TC2185 Microchip Technology Inc., TC2185 Datasheet - Page 11

• Manufacturer Part Number: TC2185
• Description: 50 Ma, 100 Ma, 150 Ma Cmos Ldos With Shutdown And Reference Bypass
• Manufacturer: Microchip Technology Inc.

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 prima-
rily a function of input voltage, output voltage and
output current.
The following equation is used to calculate worst-case
power dissipation.
EQUATION 5-1:
The maximum allowable power dissipation (P
a function of the maximum ambient temperature
(T
(T
tion-to-air (θ
of approximately 220°C/Watt when mounted on a
typical two-layer FR4 dielectric copper-clad PC board.
EQUATION 5-2:
© 2006 Microchip Technology Inc.
Where:
P
V
V
I
AMAX
JMAX
LMAX
D
INMAX
OUTMIN
Where all terms are previously defined.
) (+125°C) and the thermal resistance from junc-
), the maximum allowable die temperature
THERMAL CONSIDERATIONS
Thermal Shutdown
Power Dissipation
P D
JA
= Worst-case actual power dissipation
= Maximum voltage on V
= Minimum regulator output voltage
= Maximum output (load) current
). The 5-Pin SOT-23A package has a θ
P
≈
DMAX
(
V
INMAX
=
T
-------------------------------------- -
–
JMAX
V
OUTMIN
θ
–
JA
T
AMAX
)I
LMAX
IN
DMAX
) is
JA
The P
P
operation is within limits. For example:
Actual power dissipation:
Maximum allowable power dissipation:
In this example, the TC2014 dissipates a maximum of
only 26.7 mW; far below the allowable limit of 318 mW.
In a similar manner, the P
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:
DMAX
V
V
I
T
T
1. Actual power dissipation
2. Maximum allowable dissipation
LOADMAX
D
P
AMAX
JMAX
INMAX
OUTMIN
TC2014/2015/2185
D
equation to ensure that regulator thermal
equation can be used in conjunction with the
Layout Considerations
=
=
=
(
26.7mW
[
V
(
P
3.0 1.1
INMAX
DMAX
= 3.0V +10%
= 2.7V – 2.5%
= 40 mA
= +125°C
= +55°C
×
–
=
=
=
)
V
–
OUTMIN
T
-------------------------------------- -
318mW
125 55
-------------------- -
(
JMAX
D
2.7 0.975
220
and P
–
×
θ
–
JA
)I
T
LMAX
DMAX
AMAX
DS21662E-page 11
JA
)
]40 10
and, therefore,
equations can
×
3 –