LT3050MPMSE-3.3 Ver la hoja de datos (PDF) - Linear Technology

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LT3050MPMSE-3.3

100mA, Linear Regulator with Precision Current Limit and Diagnostic Outputs

Linear Technology 

LT3050 Series

APPLICATIONS INFORMATION

Start-up time is also affected by the presence of a feed-

forward capacitor. Start-up time is directly proportional to

the size of the feedforward capacitor and the output volt-

age, and is inversely proportional to the feedback resistor

divider current, slowing to 15ms with a 4.7nF feedforward

capacitor and a 10μF output capacitor for an output voltage

set to 5V by a 5μA feedback resistor divider.

Output Capacitance

The LT3050 regulator is stable with a wide range of output

capacitors. The ESR of the output capacitor affects stability,

most notably with small capacitors. Use a minimum output

capacitor of 2.2μF with an ESR of 3Ω or less to prevent

oscillations. If a feedforward capacitor is used with output

voltages set for greater than 24V, use a minimum output

capacitor of 4.7μF. The LT3050 is a micropower device

and output load transient response is a function of output

capacitance. Larger values of output capacitance decrease

the peak deviations and provide improved transient re-

sponse for larger load current changes. Bypass capacitors,

used to decouple individual components powered by the

LT3050, increase the effective output capacitor value. For

applications with large load current transients, a low ESR

ceramic capacitor in parallel with a bulk tantalum capacitor

often provides an optimally damped response.

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)

3050 F04

Figure 4. Ceramic Capacitor DC Bias Characteristics

Give extra consideration to the use of ceramic capacitors.

Manufacturers make ceramic capacitors with a variety of

dielectrics, each with different behavior across tempera-

ture and applied voltage. The most common dielectrics

are specified with EIA temperature characteristic codes

of Z5U, Y5V, X5R and X7R. The Z5U and Y5V dielectrics

provide high C-V products in a small package at low cost,

but exhibit 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 yield much more stable characteristics and are

more suitable for use as the output capacitor.

The X7R type works over a wider temperature range and

has better temperature stability, 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 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. Capacitor DC bias characteristics tend

to improve as component case size increases, but expected

capacitance at operating voltage should be verified.

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

3050 F05

Figure 5. Ceramic Capacitor Temperature Characteristics

3050fa

19

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