RY8411

Email: support@rychip.com

http://www.rychip.com

©RYCHIP Semiconductor Inc.

Standoff 42V 1.2A 800KHz Sync Step-Down Regulator

Page 8 / 13

Internal Soft-Start

The soft-start is implemented to prevent the converter output voltage from overshooting during startup. When the

chip starts, the internal circuitry generates a soft-start voltage (SS) ramping up from 0V to 0.8V. When it is lower

than the internal reference (REF), SS overrides REF so the error amplifier uses SS as the reference. When SS is

higher than REF, REF regains control. The SS time is internally max to 1ms.

Over Current Protection with Foldback

The RY8411 has cycle-by-cycle over current limit when the inductor current peak value exceeds the set current

limit threshold. Meanwhile, output voltage starts to drop until FB is below the Under-Voltage (UV) threshold. When

the output is shorted to the ground, the switching frequency is folded back and the current limit is reduced to lower

the short circuit current. The frequency foldback helps prevent inductor current runaway and thermal issue during

short circuit. The RY8411 exits the foldback mode once the over current condition is removed.

Startup and Shutdown

If both VIN and EN are higher than their appropriate thresholds, the chip starts. The reference block starts first,

generating stable reference voltage and currents, and then the internal regulator is enabled. The regulator provides

stable supply for the remaining circuitries. Three events can shut down the chip: EN low, VIN low and thermal

shutdown. In the shutdown procedure, the signaling path is first blocked to avoid any fault triggering. The comp

voltage and the internal supply rail are then pulled down. The floating driver is not subject to this shutdown

command.