Datasheet

REG102
9
SBVS024F
www.ti.com
FIGURE 1. Fixed Voltage Nominal Circuit for the REG102.
REG102
Enable
V
OUT
C
OUT
V
IN
0.1µF
C
NR
0.01µF
GND NR
In Out
Optional
FIGURE 2. Adjustable Voltage Circuit for the REG102A.
FIGURE 3. Foldback Current Limit of the REG102-3.3 at 25°C.
V
OUT
= (1 + R
1
/R
2
) • 1.26V
Pin numbers for the SOT-223 package.
REG102
V
IN
0.1µF
3
1
Gnd
V
OUT
R
1
C
FB
0.01µF
C
OUT
Adj
R
2
I
ADJ
Load
2
4
5
Enable
To reduce current through divider, increase resistor
values (see table at right).
As the impedance of the resistor divider increases,
I
ADJ
(~200nA) may introduce an error.
C
FB
improves noise and transient response.
V
OUT
(V) R
1
(Ω)
(1)
R
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
Optional
0 50 100 150 200 250 300 350
I
SC
I
CL
400 450
3.5
3
2.5
2
1.5
1
0.5
0
Output Voltage (V)
Output Current (mA)
CURRENT LIMIT FOLDBACK
REG102-3.3
BASIC OPERATION
The REG102 series of LDO (low dropout) linear regulators
offers a wide selection of fixed output voltage versions and
an adjustable output version as well. The REG102 belongs
to a family of new generation LDO regulators that use a
DMOS pass transistor to achieve ultra low-dropout perfor-
mance and freedom from output capacitor constraints. Ground
pin current remains under 1mA over all line, load, and
temperature conditions. All versions have thermal and over-
current protection, including foldback current limit.
The REG102 does not require an output capacitor for regulator
stability and is stable over most output currents and with almost
any value and type of output capacitor up to 10µF or more. For
applications where the regulator output current drops below
several milliamps, stability can be enhanced by adding a 1kΩ
to 2kΩ load resistor, using capacitance values smaller than
10µF, or keeping the effective series resistance greater than
0.05Ω including the capacitor ESR and parasitic resistance in
printed circuit board traces, solder joints, and sockets.
Although an input capacitor is not required, it is a good
standard analog design practice to connect a 0.1µF low ESR
capacitor across the input supply voltage. This is recom-
mended to counteract reactive input sources and 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 adjust-
able output version (REG102A) and example resistor values for
some commonly used output voltages. Values for other volt-
ages can be calculated from the equation shown in Figure 2.
INTERNAL CURRENT LIMIT
The REG102 internal current limit has a typical value of
400mA. A foldback feature limits the short-circuit current to a
typical short-circuit value of 150mA, which helps to protect
the regulator from damage under all load conditions. A
characteristic of V
OUT
versus I
OUT
is given in Figure 3 and in
the Typical Characteristics section.