LT1963A Datasheet, PDF (19/28 Pages) Linear Technology – 1.5A, Low Noise,Fast Transient Response LDO Regulators

LT1963A Series
APPLICATIONS INFORMATION
The following tables list thermal resistance for several
different board sizes and copper areas. All measurements
were taken in still air on 1/16" FR-4 board with one ounce
copper.
Table 3. Q Package, 5-Lead DD
COPPER AREA
TOPSIDE* BACKSIDE BOARD AREA
2500mm² 2500mm² 2500mm²
1000mm² 2500mm² 2500mm²
125mm² 2500mm² 2500mm²
*Device is mounted on topside
THERMAL RESISTANCE
(JUNCTION-TO-AMBIENT)
23°C/W
25°C/W
33°C/W
Table 4. S0-8 Package, 8-Lead SO
COPPER AREA
TOPSIDE* BACKSIDE
2500mm² 2500mm²
1000mm² 2500mm²
225mm² 2500mm²
BOARD AREA
2500mm²
2500mm²
2500mm²
125mm² 2500mm² 2500mm²
*Device is mounted on topside
THERMAL RESISTANCE
(JUNCTION-TO-AMBIENT)
55°C/W
55°C/W
63°C/W
69°C/W
Table 5. SOT-223 Package, 3-Lead SOT-223
COPPER AREA
THERMAL RESISTANCE
TOPSIDE* BACKSIDE BOARD AREA (JUNCTION-TO-AMBIENT)
2500mm² 2500mm²
1000mm² 2500mm²
2500mm²
2500mm²
42°C/W
42°C/W
225mm²
100mm²
2500mm²
2500mm²
2500mm²
2500mm²
50°C/W
56°C/W
1000mm² 1000mm² 1000mm²
49°C/W
1000mm² 0mm²
1000mm²
52°C/W
*Device is mounted on topside
T Package, 5-Lead TO-220
Thermal Resistance (Junction-to-Case) = 4°C/W
Calculating Junction Temperature
Example: Given an output voltage of 3.3V, an input volt-
age range of 4V to 6V, an output current range of 0mA
to 500mA 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:
I_OUT(MAX)(V_IN(MAX) – V_OUT) + I_GND(V_IN(MAX))
where,
I_OUT(MAX) = 500mA
V_IN(MAX) = 6V
I_GND at (I_OUT = 500mA, V_IN = 6V) = 10mA
So,
P = 500mA(6V – 3.3V) + 10mA(6V) = 1.41W
Using a DD package, the thermal resistance will be in the
range of 23°C/W to 33°C/W depending on the copper
area. So the junction temperature rise above ambient will
be approximately equal to:
1.41W(28°C/W) = 39.5°C
The maximum junction temperature will then be equal to
the maximum junction temperature rise above ambient
plus the maximum ambient temperature or:
T_JMAX = 50°C + 39.5°C = 89.5°C
Protection Features
The LT1963A regulators incorporate several protection
features which make them ideal for use in battery-pow-
ered circuits. In addition to the normal protection features
associated with monolithic regulators, such as current
limiting and thermal limiting, the devices are protected
against reverse input voltages, reverse output voltages
and reverse voltages from output to input.
Current limit protection and thermal overload protection
are intended to protect the device against current overload
conditions at the output of the device. For normal operation,
the junction temperature should not exceed 125°C.
The input of the device will withstand reverse voltages
of 20V. Current flow into the device will be limited to less
than 1mA (typically less than 100μA) and no negative
voltage will appear at the output. The device will protect
both itself and the load. This provides protection against
batteries that can be plugged in backward.
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