TC1186 Microchip, TC1186 Datasheet - Page 7

• Manufacturer Part Number: TC1186
• Description: CMOS LDOs with Shutdown and ERROR Output
• Manufacturer: Microchip

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
a θ
EQUATION 4-2:
©
2002 Microchip Technology Inc.
JA
I
Where:
LOAD
V
V
OUT
of approximately 220°C/Watt.
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
J
P
A
MAX
≈ (V
JA
D
MAX
MAX
). The 5-Pin SOT-23A package has
) and the thermal resistance from
), the maximum allowable die
IN
allowable
= (T
MAX
J
– V
MAX
θ
OUT
JA
– T
MIN
A
power
MAX
)I
LOAD
)
IN
MAX
dissipation
TC1054/TC1055/TC1186
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 TC1054 dissipates a maximum of
20.7mW; below the allowable limit of 318mW. In a
similar manner, Equation 4-1 and Equation 4-2 can be
used to calculate maximum current and/or input
voltage limits.
4.3
The primary path of heat conduction out of the package
is via the package leads. Therefore, layouts having a
ground plane, wide traces at the pads, and wide power
supply bus lines combine to lower θ
increase the maximum allowable power dissipation
limit.
D
= [(3.0 x 1.05) – (2.7 x .975)]40 x 10
= 20.7mW
≈ (V
V
V
I
T
T
P
LOAD
A
J
IN
OUT
D
2. Maximum allowable dissipation
MAX
MAX
MAX
IN
MAX
Layout Considerations
MAX
MIN
MAX
= (125 – 55)
= 318mW
= (T
– V
= 3.0V ±5%
= 2.7V – 2.5%
= 40mA
= 125°C
= 55°C
J
220
MAX
OUT
θ
– T
MIN
JA
)I
A
LOAD
MAX
)
MAX
JA
DS21350B-page 7
–3
and therefore,