TPS76515 Datasheet, PDF (14/18 Pages) Texas Instruments – ULTRA-LOW QUIESCIENT CURRENT 150-mA LOW-DROPOUT VOLTAGE REGULATORS

TPS76515, TPS76518, TPS76525, TPS76527
TPS76528, TPS76530, TPS76533, TPS76550, TPS76501
ULTRA-LOW QUIESCIENT CURRENT 150-mA LOW-DROPOUT VOLTAGE REGULATORS
SLVS236 – AUGUST 1999
APPLICATION INFORMATION
The TPS765xx 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 an adjustable regulator, the TPS76501 (adjustable from 1.25 V to 5.5 V).
device operation
The TPS765xx 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 (I_B = I_C/β). The TPS765xx 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 I_B 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
TPS765xx quiescent current remains low even when the regulator drops out, eliminating both problems.
The TPS765xx 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 1 µA (typ). If the
shutdown feature is not used, EN should be tied to ground. Response to an enable transition is quick; regulated
output voltage is reestablished in typically 160 µs.
minimum load requirements
The TPS765xx 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 it is shown in Figure 29. 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
is essential.
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 TPS765xx 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 TPS765xx requires an output capacitor connected between OUT and GND
to stabilize the internal control loop. The minimum recommended capacitance value is 4.7 µF and the ESR
(equivalent series resistance) must be between 300-mΩ and 20-Ω. Capacitor values 4.7 µF or larger are
acceptable, provided the ESR is less than 20 Ω. Solid tantalum electrolytic, aluminum electrolytic, and multilayer
ceramic capacitors are all suitable, provided they meet the requirements described previously.
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