LT1762 LINER [Linear Technology], LT1762 Datasheet - Page 12

• Manufacturer Part Number: LT1762
• Description: 150mA, Low Noise, LDO Micropower Regulators
• Manufacturer: LINER [Linear Technology]

APPLICATIONS
LT1762 Series
Output Capacitance and Transient Response
The LT1762 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 2.2 F with an ESR of
3 or less is recommended to prevent oscillations. The
LT1762-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 LT1762-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, 3.3 F of output capaci-
tor is recommended. With a 330pF bypass capacitor or
larger, a 4.7 F output capacitor is recommended. The
shaded region of Figure 3 defines the range over which the
LT1762 regulators are stable. The minimum ESR needed
is defined by the amount of bypass capacitance used,
while the maximum ESR is 3 .
12
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0
1
C
BYP
C
= 0
BYP
U
OUTPUT CAPACITANCE ( F)
Figure 3. Stability
= 100pF
2
C
STABLE REGION
BYP
INFORMATION
U
= 330pF
3
C
BYP
4
3300pF
5 6 7 8 9
W
1762 F03
10
U
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 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 4 and 5. 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
Figure 5. Ceramic Capacitor Temperature Characteristics
Figure 4. 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
1762 F05
1762 F04
125
16