Datasheet
12
LT3028
3028f
APPLICATIO S I FOR ATIO
WUUU
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.
Figure 2. Output 2 Stability
OUTPUT CAPACITANCE (µF)
1
ESR (Ω)
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0
310
3028 F02
245
6
78
9
STABLE REGION
C
BYP
= 330pF
C
BYP
= 100pF
C
BYP
= 0
C
BYP
> 3300pF
OUTPUT CAPACITANCE (µF)
1
ESR (Ω)
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0
310
3028 F03
245
6
78
9
STABLE REGION
C
BYP
= 330pF
C
BYP
≥ 1000pF
C
BYP
= 100pF
C
BYP
= 0
Figure 3. Output 1 Stability
Figure 4. Ceramic Capacitor DC Bias Characteristics
DC BIAS VOLTAGE (V)
CHANGE IN VALUE (%)
3028 F04
20
0
–20
–40
–60
–80
–100
0
4
8
10
26
12
14
X5R
Y5V
16
BOTH CAPACITORS ARE 16V,
1210 CASE SIZE, 10µF
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.
TEMPERATURE (°C)
–50
40
20
0
–20
–40
–60
–80
–100
25 75
3028 F05
–25 0
50 100 125
Y5V
CHANGE IN VALUE (%)
X5R
BOTH CAPACITORS ARE 16V,
1210 CASE SIZE, 10µF
Figure 5. Ceramic Capacitor Temperature Characteristics