Quiet 8A automotive dc-dc works from up to 65V

Analog Devices has announced a 65V input, 8A output, current-mode synchronous step-down switching regulator.

LT8645S - Quiet 8A automotive dc-dc works from up to 65V

It is called LT8645S, where the S indicates that it has the second generation of the firm’s ‘silent switcher’ noise reduction technology – which includes in-package ceramic capacitors on the input, bootstrap and internal supply rails (see diagram).

“These caps keep all the fast AC current loops small, which improves EMI/EMC performance,” said the firm. “Combined with well-controlled switching edges, an internal integral ground plane, and the use of copper pillars in lieu of bond wires, the LT8645S dramatically reduces EMI/EMC emissions.”

It can meet automotive CISPR25, Class 5 peak EMI limits with a 2MHz switching frequency over its entire load range, added the firm (see diagram), and sensitivity to board layout is reduced, even when using two layer PCBs.

For output ripple under 10mV, there is ‘low-ripple burst mode’ operation, and “for applications requiring the lowest noise operation, the LT8645S can be programmed to run in pulse-skipping mode,” said Analog.

Quiet 8A automotive dc-dc works from up to 65V Both power mosfets are on the die, as is the the top fet bootstrap diode, as well as oscillator, control and logic circuitry.

Due to synchronous rectification, efficiency is as high as 94% when switching at 2MHz, and is even better at 1MHz – switching frequency is programmable and synchronisable from 200kHz to 2.2MHz.

Spread spectrum frequency modulation can be enabled or disabled depending on EMI/EMC requirements. Modulation is +20% triangle, so nominal 2MHz with vary up to 2.4MHz.

An input range across 3.4V to 65V allows it to run from two cells, from 48V automotive rails, and in industrial applications. Forward drop is as low as 60mV at 1A.

8A out is available at outputs as low as 0.97V, and a 40ns minimum on-time enables 24V to 2.0V conversion at 2MHz constant frequency.

LT8645SQuiescent current can be as low as 2.5µA (in burst mode) suiting it to ‘always-on’ automotive and transport applications.

Other features include internal compensation, a power good flag, output soft-start/tracking and thermal protection.

The package is a 32 lead, 4 x 6mm LQFN.

An industrial temperature version, LT8645SIV, is tested and guaranteed to operate with junction from -40 to 125°C.

Analog Devices recently bough Linear Tech.


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