LT3081 Datasheet, PDF (15/28 Pages) Linear Dimensions Semiconductor – 1.5A Single Resistor Rugged Linear Regulator with Monitors

LT3081
APPLICATIONS INFORMATION
cases, this capacitor may already exist and no additional
capacitance is required. For example, if the LT3081 was
used as a variable current source on the output of a power
supply, the output bypass capacitance would suffice to
provide LT3081 stability. Other applications may require
the addition of a bypass capacitor. A series RC network
may also be used as necessary, and depends on the ap-
plication requirements.
In some extreme cases, capacitors or series RC networks
may be required on both the LT3081’s input and output to
stabilize the circuit. Figure 6 depicts a general application
using input and output capacitor networks rather than
an input-to-output capacitor. As the input of the current
source tends to be high impedance, placing a capacitor
on the input does not have the same effect as placing a
capacitor on the lower impedance output. Capacitors in the
range of 0.1µF to 1µF usually provide sufficient bypassing
on the input, and the value of input capacitance may be
increased without limit. Pay careful attention to using low
ESR input capacitors with long input lines (see the Stabil-
ity and Input Capacitance section for more information).
are specified with EIA temperature characteristic codes of
Z5U, Y5V, X5R and X7R. The Z5U and Y5V dielectrics are
good for providing high capacitances in a small package,
but they tend to have strong voltage and temperature
coefficients as shown in Figures 7 and 8. When used with
a 5V regulator, a 16V 10μF Y5V capacitor can exhibit an
effective value as low as 1μF to 2μF for the DC bias voltage
applied and over the operating temperature range. The X5R
and X7R dielectrics result in more stable characteristics
and are more suitable for use as the output capacitor.
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
40
20
0
X5R
–20
V_IN
R_IN LT3081
IN
C_IN
50µA
+
–
SET
R_SET
OUT
R_OUT
I_OUT
R_OUT
C_OUT OR
C_OUT
3081 F06
Figure 6. Input and/or Output Capacitors May
Be Used for Compensation
Using Ceramic Capacitors
–40
Y5V
–60
–80 BOTH CAPACITORS ARE 16V,
1210 CASE SIZE, 10µF
–100
–50 –25 0 25 50 75
TEMPERATURE (°C)
100 125
3081 F07
Figure 7. Ceramic Capacitor Temperature Characteristics
20
BOTH CAPACITORS ARE 16V,
1210 CASE SIZE, 10µF
0
X5R
–20
–40
–60
Y5V
–80
Give extra consideration to the use of ceramic capacitors.
Ceramic capacitors are manufactured with a variety of di-
electrics, each with different behavior across temperature
and applied voltage. The most common dielectrics used
–100
0 2 4 6 8 10 12 14 16
DC BIAS VOLTAGE (V)
3081 F08
Figure 8. Ceramic Capacitor DC Bias Characteristics
3081f
For more information www.linear.com/LT3081
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