lt3014bes5 Linear Technology Corporation, lt3014bes5 Datasheet - Page 8
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lt3014bes5
Manufacturer Part Number
lt3014bes5
Description
20ma, 3v To 80v Low Dropout Micropower Linear Regulator
Manufacturer
Linear Technology Corporation
Datasheet
1.LT3014BES5.pdf
(12 pages)
Available stocks
Company
Part Number
Manufacturer
Quantity
Price
Company:
Part Number:
LT3014BES5
Manufacturer:
LT
Quantity:
10 000
APPLICATIO S I FOR ATIO
LT3014B
The LT3014B regulator has internal thermal limiting de-
signed to protect the device during 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.
The following table lists thermal resistance for several
different board sizes and copper areas. All measurements
were taken in still air on 3/32" FR-4 board with one ounce
copper.
Table 1. SOT-23 Measured Thermal Resistance
Table 2. DFN Measured Thermal Resistance
For the DFN package, the thermal resistance junction-to-
case (θ
die, is 16°C/W.
Continuous operation at large input/output voltage differ-
entials and maximum load current is not practical due to
thermal limitations. Transient operation at high input/
output differentials is possible. The approximate thermal
time constant for a 2500sq mm 3/32" FR-4 board with
maximum topside and backside area for one ounce copper
is 3 seconds. This time constant will increase as more
8
2500 sq mm
1000 sq mm
2500 sq mm
1000 sq mm
225 sq mm
100 sq mm
225 sq mm
100 sq mm
50 sq mm
TOPSIDE
TOPSIDE
COPPER AREA
COPPER AREA
JC
), measured at the exposed pad on the back of the
2500 sq mm
2500 sq mm
2500 sq mm
2500 sq mm
2500 sq mm
2500 sq mm
2500 sq mm
2500 sq mm
2500 sq mm
BACKSIDE
BACKSIDE
U
BOARD AREA
BOARD AREA
2500 sq mm
2500 sq mm
2500 sq mm
2500 sq mm
2500 sq mm
2500 sq mm
2500 sq mm
2500 sq mm
2500 sq mm
U
W
(JUNCTION-TO-AMBIENT)
(JUNCTION-TO-AMBIENT)
THERMAL RESISTANCE
THERMAL RESISTANCE
125°C/W
125°C/W
130°C/W
135°C/W
150°C/W
40°C/W
45°C/W
50°C/W
62°C/W
U
thermal mass is added (i.e. vias, larger board, and other
components).
For an application with transient high power peaks, aver-
age power dissipation can be used for junction tempera-
ture calculations as long as the pulse period is significantly
less than the thermal time constant of the device and
board.
Calculating Junction Temperature
Example 1: Given an output voltage of 5V, an input voltage
range of 24V to 30V, an output current range of 0mA to
20mA, 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:
The thermal resistance for the DFN package will be in the
range of 40°C/W to 62°C/W depending on the copper area.
So 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:
Example 2: Given an output voltage of 5V, an input voltage
of 48V that rises to 72V for 5ms(max) out of every 100ms,
and a 5mA load that steps to 20mA for 50ms out of every
250ms, what is the junction temperature rise above ambi-
ent? Using a 500ms period (well under the time constant
of the board), power dissipation is as follows:
I
I
V
I
P1(48V in, 5mA load) = 5mA • (48V – 5V)
OUT(MAX)
OUT(MAX)
GND
P = 20mA • (30V – 5V) + (0.55mA • 30V) = 0.52W
0.52W • 50°C/W = 26°C
T
IN(MAX)
JMAX
at (I
= 50°C + 26°C = 76°C
= 30V
OUT
• (V
= 20mA
= 20mA, V
IN(MAX)
– V
IN
+ (100µA • 48V) = 0.22W
OUT
= 30V) = 0.55mA
) + (I
GND
• V
IN(MAX)
)
3014bf