LT3023 LINER [Linear Technology], LT3023 Datasheet - Page 10

• Manufacturer Part Number: LT3023
• Description: Dual 100mA, Low Dropout, Low Noise, Micropower Regulator
• Manufacturer: LINER [Linear Technology]

APPLICATIO S I FOR ATIO
LT3023
Output Capacitance and Transient Response
The LT3023 regulator is designed to be stable with a wide
range of output capacitors. The ESR of the output capaci-
tor affects stability, most notably with small
capacitors. A minimum output capacitor of 1 F with an
ESR of 3 or less is recommended to prevent oscilla-
tions. The LT3023 is a micropower device and output
transient response will be a function of output capaci-
tance. Larger values of output capacitance decrease the
peak deviations and provide improved transient response
for larger load current changes. Bypass capacitors, used
to decouple individual components powered by the
LT3023, will increase the effective output capacitor value.
With larger capacitors used to bypass the reference (for
low noise operation), larger values of output capacitors
are needed. For 100pF of bypass capacitance, 2.2 F of
output capacitor is recommended. With a 330pF bypass
capacitor or larger, a 3.3 F output capacitor is recom-
mended. The shaded region of Figure 2 defines the region
over which the LT3023 regulator is stable. The minimum
ESR needed is defined by the amount of bypass capaci-
tance used, while the maximum ESR is 3 .
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
10
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0
1
C
BYP
C
BYP
= 0
U
OUTPUT CAPACITANCE ( F)
= 100pF
Figure 2. Stability
C
BYP
2
STABLE REGION
= 330pF
U
C
BYP
3
> 3300pF
4
5 6 7 8 9
W
3023 F02
10
U
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 3 and 4. When
used with a 5V regulator, a 10 F Y5V capacitor can exhibit
an effective value as low as 1 F to 2 F 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 4. Ceramic Capacitor Temperature Characteristics
Figure 3. 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, 10 F
–25
2
4
DC BIAS VOLTAGE (V)
0
TEMPERATURE ( C)
BOTH CAPACITORS ARE 16V,
1210 CASE SIZE, 10 F
6
25
8
Y5V
X5R
50
10
Y5V
75
12
X5R
100
14
3023 F03
3023 F04
125
16
3023f