LT3688 - Dual 800mA Step-Down Switching Regulator with Power-On Reset and Watchdog Timer

Features

  • Wide Input Range:
    Operation from 3.8V to 36V
  • Low Ripple (<25mVP-P ) Burst Mode Operation:
    IQ = 115μA at 12VIN to 3.3V and 5V
  • Programmable, Defeatable Window Watchdog Timer
  • Two Independently Programmable Power-On-Reset Timers
  • Synchronizable, Adjustable 350kHz-2.2MHz Switching Frequency
  • Two 800mA Output Switching Regulators with Internal Power Switches
  • Programmable Input Undervoltage Lockout with Hysteresis
  • Thermally Enhanced 24-Pin TSSOP and 4mm × 4mm QFN Packages
Designed for Automotive and Transportation Applications
AEC-Q100 data available for specific packages


Typical Application

LT3688 Typical Application
LT3688 Typical Application

Description

The LT3688 is an adjustable frequency (350kHz to 2.2MHz) dual monolithic step-down switching regulator with two power-on reset timers and a watchdog timer. The regulator operates off inputs up to 36V. Low ripple Burst Mode® operation maintains high efficiency at low output current while keeping output ripple below 25mV in a typical application, with input quiescent current of just 115μA. Shutdown circuitry reduces input supply current to less than 1μA while EN/UVLO is pulled low.

The reset and watchdog timeout periods are both adjustable using external capacitors. Tight accuracy specifications and glitch immunity ensure reliable reset operation without false triggering. The open collector RST pins will pull down if the monitored output voltage drops 10% below the programmed value. The LT3688 watchdog timer monitors for watchdog falling edges grouped too close together or too far apart.

The LT3688 is available in 24-Pin TSSOP and 4mm × 4mm QFN packages, each with an exposed pad for low thermal resistance.

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
LT3688EFE#PBF TSSOP-24 FE E 05-08-1771 Yes
LT3688EFE#TRPBF TSSOP-24 FE E 05-08-1771 Yes
LT3688EUF#PBF 4x4 QFN-24 UF E 05-08-1697 Yes
LT3688EUF#TRPBF 4x4 QFN-24 UF E 05-08-1697 Yes
LT3688HFE#PBF TSSOP-24 FE H 05-08-1771 Yes
LT3688HFE#TRPBF TSSOP-24 FE H 05-08-1771 Yes
LT3688IFE#PBF TSSOP-24 FE I 05-08-1771 Yes
LT3688IFE#TRPBF TSSOP-24 FE I 05-08-1771 Yes
LT3688IUF#PBF 4x4 QFN-24 UF I 05-08-1697 Yes
LT3688IUF#TRPBF 4x4 QFN-24 UF I 05-08-1697 Yes


LT3688 Package Drawing
LT3688 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
LT3688EFE#PBF TSSOP-24 E $5.36 $3.75 Yes
LT3688EFE#TRPBF TSSOP-24 E $3.81 Yes
LT3688EUF#PBF 4x4 QFN-24 E $5.14 $3.60 Yes
LT3688EUF#TRPBF 4x4 QFN-24 E $3.66 Yes
LT3688HFE#PBF TSSOP-24 H $6.31 $4.42 Yes
LT3688HFE#TRPBF TSSOP-24 H $4.48 Yes
LT3688IFE#PBF TSSOP-24 I $5.96 $4.17 Yes
LT3688IFE#TRPBF TSSOP-24 I $4.23 Yes
LT3688IUF#PBF 4x4 QFN-24 I $5.73 $4.01 Yes
LT3688IUF#TRPBF 4x4 QFN-24 I $4.07 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
DC1439A LT3688EFE Demo Board | 7V ≤ VIN ≤ 36V, 60V Transients, Vout1 = 5V @ 0.8A, Vout2 = 3.3V @ 0.8A Contact Factory
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
LT3688HFE#PBF TSSOP-24 H $6.31 $4.42 Yes
LT3688HFE#TRPBF TSSOP-24 H $4.48 Yes
LT3688IFE#PBF TSSOP-24 I $5.96 $4.17 Yes
LT3688IFE#TRPBF TSSOP-24 I $4.23 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

  • Automotive Electronic Control Units
  • Industrial Power Supplies
  • High-Reliability μProcessor 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:
LT3688

Technical Support