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LT3009 Series

3009fd

be implemented to prevent board contamination. If the

board is to be subjected to humidity cycling or if board

cleaning measures cannot be guaranteed, consideration

should be given to using resistors an order of magnitude

smaller than in Table 1 to prevent contamination from

causing unwanted shifts in the output voltage.

Output Capacitance and Transient Response

The LT3009 is stable with a wide range of output capaci-

tors. The ESR of the output capacitor affects stability, most

notably with small capacitors. Use a minimum output

capacitor of 1μF with an ESR of 3 or less to prevent os-

cillations. The LT3009 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 response for

larger load current changes.

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

APPLICATIONS INFORMATION

DC BIAS VOLTAGE (V)

3009 F02

–20

–40

–60

–80

–100

X5R

Y5V

BOTH CAPACITORS ARE 16V,

1210 CASE SIZE, 10μF

TEMPERATURE (°C)

–50

–20

–40

–60

–80

–100

3009 F03

–25

100

125

Y5V

X5R

BOTH CAPACITORS ARE 16V,

1210 CASE SIZE, 10μF

Figure 2. Ceramic Capacitor DC Bias Characteristics

Figure 3. Ceramic Capacitor Temperature Characteristics

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 2 and 3. 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 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. One must still

exercise care 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.

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