LTC3025EDC LINER [Linear Technology], LTC3025EDC Datasheet - Page 8

• Manufacturer Part Number: LTC3025EDC
• Description: 300mA Micropower VLDO Linear Regulator
• Manufacturer: LINER [Linear Technology]

LTC3025
APPLICATIONS INFORMATION
Output Capacitance and Transient Response
The LTC3025 is designed to be stable with a wide range of
ceramic 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 0.05Ω
or less is recommended to ensure stability. The LTC3025
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 improved transient response for larger load current
changes. Note that bypass capacitors used to decouple
individual components powered by the LTC3025 will
increase the effective output capacitor value. High ESR
tantalum and electrolytic capacitors may be used, but
a low ESR ceramic capacitor must be in parallel at the
output. There is no minimum ESR or maximum capacitor
size requirements.
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 di-
electrics used are Z5U, Y5V, X5R and X7R. The Z5U and
Y5V dielectrics are good for providing high capacitances
in a small package, but exhibit large voltage and tem-
perature coeffi cients as shown in Figures 3 and 4. When
used with a 2V regulator, a 1μF Y5V capacitor can lose as
much as 75% of its intial capacitance over the operating
temperature range. The X5R and X7R dielectrics result in
8
Figure 3. Ceramic Capacitor DC Bias Characteristics
–100
–20
–40
–60
–80
20
0
0
2
DC BIAS VOLTAGE (V)
Y5V
BOTH CAPACITORS ARE 1μF,
10V, 0603 CASE SIZE
4
6
X5R
8
3025 F03
10
more stable characteristics and are usually 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. In all cases, the output
capacitance should never drop below 0.4μF , or instability
or degraded performance may occur.
Thermal Considerations
The power handling capability of the device will be limited
by the maximum rated junction temperature (125°C). The
power dissipated by the device will be the output current
multiplied by the input/output voltage differential:
Note that the BIAS current is less than 300μA even under
heavy loads, so its power consumption can be ignored
for thermal calculations.
The LTC3025 has internal thermal limiting designed to
protect the device during momentary overload conditions.
For continuous normal conditions, the maximum junction
temperature rating of 125°C must not be exceeded. It is
important to give careful consideration to all sources of
thermal resistance from junction to ambient. Additional
heat sources mounted nearby must also be considered.
For surface mount devices, heat sinking is accomplished
by using the heat-spreading capabilities of the PC board
and its copper traces. Copper board stiffeners and plated
through holes can also be used to spread the heat gener-
ated by power devices.
(I
Figure 4. Ceramic Capacitor Temperature Characteristics
OUT
) (V
–100
–20
–40
–60
–80
20
IN
0
–50
– V
BOTH CAPACITORS ARE 1μF,
10V, 0603 CASE SIZE
OUT
–25
)
TEMPERATURE (°C)
0
25
Y5V
50
X5R
3025 F04
75
3025fb