ltc3025edc-1 Linear Technology Corporation, ltc3025edc-1 Datasheet - Page 9

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

APPLICATIONS INFORMATION
The LTC3025-1/LTC3025-2 2mm × 2mm DFN package
is specifi ed as having 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
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 LTC3025-1/
LTC3025-2’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)
2
– V
double-sided 1 oz. copper plane,
OUT
)
Short-Circuit/Thermal Protection
The LTC3025-1/LTC3025-2 has built-in short-circuit cur-
rent limiting as well as overtemperature protection. During
short-circuit conditions, internal circuitry automatically
limits the output current to approximately 1130mA. 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 LTC3025-1/LTC3025-2
will cycle in and out of thermal shutdown without latch-up
or damage until the overstress condition is removed. Long
term overstress (T
degrade the performance or shorten the life of the part.
Soft-Start Operation
The LTC3025-1/LTC3025-2 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
LTC3025-1/LTC3025-2
1.2V
OFF
ON
0V
T
V
V
C
R
A
IN
BIAS
OUT
LOAD
= 25°C
J
= 1.5V
> 125°C) should be avoided as it can
= 1μF
= 3.6V
= 4Ω
500μs/DIV
302512 F05
302512fa
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