LTC3728 - Dual, 550kHz, 2-Phase Synchronous Step-Down Switching Regulator

Features

  • Dual, 180° Phased Controllers Reduce Required Input Capacitance and Power Supply Induced Noise
  • OPTI-LOOP Compensation Minimizes COUT
  • ±1% Output Voltage Accuracy
  • Power Good Output Voltage Indicator
  • Phase-Lockable Fixed Frequency 250kHz to 550kHz
  • Dual N-Channel MOSFET Synchronous Drive
  • Wide VIN Range: 3.5V to 36V Operation
  • Very Low Dropout Operation: 99% Duty Cycle
  • Adjustable Soft-Start Current Ramping
  • Foldback Output Current Limiting
  • Latched Short-Circuit Shutdown with Defeat Option
  • Output Overvoltage Protection
  • Remote Output Voltage Sense
  • Low Shutdown IQ : 20µA
  • 5V and 3.3V Regulators
  • 3 Selectable Operating Modes: Constant-Frequency, Burst Mode Operation and PWM
  • Available in 32-Pin 5mm x 5mm QFN and 28-Pin SSOP Packages
Designed for Automotive and Transportation Applications
AEC-Q100 data available for specific packages


Typical Application

LTC3728 Typical Application

Description

The LTC3728 is a dual high performance step-down switching regulator controller that drives all N-channel synchronous power MOSFET stages. A constant-frequency current mode architecture allows phase-lockable frequency of up to 550kHz. Power loss and noise due to the ESR of the input capacitors are minimized by operating the two controller output stages out of phase.

OPTI-LOOP compensation allows the transient response to be optimized over a wide range of output capacitance and ESR values. The precision 0.8V reference and power good output indicator are compatible with future microprocessor generations, and a wide 3.5V to 30V (36V maximum) input supply range encompasses all battery chemistries.

A RUN/SS pin for each controller provides both softstart and optional timed, short-circuit shutdown. Current foldback limits MOSFET dissipation during short-circuit conditions when overcurrent latchoff is disabled. Output overvoltage protection circuitry latches on the bottom MOSFET until VOUT returns to normal. The FCB mode pin can select among Burst Mode, constant-frequency mode and continuous inductor current mode or regulate a secondary winding. The LTC3728 includes a power good output pin that indicates when both outputs are within 7.5% of their designed set point.

 Vin RangeVref AccyCurrent Limit Latch Off3.3V LDO Available
LTC3728 3.5V to 36V +/-1% Yes  
LTC3728L 4.5V to 28V  +/-1% Yes Yes
LTC3728LX 4.5V to 28V +/- 1.5% Yes Yes
LTC3728L-1 4.5V to 28V  +/- 1.5% Foldback only Yes

Packaging

CAD Symbols and Footprints: The downloadable Zip file below contains the schematic symbol and PCB footprints.

For complete and up to date package information and drawings, please refer to our packaging page

Part Number Package Code Temp Package
Drawing
RoHS
LTC3728EG#PBF SSOP-28 G E 05-08-1640 (G28) Yes
LTC3728EG#TRPBF SSOP-28 G E 05-08-1640 (G28) Yes
LTC3728EUH#PBF 5x5 QFN-32 UH E 05-08-1693 Yes
LTC3728EUH#TRPBF 5x5 QFN-32 UH E 05-08-1693 Yes
LTC3728IG#PBF SSOP-28 G I 05-08-1640 (G28) Yes
LTC3728IG#TRPBF SSOP-28 G I 05-08-1640 (G28) Yes
LTC3728IUH#PBF 5x5 QFN-32 UH I 05-08-1693 Yes
LTC3728IUH#TRPBF 5x5 QFN-32 UH I 05-08-1693 Yes


LTC3728 Package Drawing
LTC3728 Package Drawing

Order Info

  • Part numbers ending in PBF are lead free. Solder plated terminal finish (SnPb) versions are non-standard and special terms and conditions and pricing applies if available. Please contact LTC marketing for information.
  • Part numbers containing TR or TRM are shipped in tape and reel or 500 unit mini tape and reel, respectively
  • Please refer to our general ordering information or the product datasheet for more details

Package Variations and Pricing

Part Number Package Temp Price
(1-99)
Price
(1k)*
RoHS
LTC3728EG#PBF SSOP-28 E $5.92 $5.00 Yes
LTC3728EG#TRPBF SSOP-28 E $5.10 Yes
LTC3728EUH#PBF 5x5 QFN-32 E $7.50 $5.10 Yes
LTC3728EUH#TRPBF 5x5 QFN-32 E $5.20 Yes
LTC3728IG#PBF SSOP-28 I $7.56 $5.29 Yes
LTC3728IG#TRPBF SSOP-28 I $5.35 Yes
LTC3728IUH#PBF 5x5 QFN-32 I $7.73 $5.41 Yes
LTC3728IUH#TRPBF 5x5 QFN-32 I $5.47 Yes
Buy NowRequest Samples
* The USA list pricing shown is for BUDGETARY USE ONLY, shown in United States dollars (FOB USA per unit for the stated volume), and is subject to change. International prices may differ due to local duties, taxes, fees and exchange rates. For volume-specific price or delivery quotes, please contact your local Linear Technology sales office or authorized distributor.

Demo Boards

Linear Technology offers many demo boards free of charge to qualified customers. Contact your local sales office or distributor to inquire about a demo board. Certain demo boards are also available for sale via credit card on this website. Demo boards are for evaluation purposes only. It remains the customer’s responsibility to verify proper and reliable operation in the actual end application.

Part Number Description Price Documentation
DC392A-B LTC3728EUH Demo Board | Dual Output, 5V to 24Vin, 5Vout1 @ 4A, 3.3Vout2 @ 5A $125.00
DC447A LTC3728EUH | 2-Phase Dual Output Power Supply, Vin = 5V - 14V, Vout1 = 2.5V @ 13A, Vout2 = 1.8V @ 13A $150.00
DC542A LTC3728EG | Dual 2-Phase, 8V to 24V Input, 5V/3.3V 0A to 12A, 3.3V/2.5V 0A to 12A $150.00
Buy Now
Click here to view our complete list of demo boards

Designed for Automotive and Transportation Applications

AEC-Q100 data is available for these specific part numbers. Please contact your local sales representative for more information regarding reliability reports or to inquire about parts that are not included. For more information, view our Automotive and Transportation page

Part Number Package Temp Price
(1-99)
Price
(1k)*
RoHS
LTC3728IG#PBF SSOP-28 I $7.56 $5.29 Yes
LTC3728IG#TRPBF SSOP-28 I $5.35 Yes
LTC3728IUH#PBF 5x5 QFN-32 I $7.73 $5.41 Yes
LTC3728IUH#TRPBF 5x5 QFN-32 I $5.47 Yes
Buy NowRequest Samples
* The USA list pricing shown is for BUDGETARY USE ONLY, shown in United States dollars (FOB USA per unit for the stated volume), and is subject to change. International prices may differ due to local duties, taxes, fees and exchange rates. For volume-specific price or delivery quotes, please contact your local Linear Technology sales office or authorized distributor.

Applications

  • Notebook and Palmtop Computers
  • Telecom Systems
  • Portable Instruments
  • Battery-Operated Digital Devices
  • DC Power Distribution Systems

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Design Tools

LTspice

LTspice® software is a powerful, fast and free simulation tool, schematic capture and waveform viewer with enhancements and models for improving the simulation of switching regulators. Click here to download LTspice

To launch a ready to run LTspice demonstration circuit for this part:

  • Step 1: If you have not installed LTspice on this computer, download and install LTspice
  • Step 2: Once LTspice is installed, click on the link(s) below to launch the simulation
  • Step 3: If LTspice does not automatically open after clicking the link above, you can instead run the simulation by right clicking on the link and selecting "Save Target As." After saving the file to your computer, start LTspice and open the demonstration circuit by selecting 'Open' from the 'File' menu

To explore other ready to run LTspice demonstration circuits, please visit our Demo Circuits Collection.

Models for the following parts are available in LTspice:
LTC3728
LTC3728L

Technical Support