Linear Technology: 35V Input (55V Transient), 2MHz Dual Channel Step-Down Regulator

MILPITAS, CA – January 21, 2010 – Linear Technology Corporation announces the LT3640, a dual channel, current mode step-down switching regulator with a power-on reset and watchdog timer. Its 4V to 35V input voltage range with 55V transient ride through makes it ideal for load dump and cold crank conditions commonly found in automotive applications. The LT3640 uses a unique dual channel design with a high input voltage (4VIN to 35VIN, 55VIN transient) nonsynchronous channel that delivers 1.1A of output current, combined with a lower input voltage (2.5VIN to 5.5VIN) synchronous channel that provides up to 0.9A of continuous output current. Although the part allows separate inputs for each channel, most applications will use the output of the high voltage channel to power the lower voltage channel, offering dual outputs while optimizing efficiency and switching frequency. For example, using a nominal 12V input and a 2MHz switching frequency, the LT3640 can deliver a 3.3V output at 600mA with 85% efficiency via its high voltage channel and a 1.8V output at 800mA with 87% secondary conversion efficiency via its lower voltage channel.
The integrated microprocessor supervisor functions support high reliability applications such as automotive electronic control units. The LT3640 includes one power-on reset timer for each channel and one common watchdog timer. The reset and watchdog timeout periods are independently adjustable using external capacitors. Tight accuracy specifications and glitch immunity ensure reliable reset operation of a system without false triggering. The LT3640 implements a windowed watchdog timer monitoring falling edges at its watchdog input pin that are grouped too close together or too far apart.
The LT3640’s switching frequency is user programmable from 350kHz to 2.5MHz, enabling the designer to optimize efficiency while avoiding critical noise-sensitive frequency bands. Similarly, its low minimum on-time enables it to offer high switching frequencies even with high step-down ratios. For example, with an input as high as 16V, the LT3640 can deliver a 3.3V output using a 2MHz switching frequency, allowing it to avoid critical frequency bands, such as AM radio while minimizing the size of external components. The LT3640 can deliver output voltages as low as 1.26V on its high voltage channel and down to 0.6V on its low voltage channel, enabling it to power the latest generation of microprocessors. Its low ripple Burst Mode® operation reduces quiescent current to only 350µA with less than 15mVPK-PK of output ripple, making it well suited for applications such as automotive or telecom systems that demand always-on operation and optimum battery life. The LT3640’s 4mm x 5mm QFN-28
(or TSSOP-28) package and high switching frequency ensure small external inductors and capacitors, providing a compact, thermally efficient footprint.
The LT3640IUFD and LT3640IFE is tested and guaranteed to operate from a -40°C to 125°C operating junction temperature. All versions are available from stock. For more information, visit www.linear.com.

Summary of Features: LT3640

• High Voltage Buck Regulator:
o 4V to 35V Operating, OVLO Protects Input to 55V
o 1.1A Output Current
• Low Voltage Synchronous Buck Regulator:
o 2.5V to 5.5V Input Voltage Range
o 0.9A Output Current
• 16VIN to 3.3VOUT Conversion at 2MHz
• Synchronizable, Adjustable 350kHz to 2.5MHz Switching Frequency
• Programmable Power-On Reset Timer
• Programmable Window Mode Watchdog Timer
• Low Ripple (15mVPK-PK) Burs Mode Operation, Quiescent Current= 350µA
• Short-Circuit Robust
• Programmable Soft-Start
• Low Shutdown Current: IQ < 1µA
• Available in Thermally Enhanced 28-Lead (4mm × 5mm) QFN & 28-Lead TSSOP Packages

MILPITAS, CA – January 21, 2010 – Linear Technology Corporation announces the LT3640, a dual channel, current mode step-down switching regulator with a power-on reset and watchdog timer. Its 4V to 35V input voltage range with 55V transient ride through makes it ideal for load dump and cold crank conditions commonly found in automotive applications. The LT3640 uses a unique dual channel design with a high input voltage (4VIN to 35VIN, 55VIN transient) nonsynchronous channel that delivers 1.1A of output current, combined with a lower input voltage (2.5VIN to 5.5VIN) synchronous channel that provides up to 0.9A of continuous output current. Although the part allows separate inputs for each channel, most applications will use the output of the high voltage channel to power the lower voltage channel, offering dual outputs while optimizing efficiency and switching frequency. For example, using a nominal 12V input and a 2MHz switching frequency, the LT3640 can deliver a 3.3V output at 600mA with 85% efficiency via its high voltage channel and a 1.8V output at 800mA with 87% secondary conversion efficiency via its lower voltage channel.
The integrated microprocessor supervisor functions support high reliability applications such as automotive electronic control units. The LT3640 includes one power-on reset timer for each channel and one common watchdog timer. The reset and watchdog timeout periods are independently adjustable using external capacitors. Tight accuracy specifications and glitch immunity ensure reliable reset operation of a system without false triggering. The LT3640 implements a windowed watchdog timer monitoring falling edges at its watchdog input pin that are grouped too close together or too far apart.
The LT3640’s switching frequency is user programmable from 350kHz to 2.5MHz, enabling the designer to optimize efficiency while avoiding critical noise-sensitive frequency bands. Similarly, its low minimum on-time enables it to offer high switching frequencies even with high step-down ratios. For example, with an input as high as 16V, the LT3640 can deliver a 3.3V output using a 2MHz switching frequency, allowing it to avoid critical frequency bands, such as AM radio while minimizing the size of external components. The LT3640 can deliver output voltages as low as 1.26V on its high voltage channel and down to 0.6V on its low voltage channel, enabling it to power the latest generation of microprocessors. Its low ripple Burst Mode® operation reduces quiescent current to only 350µA with less than 15mVPK-PK of output ripple, making it well suited for applications such as automotive or telecom systems that demand always-on operation and optimum battery life. The LT3640’s 4mm x 5mm QFN-28
(or TSSOP-28) package and high switching frequency ensure small external inductors and capacitors, providing a compact, thermally efficient footprint.
The LT3640IUFD and LT3640IFE is tested and guaranteed to operate from a -40°C to 125°C operating junction temperature. All versions are available from stock. For more information, visit www.linear.com.

Summary of Features: LT3640

• High Voltage Buck Regulator:
o 4V to 35V Operating, OVLO Protects Input to 55V
o 1.1A Output Current
• Low Voltage Synchronous Buck Regulator:
o 2.5V to 5.5V Input Voltage Range
o 0.9A Output Current
• 16VIN to 3.3VOUT Conversion at 2MHz
• Synchronizable, Adjustable 350kHz to 2.5MHz Switching Frequency
• Programmable Power-On Reset Timer
• Programmable Window Mode Watchdog Timer
• Low Ripple (15mVPK-PK) Burs Mode Operation, Quiescent Current= 350µA
• Short-Circuit Robust
• Programmable Soft-Start
• Low Shutdown Current: IQ < 1µA
• Available in Thermally Enhanced 28-Lead (4mm × 5mm) QFN & 28-Lead TSSOP Packages

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