3.5
3
100
10
2.5
2
1
1.5
1
0.1
0.5
0
0.01
0.001
0
100
200
300
400
500
600
700
800
Output Current (mA)
0
2
4
6
8
10
12
14
16
Enable Voltage
(a) Foldback Current Limit of the REG103-3.3 at 25°C.
RBOOST
FIGURE 5. ENABLE Pin Current versus Applied Voltage.
ERROR FLAG
VOUT
VIN
REG103
The error indication pin, only available on the SO-8 package
version, provides a fault indication out-of-regulation condi-
tion. During a fault condition, ERROR is pulled LOW by an
open drain output device. The pin voltage, in the fault state,
is typically less than 0.2V at 500µA.
+
+
Load
0.1µF
0.1µF(1)
Gnd
(1) Optional.
(b) Foldback Current Boost Circuit.
A fault condition is indicated when the output voltage differs
(either above or below) from the specified value by approxi-
mately 10%. Figure 6 shows a typical fault-monitoring
application.
FIGURE 3. Foldback Current Limit and Boost Circuit.
ENABLE
The ENABLE pin allows the regulator to be turned on and
off. This pin is active HIGH and compatible with standard
TTL-CMOS levels. Inputs below 0.5V (max) turn the regu-
lator off and all circuitry is disabled. Under this condition,
ground pin current drops to approximately 0.5µA. When not
used, the ENABLE pin may be connected to VIN.
+5V
10kΩ
Pull-up
µP
Internal to the part, the ENABLE pin is connected to an
input resistor-zener diode circuit, as shown in Figure 4,
creating a nonlinear input impedance. The ENABLE Pin
Current versus Applied Voltage relationship is shown in
Figure 5. When the ENABLE pin is connected to a voltage
greater than 10V, a series resistor may be used to limit the
current.
6
ERROR
3
ENABLE
Open
Drain
SO-8 Package
Only
REG103
FIGURE 6. ERROR Pin Typical Fault-Monitoring Circuit.
OUTPUT NOISE
175kΩ
ENABLE
A precision band-gap reference is used for the internal
reference voltage, VREF, for the REG103. This reference is
the dominant noise source within the REG103. It generates
approximately 45µVrms in the 10Hz to 100kHz bandwidth
at the reference output. The regulator control loop gains up
the reference noise, so that the noise voltage of the regulator
is approximately given by:
VZ = 10V
FIGURE 4. ENABLE Pin Equivalent Input Circuit.
R1 + R2
VOUT
VREF
VN = 45µVrms
= 45µVrms•
R2
REG103
SBVS010D
9
TI [ TEXAS INSTRUMENTS ]
