ltc3025edc-trpbf Linear Technology Corporation, ltc3025edc-trpbf Datasheet - Page 9

• Manufacturer Part Number: ltc3025edc-trpbf
• Description: 300ma Micropower Vldo Linear Regulator
• Manufacturer: Linear Technology Corporation

APPLICATIONS INFORMATION
The LTC3025 2mm × 2mm DFN package is specifi ed as hav-
ing a junction-to-ambient thermal resistance of 102°C/W,
which assumes a minimal heat spreading copper plane. The
actual thermal resistance can be reduced substantially by
connecting the package directly to a good heat spreading
ground plane. When soldered to 2500mm
1 oz. copper plane, the actual junction-to-ambient thermal
resistance can be less than 60°C/W.
Calculating Junction Temperature
Example: Given an output voltage of 1.2V, an input voltage
of 1.8V to 3V, an output current range of 0mA to 100mA
and a maximum ambient temperature of 50°C, what will
the maximum junction temperature be?
The power dissipated by the device will be equal to:
where:
So:
Even under worst-case conditions, the LTC3025’s BIAS pin
power dissipation is only about 1mW, thus can be ignored.
Assuming a junction-to-ambient thermal resistance of
102°C/W, the junction temperature rise above ambient
will be approximately equal to:
The maximum junction temperature will then be equal to
the maximum junction temperature rise above ambient
plus the maximum ambient temperature or:
I
I
V
P = 100mA(3V – 1.2V) = 0.18W
0.18W(102°C/W) = 18.4°C
T = 50°C + 18.4°C = 68.4°C
OUT(MAX)
OUT(MAX)
IN(MAX)
= 3V
(V
= 100mA
IN(MAX)
– V
OUT
)
2
double-sided
Short-Circuit/Thermal Protection
The LTC3025 has built-in short-circuit current limiting as
well as overtemperature protection. During short-circuit
conditions, internal circuitry automatically limits the output
current to approximately 600mA. At higher temperatures, or
in cases where internal power dissipation causes excessive
self heating on chip, the thermal shutdown circuitry will
shut down the LDO when the junction temperature exceeds
approximately 150°C. It will re enable the LDO once the
junction temperature drops back to approximately 140°C.
The LTC3025 will cycle in and out of thermal shutdown
without latch-up or damage until the overstress condition
is removed. Long term overstress (T
avoided as it can degrade the performance or shorten the
life of the part.
Soft-Start Operation
The LTC3025 includes a soft-start feature to prevent
excessive current fl ow during start-up. When the LDO is
enabled, the soft-start circuitry gradually increases the LDO
reference voltage from 0V to 0.4V over a period of about
600μs. There is a short 700μs delay from the time the
part is enabled until the LDO output starts to rise. Figure
5 shows the start-up and shutdown output waveform.
200mV/DIV
SHDN
V
OUT
Figure 5. Output Start-Up and Shutdown
1.2V
OFF
ON
0V
T
V
V
C
R
A
IN
BIAS
OUT
LOAD
= 25 C
= 1.5V
= 1 F
= 3.6V
= 4
500 s/DIV
J
> 125°C) should be
LTC3025
3025 F05
3025fa
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