ZHCSM96A November 2020 – August 2021 TPS6521835
PRODUCTION DATA
DCDC5 and DCDC6 are supplied from either the CC (coin-cell battery) input or IN_BU (main system supply). The power-path is designed to prioritize IN_BU to maximize coin-cell battery life. Whenever the PMIC is powered-up (WAIT_PWR_EN, ACTIVE, SUSPEND, and RECOVERY state), the power-path is forced to select the IN_BU input. In OFF mode the power-path selects the higher of the two inputs with a built-in hysteresis of 150 mV as shown in #SLDS2069376.
When VIN_BIAS drops below the UVLO threshold, the PMIC shuts down all rails and enters OFF mode. At this point the power-path selects the higher of the two input supplies. If the coin-cell battery is less than 150 mV above the UVLO threshold, SYS_BU remains connected to IN_BU (see #X4173). If the coin-cell is >150 mV above the UVLO threshold, the power-path switches to the CC input as shown in #X126. With no load on the main supply, the input voltage may recover over time to a value greater than the coin-cell voltage and the power-path switches back to IN_BU. This is a typical behavior in a Li-Ion battery powered system.
Depending on the system load, VIN_BIAS may drop below VINT_LDO before the power-down sequence is completed. In that case, INT_LDO is turned OFF and the digital core is reset forcing the unit into OFF mode and the power-path switches to IN_BU as shown in #X5266.