lt3028ife-trpbf Linear Technology Corporation, lt3028ife-trpbf Datasheet - Page 12

• Manufacturer Part Number: lt3028ife-trpbf
• Description: Dual 100ma/500ma Low Dropout, Low Noise, Micropower Regulators With Independent Inputs
• Manufacturer: Linear Technology Corporation

APPLICATIO S I FOR ATIO
LT3028
used to bypass the reference (for low noise operation),
larger values of output capacitors are needed. For 100pF
of bypass capacitance on Output 2, 2.2µF of output
capacitor is recommended. With a 330pF bypass capaci-
tor or larger on this output, a 3.3µF output capacitor is
recommended. For Output 1, 4.7µF of output capacitor is
recommended for 100pF of bypass capacitance. With
1000pF or larger bypass capacitor on this output, a 6.8µF
output capacitor is recommended. The shaded region of
Figures 2 and 3 define the regions over which the LT3028
regulator is stable. The minimum ESR needed is defined
by the amount of bypass capacitance used, while the
maximum ESR is 3Ω.
12
Figure 4. Ceramic Capacitor DC Bias Characteristics
–100
–20
–40
–60
–80
20
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0
0
0
1
C
BYP
C
2
Figure 2. Output 2 Stability
BYP
= 0
U
= 100pF
OUTPUT CAPACITANCE (µF)
4
C
DC BIAS VOLTAGE (V)
BYP
2
STABLE REGION
BOTH CAPACITORS ARE 16V,
1210 CASE SIZE, 10µF
6
= 330pF
C
U
BYP
8
3
Y5V
X5R
> 3300pF
10
4
5 6 7 8 9
12
W
14
3028 F04
3028 F02
16
10
U
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 Z5U, Y5V, X5R and X7R. The Z5U and
Y5V dielectrics are good for providing high capacitances
in a small package, but exhibit strong voltage and tem-
perature coefficients as shown in Figures 4 and 5. When
used with a 5V regulator, a 10µF Y5V capacitor can exhibit
an effective value as low as 1µF to 2µF 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.
Figure 5. Ceramic Capacitor Temperature Characteristics
–100
–20
–40
–60
–80
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
40
20
0
0
–50
1
BOTH CAPACITORS ARE 16V,
1210 CASE SIZE, 10µF
C
BYP
–25
Figure 3. Output 1 Stability
C
= 0
BYP
OUTPUT CAPACITANCE (µF)
= 100pF
0
TEMPERATURE (°C)
2
STABLE REGION
25
C
3
BYP
50
= 330pF
C
4
BYP
Y5V
75
5 6 7 8 9
≥ 1000pF
X5R
100
3028 F05
3028 F03
125
10
3028f