Linear Technology's step-down Silent Switcher 2 delivers 94% efficiency

Linnear's Silent Switcher

Modern automotive power management ICs continue to require higher performance. As the power requirements for these applications continues to grow, the available space for power conversion solutions continually shrinks requiring ever increasing power densities. Furthermore, the required electrical performance criteria, including EMI performance of these switching regulators becomes more demanding. Offering higher continuous output current from a tiny solution footprint becomes desirable in many applications. For example, automotive/transportation applications can have 14V to 40V battery nominal voltages and require well-regulated output voltages from 2.5V and 3.3V, even as the input voltage can swing from under 4V in a cold crank or stop/start scenario up to 40V in a load dump scenario. Similarly, high efficiency is of paramount importance as it minimises thermal design considerations while also maximising battery run time in hybrids and electric vehicles. Many automotive applications also require switching regulators to meet the EMI limits defined by CISPR25, Class 5 to minimise system EMI concerns. For applications such as security, navigation, safety and environmental control which are often required to be always on, minimal quiescent current is critical so as not to drain the battery when the car is parked for long periods of time. 2MHz frequency operation avoids noise in critical frequency bands such as AM radio and keeps external components very small. Finally very robust short-circuit and overvoltage protection ensures overall system reliability.

A new direction

Linear Technology continues to grow its family of synchronous high voltage step-down regulators by adding a 42VIN capable, Dual Channel 4A synchronous step-down converter which specifically addresses all of the above stated requirements. The LT8650S is a 42V capable Silent Switcher 2 step-down regulator that has an input voltage range of 3.0V to 42V and can deliver two channels of up to 4A of continuous load current to voltages as low as 0.8V. Its internal synchronous rectification delivers efficiencies, as high as 94.4% while switching at 2MHz, eliminating the requirement for heat sinks. Its unique Silent Switcher2 architecture minimizes EMI emissions through unique IC design, integrating internal bypass capacitors and by utilizing an internal ground plane, collectively enabling the LT8650S to easily meet automotive EMI requirements of CISPR25, Class 5.

Its Burst Mode operation requires only 6.2uA of quiescent current reduces the battery drain associated with always on systems. The LT8650S offers a minimum on-time of only 40ns, enabling it to step-down 16V to 2V with a switching frequency of 2MHz. The LT8650S offers a very robust dual output step-down regulator which provides improved performance in all key areas including high efficiency, low quiescent current, compact size and ease of design.

Key features of the LT8650S include: 

Wide Input Voltage Range: 3.0V to 42V

4A DC from Each Channel Simultaneously

Up to 6A on Either Channel

Silent Switcher 2 Architecture

Ultralow EMI Emissions on any PCB

Eliminates PCB Layout Sensitivity

Internal Capacitors for VIN, BST, INTVCC Reduce Radiated EMI

Spread Spectrum Frequency Modulation

Ultralow Quiescent Current BurstMode Operation:

2μA IQ Regulating 12VIN to 5VOUT1 and 3.3VOUT2

Output Ripple <10mVP-P

Optional External VC Pin: Fast Transient Response and Current Sharing (Extra 40µA IQ/Channel)

Forced Continuous Mode

High Efficiency Synchronous Operation:

4% Efficiency at 2A, 5VOUT from 12VIN at 2MHz

5% Efficiency at 4A, 5VOUT from 12VIN at 2MHz

Fast Minimum Switch-On Time: 40ns

Die Temperature Monitor

Adjustable and Synchronizable: 300kHz to 3MHz

Output Soft-Start and Tracking

Small Thermally Enhanced 4mm × 6mm 32-Pin LGA Package