TPS767D301, TPS767D318, TPS767D325
DUAL-OUTPUT LOW-DROPOUT VOLTAGE REGULATORS
SLVS209B – JULY 1999 – REVISED APRIL 2000
15
POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
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
TPS767D3xx quiescent current remains low even when the regulator drops out, eliminating both problems.
The TPS767D3xx 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 under 2 µA. If the
shutdown feature is not used, EN should be tied to ground. Response to an enable transition is quick; regulated
output voltage is typically reestablished in 120 µs.
minimum load requirements
The TPS767D3xx 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 as is shown in Figure 27 to close the loop. 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. In fixed output options this pin is a no connect.
external capacitor requirements
An input capacitor is not required; however, a ceramic bypass capacitor (0.047 pF to 0.1 µF) improves load
transient response and noise rejection when the TPS767D3xx 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 TPS767D3xx 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 mΩ 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 previously.
