REG104_08 Datasheet, PDF (9/21 Pages) Burr-Brown (TI) – DMOS 1A Low-Dropout Regulator

The Enable Pin Current versus Applied Voltage relationship
is shown in Figure 4. When the Enable pin is connected to
V_IN greater than 10V, a series resistor may be used to limit
the current.
100
10
1
0.1
0.01
0.001
0
2
4
6
8 10 12 14 16
Enable Voltage
FIGURE 4. Enable Pin Current versus Applied Voltage.
OUTPUT NOISE
A precision band-gap reference is used for the internal
reference voltage, V_REF, for the REG104. This reference is
the dominant noise source within the REG104. It generates
approximately 45µV_RMS 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:
V_N
=
45µV_RMS
R₁ + R₂
R2
=
45µV_RMS
•
V_OUT
V_REF
Since the value of V_REF is 1.295V, this relationship reduces to:
V_N = 35
µV_RMS
V
• V_OUT
Connecting a capacitor, C_NR, from the Noise-Reduction (NR)
pin to ground can reduce the output noise voltage. Adding
C_NR, as shown in Figure 5, forms a low-pass filter for the
voltage reference. For C_NR = 10nF, the total noise in the
10Hz to 100kHz bandwidth is reduced by approximately
a factor of 3.5. This noise reduction effect is shown in
Figure 6.
45
REG104-3.3
35
25
0.001
0.01
C_NR (µF)
C_OUT = 0
C_OUT = 10µF
0.1
1
FIGURE 6. Output Noise versus Noise Reduction Capacitor.
The REG104 adjustable version does not have the noise-
reduction pin available, however, the adjust pin is the
summing junction of the error amplifier. A capacitor, C_FB,
NR
(fixed output
versions only)
C_NR
(optional)
V_REF
(1.295V)
Enable
FIGURE 5. Block Diagram.
V_IN
Low Noise
Charge Pump
Over Current
Over Temp
Protection
DMOS
Output
V_OUT
R₁
Adj
(Adjustable
R_{2 Versions)}
REG104
NOTE: R₁ and R₂ are internal
on fixed output versions.
REG104
9
SBVS025G