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36V, 3.5A, 2.4MHz Step-Down Switching Regulator with 75關A Quiescent Current

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36V, 3.5A, 2.4MHz Step-Down Switching Regulator with 75µA Quiescent Current The LT ®3680 is an adjustable frequency (200kHz to 2.4MHz) monolithic buck switching regulator that accepts input voltages up to 36V. A high efﬁ ciency 95m switch is included on the die along with a boost Schottky diode and the necessary oscillator, control, and logic circuitry. Current mode topology is used for fast transient response and good loop stability. Low ripple Burst Mode operation maintains high efﬁ ciency at low output currents while keeping output ripple below 15mV in a typical application. In addition, the LT3680 can further enhance low output current efﬁ ciency by drawing bias current from the output when V OUT is above 3V. Shutdown reduces input supply current to less than 1μA while a resistor and capacitor on the RUN/SS pin provide a controlled output voltage ramp (soft-start). A power good ﬂ ag signals when V OUT reaches 91% of the programmed output voltage. The LT3680 is available in 10-Pin MSOP and 3mm × 3mm DFN packages with exposed pads for low thermal resistance. ■ Automotive Battery Regulation ■ Power for Portable Products ■ Distributed Supply Regulation ■ Industrial Supplies ■ Wall Transformer Regulation ■ Wide Input Voltage Range: 3.6V to 36V ■ 3.5A Maximum Output Current ■ Low Ripple (<15mVP-P) Burst Mode® Operation: IQ = 75μA at 12VIN to 3.3VOUT ■ Adjustable Switching Frequency: 200kHz to 2.4MHz ■ Low Shutdown Current: IQ < 1μA ■ Integrated Boost Diode ■ Synchronizable Between 250kHz to 2MHz ■ Power Good Flag ■ Saturating Switch Design: 95m On-Resistance ■ 0.790V Feedback Reference Voltage ■ Output Voltage: 0.79V to 30V ■ Thermal Protection ■ Soft-Start Capability ■ Small 10-Pin Thermally Enhanced MSOP and (3mm × 3mm) DFN Packages 5V Step-Down Converter SW FB VC PG RT VIN BD VIN 6.3V TO 36V VOUT 3.5A 10μF 0.47μF 680pF 47μF100k 15k 63.4k 4.7μH 536k GND OFF ON L T3680

3680 TA01a

Efﬁ ciency , LT, LTC and LTM are registered trademarks of Linear Technology Corporation. Burst Mode is a registered trademark of Linear Technology Corporation. All other trademarks are the property of their respective owners. OUTPUT CURRENT (A) 0 0.5 EFFICIENCY (%) 100 1 2 2.5

3680 G01

1.5 3 3.5 VIN = 12V VIN = 34V VOUT = 5V L = 4.7μH f = 600kHz VIN = 24V TYPICAL APPLICATION DESCRIPTION FEATURES

APPLICATIONS

ELECTRICAL CHARACTERISTICS

FB, RT, V (Note 1) PARAMETER CONDITIONS MIN TYP MAX UNITS Minimum Input Voltage ● 3 3.6 V Quiescent Current from VIN VRUN/SS = 0.2V 0.01 0.5 μA VBD = 3V, Not Switching ● 30 65 μA VBD = 0, Not Switching 120 160 μA Quiescent Current from BD VRUN/SS = 0.2V 0.01 0.5 μA VBD = 3V, Not Switching ● 90 130 μA The ● denotes the speciﬁ cations which apply over the full operating temperature range, otherwise speciﬁ cations are at TA = 25°C. VIN = 10V, VRUN/SS = 10V, VBOOST = 15V, VBD = 3.3V unless otherwise noted. (Note 2) Operating Junction Temperature Range (Note 2) Lead Temperature (Soldering, 10 sec) TOP VIEW DD PACKAGE 10-LEAD (3mm s 3mm) PLASTIC DFN 3 11 1 RT VC FB PG SYNC BD BOOST SW V IN RUN/SS θJA = 45°C/W, θJC = 10°C/W EXPOSED PAD (PIN 11) IS GND, MUST BE SOLDERED TO PCB BD BOOST SW V IN RUN/SS RT V C FB PG SYN C TOP VIEW MSE PACKAGE 10-LEAD PLASTIC MSOP θJA = 45°C/W, θJC = 10°C/W EXPOSED PAD (PIN 11) IS GND, MUST BE SOLDERED TO PCB PIN CONFIGURATION ORDER INFORMATION LEAD FREE FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE LT3680EDD#PBF LT3680EDD#TRPBF LCYK 10-Lead (3mm × 3mm) Plastic DFN –40°C to 125°C LT3680IDD#PBF LT3680IDD#TRPBF LCYK 10-Lead (3mm × 3mm) Plastic DFN –40°C to 125°C LT3680EMSE#PBF LT3680EMSE#TRPBF LTCYM 10-Lead Plastic MSOP –40°C to 125°C LT3680IMSE#PBF LT3680IMSE#TRPBF LTCYM 10-Lead Plastic MSOP –40°C to 125°C Consult LTC Marketing for parts speciﬁ ed with wider operating temperature ranges. *The temperature grade is identiﬁ ed by a label on the shipping container. Consult LTC 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/ ABSOLUTE MAXIMUM RATINGS

PARAMETER CONDITIONS MIN TYP MAX UNITS VBD = 0, Not Switching 15 μA Minimum Bias Voltage (BD Pin) 2.7 3 V Feedback Voltage 780 775 790 790 800 805 mV mV FB Pin Bias Current (Note 3) V FB = 0.8V, VC = 0.4V ● 10 40 nA FB Voltage Line Regulation 4V < V IN < 36V 0.002 0.01 %/V Error Amp gm 500 μMho Error Amp Gain 2000 VC Source Current 60 μA VC Sink Current 60 μA VC Pin to Switch Current Gain 5.3 A/V VC Clamp Voltage 2.0 V Switching Frequency R T = 8.66k RT = 29.4k RT = 187k 2.2 1.0 200 2.45 1.1 230 2.7 1.25 260 MHz MHz kHz Minimum Switch Off-Time ● 60 150 nS Switch Current Limit Duty Cycle = 5% 4.6 5.4 6.0 A Switch V CESAT ISW = 3.5A 335 mV Boost Schottky Reverse Leakage V BOOST = 10V, VBD = 0V 0.02 2 μA Minimum Boost Voltage (Note 4) ● 1.5 2.0 V BOOST Pin Current I SW = 1A 35 50 mA RUN/SS Pin Current V RUN/SS = 2.5V 5 8 μA RUN/SS Input Voltage High 2.5 V RUN/SS Input Voltage Low 0.2 V PG Threshold Offset from Feedback Voltage V FB Rising 65 mV PG Hysteresis 10 mV PG Leakage V PG = 5V 0.1 1 μA PG Sink Current V PG = 0.4V ● 200 800 μA SYNC Low Threshold 0.5 V SYNC High Threshold 0.7 V SYNC Pin Bias Current V SYNC = 0V 0.1 μA 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 LT3680E is guaranteed to meet performance speciﬁ cations from 0°C to 125°C. Speciﬁ cations over the –40°C to 125°C operating temperature range are assured by design, characterization and correlation with statistical process controls. The LT3680I speciﬁ cations are guaranteed over the –40°C to 125°C temperature range. Note 3: Bias current ﬂ ows out of the FB pin. Note 4: This is the minimum voltage across the boost capacitor needed to guarantee full saturation of the switch. The ● denotes the speciﬁ cations which apply over the full operating temperature range, otherwise speciﬁ cations are at TA = 25°C. VIN = 10V, VRUN/SS = 10V VBOOST = 15V, VBD = 3.3V unless otherwise noted. (Note 2)

INPUT VOLTAGE (V) SUPPLY CURRENT (μA)

3680 G04

VOUT = 3.3V DUTY CYCLE (%) SWITCH CURRENT LIMIT(A)

3680 G08

4.5 20 60 3.5 3.0 6.0 5.5 5.0 4.0 80 100 TEMPERATURE (°C) –50 SUPPLY CURRENT (μA) 350

3680 G05

–25 0 50 400 300 250 150 75 100 150125 VIN = 12V VOUT = 3.3V CATCH DIODE: DIODES, INC. PDS360 INCREASED SUPPLY CURRENT DUE TO CATCH DIODE LEAKAGE AT HIGH TEMPERATURE OUTPUT CURRENT (A) 0 0.5 EFFICIENCY (%) 100 1 2 2.5 1.5 3 3.5 VIN = 12V VIN = 34V VOUT = 5V L = 4.7μH f = 600kHz VIN = 24V OUTPUT CURRENT (A) 0 0.5 EFFICIENCY (%) 100 1 2 2.5

3680 G02

1.5 3 3.5 VIN = 12V VIN = 34V VOUT = 3.3V L = 3.3μH f = 600kHz VIN = 24V INPUT VOLTAGE (V) LOAD CURRENT (A)

3680 G07

4.5 10 20 3.5 3.0 5.5 5.0 4.0 25 30 TYPICAL MINIMUM VOUT = 5V TA = 25°C L = 4.7μH f = 600kHz INPUT VOLTAGE (V) LOAD CURRENT (A)

3680 G06

4.0 10 20 3.0 2.5 5.5 5.0 4.5 3.5 25 30 TYPICAL MINIMUM VOUT = 3.3V TA = 25°C L = 4.7μH f = 600kHz TEMPERATURE (°C) SWITCH CURRENT LIMIT (A) 4.0 4.5 5.5 5.0

3680 G09

3.5 3.0 2.0 2.5 6.5 6.0 DUTY CYCLE = 10 % DUTY CYCLE = 90 % –50 25–25 0 50 75 100 150 125 Efﬁ ciency Efﬁ ciency No Load Supply Current Maximum Load Current Switch Current Limit Switch Current LimitMaximum Load Current No Load Supply Current Efﬁ ciency TA = 25°C unless otherwise noted. OUTPUT CURRENT (A) 0 0.5 EFFICIENCY (%) TOTAL POWER LOSS (W) 100 1 2 2.5

3680 G03

0.5 1.5 3.0 1.0 2.5 2.0 1.5 3 3.5 VIN = 12V VOUT = 5V L = 4.7μH f = 600kHz TYPICAL PERFORMANCE CHARACTERISTICS

BOOST DIODE CURRENT (A) BOOST DIODE VF (V) 0.8 1.0 1.2 2.0

3680 G18

0.6 0.4 0.5 1.0 1.5 0.2 1.4 RUN/SS PIN VOLTAGE (V) SWITCH CURRENT LIMIT (A) 1.5

3680 G16

0.5 1 2 2.5 3 3.5 FB PIN VOLTAGE (mV) SWITCHING FREQUENCY (kHz) 800 1000 1200 600

3680 G14

200 400 800500100 300 700 900 200 TEMPERATURE (°C) MINIMUM SWITCH ON TIME (ns) 100 120

3680 G15

–50 25–25 0 50 75 100 150 125 RUN/SS PIN VOLTAGE (V) RUN/SS PIN CURRENT (μA) 15 25

3680 G17

SWITCH CURRENT (A) BOOST PIN CURRENT (mA) 120

3680 G11

TEMPERATURE (°C) FEEDBACK VOLTAGE (mV) 800

3680 G12

–50 25–25 0 50 75 100 150 125 TEMPERATURE (°C) FREQUENCY (MHz) 1.00 1.10

3680 G13

0.90 0.80 1.20 0.95 1.05 0.85 1.15 –50 25–25 0 50 75 100 150 125 SWITCH CURRENT (A) 400 500 700

3680 G10

600VOLTAGE DROP (mV) Boost Pin Current Feedback Voltage Switching Frequency Frequency Foldback Minimum Switch On-Time Soft-Start RUN/SS Pin Current Boost Diode Switch Voltage Drop TA = 25°C unless otherwise noted. TYPICAL PERFORMANCE CHARACTERISTICS

FB PIN ERROR VOLTAGE (mV) –200 –50 VC PIN CURRENT (μA) –20 0 200

3680 G19

–40 –100 100 –10 –30 Error Amp Output Current TEMPERATURE (°C) VC VOLTAGE (V) 1.50 2.00 2.50

3680 G22

1.00 0.50 CURRENT LIMIT CLAMP SWITCHING THRESHOLD –50 25–25 0 50 75 100 150 125 LOAD CURRENT (mA) INPUT VOLTAGE (V)3.0 3.5 10000

3680 G20

2.5 2.0 10 100 1000 5.0 4.5 4.0 VOUT = 3.3V TA = 25°C L = 4.7μH f = 800kHz 1 10000 10 100 1000 LOAD CURRENT (mA) INPUT VOLTAGE (V) 5.0 5.5

3680 G21

4.5 4.0 6.5 6.0 VOUT = 5V TA = 25 °C L = 4.7μH f = 800kHz

3680 G24

0.2A/DIV VSW 5V/DIV VOUT 10mV/DIV 5μs/DIVVIN = 12V VOUT = 3.3V ILOAD = 10mA TEMPERATURE (°C) THRESHOLD VOLTAGE (%)

3680 G23

–50 25–25 0 50 75 100 150 125

3680 G25

0.2A/DIV VSW 5V/DIV VOUT 10mV/DIV VIN = 12V VOUT = 3.3V ILOAD = 110mA 1μs/DIV

3680 G26

0.5A/DIV VSW 5V/DIV VOUT 10mV/DIV VIN = 12V VOUT = 3.3V ILOAD = 1A 1μs/DIV Minimum Input Voltage Minimum Input Voltage VC Voltages Power Good Threshold Switching Waveforms; Transition from Burst Mode to Full Frequency Switching Waveforms; Full Frequency Continuous Operation Switching Waveforms; Burst Mode TA = 25°C unless otherwise noted. TYPICAL PERFORMANCE CHARACTERISTICS

BD (Pin 1): This pin connects to the anode of the boost Schottky diode. BD also supplies current to the internal regulator. BOOST (Pin 2): This pin is used to provide a drive voltage, higher than the input voltage, to the internal bipolar NPN power switch. SW (Pin 3): The SW pin is the output of the internal power switch. Connect this pin to the inductor, catch diode and boost capacitor. V IN (Pin 4): The VIN pin supplies current to the LT3680’s internal regulator and to the internal power switch. This pin must be locally bypassed. RUN/SS (Pin 5): The RUN/SS pin is used to put the LT3680 in shutdown mode. Tie to ground to shut down the LT3680. Tie to 2.5V or more for normal operation. If the shutdown feature is not used, tie this pin to the V IN pin. RUN/SS also provides a soft-start function; see the Applications Information section. SYNC (Pin 6): This is the external clock synchronization input. Ground this pin for low ripple Burst Mode operation at low output loads. Tie to a clock source for synchroniza- tion. Clock edges should have rise and fall times faster than 1μs. Do not leave pin ﬂ oating. See synchronizing section in Applications Information. PG (Pin 7): The PG pin is the open collector output of an internal comparator. PG remains low until the FB pin is within 9% of the ﬁ nal regulation voltage. PG output is valid when V IN is above 3.6V and RUN/SS is high. FB (Pin 8): The LT3680 regulates the FB pin to 0.790V. Connect the feedback resistor divider tap to this pin. VC (Pin 9): The VC pin is the output of the internal error ampliﬁ er. The voltage on this pin controls the peak switch current. Tie an RC network from this pin to ground to compensate the control loop. RT (Pin 10): Oscillator Resistor Input. Connecting a resistor to ground from this pin sets the switching frequency. Exposed Pad (Pin 11): Ground. The Exposed Pad must be soldered to PCB. OSCILLATOR 200kHzTO2.4MHz BurstMode DETECT VC CLAMP SOFT-START SLOPE COMP R VINVIN RUN/SS BOOST SW SWITCH LATCH VC VOUT CF DISABLE CC RC BD RT GND ERROR AMP FB RT PG 0.7V S Q 3680 BD 11 8 INTERNAL 0.79V REF SYNC BLOCK DIAGRAM PIN FUNCTIONS

The LT3680 is a constant frequency, current mode step- down regulator. An oscillator, with frequency set by RT, enables an RS ﬂ ip-ﬂ op, turning on the internal power switch. 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 pin. 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 on the V C pin provides current limit. The VC pin is also clamped to the voltage on the RUN/SS pin; soft-start is implemented by generating a voltage ramp at the RUN/SS pin using an external resistor and capacitor. An internal regulator provides power to the control circuitry. The bias regulator normally draws power from the V IN pin, but if the BD pin is connected to an external voltage higher than 3V bias power will be drawn from the external source (typically the regulated output voltage). This improves efﬁ ciency. The RUN/SS pin is used to place the LT3680 in shutdown, disconnecting the output and reducing the input current to less than 0.5μA. The switch driver operates from either the input or from the BOOST pin. An external capacitor and 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 opera- tion. To further optimize efﬁ ciency, the LT3680 automatically switches to Burst Mode operation in light load situations. Between bursts, all circuitry associated with controlling the output switch is shut down, reducing the input supply current to 75μA in a typical application. The oscillator reduces the LT3680’s operating frequency when the voltage at the FB pin is low. This frequency foldback helps to control the output current during startup and overload. The LT3680 contains a power good comparator which trips when the FB pin is at 91% of its regulated value. The PG output is an open-collector transistor that is off when the output is in regulation, allowing an external resistor to pull the PG pin high. Power good is valid when the LT3680 is enabled and V IN is above 3.6V. OPERATION

Reference designators refer to the Block Diagram. Figure 1. Switching Frequency vs. RT Value minimum of ~150ns and turn off for a minimum of ~150ns. the inductor and capacitor values small.

be higher than in normal operation. maximum duty cycle (see equation in previous section). switching frequency should be used. and switching frequency will determine the ripple current. must be lower than the LT3680’s switch current limit (ILIM). sufﬁ cient maximum output current (IOUT(MAX)). Table 1. Inductor Vendors

Of course, such a simple design guide will not always re- sult in the optimum inductor for your application. A larger value inductor provides a slightly higher maximum load current and will reduce the output voltage ripple. If your load is lower than 3.5A, then you can decrease the value of the inductor and operate with higher ripple current. This allows you to use a physically smaller inductor, or one with a lower DCR resulting in higher efﬁ ciency. 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 maximum output current and discontinuous mode opera- tion, see Linear Technology Application Note 44. Finally, for duty cycles greater than 50% (V OUT/VIN > 0.5), there is a minimum inductance required to avoid subharmonic oscillations. See AN19. Input Capacitor Bypass the input of the LT3680 circuit with a ceramic capacitor of X7R or X5R type. Y5V types have poor performance over temperature and applied voltage, and should not be used. A 10μF to 22μF ceramic capacitor is adequate to bypass the LT3680 and will easily handle the ripple current. Note that larger input capacitance is required when a lower switching frequency is used. 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 lower performance electrolytic capacitor. Step-down regulators draw current from the input sup- ply in pulses with very fast rise and fall times. The input capacitor is required to reduce the resulting voltage ripple at the LT3680 and to force this very high frequency switching current into a tight local loop, minimizing EMI. A 10μF capacitor is capable of this task, but only if it is placed close to the LT3680 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 LT3680. A ceramic input capacitor combined with trace or cable inductance forms a high quality (under damped) tank circuit. If the LT3680 circuit is plugged into a live supply, the input voltage can ring to twice its nominal value, possibly exceeding the LT3680’s voltage rating. This situation is easily avoided (see the Hot Plugging Safety section). For space sensitive applications, a 4.7μF ceramic capaci- tor can be used for local bypassing of the LT3680 input. However, the lower input capacitance will result in in- creased input current ripple and input voltage ripple, and may couple noise into other circuitry. Also, the increased voltage ripple will raise the minimum operating voltage of the LT3680 to ~3.7V. Output Capacitor and Output Ripple The output capacitor has two essential functions. Along with the inductor, it ﬁ lters the square wave generated by the LT3680 to produce the DC output. In this role it determines the output ripple, and low impedance at the switching frequency is important. The second function is to store energy in order to satisfy transient loads and stabilize the LT3680’s control loop. Ceramic capacitors have very low equivalent series resistance (ESR) and provide the best ripple performance. A good starting value is: C VfOUT OUT SW = 100 where f SW is in MHz, and C OUT is the recommended output capacitance in μF. Use X5R or X7R types. This choice will provide low output ripple and good transient response. Transient performance can be improved with a higher value capacitor if the compensation network is also adjusted to maintain the loop bandwidth. A lower value of output capacitor can be used to save space and cost but transient performance will suffer. See the Fre- quency Compensation section to choose an appropriate compensation network. When choosing a capacitor, look carefully through the data sheet to ﬁ nd out what the actual capacitance is under operating conditions (applied voltage and temperature). A physically larger capacitor, or one with a higher volt- age rating, may be required. High performance tantalum or electrolytic capacitors can be used for the output APPLICATIONS INFORMATION

3 lists several Schottky diodes and their manufacturers. Table 3. Diode Vendors Mode operation, the noise is nearly silent to a casual ear. or electrolytic capacitor at the output. Table 2. Capacitor Vendors

output capacitor has high ESR. transconductance ampliﬁ er with ﬁ nite output impedance. the feedback divider may improve the transient response. rent is stepped from 1A to 3A and back to 1A.

3680 F02

Figure 3. Transient Load Response of the LT3680 Front Page Application as the Load Current is Stepped from 1A to 3A. Figure 2. Model for Loop Response

3680 F03

in high efﬁ ciency even at very low loads. See Figure 4. frequency at output loads higher than about 60mA. pin quiescent current comes from a lower voltage source. of the BOOST and BD pins are not exceeded. Figure 4. Burst Mode Operation

3680 F04

3680 FO5

reducing the maximum input current during start-up. up and shut-down waveforms with the soft-start circuit. pin below 0.3V (this can be ground or a logic output). input voltage to maintain regulation. Figure 6. The Minimum Input Voltage Depends on

3680 F06

5.5 TO START

Figure 5. Three Circuits For Generating The Boost Voltage

and peaks that are above 0.8V (up to 6V). skip pulses to maintain regulation. T should be chosen for 200kHz. protects against a shorted or reversed input. Figure 8. Diode D4 Prevents a Shorted Input from

3680 F08

a local, unbroken ground plane below these components. The SW and BOOST nodes should be as small as possible. Figure 7. To Soft-Start the LT3680, Add a Resisitor

3680 F07

3680 F09

Figure 9. A Good PCB Layout Ensures Proper, Low EMI Operation traces will shield them from the SW and BOOST nodes. board and on the bottom side. Figure 10. A Well Chosen Input Network Prevents Input Voltage Overshoot and

3680 F10

voltage at the VIN pin of the LT3680 can ring to twice the nominal input voltage, possibly exceeding the LT3680’s rating and damaging the part. If the input supply is poorly controlled or the user will be plugging the LT3680 into an energized supply, the input network should be designed to prevent this overshoot. Figure 10 shows the waveforms that result when an LT3680 circuit is connected to a 24V supply through six feet of 24-gauge twisted pair. The ﬁ rst plot is the response with a 4.7μF ceramic capacitor at the input. The input voltage rings as high as 50V and the input current peaks at 26A. A good solution is shown in Figure 10b. A 0.7 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. For high input voltages its impact on efﬁ ciency is minor, reducing efﬁ ciency by 1.5 percent for a 5V output at full load operating from 24V. High Temperature Considerations The PCB must provide heat sinking to keep the LT3680 cool. The Exposed Pad on the bottom of the package must be soldered to a ground plane. This ground should be tied to large copper layers below with thermal vias; these lay- ers will spread the heat dissipated by the LT3680. Place additional vias can reduce thermal resistance further. With these steps, the thermal resistance from die (or junction) to ambient can be reduced to JA = 35°C/W or less. With 100 LFPM airﬂ ow, this resistance can fall by another 25%. Further increases in airﬂ ow will lead to lower thermal re- sistance. Because of the large output current capability of the LT3680, it is possible to dissipate enough heat to raise the junction temperature beyond the absolute maximum of 125°C. When operating at high ambient temperatures, the maximum load current should be derated as the ambient temperature approaches 125°C. Power dissipation within the LT3680 can be estimated by calculating the total power loss from an efﬁ ciency measure- ment and subtracting the catch diode loss and inductor loss. The die temperature is calculated by multiplying the LT3680 power dissipation by the thermal resistance from junction to ambient. Other Linear Technology Publications Application Notes 19, 35 and 44 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. APPLICATIONS INFORMATION 5V Step-Down Converter SW FB VC PG RT VIN BD VIN 6.3V TO 36V VOUT 3.5A 10μF 0.47μF 47μF100k f = 600kHz D: ON SEMI MBRA340 L: NEC MPLC0730L4R7 D 15k 63.4k L 4.7μH 536k GND 680pF ON OFF L T3680

3680 TA02

3.3V Step-Down Converter SW FB VC PG RT VIN BD VIN 4.4V TO 36V VOUT 3.3V 3.5A 4.7μF 0.47μF 22μF100k f = 600kHz D: ON SEMI MBRA340 L: NEC MPLC0730L3R3 D 19k 63.4k L 3.3μH GND 680pF ON OFF L T3680

3680 TA03

2.5V Step-Down Converter SW FB VC PG RT VIN BD VIN 4V TO 36V VOUT 2.5V 3.5A 4.7μF 1μF 47μF100k f = 600kHz D1: ON SEMI MBRA340 D2: MBR0540 L: NEC MPLC0730L3R3 15.4k 63.4k L 3.3μH 215k GND 680pF ON OFF L T3680

3680 TA04

3.5A 10μF 0.47μF 47μF50k f = 600kHz D: ON SEMI MBRA340 L: NEC MBP107558R2P D 17.4k 63.4k L 8.2μH GND 680pF ON OFF L T3680

3680 TA06

5V, 2MHz Step-Down Converter SW FB VC PG RT VIN BD VIN 8.6V TO 22V TRANSIENT TO 36V VOUT 2.5A 4.7μF 0.47μF 22μF100k f = 2MHz D: ON SEMI MBRA340 L: NEC MPLC0730L2R2 D 15k 12.7k L 2.2μH GND 680pF ON OFF L T3680

3680 TA05

1.8V Step-Down Converter SW FB VC PG RT VIN BD VIN 3.5V TO 27V VOUT 1.8V 3.5A 4.7μF 0.47μF 47μF100k f = 500kHz D: ON SEMI MBRA340 L: NEC MPLC0730L3R3 D 16.9k 78.7k L 3.3μH 127k GND 680pF ON OFF L T3680

3680 TA08

10-Lead Plastic DFN (3mm × 3mm) (Reference LTC DWG # 05-08-1699) PACKAGE DESCRIPTION 3.00 p0.10 (4 SIDES) NOTE: 1. DRAWING TO BE MADE A JEDEC PACKAGE OUTLINE M0-229 VARIATION OF (WEED-2). CHECK THE LTC WEBSITE DATA SHEET FOR CURRENT STATUS OF VARIATION ASSIGNMENT 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 0.38 p 0.10 BOTTOM VIEW—EXPOSED PAD 1.65 p 0.10 (2 SIDES) 0.75 p0.05 R = 0.115 TYP 2.38 p0.10 (2 SIDES) 106 PIN 1 TOP MARK (SEE NOTE 6)

0.200 REF

0.00 – 0.05 (DD) DFN 1103 0.25 p 0.05 2.38 p0.05 (2 SIDES) RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS 1.65 p0.05 (2 SIDES)2.15 p0.05 0.50 BSC 0.675 p0.05 3.50 p0.05 PACKAGE OUTLINE 0.25 p 0.05

0.50 BSC

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 , Exposed Die Pad (Reference LTC DWG # 05-08-1664 Rev B) MSOP (MSE) 0307 REV B 0.53 p 0.152 (.021 p .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 p 0.152 (.193 p .006) 0.497 p 0.076 (.0196 p .003) REF8910 7 6 3.00 p 0.102 (.118 p .004) (NOTE 3) 3.00 p 0.102 (.118 p .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) 0o – 6o TYP DETAIL “A” DETAIL “A” GAUGE PLANE 5.23 (.206) MIN 3.20 – 3.45 (.126 – .136) 0.889 p 0.127 (.035 p .005) RECOMMENDED SOLDER PAD LAYOUT 0.305 p 0.038 (.0120 p .0015) TYP 2.083 p 0.102 (.082 p .004) 2.794 p 0.102 (.110 p .004) 0.50 (.0197) BSC BOTTOM VIEW OF EXPOSED PAD OPTION 1.83 p 0.102 (.072 p .004) 2.06 p 0.102 (.081 p .004) 0.1016 p 0.0508 (.004 p .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 0508 REV A • PRINTED IN USA PART NUMBER DESCRIPTION COMMENTS LT1766 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/E Package LT1767 25V, 1.2A (I OUT), 1.2MHz, High Efﬁ ciency Step-Down DC/DC Converter VIN: 3V to 25V, VOUT(MIN) = 1.2V, IQ = 1mA, ISD < 6μA, MS8E Package LT1933 500mA (I OUT), 500kHz Step-Down Switching Regulator in SOT-23 V IN: 3.6V to 36V, VOUT(MIN) = 1.2V, IQ = 1.6mA, ISD < 1μA, ThinSOTTM Package LT1936 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, LT1940 Dual 25V, 1.4A (I OUT), 1.1MHz, High Efﬁ ciency Step-Down DC/DC Converter VIN: 3.6V to 25V, VOUT(MIN) = 1.2V, IQ = 3.8mA, ISD < 30μA, LT1976/LT1967 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) = 1.2V, IQ = 100μA, ISD < 1μA, LT3434/LT3435 60V, 2.4A (I OUT), 200kHz/500kHz, High Efﬁ ciency Step-Down DC/DC Converters with Burst Mode Operation VIN: 3.3V to 60V, VOUT(MIN) = 1.2V, IQ = 100μA, ISD < 1μA, LT3437 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, 3mm × 3mm DFN10 and TSSOP16E Packages LT3480 36V with Transient Protection to 60V, 2A (I OUT), 2.4MHz, High Efﬁ ciency Step-Down DC/DC Converter with Burst Mode Operation VIN: 3.6V to 38V, VOUT(MIN) = 0.78V, IQ = 70μA, ISD < 1μA, 3mm × 3mm DFN10 and MSOP10E Packages LT3481 34V with Transient Protection to 36V, 2A (I OUT), 2.8MHz, High Efﬁ ciency Step-Down DC/DC Converter with Burst Mode Operation VIN: 3.6V to 34V, VOUT(MIN) = 1.26V, IQ = 50μA, ISD < 1μA, 3mm × 3mm DFN10 and MSOP10E Packa ges LT3493 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, 2mm x 3mm DFN6 Package LT3505 36V with Transient Protection to 40V, 1.4A (I OUT), 3MHz, High Efﬁ ciency Step-Down DC/DC Converter VIN: 3.6V to 34V, VOUT(MIN) = 0.78V, IQ = 2mA, ISD = 2μA, 3mm × 3mm DFN8 and MSOP8E Packages LT3508 36V with Transient Protection to 40V, Dual 1.4A (I OUT), 3MHz, High Efﬁ ciency Step-Down DC/DC Converter VIN: 3.7V to 37V, VOUT(MIN) = 0.8V, IQ = 4.6mA, ISD = 1μA, 4mm × 4mm QFN24 and TSSOP16E Packages LT3684 34V with Transient Protection to 36V, 2A (I OUT), 2.8MHz, High Efﬁ ciency Step-Down DC/DC Converter VIN: 3.6V to 34V, VOUT(MIN) = 1.26V, IQ = 850μA, ISD < 1μA, 3mm × 3mm DFN10 and MSOP10E Packages LT3685 36V with Transient Protection to 60V, Dual 2A (I OUT), 2.4MHz, High Efﬁ ciency Step-Down DC/DC Converter VIN: 3.6V to 38V, VOUT(MIN) = 0.78V, IQ = 70μA, ISD < 1μA, 3mm × 3mm DFN10 and MSOP10E Packages SW FB VC PG RT VIN BD VIN 3.6V TO 27V VOUT 1.2V 3.5A 4.7μF 0.47μF 100μF f = 500kHz D: ON SEMI MBRA340 L: NEC MPLC0730L3R3 D 17k 78.7k L 3.3μH GND 470pF ON OFF L T3680

3680 TA09

52.3k 1.2V Step-Down Converter RELATED PARTS TYPICAL APPLICATION

Selected Specification

Linear Technology LCYK overview.

Summary

36V, 3.5A, 2.4MHz Step-Down Switching Regulator with 75關A Quiescent Current

Description

36V, 3.5A, 2.4MHz Step-Down Switching Regulator with 75關A Quiescent Current

Source title LCYK Datasheet(PDF) - Linear Technology

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