SBVS254D February 2018 – August 2019 TPS7A05
Some applications may have transients that place the device into dropout, especially as this device can be powered from a battery with high ESR. A typical application with these conditions is using a stack of two 1.55-V coin-cell batteries with an ESR of 30 Ω to create a 2.5-V rail and experiencing a load transient from 1 µA to 25 mA. This load transient causes the input supply to drop 750 mV, placing the device into dropout.
The load transient saturates the output stage of the error amplifier when the pass element is driven fully on, making the pass element function like a resistor from VIN to VOUT. The error amplifier response time to this load transient is limited because the error amplifier must first recover from saturation and then place the pass element back into active mode. During this time VOUT overshoots because the pass element is functioning as a resistor from VIN to VOUT. This device uses a loop pulldown circuit to help mitigate the overshoot.
If operating under these conditions, applying a higher dc load or increasing the output capacitance reduces the overshoot because these solutions provide a path to dissipate the excess charge.