Features and Benefits
- 3.6V to 15V Input Voltage Range
- ±3A Output Current per Channel
- Up to 95% Efficiency
- Selectable 90°/180° Phase Shift Between Channels
- Adjustable Switching Frequency: 500kHz to 4MHz
- VTTR = VDDQ/2 = VTT Reference
- ±1.6% Accurate VTTR at 0.75V
- Optimal VOUT Range: 0.6V to 3V
- ±10mA Buffered Output Supplies VREF Reference Voltage
- Current Mode Operation for Excellent Line and Load Transient Response
- External Clock Synchronization
- Short-Circuit Protected
- Input Overvoltage and Overtemperature Protection
- Power Good Status Outputs
- Available in (4mm × 5mm) QFN-28 and Thermally Enhanced 28-Lead TSSOP Packages
The LTC3634 is a high efficiency, dual-channel monolithic synchronous step-down regulator which provides power supply and bus termination rails for DDR1, DDR2, and DDR3 SDRAM controllers. The operating input voltage range is 3.6V to 15V, making it suitable for point-of-load power supply applications from a 5V or 12V input, as well as various battery powered systems.
The VTT regulated output voltage is equal to VDDQIN • 0.5. An on-chip buffer capable of driving a 10mA load provides a low noise reference output (VTTR) also equal to VDDQIN • 0.5.
The operating frequency is programmable and synchronizable from 500kHz to 4MHz with an external resistor. The two channels can operate 180° out-of-phase, which relaxes the requirements for input and output capacitance. The unique controlled on-time architecture is ideal for powering DDR applications from a 12V supply at high switching frequencies, allowing the use of smaller external components.
The LTC3634 is offered in both 28-pin 4mm × 5mm QFN and 28-pin exposed pad TSSOP packages.
- DDR Memory Power Supplies
Product Lifecycle Production
At least one model within this product family is in production and available for purchase. The product is appropriate for new designs but newer alternatives may exist.
Evaluation Kits (2)
Demonstration circuit 1839A is a dual output regulator focused specifically for DDR memory power applications. It is built based on the LTC3634EFE (TSSOP-28E package), a high voltage dual channel, controlled on-time monolithic synchronous buck regulator. The DC1839A has an input voltage range of 3.6V to 15V. demo board's output voltage of the first channel, VDDQ, has three fixed voltage settings; 1.5V, 1.8V, and 2.5V, and is capable of delivering up to ±3A of output current. The second channel, VTT, is set to regulate to half the voltage on the VDDQIN pin, which can be either the channel 1 output or an external reference voltage. It can also source or sink a maximum of 3A. The LTC3634 also provides a ±10mA buffered output, VTTR, which is half of VDDQIN and is used to provide the reference voltage needed for DDR applications.
Demonstration circuit DC1708A is a dual-output regulator focused specifically for DDR memory power applications. It is built based on the LTC3634, a high voltage dualchannel, controlled on-time monolithic synchronous buck regulator. The DC1708A has an input voltage range of 3.6V to 15V. The output voltage of the first channel, VDDQ, of the DC1708A has three fixed voltage settings: 1.5V, 1.8V and 2.5V, and is capable of delivering up to 3A of output current. The second channel, VTT, is set to regulate to half the voltage on the VDDQIN pin, which can be either the channel 1 output or an external reference voltage. It can source or sink a maximum of 3A of output current. The LTC3634 also provides a 10mA buffered output of half VDDQIN – VTTR, which is used to provide the reference voltage needed for DDR applications. With the use of a timing resistor, the DC1708A can have its operating frequency programmed from 500kHz to 4MHz. Additionally the DC1708A can be easily synchronized to an external clock, due to an internal phase-locked loop, within this same frequency range. The DC1708A VDDQ output can operate in either Burst Mode® operation or forced continuous mode. In Burst Mode operation, which is the preferred mode of low load current operation, the DC supply current is typically only 1.3mA (both channels) at no load (sleep mode), and less than 15µA in shutdown. In Burst Mode operation or continuous mode operation, the DC1708A is a very efficient circuit at high load currents: over 80% for either channel. The LTC3634 is also capable of 90° or 180° out-of-phase operation, and can allow its output to track an external voltage, either coincidentally or ratiometrically. The LTC3634 comes in a 28-pin QFN package, featuring an exposed pad on the bottom-side of the IC for better thermal performance. All of these features make the DC1708A an ideal circuit for powering DDR memory applications.
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.
Design tools for the following parts are available in LTpowerCAD:
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.