REG103_07 Datasheet, PDF (10/27 Pages) Burr-Brown (TI) – DMOS 500mA Low-Dropout Regulator

Since the value of V_REF is 1.295V, this relationship reduces to:
V_N
= 35
µVrms
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 7, 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, as shown in Figure 8.
45
10.0
1.0
0.1
10
C_OUT = 0, C_FB = 0
C_OUT = 0, C_FB = 0.01µF
C_OUT = 10µF, C_FB = 0.01µF
100
1000
Frequency
10000
100000
35
25
0.001
0.01
C_NR (µF)
C_OUT = 0
C_OUT = 10µF
0.1
1
FIGURE 8. Output Noise versus Noise-Reduction Capacitor.
The REG103 adjustable version does not have the noise-
reduction pin available, however, the adjust pin is the sum-
ming junction of the error amplifier. A capacitor, C_FB,
connected from the output to the adjust pin will reduce both
the output noise and the peak error from a load transient.
Figure 9 shows improved output noise performance for two
capacitor combinations.
FIGURE 9. Output Noise Density on Adjustable Versions.
The REG103 utilizes an internal charge pump to develop an
internal supply voltage sufficient to drive the gate of the
DMOS pass element above V_IN. The charge-pump switch-
ing noise (nominal switching frequency = 2MHz) is not
measurable at the output of the regulator.
DROP-OUT VOLTAGE
The REG103 uses an N-channel DMOS as the “pass”
element. When the input voltage is within a few hundred
millivolts of the output voltage, the DMOS device behaves
like a resistor. Therefore, for low values of V_IN to V_OUT, the
regulator’s input-to-output resistance is the Rds_ON of the
DMOS pass element (typically 230mΩ). For static (DC)
loads, the REG103 will typically maintain regulation down
to V_IN to V_OUT voltage drop of 115mV at full-rated output
current. In Figure 10, the bottom line (DC dropout) shows
the minimum V_IN to V_OUT voltage drop required to prevent
drop-out under DC load conditions.
NR
(fixed output
versions only)
C_NR
(optional)
V_REF
(1.295V)
ENABLE
FIGURE 7. Block Diagram.
V_IN
Low Noise
Charge Pump
Over Current
Over Temp
Protection
ERROR
DMOS
Output
V_OUT
R₁
Adj
(Adjustable
R_{2 Versions)}
REG103
NOTE: R₁ and R₂ are internal
on fixed output versions.
10
REG103
SBVS010D