TC2186 Microchip Technology Inc., TC2186 Datasheet - Page 10

• Manufacturer Part Number: TC2186
• Description: 50 Ma, 100 Ma, And 150 Ma Cmos Ldos With Shutdown And Error Output
• Manufacturer: Microchip Technology Inc.

TC2054/2055/2186
5.0
5.1
Integrated thermal protection circuitry shuts the regula-
tor off when the die temperature exceeds approxi-
mately 160°C. The regulator remains off until the die
temperature cools to approximatley 150°C.
5.2
The amount of power the regulator dissipates is
primarily a function of input and output voltage, and
output current.
Equation 5-1 is used to calculate worst case power
dissipation:
EQUATION 5-1:
The
(Equation 5-2) is a function of the maximum ambient
temperature (T
temperature (125 °C) and the thermal resistance from
junction-to-air (θ
a θ
typical two layer FR4 dielectric copper clad PC board.
EQUATION 5-2:
DS21663C-page 10
Where:
P
V
V
I
LOADMAX
JA
D
INMAX
OUTMIN
of approximately 220°C/Watt when mounted on a
Where all terms are previously defined.
maximum
THERMAL CONSIDERATIONS
Thermal Shutdown
Power Dissipation
P D
≈
= Worst-case actual power dissipation
= Maximum voltage on V
= Minimum regulator output voltage
= Maximum output (load) current
P
(
V
A MAX
DMAX
JA
INMAX
). The 5-Pin SOT-23A package has
allowable
), the maximum allowable die
=
–
T
-------------------------------------- -
V
JMAX
OUTMIN
θ
–
JA
T
power
)I
AMAX
LOADMAX
IN
dissipation
Equation 5-1 can be used in conjunction with
Equation 5-2 to ensure regulator thermal operation is
within limits. For example:
Actual power dissipation:
Maximum allowable power dissipation:
In this example, the TC2054 dissipates a maximum of
only 26.7 mW; far below the allowable limit of 318 mW.
In a similar manner, Equation 5-1 and Equation 5-2 can
be used to calculate maximum current and/or input
voltage limits.
5.3
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.
Given:
Find:
V
V
I
T
1. Actual power dissipation
2. Maximum allowable dissipation
P
LOADMAX
AMAX
INMAX
OUTMIN
D
=
Layout Considerations
=
=
(
V
26.7mW
[
INMAX
P
(
3.0 1.1
DMAX
= 3.0V +10%
= 2.7V – 2.5%
= 40 mA
= +55°C
×
–
V
=
=
=
OUTMIN
)
© 2006 Microchip Technology Inc.
T
-------------------------------------- -
318mW
125 55
-------------------- -
–
JMAX
(
220
2.7 0.975
–
θ
)I
×
–
JA
LOADMAX
T
AMAX
JA
)
]40 10
and, therefore,
×
3 –