tc1073 Microchip Technology Inc., tc1073 Datasheet - Page 13

• Manufacturer Part Number: tc1073
• Description: 50ma And 100ma Cmos Ldos With Shutdown, Error Output And V Bypass Ref
• Manufacturer: Microchip Technology Inc.

5.0
5.1
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.
5.2
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 5-1:
The
(Equation
temperature (T
perature (T
tion-to-air (θ
of approximately 220°C/Watt.
EQUATION 5-2:
© 2007 Microchip Technology Inc.
I
Where:
V
LOAD
OUT
V
IN
maximum
where all terms are previously defined.
THERMAL CONSIDERATIONS
Thermal Shutdown
Power Dissipation
MAX
MAX
P
MIN
5-2) is a function of the maximum ambient
D
J
MAX
JA
P
= Worst-case actual power dissipation
= Maximum voltage on V
= Minimum regulator output voltage
= Maximum output (load) current
D
P
). The 6-Pin SOT-23 package has a θ
A
DMAX
) and the thermal resistance from junc-
≈
MAX
(V
), the maximum allowable die tem-
INMAX
allowable
= (T
JMAX
– V
θ
OUTMIN
JA
– T
AMAX
power
)I
LOADMAX
IN
)
dissipation
JA
Equation 5-1
Equation 5-2
within limits. For example:
Given:
Find:
Actual power dissipation:
P
Maximum allowable power dissipation:
In this example, the TC1072 dissipates a maximum of
20.7 mW; below the allowable limit of 318 mW. In a
similar manner,
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.
D
≈
= [(3.0 x 1.05) – (2.7 x 0.975)] x 40 x 10
= 20.7 mW
V
V
I
T
T
P
LOAD
(V
A
J
IN
OUT
DMAX
MAX
MAX
INMAX
MAX
1. Actual power dissipation
2. Maximum allowable dissipation
Layout Considerations
MIN
MAX
= (125 – 55)
= 318 mW
= (T
– V
TC1072/TC1073
to ensure regulator thermal operation is
can be used in conjunction with
JMAX
Equation 5-1
OUTMIN
220
= 3.0V ±5%
= 2.7V – 2.5%
= 40 mA
= 125°C
= 55°C
θ
JA
– T
)I
AMAX
LOADMAX
)
and
Equation 5-2
DS21354D-page 13
JA
–3
and therefore
can be