REG103FA-ASLASH500 datasheet(8/26 Pages) TI1

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REG103

SBVS010D

BASIC OPERATION

The REG103 series is a family of LDO (Low Drop-Out)

linear regulators. The family includes five fixed output

versions (2.5V to 5.0V) and an adjustable output version. An

internal DMOS power device provides low dropout regula-

tion with near constant ground pin current (largely indepen-

dent of load and drop-out conditions) and very fast line and

load transient response. All versions include internal current

limit and thermal shutdown circuitry.

Figure 1 shows the basic circuit connections for the fixed

voltage models. Figure 2 gives the connections for the

adjustable output version (REG103A) and example resistor

values for some commonly used output voltages. Values for

other voltages can be calculated from the equation shown in

Figure 2. The SO-8 package provides two pins each for VIN

and VOUT. Both sets of pins MUST be used and connected

adjacent to the device.

FIGURE 1. Fixed Voltage Nominal Circuit for REG103.

REG103

ENABLE

OUT

0.1

µF

0.01

µF

ERROR

Gnd

Out

Optional

None of the versions require an output capacitor for regula-

tor stability. The REG103 will accept any output capacitor

type less than 1

µF. For capacitance values larger than 1µF,

the effective ESR should be greater than 0.1

Ω. This mini-

mum ESR value includes parasitics such as printed circuit

board traces, solder joints, and sockets. A minimum 0.1

µF

low ESR capacitor connected to the input supply voltage is

recommended.

INTERNAL CURRENT LIMIT

The REG103 internal current limit has a typical value of

700mA. A fold-back feature limits the short-circuit current

to a typical short-circuit value of 40mA. This circuit will

protect the regulator from damage under all load conditions.

A typical characteristic of VOUT versus IOUT is given in

Figure 3a.

Care should be taken in high current applications to avoid

ground currents flowing in the circuit board traces causing

voltage drops between points on the circuit. If voltage drops

occur on the circuit board ground that causes the load ground

voltage to be much lower than the ground voltage seen by

the ground pin on the REG103, the foldback current may

approach zero and the REG103 may not start up. In these

types of applications, a large value resistor can be placed

between VIN and VOUT to help “boost” up the output of the

REG103 during start-up, see Figure 3b. The value for the

“boost” resistor should be chosen so that the current through

the “boost” resistor is less than the minimum load current:

RBOOST > (VIN – VOUT)/ILOAD. Typically, a good value for a

“boost” resistor is 5k

Ω.

FIGURE 2. Adjustable Voltage Circuit for REG103A.

OUT = (1 + R1/R2) • 1.295V

Pin numbers for SO-8 package.

REG103

0.1

µF

Gnd

OUT

0.01

µF

OUT

Adj

ADJ

Load

ERROR

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.

OUT (V)

1 (Ω)

(1)

2 (Ω)

(1)

1.295

Short

Open

2.5

12.1k

13k

1.21k

1.3k

16.9k

13k

1.69k

1.3k

3.3

20k

13k

2.0k

1.3k

37.4k

13k

3.74k

1.3k

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

EXAMPLE RESISTOR VALUES

Optional

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