1.5 1.0 0 50 150 0.5 3.0 VIN (V) TEMPERATURE (°C) –50 FREQUENCY (MHz) 1.0 1.5 150

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0.5 0 50 100 2.5 2.0 L T3502A L T3502 SHDN PIN VOL TAGE (mV) –0.1 SWITCH CURRENT LIMIT (A) 0.2 0.3 0.4 0.9 0.6 400 800 1000

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0.1 0.7 0.8 0.5 200 600 1200 1400 1600 TYPICAL PERFORMANCE CHARACTERISTICS(TA = 25°C unless otherwise noted) L T3502A Maximum VIN for Full Frequency (VOUT = 3.3V) SHDN Pin Current SHDN PIN VOL TAGE (V) SHDN PIN CURRENT (µA) 150 200 250 10 20 25 45

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TEMPERATURE (°C) –50 CURRENT LIMIT (A) 0.1 0.3 0.4 0.5 1.0 0.7 0 50

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0.2 0.8 0.9 0.6 100 150 DA VALLEY CURRENT LIMIT SW PEAK CURRENT LIMIT LOAD CURRENT (A) VIN (V) 0.4

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40 TA = 25°C

TA = 85°C Switch Current Limit L T3502A Maximum VIN for Full Frequency (VOUT = 5V) LOAD CURRENT (A) VIN (V) 0.4

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TA = 85°C TA = 25°C L T3502 Maximum VIN for Full Frequency (VOUT = 3.3V) LOAD CURRENT (A) VIN (V) 0.4

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TA = 85°C TA = 25°C Switch Current Limit DUTY CYCLE (%) CURRENT LIMIT (A) 0.2 0.4 0.6 0.8 1.0 1.2 50 100

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Rev. F For more information www.analog.com L T3502A Typical Minimum Input Voltage (VOUT = 3.3V) LOAD CURRENT (A) 0.001

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0.01 0.1 1 VIN (V) L T3502A Typical Minimum Input Voltage (VOUT = 5V) LOAD CURRENT (A) 0.001 VIN (V) 0.01 0.1 1

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L T3502 Typical Minimum Input Voltage (VOUT = 3.3V) LOAD CURRENT (A) 0.001

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0.01 0.1 1 VIN (V) TYPICAL PERFORMANCE CHARACTERISTICS(TA = 25°C unless otherwise noted) Continuous Mode Waveform Discontinuous Mode Waveform VSW 5V/DIV IL 200mA/DIV VOUT 20mV/DIV 200ns/DIV

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VIN = 12V VOUT = 3.3V L = 6.8µH COUT = 10µF IOUT = 250mA VSW 5V/DIV IL 200mA/DIV VOUT 20mV/DIV 200ns/DIV

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VIN = 12V VOUT = 3.3V L = 6.8µH COUT = 10µF IOUT = 30mA L T3502 Typical Minimum Input Voltage (VOUT = 5V) LOAD CURRENT (A) 0.001 VIN (V) 0.01 0.1 1

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Rev. FFor more information www.analog.com PIN FUNCTIONS VIN (Pin 1/Pin 10): The V IN pin supplies current to the L T3502/L T3502A’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 L T3502/L T3502A regulate their feedback pin to 0.8V. Connect the feedback resistor di - vider 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 L T3502 in shutdown mode. Tie to ground to shut down the L T3502/L T3502A. 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. (DFN/MS)

Rev. F For more information www.analog.com BLOCK DIAGRAM R DRIVER Q1S OSC SLOPE COMP FREQUENCY FOLDBACK INT REG AND UVLO VC gm 0.8V 3502 BD Q Q BOOST BD SW DA GND FB R2 R1 VOUT VIN VIN ON OFF SHDN

Rev. FFor more information www.analog.com The L T3502/L T3502A 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 cir - cuitry. This regulator includes an undervoltage lockout to prevent switching when VIN is less than ~3V. The SHDN pin is used to place the L T3502/L T3502A in shutdown, disconnecting the output and reducing the input current to less than 2µA. The switch driver operates from either V IN 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 L T3502/ L T3502A’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 volt - age. The DA comparator works in conjunction with the switch peak current limit comparator to determine the maximum deliverable current of the L T3502/L T3502A. 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. OPERATION

Figure 1. Continuous Mode Operation Near R2 should be 20k or less to avoid bias current errors. Reference designators refer to the Block Diagram. maximum ratings of the VIN and BOOST pins. with DCMAX = 0.80 for the L T3502A and 0.90 for the L T3502. DCMIN = 0.15 for the L T3502A and 0.08 for the L T3502.

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the VIN operating range (40V) during overload conditions. requirement, the switch pulse width remains fixed at 60ns. grammed value before it begins switching again (Figure 2).

Figure 2. Pulse-Skipping Occurs when

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and types that are suitable. Figure 3. Pulse-Skipping with Large Load Current Will be during this operating regime.

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Rev. F For more information www.analog.com APPLICATIONS INFORMATION current. For details of the maximum output current and discontinuous mode operation, see Linear Technology Application Note 44. 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 Diodes Inc. SBR1U40LP , ON Semi MBRM140, and Diodes Inc. DFLS140 are good choices for the catch diode. Input Capacitor Bypass the input of the L T3502/L T3502A 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 L T3502/L T3502A 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 ca - pacitor is required to reduce the resulting voltage ripple at the L T3502/L T3502A 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 L T3502/L T3502A and the catch diode (see the PCB Layout section). A second precaution regard- ing the ceramic input capacitor concerns the maximum input voltage rating of the L T3502/L T3502A. A ceramic input capacitor combined with trace or cable inductance forms a high quality (underdamped) tank circuit. If the L T3502/L T3502A circuit is plugged into a live supply, the input voltage can ring to twice its nominal value, possibly exceeding the L T3502/L T3502A’s voltage rating. This situa- tion 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 L T3502/L T3502A to produce the DC output. In this role it determines the output ripple so low impedance at the switching frequency is important. The second func - tion is to store energy in order to satisfy transient loads and stabilize the L T3502/L T3502A’s control loop. Ceramic capacitors have very low equivalent series resistance (ESR) and provide the best ripple performance. A good value is: COUT = 33 VOUT for the LT3502A COUT = 66 VOUT for the LT3502 where COUT is in µF . Use an X5R or X7R type and keep in mind that a ceramic capacitor biased with V OUT will have less than its nominal capacitance. This choice will provide low output ripple and good transient response. T ransient 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). For small size, the output capacitor can be chosen according to: COUT = 25 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 L T3502A with

Rev. FFor more information www.analog.com Table 2 VENDOR PHONE URL PART SERIES COMMENTS Panasonic (714) 373-7366 www.panasonic.com Ceramic Polymer , Tantalum EEF Series Kemet (864) 963-6300 www.kemet.com Ceramic, Tantalum T494,T495 Sanyo (408)794-9714 www.sanyovideo.com Ceramic Polymer , Tantalum POSCAP Murata (404) 436-1300 www.murata.com Ceramic AVX www.avxcorp.com Ceramic, Tantalum TPS Series Taiyo Yuden (864) 963-6300 www.taiyo-yuden.com Ceramic APPLICATIONS INFORMATION 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 sec- ond 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. T ransient 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/(V BD + VCATCH – VD – 2.2) for the L T3502A 0.030/(V BD + VCATCH – VD– 2.2) for the L T3502 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 start-up 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. The minimum operating voltage of an L T3502/L T3502A 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 L T3502/L T3502A 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 L T3502/L T3502A, requiring a higher input voltage to maintain regulation.

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Figure 4. T ransient Load Response of the L T3502A with Different Output Capacitors

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Rev. FFor more information www.analog.com APPLICATIONS INFORMATION Figure 6 (6a) L T3502A Typical Minimum Input Voltage, VOUT = 3.3V (6b) L T3502A Typical Minimum Input Voltage, VOUT = 5V (6c) L T3502 Typical Minimum Input Voltage, VOUT = 3.3V (6d) L T3502 Typical Minimum Input Voltage, VOUT = 5V Soft-Start The SHDN pin can be used to soft start the L T3502/ L T3502A, 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 exces - sively, the L T3502/L T3502A will tolerate a shorted output. When operating in short-circuit condition, the L T3502/ L T3502A will reduce their frequency until the valley cur- rent is 650mA (Figure 8a). There is another situation to consider in systems where the output will be held high when the input to the L T3502/L T3502A 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 L T3502/L T3502A’s output. If the VIN pin is allowed to float and the SHDN pin is held high (either by a LOAD CURRENT (A) 0.001 0.01 0.1 1 VIN (V) RUN START LOAD CURRENT (A) 0.001 VIN (V) 0.01 0.1 1 LOAD CURRENT (A) 0.001 0.01 0.1 1 VIN (V) RUN START LOAD CURRENT (A) 0.001 VIN (V) 0.01 0.1 1

Figure 7. To Soft-Start the L T3502A, Add a Resistor and Capacitor to the SHDN Pin

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Figure 9. A Well Chosen Input Network Prevents Input Voltage Overshoot and

Figure 10. Model for Loop Response

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voltage overshoot (it also reduces the peak input current). a 5V output at full load operating from 24V. to achieve low output ripple and small circuit size. output current proportional to the voltage at the VC node. capacitor , the loop crossover occurs above the RCCC zero. how to test the stability using a transient load. SW pins, the catch diode (D1) and the input capacitor (C2).

the L T3502/L T3502A to the ground plane. a concern unless the ambient temperature is above 85°C. the (2mm × 2mm) DFN and MS10 packages respectively. Figure 12. 15V Step-Down Converter

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overcome this limitation using an additional Zener diode.

Rev. F For more information www.analog.com TYPICAL APPLICATIONS 0.8V Step-Down Converter VIN 0.1µF 0.1µF

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3.3µH SHDN BOOST SW L T3502A BD GND DA FBOFF ON 47µF 1µF VIN 3V TO 40V VBD 3V TO 7V VOUT 0.8V 500mA C1: JMK212BJ476MG C3: HMK212BJ104MG L1: LQH43CN3R3M03 VIN 0.1µF C1: JMK316BJ107ML L1: LQH43CN100K03

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10µH SHDN BOOST SW L T3502 BD GND DA FBOFF ON 100µF 1µF VIN 3V TO 40V VBD 3V TO 7V VOUT 0.8V 500mA 0.1µF 1.8V Step-Down Converter VIN 0.1µF

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4.7µH SHDN BOOST SW L T3502A BD GND DA FBOFF ON 22µF 10k 12.5k 1µF VIN 3V TO 40V VBD 3V TO 7V VOUT 1.8V 500mA C1: JMK212BJ226MG L1: LQH43CN4R7M03 0.1µF VIN 0.1µF

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15µH SHDN BOOST SW L T3502 BD GND DA FBOFF ON 47µF 10k 12.5k 1µF VIN 3V TO 40V VBD 3V TO 7V VOUT 1.8V 500mA C1: JMK212BJ476MG L1: LQH55DN150M03 0.1µF

Rev. FFor more information www.analog.com 2.5V Step-Down Converter VIN 0.1µF

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6.8µH SHDN BOOST SW L T3502A BD GND DA FBOFF ON 22µF 10k 21.3k 1µF VIN 3.5V TO 40V VBD 3V TO 7V VOUT 2.5V 500mA C1: JMK212BJ226MG L1: LQH43DN6R8M03 0.1µF VIN 0.1µF

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15µH SHDN BOOST SW L T3502 BD GND DA FBOFF ON 22µF 10k 21.3k 1µF VIN 3.5V TO 40V VBD 3V TO 7V VOUT 2.5V 500mA C1: JMK212BJ226MG L1: LQH55DN150M03 0.1µF TYPICAL APPLICATIONS 3.3V Step-Down Converter VIN 0.1µF

3502 TA05a

6.8µH SHDN BOOST SW L T3502A BD GND DA FBOFF ON 10µF 10k 31.6k 1µF VIN 4.7V TO 40V VOUT 3.3V 500mA C1: LMK316BJ106ML-BR L1: LQH43CN6R8M03 VIN 0.1µF

3502 TA05b

15µH SHDN BOOST SW L T3502 BD GND DA FBOFF ON 22µF 10k 31.6k 1µF VIN 4.5V TO 40V VOUT 3.3V 500mA C1: JMK212BJ226MG L1: LQH55DN150M03

Rev. F For more information www.analog.com PACKAGE DESCRIPTION 8-Lead Plastic DFN (2mm × 2mm) (Reference L TC DWG # 05-08-1719 Rev A) 2.00 ±0.10 (4 SIDES) 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 0.40 ± 0.10 BOTTOM VIEW—EXPOSED PAD 0.64 ± 0.10 (2 SIDES) 0.75 ±0.05 R = 0.115 TYP R = 0.05 TYP 1.37 ±0.10 (2 SIDES) PIN 1 BAR TOP MARK (SEE NOTE 6)

0.200 REF

0.00 – 0.05 (DC8) DFN 0106 REVØ 0.23 ± 0.05

0.45 BSC

0.25 ± 0.05 1.37 ±0.05 (2 SIDES) RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED 0.64 ±0.05 (2 SIDES)1.15 ±0.05 0.70 ±0.05 2.55 ±0.05 PACKAGE OUTLINE R = 0.20 OR 0.25 × 45° CHAMFER

Rev. FFor more information www.analog.com PACKAGE DESCRIPTION 10-Lead Plastic MSOP (Reference L TC DWG # 05-08-1661 Rev E) MSOP (MS) 0307 REV E 0.53 ± 0.152 (.021 ± .006) SEATING PLANE 0.18 (.007) 1.10 (.043) MAX 0.17 –/uni00A00.27 (.007 – .011) TYP 0.86 (.034) REF 0.50 (.0197) BSC 1 2 3 4 5 4.90 ± 0.152 (.193 ± .006) 0.497 ± 0.076 (.0196 ± .003) REF8910 7 6 3.00 ± 0.102 (.118 ± .004) (NOTE 3) 3.00 ± 0.102 (.118 ± .004) (NOTE 4) 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 0.254 (.010) 0° – 6° TYP DETAIL “A” DETAIL “A” GAUGE PLANE 5.23 (.206) MIN 3.20 – 3.45 (.126 – .136) 0.889 ± 0.127 (.035 ± .005) RECOMMENDED SOLDER PAD LAYOUT 0.305 ± 0.038 (.0120 ± .0015) TYP 0.50 (.0197) BSC 0.1016 ± 0.0508 (.004 ± .002)

Rev. F For more information www.analog.com

REVISION HISTORY

REV DATE DESCRIPTION PAGE NUMBER E 07/24 Added AEC-Q100 Statement in Features section Updated Order Information table F 05/25 Updated Features Added Electrostatic Discharge Ratings Information furnished by Analog Devices is believed to be accurate and reliable. However , no responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other rights of third parties that may result from its use. Specifications subject to change without notice. No license is granted by implication or otherwise under any patent or patent rights of Analog Devices. www.analog.com

Rev. FFor more information www.analog.com PART NUMBER DESCRIPTION COMMENTS L T1766 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 L T1933 500mA (IOUT), 500kHz, Step-Down Switching Regulator in SOT-23 VIN: 3.6V to 36V, VOUT(MIN) = 1.2V, IQ = 1.6mA, ISD < 1µA, ThinSOT™ Package L T1936 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, L T1940 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, L T1976/ L T1977 60V, 1.2A (IOUT), 200kHz/500kHz High Efficiency Step-Down DC/DC Converters with Burst Mode Operation VIN: 3.3V to 60V, VOUT(MIN) = 1.20V, IQ = 100µA, ISD < 1µA, LT C 3407/ L TC3407-2 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 L T3434/ L T3435 60V, 1.2A (IOUT), 200kHz/500kHz High Efficiency Step-Down DC/DC Converters with Burst Mode Operation VIN: 3.3V to 60V, VOUT(MIN) = 1.20V, IQ = 100µA, ISD < 1µA, L T3437 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, L T3493 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, L T3501 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, L T3503 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 L T3505 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 L T3506/ L T3506A 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 L T3508 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 L T3510 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, L TC3548 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. TYPICAL APPLICATION 5V Step-Down Converter VIN 0.1µF

3502 TA06a

10µH SHDN BOOST SW L T3502A BD GND DA FBOFF ON 10µF 10k 52.3k 1µF VIN 6.7V TO 40V VOUT 500mA C1: LMK316BJ106ML-BR L1: LQH43CN100K03 VIN 0.1µF

3502 TA06b

22µH SHDN BOOST SW L T3502 BD GND DA FBOFF ON 22µF 10k 52.3k 1µF VIN 6.4V TO 40V VOUT 500mA C1: LMK316BJ106ML-BR L1: LQH43CN100K03 RELATED PARTS  ANALOG DEVICES, INC. 2007-2025 www.analog.com