3681

LT3681 LINER

Document overview

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Technical content

36V, 2A, 2.8MHz Step-Down Switching Regulator with Integrated Power Schottky Diode The LT®3681 is an adjustable frequency (300kHz to 2.8MHz) monolithic buck switching regulator that accepts input voltages up to 34V (36V maximum). A high effi ciency 0.18Ω switch is included on the die along with a boost Schottky diode and the necessary oscillator, control, and logic circuitry. An undedicated power Schottky diode is integrated into the LT3681 to minimize the solution size. 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 LT3681 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 90% of the programmed output voltage. The LT3681 is available in 14-Pin 4mm x 3mm DFN package 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 34V Operating, 36V Maximum ■ 2A Maximum Output Current ■ Low Ripple Burst Mode® Operation 50µA IQ at 12VIN to 3.3VOUT Output Ripple < 15mVP-P ■ Adjustable Switching Frequency: 300kHz to 2.8MHz ■ Low Shutdown Current: IQ < 1µA ■ Integrated Boost Diode ■ Integrated Power Schottky Diode ■ Power Good Flag ■ Saturating Switch Design: 0.18 Ω On-Resistance ■ 1.265V Feedback Reference Voltage ■ Output Voltage: 1.265V to 20V ■ Soft-Start Capability ■ Small 14-Pin Thermally Enhanced (4mm x 3mm) DFN Package 5V Step-Down Converter APPLICATIO SU FEATURES DESCRIPTIO U TYPICAL APPLICATIO U SW DC DA BIAS FB VC PG RT VIN BD VIN 6.3V TO 34V VOUT 4.7/K6D F 0.47/K6D F 330pF 22/K6D F200k 20k 60.4k L 6.8/K6D H 590k GND OFF ON LT3681

3681 TA01

L: NEC PLC-0745-6R8 Effi ciency ILOAD (A) 0.0001 EFFICIENCY (%) POWER LOSS (W) 0.001 0.01 0.1 1 10

3681 TA01b

0.0001 0.0100 0.0010 10.0000 1.0000 0.1000 VIN = 12V VOUT = 3.3V L = 4.7/K6D H F = 800 kHz , 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.

ELECTRICAL CHARACTERISTICS

FB, RT, V Operating Temperature Range (Note 2) (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 VBIAS = 3V, Not Switching ● 22 60 μA VBIAS = 0, Not Switching 75 120 μA Quiescent Current from BIAS V RUN/SS = 0.2V 0.01 0.5 μA VBIAS = 3V, Not Switching ● 50 120 μA VBIAS = 0, Not Switching 05 μA Minimum Bias Voltage 2.7 3 V Feedback Voltage 1.25 1.24 1.265 1.265 1.29 1.3 V V FB Pin Bias Current (Note 3) V FB = 1.25V, VC = 0.4V ● 30 100 nA FB Voltage Line Regulation 4V < V IN < 34V 0.002 0.02 %/V Error Amp GM 330 μMho Error Amp Gain 800 VC Source Current 65 μA VC Sink Current 85 μA VC Pin to Switch Current Gain 3.5 A/V VC Clamp Voltage 2V The ● denotes the specifi cations which apply over the full operating temperature range, otherwise specifi cations are at TA = 25°C. VIN = 10V, VRUNS/SS = 10V, VBOOST = 15V, VBIAS = 3.3V unless otherwise noted. (Note 2) ABSOLUTE AXI U RATI GSW WW U PACKAGE/ORDER I FOR ATIOUU W RUN/SS V IN SW BOOST BD DC DA PG BIAS FB GND V C RT GND TOP VIEW DE14MA PACKAGE 14-LEAD (4mm /KB4 3mm) PLASTIC DFN TJMAX = 125°C, θJA = 43°C/W EXPOSED PAD (PIN 15) IS GND, MUST BE SOLDERED TO PCB EXPOSED PAD PIN 16 IS DC ORDER PART NUMBER DE PART MARKING LT3681EDE 3681 Order Options Tape and Reel: Add #TR Lead Free: Add #PBF Lead Free Tape and Reel: Add #TRPBF Lead Free Part Marking: http://www.linear.com/leadfree/ Consult LTC Marketing for parts specifi ed with wider operating temperature ranges.

PARAMETER CONDITIONS MIN TYP MAX UNITS Power Schottky Diode Forward Voltage I DA = 1A IDA = 2A 0.50 0.56 V V Power Schottky Diode Leakage Current V DC-DA = 40V 100 μA Switching Frequency RT = 8.66k RT = 29.4k RT = 187k 2.5 1.25 250 2.8 1.4 300 3.1 1.55 350 MHz MHz kHz Minimum Switch Off-Time

• 130 200 nS Switch Current Limit Duty Cycle = 5% 3.2 3.8 4.4 A Switch VCESAT ISW = 2A 360 mV Boost Schottky Reverse Leakage V SW = 10V, VBIAS = 0V 0.02 2 µA Minimum Boost Voltage (Note 4) ● 1.5 2.1 V BOOST Pin Current I SW = 1A 18 35 mA RUN/SS Pin Current V RUN/SS = 2.5V 5 10 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 122 mV PG Hysteresis 5 mV PG Leakage V PG = 5V 0.1 1 μA PG Sink Current V PG = 3V ● 100 600 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 LT3681E is guaranteed to meet performance specifi cations from 0°C to 85°C. Specifi cations over the –40°C to 85°C operating temperature range are assured by design, characterization and correlation with statistical process controls. Note 3: Bias current fl ows into 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, VRUNS/SS = 10V VBOOST = 15V, VBIAS = 3.3V unless otherwise noted. (Note 2)

DUTY CYCLE (%) SWITCH CURRENT LIMIT(A)

3681 G08

2.5 20 60 1.5 1.0 4.0 3.5 3.0 2.0 80 100 TEMPERATURE (°C) –40 SUPPLY CURRENT (µA)

3681 G05

–20 0 40 100 60 80 VIN = 12V VOUT = 3.3V INCREASED SUPPLY CURRENT DUE TO CATCH DIODE LEAKAGE AT HIGH TEMPERATURE Effi ciency (VOUT = 5.0V) Effi ciency (VOUT = 3.3V) No Load Supply Current No Load Supply Current vs Temperature Maximum Load Current TYPICAL PERFOR A CE CHARACTERISTICSUW LOAD CURRENT (A) 0.0001 EFFICIENCY (%) 100 0.001 0.01 0.1 1 10

3681 G01

VIN = 24V VIN = 12V L: NEC PLC-0745-4R7 f: 800kHz LOAD CURRENT (A) 0.0001 EFFICIENCY (%) 100 0.001 0.01 0.1 1 10

3681 G02

VIN = 12V VIN = 24V VIN = 7V L: NEC PLC-0745-4R7 f: 800kHz INPUT VOLTAGE (V) SUPPLY CURRENT (µA)

3681 G04

INPUT VOLTAGE (V) LOAD CURRENT (A)

3681 G07

2.5 10 20 1.5 1.0 4.0 3.5 3.0 2.0 25 30 VOUT = 5.0V L = 4.7µH f = 800 kHz Switch Current Limit INPUT VOLTAGE (V) LOAD CURRENT (A)

3681 G06

2.5 10 20 1.5 1.0 4.0 3.5 3.0 2.0 25 30 VOUT = 3.3V L = 4.7µH f = 800 kHz TEMPERATURE (°C) –50 SWITCH CURRENT LIMIT (A) 2.0 2.5 3.0 125

3681 G09

1.5 1.0 0–25 50 25 100 75 0.5 4.5

4.0 DUTY CYCLE = 10 %

DUTY CYCLE = 90 % Maximum Load Current Switch Current Limit SWITCHING FREQUENCY (MHz) EFFICIENCY (%) 1.5

3681 G03

0.5 1 2 2.5 3 VIN = 12V VIN = 24V VOUT = 3.3V L = 10µH LOAD = 1A Effi ciency vs Switching Frequency TA = 25°C unless otherwise noted.

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

3681 G18

0.6 0.4 0.5 1.0 1.5 0.2 1.6 1.4 RUN/SS PIN VOLTAGE (V) RUN/SS PIN CURRENT (µA) 15 25

3681 G17

Switch Voltage Drop Boost Pin Current Feedback Voltage Switching Frequency Frequency Foldback Minimum Switch On-Time Soft Start RUN/SS Pin Current Boost Diode SWITCH CURRENT (mA) 400 500 700 1500 2500

3681 G10

600VOLTAGE DROP (mV) SWITCH CURRENT (mA) BOOST PIN CURRENT (mA) 2000

3681 G11

1000500 2500 30001500 3500 TEMPERATURE (°C) –50 FEEDBACK VOLTAGE (V) 1.270 1.280 125

4681 G12

1.260 1.250 0 50 100–25 25 75 1.290 1.265 1.275 1.255 1.285 TEMPERATURE (°C) –50 FREQUENCY (MHz) 1.00 1.10 125

4681 G13

0.90 0.80 0 50 100–25 25 75 1.20 RT = 45.3kΩ 0.95 1.05 0.85 1.15 FB PIN VOLTAGE (mV) SWITCHING FREQUENCY (kHz) 800 1000 1200 600 1000

3681 G14

RT = 45.3kΩ TEMPERATURE (˚C) –50 MINIMUM SWITCH ON TIME (ns) 100 120

3681 G15

–25 0 50 75 100 125 140 RUN/SS PIN VOLTAGE (V) SWITCH CURRENT LIMIT (A) 3.5 1.5

3681 G16

2.0 1.0 0.5 1 2 0.5 4.0 3.0 2.5 1.5 2.5 3 3.5 TYPICAL PERFOR A CE CHARACTERISTICSUW TA = 25°C unless otherwise noted.

TEMPERATURE (°C) –50 THRESHOLD VOLTAGE (V) 1.50 2.00 2.50 25 75 125

3681 G22

1.00 0.50 –25 0 50 100 CURRENT LIMIT CLAMP SWITCHING THRESHOLD VC Voltages

3681 G24

0.5A/DIV VSW 5V/DIV VOUT 10mV/DIV 2µs/DIV VIN = 12V; FRONT PAGE APPLICATION ILOAD = 10mA FB PIN VOLTAGE (V) 1.065 –80 VC PIN CURRENT (µA) –60 –20 1 .265 1.465 100

3681 G19

–40 1.165 1.365 LOAD CURRENT (A) 0.001 INPUT VOLTAGE (V) 3.0 3.5

3681 G20

2.5 2.0 0.01 0.1 1 4.5 4.0 VOUT = 3.3V L = 4.7/K6D f = 800kHz LOAD CURRENT (A) 0.001 INPUT VOLTAGE (V) 5.0 5.5 4.5 4.0 0.01 0.1 1 6.5 6.0 VOUT = 5.0V L = 4.7/K6D f = 800kHz TEMPERATURE (°C) –50 THRESHOLD VOLTAGE (V) 1.160 1.180 1.200 25 75 125

3681 G23

1.140 1.120 1.100 –25 0 50 100 PG RISING

3681 G25

0.5A/DIV VRUN/SS 5V/DIV VOUT 10mV/DIV VIN = 12V; FRONT PAGE APPLICATION ILOAD = 140mA 1µs/DIV

3681 G26

0.5A/DIV VRUN/SS 5V/DIV VOUT 10mV/DIV VIN = 12V; FRONT PAGE APPLICATION ILOAD = 1A 1µs/DIV Error Amp Output Current Minimum Input Voltage Minimum Input Voltage Power Good Threshold Switching Waveforms; Transition from Burst Mode to Full Frequency Switching Waveforms; Full Frequency Continuous Operation Switching Waveforms; Burst Mode TYPICAL PERFOR A CE CHARACTERISTICSUW Power Schottky Diode Forward Voltage vs Current FORWARD VOLTAGE (V) CURRENT (mA) 0.2

3681 G29

0.1 0.3 1000 6000 5000 4000 2000 0.4 0.5 0.6 0.7 TA = 25°C unless otherwise noted.

PG (Pin 1): The PG pin is the open collector output of an internal comparator. PG remains low until the FB pin is within 10% of the fi nal regulation voltage. PG output is valid when V IN is above 3.5V and RUN/SS is high. BIAS (Pin 2): The BIAS pin supplies the current to the LT3681’s internal regulator. Tie this pin to the lowest available voltage source above 3V (typically V OUT). This architecture increases effi ciency especially when the input voltage is much higher than the output. FB (Pin 3): The LT3681 regulates the FB pin to 1.265V. Connect the feedback resistor divider tap to this pin. V C (Pin 5): 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 6): Oscillator Resistor Input. Connecting a resistor to ground from this pin sets the switching frequency. DA (Pin 8): This is the anode of the integrated power Schottky diode. High frequency, large amplitude currents fl ow through this pin, so tie it to ground through a low impedance connection. DC (Pin 9, Exposed Pad 16): These pins connect to the cathode of the integrated power Schottky diode. High fre- quency, large amplitude currents fl ow through these pins, so tie them to SW through a low impedance connection. BD (Pin 10): This pin connects to the anode of the internal boost Schottky diode. BOOST (Pin 11): This pin is used to provide a drive voltage, higher than the input voltage, to the internal bipolar NPN power switch. Connect a capacitor between this pin and SW. SW (Pin 12): The SW pin is the output of the internal power switch. Connect this pin to the inductor, DC and boost capacitor. V IN (Pin 13): The VIN pin supplies current to the LT3681’s internal regulator and to the internal power switch. This pin must be locally bypassed. RUN/SS (Pin 14): The RUN/SS pin is used to put the LT3681 in shutdown mode. Tie to ground to shut down the LT3681. Tie to 2.3V 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. GND (Pins 4, 7, Exposed Pad 15): All three of these terminals internally connect to the LT3681 control IC’s signal return, while exposed pad 15 performs the added function of providing a low thermal resistance heat fl ow path between the IC and the system heatsink. Tie all of these terminals to a copper pour on the top layer of the printed circuit board. Please refer to the Applications Information section for more details.

The LT3681 is a constant frequency, current mode step- down regulator. An oscillator, with frequency set by RT, sets 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 cur- rent 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 cir- cuitry. The bias regulator normally draws power from the V IN pin, but if the BIAS 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 LT3681 in shutdown, disconnecting the output and reducing the input current to less than 1µA. The switch driver operates from either the input or from the BOOST pin. An external capacitor is 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. To further optimize effi ciency, the LT3681 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 55µA in a typical application. The oscillator reduces the LT3681’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 LT3681 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 LT3681 is enabled and V IN is above 3.6V. The LT3681 integrates a high quality, 36V, 2A power Schottky diode to reduce the overall solution size. OPERATION BLOCK DIAGRA W OSCILLATOR 300kHz–2.8MHz BurstMode DETECT VC CLAMP SOFT-START SLOPE COMP INTERNAL 1.265V REF R VINVIN BIAS RUN/SS BOOST SW SWITCH LATCH VC VOUT CF DC DC DA DISABLE CC RC BD RT ERROR AMP FB RT PG 1.12V S Q /K53 3681 BD GND GND GND

Reference designators refer to the Block Diagram. is necessary to safely accommodate high VIN/VOUT ratio. the inductor and capacitor values small. IN and BOOST pins, and on operating mode. Figure 1. Switching Frequency vs. RT Value

36V are acceptable regardless of the switching frequency. 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 LT3681’s switch current limit (ILIM). suffi cient maximum output current (IOUT(MAX)). (set by RT), and L is in the inductor value. 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 2A, 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 Application Note 19. Input Capacitor Bypass the input of the LT3681 circuit with a ceramic capaci- tor of X7R or X5R type. Y5V types have poor performance over temperature and applied voltage, and should not be used. A 4.7µF to 10µF ceramic capacitor is adequate to bypass the LT3681 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 low 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 LT3681 and to force this very high frequency switching current into a tight local loop, minimizing EMI. A 4.7µF capacitor is capable of this task, but only if it is placed close to the LT3681 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 LT3681. A ceramic input capacitor combined with trace or cable inductance forms a high quality (under damped) tank circuit. If the LT3681 circuit is plugged into a live supply, the input voltage can ring to twice its nominal value, possibly exceeding the LT3681’s voltage rating. This situation is easily avoided (see the Hot Plugging Safely section). For space sensitive applications, a 2.2µF ceramic capaci- tor can be used for local bypassing of the LT3681 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 LT3681 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 LT3681 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 LT3681’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. APPLICATIONS INFORMATION

operating conditions (applied voltage and temperature). electrolytic capacitors can be used for the output capacitor. where IOUT is the output load current. when used with the LT3681 due to their piezoelectric nature. eration, the noise is typically very quiet to a casual ear. or electrolytic capacitor at the output. the Hot Plugging Safely section). dition, there may be a lower value capacitor in parallel. output capacitor has high ESR. Table 2. Capacitor Vendors

the compensation network to optimize the performance. shows an equivalent circuit for the LT3681 control loop. frequency is much lower than the switching frequency. 500mA to 1500mA and back to 500mA. current is greatly reduced resulting in higher effi ciency.

3681 F02

Figure 2. Model for Loop Response Figure 3. Transient Load Response of the LT3681 3.3V Application as the Load Current is Stepped from 500mA to 1500mA.

3681 F03

Figure 4. Burst Mode Operation

3681 F04

requiring a higher input voltage to maintain regulation. pin quiescent current comes from a lower voltage source. of the BOOST and BIAS pins are not exceeded.

3681 FO5

Figure 5. Three Circuits For Generating The Boost Voltage

reducing the maximum input current during start-up. up and shut-down waveforms with the soft-start circuit. Switching Frequency section). Figure 6. The Minimum Input Voltage Depends on

3681 F06

Figure 7. To Soft-Start the LT3681, Add a Resistor

3681 F07

Figure 8. Diode D4 Prevents a Shorted Input from Discharging a Backup Battery Tied

3681 F08

protects against a shorted or reversed input.

Figure 9. A Good PCB Layout Ensures Proper, Low EMI Operation

3681 F11

rings as high as 50V and the input current peaks at 26A. electrolytic capacitor, as shown in Figure 10c. 100 LFPM airfl ow, this resistance can fall by another 25%. temperature approaches 125°C. resistance from junction to ambient. Figure 11. Like all Schottky Diodes, the LT3681 Integrated Power

3681 F12

Figure 10. A Well Chosen Input Network Prevents Input Voltage Overshoot and

3681 F10

6.3V TO 34V VOUT 4.7/K6D F 0.47/K6D F 22/K6D F200k f = 800kHz L: NEC PLC-0745-6R8 20k 60.4k L 6.8/K6D H 590k GND DA 330pF ON OFF LT3681

3681 TA02

3.3V Step-Down Converter SW BIAS FB VC PG RT VIN BD VIN 4.4V TO 34V VOUT 3.3V 4.7/K6D F 0.47/K6D F 22/K6D F200k f = 800kHz L: NEC PLC-0745-4R7 20k 60.4k L 4.7/K6D H 324k GND 330pF ON OFF LT3681

3681 TA03

5V, 2MHz Step-Down Converter SW BIAS FB VC PG RT VIN BD VIN 8.6V TO 22V TRANSIENT TO 36V VOUT 2.2/K6D F 0.47/K6D F 10/K6D F200k f = 2MHz L: TOKO FDV0620-2R2 6.8k 16.9k L 2.2/K6D H 590k GND 470pF ON OFF LT3681

3681 TA05

2.5V 4.7/K6D F 1/K6D F 47/K6D F200k f = 600kHz D2: MBR0540 L: SUMIDA CDRH8D43-4R7 22k 84.5k L 4.7/K6D H 196k GND 680pF ON OFF LT3681

3681 TA04

2.5V Step-Down Converter

0.47/K6D F 22/K6D F100k f = 800kHz L: SUMIDA CDRH8D43-100 24k 60.4k L 10/K6D H 845k GND 470pF ON OFF LT3681

3681 TA06

1.8V Step-Down Converter SW DC DA BIAS FB VC PG RT VIN BD VIN 3.6V TO 27V VOUT 1.8V 10µF 0.47µF 47µF200k f = 500kHz L: SUMIDA CDRH8D28-3R3 15k 105k L 3.3µH 84.5k GND 330pF ON OFF LT3681

3681 TA09

14-Lead Plastic DFN, Multichip (4mm × 3mm) (Reference LTC DWG # 05-08-1731 Rev 0) 3.00 ±0.10 (2 SIDES) 4.00 ±0.10 (2 SIDES) NOTE: 1. DRAWING PROPOSED 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 0.75 ±0.05 R = 0.115 TYP R = 0.05 TYP

3.00 REF

(SEE NOTE 6)

0.200 REF

0.00 – 0.05 (DE14MA) DFN 1106 REV Ø PIN 1 NOTCH R = 0.20 OR 0.25 × 45° CHAMFER RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED 2.10 ±0.05 0.70 ±0.05 3.50 ±0.05 PACKAGE OUTLINE 0.25 ± 0.05 0.25 ± 0.05

0.50 BSC

1.78 ±0.10

0.10 TYP

1.07 ±0.10 1.07 ±0.05

0.51 TYP

1.78 ±0.05 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.

Linear Technology Corporation 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com © LINEAR TECHNOLOGY CORPORATION 2006 LT 0407 • PRINTED IN USA TYPICAL APPLICATIO U RELATED PARTS SW BIAS FB VC PG RT VIN BD VIN 3.6V TO 27V VOUT 1.265V 4.7/K6D F 0.47/K6D F 47/K6D F f = 500kHz L: NEC PLC-0745-3R3 13k 105k L 3.3/K6D H GND 330pF ON OFF LT3681

3681 TA10

1.265V Step-Down Converter 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 = 1.20V, IQ = 2.5mA, ISD 25μA LT1767 25V, 1.2A (I OUT), 1.2MHz, High Effi ciency Step-Down DC/DC Converter VIN = 3.0V to 25V, VOUT = 1.20V, IQ = 1mA, ISD < 6μA LT1933 500mA (I OUT), 500kHz Step-Down Switching Regulator in SOT-23 V IN = 3.6V to 36V, VOUT = 1.2V, IQ = 1.6mA, ISD < 1μA ThinSOT Package LT1936 36V, 1.4A (I OUT), 500kHz High Effi ciency Step-Down DC/DC Converter V IN = 3.6V to 36V, VOUT = 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 = 1.20V, IQ = 3.8mA, ISD < 30μA LT1976/LT1977 60V, 1.2A (I OUT), 200kHz/500kHz, High Effi ciency Step-Down DC/DC Converter with Burst Mode VIN = 3.3V to 60V, VOUT = 1.20V, IQ = 100μA, ISD < 1μA LT3434/LT3435 60V, 2.4A (I OUT), 200/500kHz, High Effi ciency Step-Down DC/DC Converter with Burst Mode VIN = 3.3V to 60V, VOUT = 1.20V, IQ = 100μA, ISD < 1μA LT3437 60V, 400mA (I OUT), MicroPower Step-Down DC/DC Converter with Burst Mode VIN = 3.3V to 60V, VOUT = 1.25V, IQ = 100μA, ISD < 1μA (3mm × 3mm) DFN-10 TSSOP16E Package 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 = 0.78V, IQ = 70μA, ISD < 1μA (3mm × 3mm) DFN-10 MSOP10E Package 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 = 1.265V, IQ = 50μA, ISD < 1μA (3mm × 3mm) DFN-10 MSOP10E Package LT3493 36V, 1.4A (I OUT), 750kHz High Effi ciency Step-Down DC/DC Converter V IN = 3.6V to 36V, VOUT = 0.8V, IQ = 1.9mA, ISD < 1μA (2mm × 3mm)DFN-6 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 = 0.78V, IQ = 2mA, ISD < 2μA (3mm × 3mm) DFN-8 MSOP8E Package 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 = 0.8V, IQ = 4.6mA, ISD < 1μA (4mm × 4mm) QFN-24 TSSOP16E Package 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 = 01.26V, IQ = 850mA, ISD < 1μA (3mm × 3mm) DFN-10 MSOP10E Package LT3685 36V with Transient Protection to 60V, 2A (I OUT), 2.4MHz, High Effi ciency Step-Down DC/DC Converter VIN = 3.6V to 38V, VOUT = 0.78V, IQ = 70mA, ISD < 1μA (3mm × 3mm) DFN-10 MSOP10E Package