SBVS067R January 2006 – December 2019 TPS737
The TPS737xx uses an NMOS pass transistor to achieve extremely low dropout. When (VIN – VOUT) is less than the dropout voltage (VDO), the NMOS pass device is in its linear region of operation and the input-to-output resistance is the RDS(on) of the NMOS pass element.
For large step changes in load current, the TPS737xx requires a larger voltage drop from VIN to VOUT to avoid degraded transient response. The boundary of this transient dropout region is approximately twice the DC dropout. Values of (VIN – VOUT) above this line ensure normal transient response.
Operating in the transient dropout region can cause an increase in recovery time. The time required to recover from a load transient is a function of the magnitude of the change in load current rate, the rate of change in load current, and the available headroom (VIN-to-VOUT voltage drop). Under worst-case conditions [full-scale instantaneous load change with (VIN – VOUT) close to DC dropout levels], the TPS737xx can take a couple of hundred microseconds to return to the specified regulation accuracy.