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LT3502 LINER | Alldatasheet

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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 ■ 3V to 40V Input Voltage Range ■ 500mA Output Current ■ Switching Frequency: 2.2MHz (L T3502A), 1.1MHz (L T3502) ■ 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 ■ Automotive Systems ■ Battery-Powered Equipment ■ Wall T ransformer Regulation ■ Distributed Supply Regulation L T3502A 12VIN Effi ciency 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 L, L T , L TC and L TM are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners.

(Note 1) ORDER INFORMATION LEAD FREE FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE L T3502EDC#PBF L T3502EDC#TRPBF LCLV 8-Lead 2mm × 2mm Plastic DFN –40°C to 125°C L T3502IDC#PBF L T3502IDC#TRPBF LCLV 8-Lead 2mm × 2mm Plastic DFN –40°C to 125°C L T3502AEDC#PBF L T3502AEDC#TRPBF LCL T 8-Lead 2mm × 2mm Plastic DFN –40°C to 125°C L T3502AIDC#PBF 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 Consult L TC Marketing for parts specifi ed with wider operating temperature ranges. *The temperature grade is identifi ed by a label on the shipping container . Consult L TC Marketing for information on non-standard lead based fi nish parts. For more information on lead free part marking, go to: http://www.linear .com/leadfree/ For more information on tape and reel specifi cations, go to: http://www.linear .com/tapeandreel/ 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 V IN NC BD FB SHDN TOP VIEW MS PACKAGE 10-LEAD PLASTIC MSOP θJA = 110°C/W Operating Junction Temperature Range (Note 2)

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 specifi cations from 0°C to 125°C junction temperature range. Specifi cations over the –40°C to 125°C operating junction temperature range are assured by design, characterization and correlation ELECTRICAL CHARACTERISTICS The ● denotes the specifi cations which apply over the full operating temperature range, otherwise specifi cations 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 fl ows into pin. Note 5: Current fl ows out of pin. PARAMETER CONDITIONS MIN TYP MAX UNITS Undervoltage Lockout 2.6 2.8 3 V Quiescent Current at Shutdown V SHDN = 0V 0.5 2 μA Quiescent Current Not Switching 1.5 2 mA Feedback Voltage 2mm × 2mm DFN 2mm × 2mm DFN MS10 MS10 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)

• 15 50 nA Switching Frequency I DA < 500mA (L T3502A) IDA < 500mA (L T3502A) IDA < 500mA (L T3502) IDA < 500mA (L T3502) 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 V CESAT 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 I SW = 500mA 10 13 mA Minimum BOOST Voltage Above Switch I SW = 500mA 1.9 2.2 V BOOST Schottky Forward Drop I OUT = 100mA 0.8 1 V DA Pin Current to Stop OSC 500 650 mA SHDN Bias Current V SHDN = 5V VSHDN = 0V 55 80 μA μA SHDN Input Voltage High 2V SHDN Input Voltage Low 0.3 V

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 Effi ciency 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 Effi ciency L T3502A 5V OUT Effi ciency L T3502 3.3V OUT Effi ciency 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)

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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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 C OUT = 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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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 V OUT = 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 V IN 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 V IN. 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)

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

The L T3502/L T3502A are constant frequency, current mode step-down regulators. An oscillator enables an RS fl ip-fl op, turning on the internal 500mA power switch Q1. An amplifi er and comparator monitor the current fl owing between the V IN and SW pins, turning the switch off when this current reaches a level determined by the voltage at V C. An error amplifi er measures the output voltage through an external resistor divider tied to the FB pin and servos the V C node. If the error amplifi er’s output increases, more current is delivered to the output; if it decreases, less current is delivered. An active clamp (not shown) on the V C 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 V IN 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 effi cient operation. A comparator monitors the current fl owing 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. DCMIN = 0.15 for the L T3502A and 0.08 for the L T3502.

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Figure 2. Pulse Skip Occurs when

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oscillation for applications with 50% or greater duty cycle. conditions, the saturation current should be above 1.2A. Figure 3. Pulse Skip with Large Load Current Will be Limited value before it begins switching again (Figure 2). during this operating regime.

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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 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 signifi cant 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 regarding the ceramic input capacitor concerns the maximum input volt- age rating of the L T3502/L T3502A. A ceramic input capaci- tor 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 situation is easily avoided; see the Hot Plugging Safely section. Output Capacitor The output capacitor has two essential functions. Along with the inductor, it fi lters 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 function 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 benefi t (see the Compensation section). Table 1 VENDOR URL PART SERIES INDUCTANCE RATE (μH) SIZE (mm) Sumida www.sumida.com CDRH4D28 CDRH5D28 CDRH8D28 1.2 to 4.7 2.5 to 10 2.5 to 33 4.5 × 4.5 5.5 × 5.5 8.3 × 8.3 Toko www.toko.com A916CY D585LC 2 to 12 1.1 to 39 6.3 × 6.2 8.1 × 8 Würth Elektronik www.we-online.com WE-TPC(M) WE-PD2(M) WE-PD(S) 1 to 10 2.2 to 22 1 to 27 4.8 × 4.8 5.2 × 5.8 7.3 × 7.3

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

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(6a) L T3502A Typical Minimum Input Voltage, VOUT = 3.3V (6b) L T3502A Typical Minimum Input Voltage, V OUT = 5V (6c) L T3502 Typical Minimum Input Voltage, VOUT = 3.3V (6d) L T3502 Typical Minimum Input Voltage, V OUT = 5V 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 V IN 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 V OUT. 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. 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 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 L T3502/L T3502A Runs Only When the Input is Present VIN

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internal circuitry will pull its quiescent current through its SW pin. This is fi ne 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 V IN pin is grounded while the output is held high, then parasitic diodes inside the L T3502/L T3502A can pull large currents from the output through the SW pin and the V IN 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 L T3502/L T3502A circuits. However, these capacitors can cause problems if the L T3502/L T3502A 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 V IN pin of the L T3502/L T3502A can ring to twice the nominal input voltage, possibly ex- ceeding the L T3502/L T3502A’s rating and damaging the part. If the input supply is poorly controlled or the user will be plugging the L T3502/L T3502A into an energized supply, the input network should be designed to prevent this overshoot. Figure 9 shows the waveforms that result when an L T3502/L T3502A circuit is connected to a 24V supply through six feet of 24-gauge twisted pair. The fi rst 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 fi ltering and can slightly improve the effi ciency 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 fi ltering. This solution is smaller and less expensive than the electrolytic capacitor. For high input voltages its impact on effi ciency is minor , reducing effi ciency less than one half percent for a 5V output at full load operating from 24V. Frequency Compensation The L T3502/L T3502A use current mode control to regulate the output. This simplifi es loop compensation. In particular, the L T3502/L T3502A 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 L T3502/ L T3502A control loop. The error amp is a transconductance amplifi er with fi nite output impedance. The power section, consisting of the modulator, power switch and inductor, is modeled as a transconductance amplifi er generating an output current proportional to the voltage at the V C node. Note that the output capacitor integrates this current, and that the capacitor on the V C node (CC) integrates the error amplifi er 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 (C PL) 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.

Figure 10. Model for Loop Response

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

If the output capacitor is different than the recommended capacitor, stability should be checked across all operat- ing conditions, including load current, input voltage and temperature. The L T1375 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 fl ow in the L T3502/L T3502A’s V IN 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 L T3502/L T3502A to help remove heat from the L T3502/L T3502A to the ground plane. High Temperature Considerations The die temperature of the L T3502/L T3502A 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 L T3502/L T3502A. The maximum load current should be derated as the ambient temperature approaches 125°C. The die temperature is calculated by multiplying the L T3502/L T3502A power dissipation by the thermal resistance from junction to ambient. Power dissipation within the L T3502/L T3502A can be estimated by calculat- ing the total power loss from an effi ciency 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 detailed descriptions and design information for Buck regulators and other switching regulators. The L T1376 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. Figure 11 Figure 12. 15V Step-Down Converter BST DA GND FB VIN VOUT L1C1 = VIA 3502 F11 BD SHDN VIN 0.1μF 22pF

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33μH 10V SHDN BOOST SW L T3502A BD GND DA FBOFF ON 10μF 10k 180k 1μF VIN 20V TO 40V VOUT 15V 500mA

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 V IN 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 V IN 3V TO 40V VBD 3V TO 7V VOUT 1.8V 500mA C1: JMK212BJ476MG L1: LQH55DN150M03 0.1μF

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 V IN 3.5V TO 40V VBD 3V TO 7V VOUT 2.5V 500mA C1: JMK212BJ226MG L1: LQH43DN6R8M03 0.1μF VIN 0.1μF

3502 TA04b

15μH SHDN BOOST SW L T3502 BD GND DA FBOFF ON 22μF 10k 21.3k 1μF V IN 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 V IN 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 V IN 4.5V TO 40V VOUT 3.3V 500mA C1: JMK212BJ226MG L1: LQH55DN150M03

8-Lead Plastic DFN (2mm × 2mm) (Reference L TC DWG # 05-08-1719 Rev Ø) 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

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 representa- tion that the interconnection of its circuits as described herein will not infringe on existing patent rights. PACKAGE DESCRIPTION 10-Lead Plastic MSOP (Reference L TC DWG # 05-08-1661) MSOP (MS) 0307 REV E 0.53 ± 0.152 (.021 ± .006) SEATING PLANE 0.18 (.007) 1.10 (.043) MAX 0.17 – 0.27 (.007 – .011) TYP 0.86 (.034) REF 0.50 (.0197) BSC 12 3 45 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)

Linear Technology Corporation 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 ● FAX: (408) 434-0507 ● www.linear .com © LINEAR TECHNOLOGY CORPORATION 2007 LT 0908 REV C • PRINTED IN USA PART NUMBER DESCRIPTION COMMENTS L T1766 60V, 1.2A (I OUT), 200kHz, High Effi ciency 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 (I OUT), 500kHz, Step-Down Switching Regulator in SOT-23 VIN: 3.6V to 36V, VOUT(MIN) = 1.2V, IQ = 1.6mA, ISD < 1μA, ThinSOT TM Package L T1936 36V, 1.4A (I OUT), 500kHz, High Effi ciency 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 (I OUT), 1.1MHz, High Effi ciency 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 (I OUT), 200kHz/500kHz High Effi ciency 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 (I OUT), 200kHz/500kHz High Effi ciency 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 (I OUT), 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 (I OUT), 750kHz, High Effi ciency Step-Down DC/DC Converter VIN: 3.6V to 36V, VOUT(MIN) = 0.8V, IQ = 1.9mA, ISD < 1μA, L T3501 Dual 25V, 3A (I OUT), 1.5MHz, High Effi ciency Step-Down DC/DC Converter VIN: 3.3V to 25V, VOUT(MIN) = 0.8V, IQ = 3.7mA, ISD < 10μA, L T3503 20V, 1A (I OUT), 2.2MHz, High Effi ciency 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 (I OUT), 3MHz, High Effi ciency 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 (I OUT), 575kHz/1.1MHz, High Effi ciency 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 (I OUT), 2.5MHz, High Effi ciency 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 (I OUT), 1.5MHz, High Effi ciency 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 V IN 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 V IN 6.4V TO 40V VOUT 500mA C1: LMK316BJ106ML-BR L1: LQH43CN100K03 RELATED PARTS