LT1242 - High Speed Current Mode Pulse Width Modulators

Features

  • Low Start-Up Current: <250µA
  • 50ns Current Sense Delay
  • Current Mode Operation: To 500kHz
  • Pin Compatible with UC1842 Series
  • Undervoltage Lockout with Hysteresis
  • No Cross-Conduction Current
  • Trimmed Bandgap Reference
  • 1A Totem Pole Output
  • Trimmed Oscillator Frequency and Sink Current
  • Active Pull-Down on Reference and Output During Undervoltage Lockout
  • High Level Output Clamp: 18V
  • Current Sense Leading Edge Blanking

Typical Application

LT1242 Typical Application

Description

The LT®1241 series devices are 8-pin, fixed frequency, current mode, pulse width modulators. They are improved plug compatible versions of the industry standard UC1842 series. These devices have both improved speed and lower quiescent current. The LT1241 series is optimized for off-line and DC/DC converter applications. They contain a temperature-compensated reference, high gain error amplifier, current sensing comparator and a high current totem pole output stage ideally suited to driving power MOSFETs. Start-up current has been reduced to less than 250µA. Cross-conduction current spikes in the output stage have been eliminated, making 500kHz operation practical. Several new features have been incorporated. Leading edge blanking has been added to the current sense comparator. Trims have been added to the oscillator circuit for both frequency and sink current, and both of these parameters are tightly specified. The output stage is clamped to a maximum VOUT of 18V in the on state. The output and the reference output are actively pulled low during undervoltage lockout.

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
LT1242CN8#PBF N-8 N C 05-08-1510 (N8) Yes
LT1242CS8#PBF SO-8 S8 C 05-08-1610 (S8) Yes
LT1242CS8#TRPBF SO-8 S8 C 05-08-1610 (S8) Yes
LT1242IN8#PBF N-8 N I 05-08-1510 (N8) Yes
LT1242IS8#PBF SO-8 S8 I 05-08-1610 (S8) Yes
LT1242IS8#TRPBF SO-8 S8 I 05-08-1610 (S8) Yes


LT1242 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
LT1242CN8#PBF N-8 C $2.33 $1.95 Yes
LT1242CS8#PBF SO-8 C $2.58 $2.20 Yes
LT1242CS8#TRPBF SO-8 C $2.26 Yes
LT1242IN8#PBF N-8 I $2.58 $2.20 Yes
LT1242IS8#PBF SO-8 I $2.83 $2.40 Yes
LT1242IS8#TRPBF SO-8 I $2.46 Yes
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* 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.

Click here to view our complete list of demo boards

Applications

  • Off-Line Converters
  • DC/DC Converters

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

Models for the following parts are available in LTspice:
LT1242

Technical Support