LT3071EUFD LINER [Linear Technology], LT3071EUFD Datasheet - Page 19

• Manufacturer Part Number: LT3071EUFD
• Description: 5A, Low Noise, Programmable Output, 85mV Dropout Linear Regulator with Analog Margining
• Manufacturer: LINER [Linear Technology]

ApplicAtions inFormAtion
The X7R type has better stability across temperature,
while the X5R is less expensive and is available in higher
values. Care still must be exercised when using X5R and
X7R capacitors; the X5R and X7R codes only specify
operating temperature range and maximum capacitance
change over temperature. Capacitance change due to
DC bias with X5R and X7R capacitors is better than Y5V
and Z5U capacitors, but can still be significant enough to
drop capacitor values below appropriate levels. Capacitor
DC bias characteristics tend to improve as component
case size increases, but expected capacitance at operat-
ing voltage should be verified. Voltage and temperature
Figure 5. Ceramic Capacitor Temperature Characteristics
Figure 4. Ceramic Capacitor DC Bias Characteristics
–100
–100
–20
–40
–80
–60
–20
–40
–60
–80
20
40
20
0
0
–50
0
–25
2
4
DC BIAS VOLTAGE (V)
0
TEMPERATURE (°C)
BOTH CAPACITORS ARE 16V,
1210 CASE SIZE, 10µF
BOTH CAPACITORS ARE 16V,
1210 CASE SIZE, 10µF
6
25
8
X5R
Y5V
50
Y5V
10
X5R
75
12
100
14
3071 F04
3071 F05
125
16
coefficients are not the only sources of problems. Some
ceramic capacitors have a piezoelectric response. A piezo-
electric device generates voltage across its terminals due
to mechanical stress, similar to the way a piezoelectric
microphone works. For a ceramic capacitor the stress
can be induced by vibrations in the system or thermal
transients.
Stability and Input Capacitance
The LT3071 is stable with a minimum capacitance of
47µF connected to its IN pins. Use low ESR capacitors to
minimize instantaneous voltage drops under large load
transient conditions. Large V
transients may cause the regulator to enter dropout with
corresponding degradation in load transient response.
Increased values of input and output capacitance may be
necessary depending on an application’s requirements.
Sufficient input capacitance is critical as the circuit is
intentionally operated close to dropout to minimize power.
Ideally, the output impedance of the supply that powers
IN should be less than 10mΩ to support a 5A load with
large transients.
In cases where wire is used to connect a power supply
to the input of the LT3071 (and also from the ground of
the LT3071 back to the power supply ground), large input
capacitors are required to avoid an unstable application.
This is due to the inductance of the wire forming an LC
tank circuit with the input capacitor and not a result of the
LT3071 being unstable. The self inductance, or isolated
inductance, of a wire is directly proportional to its length.
However, the diameter of a wire does not have a major
influence on its self inductance. For example, one inch of
18-AWG, 0.04 inch diameter wire has 28nH of self induc-
tance. The self inductance of a 2-AWG isolated wire with
a diameter of 0.26 inch is about half the inductance of a
18-AWG wire. The overall self inductance of a wire can
be reduced in two ways. One is to divide the current flow-
ing towards the LT3071 between two parallel conductors
which flows in the same direction in each. In this case,
IN
droops during large load
LT3071

3071f