lt1763cs8-trpbf Linear Technology Corporation, lt1763cs8-trpbf Datasheet - Page 14

• Manufacturer Part Number: lt1763cs8-trpbf
• Description: 500ma, Low Noise, Ldo Micropower Regulators
• Manufacturer: Linear Technology Corporation

APPLICATIONS
LT1763 Series
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.
The shaded region of Figure 3 defines the range over which
the LT1763 regulators are stable. The minimum ESR
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 di-
electrics used are specified with EIA temperature charac-
teristic 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 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 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
available 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 maxi-
mum 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
14
U
INFORMATION
U
W
U
Figure 5. Ceramic Capacitor Temperature Characteristics
Figure 4. Ceramic Capacitor DC Bias Characteristics
–100
–100
–20
–40
–60
–80
–20
–40
–60
–80
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
20
40
20
0
0
0
–50
1
0
C
BYP
BOTH CAPACITORS ARE 16V,
1210 CASE SIZE, 10µF
–25
2
C
= 0
BYP
Figure 3. Stability
OUTPUT CAPACITANCE (µF)
4
= 100pF
DC BIAS VOLTAGE (V)
0
2
TEMPERATURE (°C)
STABLE REGION
BOTH CAPACITORS ARE 16V,
1210 CASE SIZE, 10µF
6
25
C
3
BYP
8
Y5V
X5R
50
= 330pF
C
4
BYP
10
Y5V
5 6 7 8 9
≥ 1000pF
75
12
X5R
100
14
1763 F03
1763 F04
1763 F05
125
16
10
1763fc