lt3083idf Linear Technology Corporation, lt3083idf Datasheet - Page 14

• Manufacturer Part Number: lt3083idf
• Description: Lt3083 - Adjustable 3a Single Resistor Low Dropout Regulator
• Manufacturer: Linear Technology Corporation

APPLICATIONS INFORMATION
LT3083
14
TO 20V
10μF
4.8V
Figure 4. Ceramic Capacitor Temperature Characteristics
V
IN
Figure 3. Ceramic Capacitor DC Bias Characteristics
–100
–100
–20
–40
–60
–80
–20
–40
–60
–80
20
40
20
0
0
V
V
–50
0
CONTROL
CONTROL
BOTH CAPACITORS ARE 16V,
1210 CASE SIZE, 10μF
V
V
2
–25
Figure 5. Parallel Devices
IN
IN
4
DC BIAS VOLTAGE (V)
0
TEMPERATURE (°C)
SET
SET
33k
BOTH CAPACITORS ARE 16V,
1210 CASE SIZE, 10μF
6
25
LT3083
LT3083
+
–
+
–
8
Y5V
X5R
50
10
Y5V
75
12
X5R
100
OUT
OUT
14
3083 F03
3083 F04
16
125
10mΩ
10mΩ
3083 F05
10μF
V
3.3V
6A
OUT
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 signifi cant 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 verifi ed.
Voltage and temperature coeffi cients 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
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
WEIGHT (oz)
1
2
10mil WIDTH
54.3
27.1
20mil WIDTH
27.1
13.6
3083f