lt3023emse-trpbf Linear Technology Corporation, lt3023emse-trpbf Datasheet - Page 10

• Manufacturer Part Number: lt3023emse-trpbf
• Description: Dual 100ma, Low Dropout, Low Noise, Micropower Regulator
• Manufacturer: Linear Technology Corporation

LT3023
APPLICATIONS INFORMATION
Output Capacitance and Transient Response
The LT3023 regulator is designed to be stable with a
wide range of output capacitors. The ESR of the out-
put capacitor affects stability, most notably with small
capacitors. A minimum output capacitor of 1μF with an
ESR of 3Ω or less is recommended to prevent oscilla-
tions. The LT3023 is a micropower device and output
transient response will be a function of output capacitance.
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, 2.2μF of output
capacitor is recommended. With a 330pF bypass capacitor
or larger, a 3.3μF output capacitor is recommended. The
shaded region of Figure 2 defi nes the region over which
the LT3023 regulator is stable. The minimum ESR needed
is defi ned by the amount of bypass capacitance used, while
the maximum ESR is 3Ω.
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 char-
acteristic 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
10
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0
1
C
BYP
C
BYP
= 0
= 100pF
OUTPUT CAPACITANCE (μF)
Figure 2. Stability
C
BYP
2
STABLE REGION
= 330pF
C
BYP
3
> 3300pF
4
5 6 7 8 9
3023 F02
10
and temperature coeffi cients as shown in Figures 3 and 4.
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 tempera-
ture 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 avail-
able 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. Capaci-
tor DC bias characteristics tend to improve as component
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, 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
3023 F03
3023 F04
125
16
3023fa