1 OOB Operation Principle

TPS56C230 has the Out-of-bounds (OOB) overvoltage protection that protects the output load at a much lower overvoltage threshold of 8% above the target voltage. OOB does not trigger overvoltage fault protection. OOB protection operates as an early no-fault overvoltage protection mechanism, differs from fault overvoltage protection (OVP).

During the OOB operation, the device operates in forced PWM mode by turning on the low-side FET to discharge the output capacitor, thus causing the output voltage to fall quickly toward the target value. Turning off low-side FET logic is controlled by either triggering the cycle-by-cycle negative overcurrent (NOC) limit or output voltage falling below target value (FB voltage falling below reference voltage). For TPS56C230, OOB control logic allows maximum 16-cycle NOC triggered in order to ensure the safe operation of internal FETs. After 16-cycle NOC triggered, the device would stop switching to wait OVP or output falls to target voltage.

OOB operation is blanked in forced continuous conduction mode (FCCM), since the control logic of FCCM-mode itself allows continuous current until the output voltage decreases to target value.