42V quad synchronous step-down DC/DC has high efficiency

July 28, 2015 // By Graham Prophet
LT8602 is a 42V input capable, quad output synchronous monolithic step-down switching regulator. Its quad channel design combines two high voltage 2.5A and 1.5A channels with two lower voltage 1.8A channels to provide four independent outputs, delivering voltages as low as 0.8V.

Its synchronous rectification topology delivers up to 93% efficiency while Burst Mode operation keeps quiescent current under 30 µA (all channels) in no-load standby conditions, suiting it for always-on systems. For noise-sensitive applications, the LT8602 uses its pulse-skipping mode to minimise switching noise and meet the CISPR25, Class 5 EMI requirements. Switching frequency can be programmed from 250 kHz to 2.2 MHz and is synchronisable throughout this range.

The LT8602’s 60 nsec minimum on-time enables 16VIN to 0.8VOUT step-down conversions while switching at 2 MHz, enabling designers to avoid critical noise-sensitive frequency bands such as AM radio, while using a very compact solution footprint. Its 3V to 42V input voltage range suits it for automotive applications that must regulate through cold-crank and stop-start scenarios with minimum input voltages as low as 3V and load dump transients in excess of 40V. Each channel of the LT8602 maintains a minimum dropout voltage of 200 mV (at 1A) under all conditions, handling automotive cold-crank. Programmable power-on reset and power-good indicators for each channel ensure overall system reliability. The LT8602’s 40-lead thermally enhanced 6 x 6 mm QFN package and high switching frequency keep external inductors and capacitors small, providing a compact, thermally efficient footprint.

The LT8602 uses quad internal top and bottom high efficiency power switches with the necessary boost diodes, oscillator, control and logic circuitry integrated into a single die. Channel 1 and 3 switch 180° out of phase with channels 2 and 4 to reduce output ripple. Each channel has a separate input for added design flexibility, but most applications will run the two low voltage channels directly from the two high voltage channels to provide a very simple, high frequency quad output design. Low ripple Burst Mode operation maintains high efficiency at low output currents while keeping output ripple below 15mVP-P. Efficiency is maintained over a wide input voltage range, and the LT8602’s current-mode topology enables fast transient response and good loop stability. Other features include internal compensation, power good flags, output soft-start/tracking, short-circuit and thermal protection.

The LT8602 is available in a thermally enhanced 40-lead 6 x 6 mm QFN package. Three temperature grades are available, with operation from –40°C to 125°C (junction) for the extended E- and industrial I-grades; pricing starts at $5.67 (1000).

Linear Technology; www.linear.com/product/LT8602

next page; feature list...