Datasheet

LT3070
23
3070fb
For more information www.linear.com/LT3070
APPLICATIONS INFORMATION
Keep this ballast trace area free of solder to maintain a
controlled resistance.
Table 4 shows a simple guideline for PCB trace resistance
as a function of weight and trace width.
Table 4. PC Board Trace Resistance
WEIGHT (Oz) 100 MIL WIDTH* 200 MIL WIDTH*
1 5.43 2.71
2 2.71 1.36
*Trace resistance is measured in milliohms/in
Quieting the Noise
The LT3070 offers numerous noise performance advan-
tages. Each LDO has several sources of noise. An LDO’s
most critical noise source is the reference, followed by
the LDO error amplifier. Traditional low noise regulators
buffer the voltage reference out to an external pin (usually
through a large value resistor) to allow for bypassing and
noise reduction of reference noise. The LT3070 deviates
from the traditional voltage reference by generating a
low voltage V
REF
from a reference current into an inter-
nal resistor ≅19k. This intermediate impedance node
(REF/BYP) facilitates external filtering directly. A 10nF filter
capacitor minimizes reference noise to 10µV
RMS
at the
600mV REF/BYP pin, equivalently a 17µV contribution to
output noise at V
OUT
= 1V. See the Typical Performance
Characteristics for Noise vs Output Voltage performance
as a function of C
REF/BYP
.
This approach also accommodates reference sharing
between LT3070 regulators that are hooked up in cur-
rent sharing applications. The REF/BYP filter capacitor
delays the initial power-up time by a factor of the RC time
constant. V
REF
remains active in nap mode, thus start-up
time is significantly reduced and well controlled coming
out of nap mode (EN:LO↑HI).
BIAS
50k
LT3070
IN
EN
V
O0
V
O1
330µF
2.2µF
2.2µF*
0.01µF
1nF
4.7µF*
3070 F06
10µF*
*X5R OR X7R CAPACITORS
PWRGD
V
OUT
1.2V
5A
V
O2
MARGSEL
MARGTOL
NC
NC
VIOC
SENSE
OUT
V
BIAS
2.5V TO 3.6V
V
IN
1.5V
PWRGD
REF/BYP
GND
Figure 6. 1.5V to 1.2V Linear Regulator