ZHCSOO0C september 2021 – june 2023 TPS7A94
PRODUCTION DATA
The dropout voltage refers to the minimum voltage difference between the input and output voltage (VDO = VIN – VOUT) that is required for regulation. When the input voltage (VIN) drops to or below the maximum dropout voltage (VDO(Max)) for the given load current, see the Electrical CharacteristicsElectrical CharacteristicsElectrical CharacteristicsElectrical CharacteristicsElectrical CharacteristicsElectrical CharacteristicsElectrical Characteristics table, the device functions as a resistive switch and does not regulate the output voltage. When the device is operating in dropout, the output voltage tracks the input voltage. For high current, the dropout voltage (VDO) is proportional to the output current because the device is operating as a resistive switch. For low current, internal nodes are saturating and the dropout plateaus to the minimum value. As mentioned in the Output Voltage Restart (Overshoot Prevention Circuit)Output Voltage Restart (Overshoot Prevention Circuit) section, transient events such as an input voltage brownout, heavy load transient, or short-circuit event can trigger the overshoot prevention circuit. Operating the device at or near dropout significantly degrades both transient performance and PSRR, and can also trigger the overshoot prevention circuit. Maintaining sufficient operating headroom (VOpHr = VIN – VOUT) significantly improves the device transient performance and PSRR, and prevents triggering the overshoot prevention circuit.
For this device, the pass element is not the limiting dropout voltage factor. Because the reference voltage is generated by a current source and the NR/SS resistor, and because the operating headroom is reducing (even at low load), the internal current source (INR/SS) saturates faster than the pass transistor. This behavior is described in the dropout voltage plot (Figure 6-43). Notice that the dropout does not go to 0 V at light loads.