LT3085 LINER [Linear Technology], LT3085 Datasheet - Page 11

• Manufacturer Part Number: LT3085
• Description: Adjustable 500mA Single Resistor Low Dropout Regulator
• Manufacturer: LINER [Linear Technology]

APPLICATIONS INFORMATION
For improvement in transient performance, place a capaci-
tor across the voltage setting resistor. Capacitors up to
1μF can be used. This bypass capacitor reduces system
noise as well, but start-up time is proportional to the time
constant of the voltage setting resistor (R
and SET pin bypass capacitor.
Extra consideration must be given to the use of ceramic
capacitors. Ceramic capacitors are manufactured with a
variety of dielectrics, each with different behavior across
temperature and applied voltage. The most common
dielectrics used are specifi ed 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 coeffi cients as shown in Figures 2
and 3. 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 bias with X5R and X7R capacitors is better than
Y5V and Z5U capacitors, but can still be signifi cant enough
to drop capacitor values below appropriate levels. Capacitor
DC bias characteristics tend to improve as component
case size increases, but expected capacitance at operating
voltage should be verifi ed.
SET
in Figure 1)
Figure 3. Ceramic Capacitor Temperature Characteristics
Figure 2. Ceramic Capacitor DC Bias Characteristics
–100
–100
–20
–40
–60
–80
–20
–40
–60
–80
20
40
20
0
0
–50
0
BOTH CAPACITORS ARE 16V,
1210 CASE SIZE, 10μF
–25
2
4
DC BIAS VOLTAGE (V)
0
TEMPERATURE (°C)
BOTH CAPACITORS ARE 16V,
1210 CASE SIZE, 10μF
6
25
8
Y5V
X5R
50
10
Y5V
75
12
X5R
100
14
3085 F02
3085 F03
125
LT3085
16
11
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