TPS76815EP, TPS76818EP, TPS76825EP, TPS76827EP
TPS76828EP, TPS76830EP TPS76833EP, TPS76850EP, TPS76801EP
FAST TRANSIENT RESPONSE 1A LOW DROPOUT VOLTAGE REGULATORS
SGLS011B − MARCH 2003 − REVISED DECEMBER 2008
POST OFFICE BOX 655303
• DALLAS, TEXAS 75265
The TPS768xx family includes eight fixed-output voltage regulators (1.5 V, 1.8 V, 2.5 V, 2.7 V, 2.8 V, 3.0 V,
3.3 V, and 5.0 V), and offers an adjustable device, the TPS76801 (adjustable from 1.2 V to 5.5 V).
The TPS768xx features very low quiescent current, which remains virtually constant even with varying loads.
Conventional LDO regulators use a pnp pass element, the base current of which is directly proportional to the
load current through the regulator (IB = IC/β). The TPS768xx uses a PMOS transistor to pass current; because
the gate of the PMOS is voltage driven, operating current is low and invariable over the full load range.
Another pitfall associated with the pnp-pass element is its tendency to saturate when the device goes into
dropout. The resulting drop in
β forces an increase in IB to maintain the load. During power up, this translates
to large start-up currents. Systems with limited supply current may fail to start up. In battery-powered systems,
it means rapid battery discharge when the voltage decays below the minimum required for regulation. The
TPS768xx quiescent current remains low even when the regulator drops out, eliminating both problems.
The TPS768xx family also features a shutdown mode that places the output in the high-impedance state
(essentially equal to the feedback-divider resistance) and reduces quiescent current to 2
µA. If the shutdown
feature is not used, EN should be tied to ground.
minimum load requirements
The TPS768xx family is stable even at zero load; no minimum load is required for operation.
FB - pin connection (adjustable version only)
The FB pin is an input pin to sense the output voltage and close the loop for the adjustable option. The output
voltage is sensed through a resistor divider network to close the loop as shown in Figure 27. Normally, this
connection should be as short as possible; however, the connection can be made near a critical circuit to
improve performance at that point. Internally, FB connects to a high-impedance wide-bandwidth amplifier and
noise pickup feeds through to the regulator output. Routing the FB connection to minimize/avoid noise pickup
external capacitor requirements
An input capacitor is not usually required; however, a ceramic bypass capacitor (0.047
µF or larger) improves
load transient response and noise rejection if the TPS768xx is located more than a few inches from the power
supply. A higher-capacitance electrolytic capacitor may be necessary if large (hundreds of milliamps) load
transients with fast rise times are anticipated.
Like all low dropout regulators, the TPS768xx requires an output capacitor connected between OUT and GND
to stabilize the internal control loop. The minimum recommended capacitance value is 10
µF and the ESR
(equivalent series resistance) must be between 50 m
Ω and 1.5 Ω. Capacitor values 10 µF or larger are
acceptable, provided the ESR is less than 1.5
Ω. Solid tantalum electrolytic, aluminum electrolytic, and
multilayer ceramic capacitors are all suitable, provided they meet the requirements described above. Most of
the commercially available 10
µF surface-mount ceramic capacitors, including devices from Sprague and
Kemet, meet the ESR requirements stated above.