The 42V, 6A (IOUT), synchronous step-down Silent Switcher 2 delivers 95% efficiency at 2 MHZ and has ultra-low EMI/EMC radiation

     Analog Devices, which recently acquired Linear Technology Corporation, announced the LT8640S, a 6A, 42V input synchronous step-down switching regulator. Its unique Silent Switcher 2 architecture features two internal input capacitors as well as internal BST and INTVCC capacitors to minimize the thermal loop area. Combined with a very well-controlled switching edge and an internal construction with an integral ground plane and copper posts instead of bonding wires, the LT8640S design significantly reduces EMI/EMC radiation.

     This improved EMI/EMC performance is less susceptible to board layout, simplifying design and reducing risk, even when using two-layer PC boards. The LT8640S uses a 2MHz switching frequency over its entire load range to easily meet the automotive CISPR25 Class 5 peak EMI limits. In addition, spread spectrum frequency modulation can be used to further reduce EMI/EMC radiation levels.

     Synchronous rectification of the LT8640S provides up to 95% efficiency at 2MHz switching frequency. Its 3.4V to 42V input voltage range is ideal for automotive and industrial applications. Internal high-efficiency switches provide continuous output current up to 6A and peak load of 7A at voltages as low as 0.97V. The LT8640S 'Burst Mode operation delivers static current of as little as 2.5µA, making it ideal for applications such as altime-on automotive systems that require extended battery life.

     The LT8640S 'unique design maintains a minimum differential voltage of only 100mV (at 1A) under all conditions, enabling the device to perform well in situations such as cold car start-up. In addition, a fast and shortest on-time of just 30ns enables a 2MHz constant frequency switch from 16V input to 1.5V output, allowing designers to optimize efficiency while avoiding critical noise sensitive bands. The LT8640S 24-lead, 4mm x 4mm LQFN package and high switching frequency allow the use of small external inductors and capacitors, resulting in a compact and thermally efficient board area.

     The LT8640S uses internal top and bottom high efficiency power switches and integrates the necessary boost diodes, oscillators, control and logic circuits in a single chip. Low Ripple Burst mode operates at low output currents to maintain high efficiency while keeping the output ripple below 10mVP-P. For applications that require minimal noise operation, the LT8640S can be configured to operate in forced continuous mode over the entire load range. Its switching frequency is programmable and synchronizable in the range of 200kHz to 3MHz. Special design methods and new high-speed processes allow the device to achieve high efficiency over a wide input voltage range, and the LT8640's current mode topology enables fast transient response and excellent loop stability. Other features include internal compensation, well-marked power supply, output soft start/tracking, and overheat protection.