參數(shù)資料
型號: TC1264
廠商: Microchip Technology Inc.
英文描述: 800mA Fixed Output CMOS LDO
中文描述: 800mA的固定輸出CMOS低壓
文件頁數(shù): 4/12頁
文件大?。?/td> 448K
代理商: TC1264
TC1264
DS21375B-page 4
2002 Microchip Technology Inc.
4.0
THERMAL CONSIDERATIONS
4.1
Thermal Shutdown
Integrated
regulator off when die temperature exceeds 160°C.
The regulator remains off until the die temperature
drops to approximately 150°C.
thermal
protection
circuitry
shuts
the
4.2
Power Dissipation
The amount of power the regulator dissipates is
primarily a function of input and output voltage, and
output current. The following equation is used to
calculate worst case actual power dissipation:
EQUATION 4-1:
The maximum allowable power dissipation (Equation
4-2) is a function of the maximum ambient temperature
(T
A
MAX
), the maximum allowable die temperature
(T
J
MAX
) and the thermal resistance from junction-to-air
(
θ
JA
EQUATION 4-2:
Table 4-1 and Table 4-2 show various values of
θ
JA
for
the TC1264 packages.
TABLE 4-1:
THERMAL RESISTANCE
GUIDELINES FOR TC1264 IN
SOT-223 PACKAGE
*Tab of device attached to topside copper
TABLE 4-2:
THERMAL RESISTANCE
GUIDELINES FOR TC1264 IN
3-PIN DDPAK/TO-220
PACKAGE
*Tab of device attached to topside copper
Equation 4-1 can be used in conjunction with Equation
4-2 to ensure regulator thermal operation is within
limits. For example:
Given:
V
IN
MAX
V
OUT
MIN
I
LOAD
MAX
= 275mA
T
J
MAX
T
A
MAX
θ
JA
Find: 1. Actual power dissipation
2. Maximum allowable dissipation
= 3.3V ± 10%
= 2.7V ± 0.5%
= 125°C
= 95°C
= 59°C/W (SOT-223)
Actual power dissipation:
P
D
(V
IN
MAX
– V
OUT
MIN
)I
LOAD
MAX
= [(3.3 x 1.1) – (2.7 x .995)]275 x 10
–3
= 260mW
Maximum allowable power dissipation:
P
D
MAX
= (T
J
MAX
– T
A
MAX
)
θ
JA
= (125 – 95)
59
= 508mW
In this example, the TC1264 dissipates a maximum of
260mW; below the allowable limit of 508mW. In a
similar manner, Equation 4-1 and Equation 4-2 can be
used to calculate maximum current and/or input
voltage limits. For example, the maximum allowable
V
IN
, is found by substituting the maximum allowable
power dissipation of 508mW into Equation 4-1, from
which V
IN
MAX
= 4.6V.
Copper
Area
(Topside)*
Copper
Area
(Backside)
Board
Area
Thermal
Resistance
JA
)
45°C/W
45°C/W
53°C/W
59°C/W
52°C/W
55°C/W
2500 sq mm
1000 sq mm
225 sq mm
100 sq mm
1000 sq mm
1000 sq mm
2500 sq mm
2500 sq mm
2500 sq mm
2500 sq mm
1000 sq mm
0 sq mm
2500 sq mm
2500 sq mm
2500 sq mm
2500 sq mm
1000 sq mm
1000 sq mm
Where:
P
D
(V
IN
MAX
– V
OUT
MIN
)I
LOAD
MAX
P
D
V
IN
MAX
V
OUT
MIN
I
LOAD
MAX
= Worst case actual power dissipation
= Maximum voltage on V
IN
= Minimum regulator output voltage
= Maximum output (load) current
P
D
MAX
= (T
J
MAX
– T
A
MAX
)
θ
JA
Where all terms are previously defined.
Copper
Area
(Topside)*
Copper
Area
(Backside)
Board
Area
Thermal
Resistance
JA
)
25°C/W
27°C/W
35°C/W
2500 sq mm
1000 sq mm
125 sq mm
2500 sq mm
2500 sq mm
2500 sq mm
2500 sq mm
2500 sq mm
2500 sq mm
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