LT3083MPDF datasheet(14/28 Pages) LINER

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LT3083

3083f

APPLICATIONS INFORMATION

Figure 5. Parallel Devices

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 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 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.

Voltage and temperature coefﬁcients are not the only

sources of problems. Some ceramic capacitors have a

piezoelectric response. A piezoelectric device generates

voltage across its terminals due to mechanical stress. In a

ceramic capacitor, the stress can be induced by vibrations

in the system or thermal transients.

Paralleling Devices

Higher output current is obtained by paralleling multiple

LT3083s together. Tie the individual SET pins together and

tie the individual IN pins together. Connect the outputs in

common using small pieces of PC trace as ballast resistors

to promote equal current sharing. PC trace resistance in

mΩ/inch is shown in Table 2. Ballasting requires only a

tiny area on the PCB.

Table 2. PC Board Trace Resistance

WEIGHT (oz)

10mil WIDTH

20mil WIDTH

54.3

27.1

13.6

Trace resistance is measured in mΩ/in

The worst-case room temperature offset, only ±4mV

(DD-PAK, T Packages) between the SET pin and the OUT

pin, allows the use of very small ballast resistors.

As shown in Figure 5, each LT3083 has a small 10mΩ

ballast resistor, which at full output current gives better

than 80% equalized sharing of the current. The external

Figure 3. Ceramic Capacitor DC Bias Characteristics

Figure 4. Ceramic Capacitor Temperature Characteristics

DC BIAS VOLTAGE (V)

3083 F03

–20

–40

–60

–80

–100

X5R

Y5V

BOTH CAPACITORS ARE 16V,

1210 CASE SIZE, 10μF

TEMPERATURE (°C)

–50

–20

–40

–60

–80

–100

3083 F04

–25

100

125

Y5V

X5R

BOTH CAPACITORS ARE 16V,

1210 CASE SIZE, 10μF

–

LT3083

VIN

VCONTROL

OUT

SET

10mΩ

–

LT3083

VIN

4.8V

TO 20V

VOUT

3.3V

VCONTROL

OUT

10μF

SET

33k

3083 F05

10mΩ

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