Features and Benefits
- Silent Switcher®2 Architecture
- Ultralow EMI Emissions On Any PCB
- Eliminates PCB Layout Sensitivity
- Internal Bypass Capacitors Reduce Radiated EMI
- Optional Spread Spectrum Modulation
- High Efficiency at High Frequency
- Up to 96% Efficiency at 1MHz, 12VIN to 3.3VOUT
- Up to 95% Efficiency at 2MHz, 12VIN to 3.3VOUT
- Wide Input Voltage Range: 2.8V to 18V
- 10A Output Current
- External Compensation: Fast Transient Response and Current Sharing
- Low Quiescent Current Burst Mode® Operation
- n 240µA IQ Regulating 12VIN to 1.2VOUT
- Output Ripple < 10mVP-P
- Fast Minimum Switch On-Time: 25ns
- Low Dropout Under All Conditions: 50mV at 1A
- Forced Continuous Mode
- Adjustable and Synchronizable: 200kHz to 3MHz
- Output Soft-Start and Power Good
- Small 24-Lead 4mm × 4mm LQFN Package
The LT®8642S synchronous step-down regulator features second generation Silent Switcher architecture designed to minimize EMI emissions while delivering high efficiency at high switching frequencies. This includes the integration of bypass capacitors to optimize all the fast current loops inside and make it easy to achieve advertised EMI performance by eliminating layout sensitivity. This performance makes the LT8642S ideal for noise sensitive applications and environments.
The fast, clean, low-overshoot switching edges enable high efficiency operation even at high switching frequencies, leading to a small overall solution size. Peak current mode control with a 25ns minimum on-time allows high step down ratios even at high switching frequencies. External compensation via the VC pin allows for fast transient response at high switching frequencies. The VC pin also enables current sharing and a CLKOUT pin enables synchronizing other regulators to the LT8642S.
Burst Mode operation enables low standby current consumption, forced continuous mode can control frequency harmonics across the entire output load range, or spread spectrum operation can further reduce EMI emissions. Soft-start and tracking functionality is accessed via the SS pin, and an accurate input voltage UVLO threshold can be set using the EN/UV pin.
- Server Power Applications
- General Purpose Step-Down
Product Lifecycle Recommended for New Designs
This product has been released to the market. The data sheet contains all final specifications and operating conditions. For new designs, ADI recommends utilization of these products.
Evaluation Kits (1)
Demonstration circuit 2560A is a 18V, 10A synchronous step-down Silent Switcher®2 with spread spectrum frequency modulation featuring the LT8642S. The demo board is designed for 1.2V output from a 2.8V to 18V input. The LT8642S is a compact, ultralow emission, high efficiency, and high speed synchronous monolithic step-down switching regulator. The integrated bypass capacitors optimize all the fast current loops and make it easier to minimize EMI/EMC emissions by reducing layout sensitivity. Selectable spread spectrum mode can further improve EMI/EMC performance. Fast minimum on-time of 20ns enables high VIN to low VOUT conversion at high frequency.
The LT8642S switching frequency can be programmed either via a resistor or external clock over a 200kHz to 3MHz range. The default frequency of demo circuit 2560A is 2MHz. The SYNC pin on the demo board is grounded (JP1 at BURST position) by default for low ripple Burst Mode® operation. To synchronize to an external clock, move JP1 to SYNC and apply the external clock to the SYNC terminal. Spread spectrum mode and forced continuous mode can be selected respectively by moving JP1 shunt.
The demo board has an EMI filter installed. This EMI filter can be included by applying the input voltage at the VIN_ EMI terminal.
The LT8642S data sheet gives a complete description of the part, operation and application information. The data sheet must be read in conjunction with this demo manual for demo circuit 2560A. The LT8643S is assembled in a 4mm × 4mm LQFN package with exposed pads for low thermal resistance. The layout recommendations for low EMI operation and maximum thermal performance are available in the data sheet section Low EMI PCB Layout and Thermal Considerations.
Tools & Simulations
LTspice® is a powerful, fast and free simulation software, schematic capture and waveform viewer with enhancements and models for improving the simulation of analog circuits.
Models for the following parts are available in LTspice:
LTpowerCAD® is a power supply design program which selects power stage components, provides detailed power efficiency, shows quick loop Bode plot stability and load transient analysis, and can export to LTspice for simulation.
To open the project file for this circuit:
Step 1: Download and install LTpowerCAD on your computer.
Step 2: Click on the link(s) in the section below to download part-specific project files.
Step 3: If the project file doesn't run, right-click the link and select "Save Target As." Then start the LTpowerCAD tool and open the project file by selecing "Open Project" from the "File" menu.
LTpowerCAD Project Files
Design tools for the following parts are available in LTpowerCAD:
Press Releases (1)
ADI has always placed the highest emphasis on delivering products that meet the maximum levels of quality and reliability. We achieve this by incorporating quality and reliability checks in every scope of product and process design, and in the manufacturing process as well. "Zero defects" for shipped products is always our goal.
Sample & Buy
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 Analog Devices, Inc. sales office or authorized distributor. Pricing displayed for Evaluation Boards and Kits is based on 1-piece pricing.