Datasheet

LT3023
10
3023fa
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
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 2. Stability Figure 4. Ceramic Capacitor Temperature Characteristics
Figure 3. Ceramic Capacitor DC Bias Characteristics
OUTPUT CAPACITANCE (μF)
1
ESR (Ω)
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0
310
3023 F02
245
6
78
9
STABLE REGION
C
BYP
= 330pF
C
BYP
= 100pF
C
BYP
= 0
C
BYP
> 3300pF
DC BIAS VOLTAGE (V)
CHANGE IN VALUE (%)
3023 F03
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
TEMPERATURE (°C)
–50
40
20
0
–20
–40
–60
–80
–100
25 75
3023 F04
–25 0
50 100 125
Y5V
CHANGE IN VALUE (%)
X5R
BOTH CAPACITORS ARE 16V,
1210 CASE SIZE, 10μF