JAJSIR5C October 2019 – October 2023 TPS65313-Q1
PRODUCTION DATA
Currents through both the high-side (HS) power MOSFET and the low-side (LS) power MOSFET are continuously monitored to protect the internal power MOSFETs from damage. Cycle-by-cycle currents through the HS MOSFET and LS MOSFET are compared against the IHS_ LIMIT_BUCK2 and ILS_ LIMIT_BUCK2 current limits, respectively. The former current limit is to detect short-circuit events and the latter is to detect overload conditions when the BUCK2 regulator load current exceeds the specified current limit threshold value.
As the load current increases to greater than the maximum IBUCK2_LOAD current defined in Section 9.8, the LS MOSFET current exceeds the ILS_LIMIT_BUCK current limit. Consequently, an overload event is detected and the BUCK2_LS_OVC status bit is set in the SAFETY_BUCK2_STAT1 register. However, the regulator does not shut down. If the load current continues to increase, the HS-MOSFET current exceeds the short-circuit current limit (IHS_LIMIT_BUCK). The HS MOSFET is turned off immediately and the LS MOSFET is turned on until the inductor current drops to less than the overload threshold value (ILS_ LIMIT_BUCK2). The BUCK2 regulator is then disabled and the BUCK2_HS_OVC (BUCK2_SCG) status bit is set in the SAFETY_BUCK2_STAT1 register. The BUCK2_EN control bit is cleared and the device does not change the state, if the BUCK2_UV_RST_EN bit is 0b. If the BUCK2_UV_RST_EN bit is set to 1b (BUCK2 UV event configured as a RESET state event), as the VBUCK2 voltage rail is discharged to less than its UV-threshold level, then the device goes into the RESET state.
The LS MOSFET is also protected by detection circuitry for cycle-by-cycle sink-current limit. This detection circuitry protects the LS MOSFET from excessive reverse current caused by switching the PH2 pin to the PGND2 pin. If the LS sinking current exceeds the ILS_SINK_BUCK2 sink-current limit, an event is detected and the BUCK2_LS_SINK_OVC SPI status bit is set in the SAFETY_BUCK2_STAT1 register. If the event occurs for more than 20 µs (typical), the BUCK2 regulator is turned off. The inductor current continues to flow to the supply at the VSUP2 pin through the body diode of the HS MOSFET. The device response after detection of a LS sink-current limit is identical to that of a short-circuit event.
The LS sink current-limit event can also be detected when the regulator is enabled while the VBUCK2 voltage rail has not been discharged to less than the voltage level defined by the VBUCK2_RESTART_LEVEL level. Therefore, the LS sink current-limit event is masked when the BUCK2 regulator is enabled, and until the VBUCK2 voltage rail exceeds its UV-threshold level.