LT3023 查看數據表（PDF） - Linear Technology

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LT3023

Dual 100mA,Low Dropout, Low Noise, Micropower Regulator

Linear Technology 

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 defines the region over which

the LT3023 regulator is 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

dielectrics used are specified 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 coefficients 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 significant enough

to drop capacitor values below appropriate levels. Capaci-

tor DC bias characteristics tend to improve as component

20

BOTH CAPACITORS ARE 16V,

1210 CASE SIZE, 10μF

0

X5R

–20

–40

–60

Y5V

–80

–100

0 2 4 6 8 10 12 14 16

DC BIAS VOLTAGE (V)

3023 F03

Figure 3. Ceramic Capacitor DC Bias Characteristics

4.0

3.5

3.0

STABLE REGION

2.5

2.0

1.5 CBYP = 0

CBYP = 100pF

1.0

CBYP = 330pF

CBYP > 3300pF

0.5

0

1

2

3 4 5 6 7 8 9 10

OUTPUT CAPACITANCE (μF)

3023 F02

Figure 2. Stability

10

40

20

0

X5R

–20

–40

Y5V

–60

–80 BOTH CAPACITORS ARE 16V,

1210 CASE SIZE, 10μF

–100

–50 –25 0 25 50 75

TEMPERATURE (°C)

100 125

3023 F04

Figure 4. Ceramic Capacitor Temperature Characteristics

3023fa

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