LT3024IFE データシートの表示（PDF） - Linear Technology

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LT3024IFE

Dual 100mA/500mA Low Dropout, Low Noise, Micropower Regulator

Linear Technology 

LT3024

APPLICATIONS INFORMATION

within 1% for the same load step. Both outputs exhibit this

improvement in transient response (see Transient Reponse

in Typical Performance Characteristics section). However,

regulator start-up time is proportional to the size of the

bypass capacitor, slowing to 15ms with a 0.01μF bypass

capacitor and 10μF output capacitor.

Output Capacitance and Transient Response

The LT3024 regulator is designed to be stable with a wide

range of output capacitors. The ESR of the output capaci-

tor affects stability, most notably with small capacitors. A

minimum output capacitor of 1μF with an ESR of 3Ω or

less is recommended for Output 2 to prevent oscillations.

A minimum output capacitor of 3.3μF with an ESR of 3Ω

or less is recommended for Output 1. The LT3024 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 im-

proved transient response for larger load current changes.

Bypass capacitors, used to decouple individual components

powered by the LT3024, 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 on

Output 2, 2.2μF of output capacitor is recommended. With

a 330pF bypass capacitor or larger on this output, a 3.3μF

output capacitor is recommended. For Output 1, 4.7μF of

output capacitor is recommended for 100pF of bypass

capacitance. With 1000pF or larger bypass capacitor on

this output, a 6.8μF output capacitor is recommended. The

shaded region of Figures 2 and 3 define the regions over

which the LT3024 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 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 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

case size increases, but expected capacitance at operating

voltage should be verified.

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)

3024 F02

Figure 2. Output 2 Stability

14

4.0

3.5

3.0

STABLE REGION

2.5

2.0

1.5 CBYP = 0

CBYP = 100pF

1.0

CBYP = 330pF

CBYP ≥ 1000pF

0.5

0

1

2

3 4 5 6 7 8 9 10

OUTPUT CAPACITANCE (μF)

3024 F03

Figure 3. Output 1 Stability

3024fa

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