ltc3025edc-1 Linear Technology Corporation, ltc3025edc-1 Datasheet - Page 8

• Manufacturer Part Number: ltc3025edc-1
• Description: 500ma Micropower Vldo Linear Regulator
• Manufacturer: Linear Technology Corporation

LTC3025-1/LTC3025-2
APPLICATIONS INFORMATION
Output Capacitance and Transient Response
The LTC3025-1/LTC3025-2 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
LTC3025-1/LTC3025-2 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
LTC3025-1/LTC3025-2 will increase the effective output
capacitor value. High ESR tantalum and electrolytic capaci-
tors 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
more stable characteristics and are usually more suitable
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
302512 F03
10
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 500μA even under
heavy loads, so its power consumption can be ignored
for thermal calculations.
The LTC3025-1/LTC3025-2 has internal thermal limiting
designed to protect the device during momentary overload
conditions. For continuous normal conditions, the maxi-
mum 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 ambi-
ent. 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 generated by power devices.
(I
Figure 4. Ceramic Capacitor Temperature Characteristics
OUT
) (V
IN
–100
–80
–20
–40
–60
20
– V
0
–50
BOTH CAPACITORS ARE 1μF,
10V, 0603 CASE SIZE
OUT
–25
)
TEMPERATURE (°C)
0
25
Y5V
50
X5R
302512 F04
75
302512fa