TC1268 MICROCHIP [Microchip Technology], TC1268 Datasheet - Page 6

• Manufacturer Part Number: TC1268
• Description: 500mA Fixed Output, Fast Response CMOS LDO with Shutdown
• Manufacturer: MICROCHIP [Microchip Technology]

TC1268
4.0
4.1
Integrated thermal protection circuitry shuts the
regulator off when die temperature exceeds 160°C.
The regulator remains off until the die temperature
drops to approximately 150°C.
4.2
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
(Equation 4-2) is a function of the maximum ambient
temperature (T
temperature (T
junction-to-air (θ
EQUATION 4-2:
Table 4-1 shows various values of θ
package.
TABLE 4-1:
*Pin 2 is ground. Device is mounted on topside.
DS21379B-page 6
2500 sq mm 2500 sq mm 2500 sq mm
1000 sq mm 2500 sq mm 2500 sq mm
225 sq mm
100 sq mm
(Topside)*
Copper
I
Where:
LOAD
V
Area
OUT
V
IN
maximum
Where all terms are previously defined.
THERMAL CONSIDERATIONS
Thermal Shutdown
Power Dissipation
MAX
MAX
P
MIN
D
P
= Worst case actual power dissipation
= Maximum voltage on V
= Minimum regulator output voltage
= Maximum output (load) current
D
2500 sq mm 2500 sq mm
2500 sq mm 2500 sq mm
(Backside)
J
≈ (V
A
P
MAX
JA
Copper
MAX
D
THERMAL RESISTANCE
GUIDELINES FOR TC1268 IN
8-PIN SOIC PACKAGE
Area
).
MAX
) and the thermal resistance from
IN
), the maximum allowable die
allowable
MAX
= (T
– V
J
MAX
OUT
θ
– T
JA
Board
Area
MIN
power
A
)I
MAX
JA
LOAD
IN
)
for the TC1268
MAX
Resistance
Thermal
dissipation
60°C/W
60°C/W
68°C/W
74°C/W
(θ
JA
)
Equation 4-1 can be used in conjunction with
Equation 4-2 to ensure regulator thermal operation is
within limits. For example:
Given:
Find: 1. Actual power dissipation
Actual power dissipation:
P
Maximum allowable power dissipation:
In this example, the TC1268 dissipates a maximum of
314mW; below the allowable limit of 500mW. 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
power dissipation of 500mW into Equation 4-1, from
which V
D
IN
≈ (V
= [(3.3 x 1.1) – (2.5 x .995)]275 x 10
= 314mW
P
is found by substituting the maximum allowable
V
V
I
T
T
θ
D
LOAD
A
JA
J
IN
OUT
MAX
2. Maximum allowable dissipation
MAX
MAX
IN
MAX
IN
MAX
= (125 – 95)
= 500mW
MAX
MIN
= (T
MAX
– V
= 3.94V.
J
= 3.3V ± 10%
= 2.5V ± 0.5%
= 275mA
= 125°C
= 95°C
= 60°C/W
MAX
60
OUT
θ
– T
JA
MIN
A
)I
MAX
©
LOAD
)
2002 Microchip Technology Inc.
MAX
-3