LT1763 Series
APPLICATIONS INFORMATION
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0
Output Capacitance and Transient Response
The LT1763 regulators are designed to be stable with a
wide range of output capacitors. The ESR of the output
capacitor affects stability, most notably with small capaci-
tors. A minimum output capacitor of 3.3μF with an ESR
of 3Ω, or less, is recommended to prevent oscillations.
The LT1763-X 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 LT1763-X, 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, 4.7μF of output capaci-
tor is recommended. With a 1000pF bypass capacitor or
larger, a 6.8μF output capacitor is recommended.
STABLE REGION
C
= 0
BYP
C
= 100pF
BYP
C
= 330pF
BYP
C
r 1000pF
BYP
1
3
6 9 10
7 8
2
4
5
OUTPUT CAPACITANCE (μF)
1763 F03
Figure 3. Stability
20
0
BOTH CAPACITORS ARE 16V,
1210 CASE SIZE, 10μF
X5R
Y5V
–20
–40
–60
–80
–100
The shaded region of Figure 3 defines the range over
whichtheLT1763regulatorsarestable. TheminimumESR
needed is defined 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 specified with EIA temperature
characteristic codes of Z5U, Y5V, X5R and X7R. The Z5U
andY5Vdielectricsaregoodforprovidinghighcapacitances
in a small package, but they tend to have strong voltage
and temperature coefficients, as shown in Figures 4
and 5. 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
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
availableinhighervalues.Carestillmustbeexercisedwhen
using X5R and X7R capacitors; the X5R and X7R codes
only specify operating temperature range and maximum
capacitancechangeovertemperature.Capacitancechange
due to DC bias with X5R and X7R capacitors is better than
0
8
12 14
2
4
6
10
16
DC BIAS VOLTAGE (V)
1763 F04
Figure 4. Ceramic Capacitor DC Bias Characteristics
40
20
X5R
0
–20
–40
Y5V
–60
–80
BOTH CAPACITORS ARE 16V,
1210 CASE SIZE, 10μF
–100
50
TEMPERATURE (°C)
100 125
–50 –25
0
25
75
1763 F05
Figure 5. Ceramic Capacitor Temperature Characteristics
1763fe
15
Linear [ Linear ]
