REG101NA-2.5SLASH250 datasheet(9/18 Pages) TI

9 / 18 page

REG101

SBVS026D

BASIC OPERATION

The REG101 series of LDO (Low Drop-Out) linear regula-

tors offers a wide selection of fixed output voltage versions

and an adjustable output version. The REG101 belongs to a

family of new generation LDO regulators that utilize a

DMOS pass transistor to achieve ultra-low dropout perfor-

mance and freedom from output capacitor constraints. Ground

pin current remains under 650

µA over all line, load, and

temperature conditions. All versions have thermal and over-

current protection, including foldback current limit.

The REG101 does not require an output capacitor for regu-

lator stability and is stable over most output currents and

with almost any value and type of output capacitor up to

µF or more. For applications where the regulator output

current drops below several milliamps, stability can be

enhanced by: adding a 1k

Ω to 2kΩ load resistor; using

capacitance values less than 10

µF; or keeping the effective

series resistance greater than 0.05

Ω including the capacitor’s

ESR and parasitic resistance in printed circuit board traces,

solder joints, and sockets.

Although an input capacitor is not required, it is good analog

design practice to connect a 0.1

µF low ESR capacitor across

FIGURE 1. Fixed Voltage Nominal Circuit for REG101.

REG101

Enable

OUT

0.1

µF

0.01

µF

Gnd

Out

Optional

the input supply voltage. This is recommended to improve

ripple rejection by reducing input voltage ripple.

Figure 1 shows the basic circuit connections for the fixed

voltage models. Figure 2 gives the connections for the

adjustable output version (REG101A) and example resistor

values for some commonly used output voltages. Values for

other voltages can be calculated from the equation shown in

Figure 2.

INTERNAL CURRENT LIMIT

The REG101 internal current limit has a typical value of

170mA. A foldback feature limits the short-circuit current to

a typical short-circuit value of 60mA. This helps to protect

the regulator from damage under all load conditions. A

characteristic of VOUT versus IOUT is given in Figure 3 and

in the Typical Characteristics section.

FIGURE 2. Adjustable Voltage Circuit for REG101A.

FIGURE 3. Foldback Current Limit of the REG101-3.3 at

°C.

040

140

160

100

120

180

3.5

3.0

2.5

2.0

1.5

1.0

0.5

Output Current (mA)

FOLDBACK CURRENT LIMIT

REG101-3.3

OUT = (1 + R1/R2) • 1.267V

Pin numbers for SOT23 package.

REG101

0.1

µF

Gnd

OUT

0.01

µF

OUT

Adj

ADJ

Load

Enable

To reduce current through divider, increase resistor

values (see table at right).

As the impedance of the resistor divider increases,

ADJ (~200nA) may introduce an error.

FB improves noise and transient response.

Optional

OUT (V)

1 (W)

(1)

2 (Ω)

(1)

2.5

11.3k

11.5k

1.13k

1.15k

3.0

15.8k

11.5k

1.58k

1.15k

3.3

18.7k

11.5k

1.87k

1.15k

5.0

34.0k

11.5k

3.40k

1.15k

NOTE: (1) Resistors are standard 1% values.

EXAMPLE RESISTOR VALUES

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