10

100

1k

10k

100k

Frequency(Hz)

100

10

1

0.1

0.01

0.001

150mA

109 V

m

RMS

50mA

109 V

m

RMS

1mA

108 V

m

RMS

10

10M

100

1k

10k

100k

1M

Frequency(Hz)

80

70

60

50

40

30

20

10

0

150mA

50mA

1mA

TPS782

www.ti.com

SBVS115D – AUGUST 2008 – REVISED JANUARY 2015

Typical Application (continued)

8.2.2.2 Dropout Voltage

The TPS782 uses a PMOS pass transistor to achieve low dropout. When (VIN – VOUT) is less than the dropout

voltage (VDO), the PMOS pass device is the linear region of operation and the input-to-output resistance is the

RDS(ON) of the PMOS pass element. VDO approximately scales with output current because the PMOS device

behaves like a resistor in dropout. As with any linear regulator, PSRR and transient response are degraded as

(VIN – VOUT) approaches dropout. This effect is shown in the Typical Characteristics section. Refer to application

report SLVA207, Understanding LDO Dropout, available for download from www.ti.com.

8.2.2.3 Transient Response

As with any regulator, increasing the size of the output capacitor reduces over/undershoot magnitude but

increases duration of the transient response. For more information, see Figure 19.

8.2.2.4 Minimum Load

The TPS782 series is stable with no output load. Traditional PMOS LDO regulators suffer from lower loop gain at

very light output loads. The TPS782 employs an innovative, low-current circuit under very light or no-load

conditions, resulting in improved output voltage regulation performance down to zero output current. See

Figure 19 for the load transient response.

8.2.3 Application Curves

Figure 24. Output Spectral Noise Density vs Frequency,

Figure 25. Ripple Rejection vs Frequency, VIN = 4.2 V,

CIN = 1 μF, COUT = 2.2 μF, VIN = 3.2 V, TPS78227

VOUT = 2.7 V, COUT = 2.2 μF, TPS78227

8.3 Do's and Don’ts

Do place at least one 1-µF ceramic capacitor as close as possible to the OUT pin of the regulator.

Do not place the output capacitor more than 10 mm away from the regulator.

Do connect a 0.1-

μF to 1.0-μF low equivalent series resistance (ESR) capacitor across the IN pin and GND of

the regulator.

Do not exceed the absolute maximum ratings.

9 Power Supply Recommendations

For best performance, connect a low-output impedance power supply directly to the IN pin of the TPS782 series.

Inductive impedances between the input supply and the IN pin create significant voltage excursions at the IN pin

during startup or load transient events. If inductive impedances are unavoidable, use an input capacitor.

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