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APPLICATION INFORMATION

Minimum Load Requirements

FB—Pin Connection (Adjustable Version Only)

External Capacitor Requirements

IN

IN

EN

GND

OUT

OUT

RESET/

PG

6

7

5

16

14

13

3

+

10 F

m

C

OUT

RESET/PG

V

OUT

V

IN

C

0.1 F

m

1

250kW

TPS775xx, TPS776xx

SLVS232I – SEPTEMBER 1999 – REVISED AUGUST 2007

The TPS775xx and TPS776xx feature 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

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

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 TPS775xx and TPS776xx quiescent currents remain low even when the regulator drops out, eliminating

both problems.

The TPS775xx and TPS776xx families also feature 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.

The TPS775xx and TPS776xx families are stable at zero load; no minimum load is required for operation.

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 25. 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.

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 TPS775xx or TPS776xx are 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 TPS775xx and TPS776xx require 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 50m

Ω and 1.5Ω. Capacitor values 10μF 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.

Figure 24. Typical Application Circuit (Fixed Versions)

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