2MHz Dual Channel Step-Down Regulator

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.